energy transfer questions
DESCRIPTION
Biology Practise QuestionsTRANSCRIPT
1. The diagram shows a vertical section through an area of tropical rainforest in Malaysia.
P o in t A
P o in t B
5 0 m
4 0
3 0
2 0
1 0
0
The graph shows the daily fluctuations in carbon dioxide concentration at points A and B.
C arb o n d io x id eco n ce n tra tio n inp arts p er m illio n
5 0 0
4 5 0
4 0 0
3 5 0
3 0 0
01 2 00 1 6 0 0 2 0 0 0
M id n ig h t0 4 0 0 0 8 0 0 1 2 00 1 6 0 0
T im e o f d ay
P o in t B
P o in t A
(a) (i) Explain the fluctuations in the carbon dioxide concentration which take place at point A over a 24-hour period.
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(ii) At 1600 hours, the carbon dioxide concentrations at points A and B differ from each other. Explain why.
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(b) Use information in the diagram to help explain why replacing rain forest with agricultural crops will reduce the diversity of animals.
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(Total 5 marks)
2. Soybeans are rich in protein. Raw soybeans, however, may contain a trypsin inhibitor. This is a chemical which prevents the digestion of protein. The presence of this trypsin inhibitor is
genetically controlled. A single gene has alleles TA, TB and TC each of which codes for a different sort of trypsin inhibitor. These alleles are codominant so plant with the genotype
TATB will produce two sorts of trypsin inhibitor, inhibitor A and inhibitor B. A fourth,
recessive allele, To does not code for a trypsin inhibitor. This information is summarised in the table.
Allele Inhibitor produced
TA A
TB B
TC C
To None
(a) The inheritance of trypsin inhibitors in soybeans is an example of multiple allele inheritance. Explain how multiple allele inheritance differs from polygenic inheritance.
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(b) (i) Give all the possible genotypes of a plant which only contains inhibitor A.
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(ii) Give all the possible genotypes of the gametes produced by a plant which contains inhibitors B and C.
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(c) Two soybean plants were crossed and the seeds collected and counted. The results are shown in the table.
Inhibitors present in seed Number of seeds
A and B 23
A 25
B 48
(i) Complete the genetic diagram to explain the results of this cross.
Phenotypes of parents:.................................. .......................................
Genotypes of parents:.................................. .......................................
Genotypes of gametes ......................................................................................
Genotypes of offspring: ....................................................................................
Phenotypes of offspring Inhibitor A Inhibitor A Inhibitor Band
Inhibitor B(3)
(ii) A chi-squared test was applied to the data collected in this investigation. Explain why statistical tests such as the Chi-squared test should be carried out on data like these.
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An investigation was carried out on the insects living on bean crops. The graph shows the relationship between the biomass of primary consumers, secondary consumers and producers.
1 0 0
9 0
8 0
7 0
6 0
5 0
4 0
3 0
2 0
1 0
00 2 00 4 0 0 6 0 0 80 0 1 0 0 0
C o n su m erb io m ass /g m –2
–2
P rim a ryco n su m ers
S ec o nd a ryco n su m ers
P ro d u ce rs b io m ass /g m
(d) Briefly describe how the data on the biomass of the producers might have been collected.
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(e) (i) In this investigation, the efficiency with which the energy in sunlight was converted into energy in the biomass of the producers was found to be 4%. For every 10 000 kJ of light energy falling on the beans, 400 kJ was therefore converted into energy in producer biomass. Use the data in the graph to complete the diagram below which shows the amount of biomass in the primary consumers and the secondary consumers.
Energy in sunlight 10 000 kJ
4%
Energy in producer biomass 400 kJ
......... %
Energy in primary consumer biomass. ...... kJ
......... %
Energy in secondary consumer biomass. ...... kJ(2)
(ii) Explain why not all of the energy in producer biomass can be converted into energy in primary consumer biomass.
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(Total 14 marks)
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3. Answers should be written in continuous prose. Credit will be given for biological accuracy, the organisation and presentation of the information and the way in which the answer is expressed.
The diagram shows part of a system designed to meet all the basic needs of a family of four living in the tropics.
C ro p p la n ts C ro p w as te
C a ttle a n dch ick en sU rin e an d fae ces
S o lid w as teu sed as fe rtilise r
F erm en te rco n ta in in g
b ac te ria
L iq u id w a s te
G as u sed as fu e l fo rco o k in g an d lig h tin g
C a rb o nd io x id e
F ish
H u m a n s
U rin e an dfaec es
A lg ae insha llo w p o n d
(a) The processes which naturally form part of the nitrogen cycle can make nitrogen contained in urine and faeces available to crop plants. Describe how these processes occur.
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(b) Explain the advantage in this system of:
(i) growing leguminous plants such as groundnuts or beans;
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(ii) stocking the pond with fish that feed on algae rather than with carnivorous fish.
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(Total 13 marks)
4. The diagram represents annual energy flow, in kJ m–2 year–1, through an aquatic ecosystem.
D ec o m p o sers
H erb iv o re s
P ro d u cers
S u nlig h t7 1 4 0 0 0 0
1 4 1 5 0
8 7 4 0 0
7 2 5 0
1 7 80 0
lo s t9 5 0 0
lo s t7 0 5 2 6 0 0
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(a) Give two ways in which energy is lost between producers and herbivores.
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(b) Calculate the percentage of available sunlight trapped by the producers.Show your working.
Answer..............................(1)
(c) What is the importance of decomposers to the producers?
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(Total 4 marks)
5. Heather is a woody plant found in many moorland areas on higher ground in Britain. Grouse are chicken-sized birds which feed on the young shoots of heather. On many moorlands, the heather is managed to produce better conditions for grouse. This involves burning large areas. After burning, heather goes through the cycle of growth described below.
Pioneer phase0-7 years
New plants grow either fromseed or from stem basesundamaged by fire.
Building phase7-15 years
Phase of rapid growthproducing dense cover ofheather plants.
Mature phase15 - 25 years
Plants still growing but gapsstart to appear in the canopy.
Degenerate phase25+ years
Branches break. Central partof plant dies although outerbranches may remain alive.
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Table 1 summarises some data collected from a study of heather plants of different ages.
Age/years Total
biomass/g m2Biomass of green
shoots/g m–2Percentage cover Light at ground level
as percentage of lightin open
5 287 78 10 84
10 1508 203 85 5
20 1924 208 76 22
30 1043 n/a 34 56
Table 1
Key:n/a = figures not available
(a) To determine the total biomass, quadrats were used to collect the heather samples.Describe the procedure you would have used to place these quadrats.
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(b) Describe how and explain why the diversity of plant species would be likely to change during the cycle of growth of the heather.
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(c) (i) Calculate the mean rate of increase in the biomass of green shoots between 10 and 20 years. Show your working.
Answer: ............................................(2)
(ii) Explain why the mean rate of increase in the biomass of green shoots decreases with age.
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(iii) Management of heather by burning allows an area of land to support a larger population of grouse than if the heather is unmanaged. Use the information in Table 1 to suggest why.
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Table 2 shows the nitrogen content of heather plants, leaf litter and the soil in plots of land at various stages after burning.
Time after Nitrogen content/kg ha–1
burning/years Heather plants Leaf litter Soil
3 59 28 5794
8 92 61 5952
15 192 58 5394
Table 2
(d) (i) Give one organic compound in which the nitrogen will be found in the heather plants.
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(ii) Give one ion in which the nitrogen will be found in the soil.
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(e) Explain how bacteria make nitrogen present in the leaf litter available to the heather plants.
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(f) It has been suggested that if heather moorland is to be managed by burning, this should take place before the heather is 15 years old. Use the information in Table 2 to suggest why.
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(Total 20 marks)
6. Figure 1 shows a food web in a heathland ecosystem.
H ea th e r
F o x
K e stre l
Sto a t
R ab b itVo le
S h o rt-ea redo w l
Figure 1
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(a) In this food web name the organism which has the largest population biomass.
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(b) Figure 2 shows a pyramid of numbers representing another food web.
S eco n d ary co n su m er
P rim a ry c o n su m er
P ro d u cer
Figure 2
There are more secondary consumers than primary consumers in this pyramid. Suggest one explanation for this.
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(c) Figure 3 shows a pyramid of energy for an ecosystem. The units used are kJ m–2 year–1.
5 0
1 5 0 0
1 3 0 0 0
8 5 0 0 0
Figure 3
(i) Calculate the percentage of energy transferred from the secondary consumer to the tertiary consumer.
Answer: ..............................................(1)
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(ii) Give two reasons why the percentage of energy transferred between consumers is generally low.
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(Total 5 marks)
7. (a) The diagram shows an outline of the nitrogen cycle.
N itro ge n g a sin
a tm o sp h e re
D ea th an d d eca yin
so il
P lan tp ro te in
A n im alp ro te in
N itro g eng as
A m m o n ia
S u b s tan ce A
P ro c ess X
P ro ce ss Z
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Name:
(i) substance A;
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(ii) process X;
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(iii) process Z.
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(b) The table shows the yield of a crop when different levels of nitrogen fertiliser were applied.
Nitrogen fertiliser
applied/ kg hectare–1Yield/
tonnes hectare–1
0 2.8
50 3.3
100 4.2
150 4.7
200 4.7
(i) Describe the effect that the fertiliser had on the yield of the crop.
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(ii) Explain two disadvantages of applying nitrogen fertiliser at levels above 150 kg
hectare–1.
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(c) The graphs show the range of heights of samples of two varieties of wheat grown under the same conditions. Variety A is a modem form and Variety B is a form that was commonly grown 100 years ago.
2 0 0
1 5 0
1 0 0
5 0
0
2 0 0
1 5 0
1 0 0
5 0
0
N u m b er N um b ero f o f
p lan ts p la n ts
H eig h t / cm H e ig h t / cm
Varie ty A Va rie ty B
5 0 5 01 0 0 1 0 01 50 1 5 0
(i) Name the type of variation shown in these two graphs.
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(ii) Describe two differences shown in the graphs between Variety A and B.
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(iii) Suggest how the differences between the two varieties could have been brought about.
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(iv) Suggest the advantages that these differences could have for modern farmers.
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Assume that two genes affect the height of wheat plants and both of these genes have two alleles. The table gives a summary of some possible genotypes and phenotypes.
Genotype Phenotypeheight of wheat/cm
AABB 100
AaBb 70
AAbb 70
aabb 40
A wheat plant that was 100 cm tall was crossed with a wheat plant that was 40 cm tall, fertilisation occurred and the seeds were planted and grown.
(d) Using only the information in the table, answer the following questions.
(i) What are the genotypes of the gametes in this cross?
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(ii) What would be the expected genotype and phenotype of the resulting offspring?
Genotype ...........................................................................................................
Phenotype ..........................................................................................................(2)
(Total 18 marks)
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8. The diagram shows the flow of energy through a marine ecosystem.
The units are kJ m–2 year–1.
6 2 5 0
1 0 0 0
5 0 0
1 0 0
4 0 0 0
7 0 0
5 0
P ro d u ce rs
P rim ary co n su m e rs
S ec o n d ary c o n sum ers
R esp ira tion 1 2 5 0
R esp ira tion 2 8 0 0
R esp ira tio n 5 5 0
L ig ht en erg y m easu re d a t se a su r fac e1 2 .5 × 1 0 5
E n erg y in fa ec esan d d e ad o rg an ism s
w h ich fa ll to th e b o tto m
(a) (i) Calculate the percentage of the light energy at the sea surface which is converted into chemical energy in the producers. Show your working.
(2)
(ii) The percentage of the light energy at the sea surface which is converted into chemical energy in the producers is very small. Give two reasons for this.
(2)
(b) Use the information in the diagram to explain why marine ecosystems such as this rarely have more than five trophic levels.
(2)
(c) What happens to the energy in faeces and dead organisms which fall to the bottom of the sea?
(2)
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(d) Light energy is important in the light-dependent reaction of photosynthesis. The energy changes which take place in the light-dependent reaction are shown in the diagram.
E n e rg yL ev e l
AT P
A D P + P i
L ig h t
L ig h t
C h lo ro p h y ll
C hlo ro p h y ll
N A D PR ed u c edN A D P
C h ain o fe le c tro nc arrie rs
C h ain o fe le c tro nca rrie r s
(i) Describe what happens to the chlorophyll when it is struck by light.(2)
(ii) The weedkiller DCMU blocks the flow of electrons along the chains of electron carriers. Describe and explain the effect this will have on the production of triose phosphate in the light-independent reaction.
(3)
(e) Living organisms release energy from organic molecules such as glucose during respiration.Much of this energy is used to produce ATP.Explain why ATP is better than glucose as an immediate energy source for cell metabolism.
(2)
(f) The production of ATP is said to be coupled to the transport of electrons along the carrier chain. Normally, electrons are only passed along the carrier chain if ADP is being converted to ATP at the same time. When the amount of ADP in a cell is low, electrons do not flow from reduced coenzyme to oxygen.
(i) Suggest how the rate of respiration is linked to the needs of the cell.(3)
(ii) DNP is a substance which allows electron transport to take place without the production of ATP. When DNP is given to rats, their body temperatures rise. Explain why.
(2)(Total 20 marks)
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9. Write an essay on the topic below. Credit will be given not only for biological content but also for the organisation and presentation of the essay, and use of grammar; punctuation and spelling.
The different ways in which living organisms obtain their nutrients.(Total 25 marks)
10. The graph shows the effect of different conditions on the rate of photosynthesis.
R ate o fp h o to sy n th es is
L ig h t in te n s ity
2 5 ° C 0 .4 % C O
1 5 ° C 0 .4 % C O
2 5 ° C 0 .0 1 % C O
2
2
2
B
A
(a) (i) Name the factor which is limiting photosynthesis at A.
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(ii) Give a reason for your answer.
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(b) Carbon dioxide is limiting the rate of photosynthesis at B. How does the graph show this?
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(c) A commercial grower is considering increasing the temperature in a glasshouse during the winter to 25 °C. What would the grower need to consider before deciding to do this?
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(Total 6 marks)
11. The graph shows the effect of applying different amounts of nitrogen fertiliser on the yield of wheat.
5 .0
4 .0
3 .0
2 .0
0 .00 2 0 40 6 0 8 0 1 0 0 12 0 1 4 0 1 6 0 1 8 0 2 0 0
Yie ld /to n n e s h a– 1
–1N itro g en fe r tilise r ap p lie d /k g h a
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(i) Calculate the percentage increase in yield obtained when the amount of nitrogen fertiliser
is increased from 50 to 100 kg ha–1. Show your working.
(2)
(ii) It would not be advisable for a farmer to apply more than 160 kg ha–1 of fertiliser to this wheat crop. Use the graph to explain why.
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(iii) Give two advantages of using an inorganic nitrogen fertiliser, rather than an organic fertiliser.
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(Total 6 marks)
12. The enviromment of crop plants can be altered to increase their growth rates and productivity.
(a) Fields which are regularly used to grow crops must have fertilisers added to them. Explain why
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(b) The table shows a comparison of some features of organic and inorganic fertilisers.
Feature Organic Fertilisers Inorganic Fertilisers
Nutrient concentration Low High
Solubility Low High
Rate of nutrient release into soil Slow Rapid
Using information from the table explain one disadvantage of adding inorganic rather than organic fertiliser to farmland
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(c) The graph shows the rate of photosynthesis of wheat plants in different conditions inside a glasshouse.
R ate o fp h o tosy n th es is
P o in tA
0 .1 2 % c arb o n d io x id e a t 2 0 °C
0 .0 3 % c arb o n d io x id e a t 3 0 °C0 .0 3 % c arb o n d io x id e a t 2 0 °C
L ig h t in ten s ity
Which factor is limiting the rate of photosynthesis at point A?Explain your answer.
Factor ..........................................................................................................................
Explanation ................................................................................................................
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(Total 5 marks)
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13. (a) Hoverfly larvae and lacewing larvae are both predators of black bean aphids. An investigation was carried out to see which of these predators would be the better biological control of black bean aphids.The graphs show the results of this investigation.
7 5 0
5 0 0
2 5 0
0
7 5 0
5 0 0
2 5 0
00 05 51 0 1 01 5 1 5
N u m b e r o fin d iv id ua ls/p er m
N u m b e r ofin d iv id u a ls /p er m2 2
Tim e/d ay s T im e/d ay s
F ie ld A F ie ld B
B lack b ea nap h id s B lack b ean
ap h id s
L a cew in glarv ae
H o v erflyla rv ae
It was concluded that hoverfly larvae are better for biological control of black bean aphids. Explain the evidence from the graphs that
(i) supports this conclusion
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(ii) conflicts with this conclusion.
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(b) Describe and explain the ways in which weeds and insect pests reduce crop yields
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(Total 11 marks)
14. Wheat is a cereal crop grown mainly for grain. Wheat straw consists of dead leaves and stems. An investigation was carried out into the effect of adding nitrogen-containing fertiliser on the yield of wheat.
M a ss o f fe rtilise ra d d ed /g m – 2
– 2Y ie ld / g m
G ra in
4 7 8
5 4 9
6 2 2
0 .0
6 .3
5 0 .0
S traw
2 4 5
2 8 4
3 2 4
(a) Does adding 50 g m–2 of nitrogen-containing fertiliser have a greater effect on the grain or the straw? Use suitable calculations based on the figures in the table to support your answer.
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(b) (i) When 6.3 g m–2 of nitrogen-containing fertiliser was added, the ratio of straw to
grain was 0.517. Calculate the ratio of straw to grain when 50 gm–2 of nitrogen-containing fertiliser was added. Show your working.
(2)
(ii) Suggest why the grain to straw ratio may be important to a farmer.
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(c) Farmers remove weeds from land on which wheat is growing. Suggest why the yield of wheat grain is higher if weeds are removed at the beginning of the growing season than if they are removed later in the growing season.
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(Total 8 marks)
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15. The diagram shows the annual transfer of energy in a forest ecosystem. The figures are in
kJ m–2.
A bso rb e dby p ro d u cers
4 .6 × 1 0
O rg an icm o lec u le s
4 4 0 9 0
H eat lo ss inresp ira tio n
2 0 0 0 0
P r im aryco n su m e rs
D e tr itu s1 5 3 3 0
S u n lig h t7 .1 × 1 0
M a te ria ls n o tc on su m ed
5 8 4 0
6
6
(a) Although the producers absorb 4.6 106 kJm–2, only about 1% of this is transferred to organic molecules. Suggest one reason for this.
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(b) Calculate the energy transferred to primary consumers in this ecosystem.
................................................... kJm–2
(1)(c) Nitrogen compounds in the detritus are broken down by bacteria to ammonium ions
)NH( 4
. Describe how ammonium ions are converted into a form that can be readilyabsorbed by the producers.
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(Total 5 marks)
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16. (a) Explain two environmental problems that are normally associated with large-scale deforestation.
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(b) Logging is the removal of mature trees from a forest. The diagram shows a method of sustainable logging of an area of tropical rainforest. Each of sectors 1 to 9 is logged in sequence and the “old growth” area is never felled. Felling in each sector takes about 35 years.
O ldg ro w th
1
2
3
4
5
6
7
89
5 0 k m
Explain how the pattern of logging shown in the diagram would help to conserve the rainforest community.
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(Total 5 marks)
17. (a) (i) What is meant by biological control?
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(ii) Give two characteristics of a successful biological control agent.
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Spider mites are pests which cause damage to cucumbers that are grown in glasshouses. The graphs show the results of an investigation into different ways of controlling spider mites. In one glasshouse, spider mites were treated with pesticides. In another glasshouse, a predatory mite was used as a biological control agent.
Chemical control
2 5
1 5
5
5
0
0
F eb
F eb
M ar
M ar
A pr
A pr
M a y
M a y
Ju n
Ju n
Ju l
Ju l
A u g
A u g
M on th
M on th
N u m b er o fin d iv id u a lsp er 5 cm o fle a f su rfac e
N u m b er o fin d iv id u a lsp er 5 cm o fle a f su rfac e
2
2
B io log ica l C o n tro l
K eyA p p lica tio n o fp es tic id e
P red a to ry m ite
S pid e r m ite
(b) Which method of controlling spider mites was more effective? Give evidence from the graphs to support your answer.
Method .......................................................................................................................
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Evidence .....................................................................................................................
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(c) Neither method gets rid of the spider mites completely. Explain the reason for this for:
(i) chemical control; ..............................................................................................
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(ii) biological control...............................................................................................
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(Total 8 marks)
18. The diagram shows the annual flow of energy through a terrestrial ecosystem.
The figures are in kJ m–2.
S u n lig h t4 × 1 0
G re en p lan ts2 .4 × 1 0
H e rb iv o ro u sin sec ts
In se c tiv e ro u sb ird s
P red a to ryb ird s
2 5 0 0 2 0 0 1 564
(a) Give two reasons why very little of the sunlight energy falling on the leaves of a plant can be used in primary production.
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(b) Explain why a food chain rarely contains more than four trophic levels.
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(Total 5 marks)
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19. Read the following passage.
Deforestation, particularly in tropical rain forests, has proceeded at an alarming rate over thelast 60 years. In addition to local decreases in biodiversity, there have been other, global,effects, especially on climate. Deforestation has been paralleled by an enormous rise in theburning of fossil fuels. These two factors have been important contributors to rising levels of
5 carbon dioxide in the earth’s atmosphere and increases in global temperatures.
Recent discussions on what to do about global warming have produced two new ideas. Oneis that farmers should plant trees on their land to act as carbon ‘sinks’. These would offsetincreased carbon dioxide emissions by industry.
The second idea is that farmers should reduce the amount of ploughing they do. Ploughing10 allows air to enter the soil and helps with the recycling of both carbon and nitrogen. A
reduction in ploughing would cut the oxidation of organic matter being stored in soils, whichwould then act as another carbon ‘sink’.
Use information from the passage and your own knowledge to answer the following questions.
(a) Explain how deforestation could lead to decreases in biodiversity (line 2).
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(b) Explain how trees can act as carbon ‘sinks’ (line 7).
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(c) (i) Explain how a reduction in the amount of ploughing would lead to more carbon being stored in the soil (lines 9 – 12).
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(ii) Ploughing can increase the activity of nitrifying bacteria in the soil. Explain how ploughing can do this and how the activity of nitrifying bacteria can benefit crop plants.
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(Total 15 marks)
34
20. The table shows the effect of a fertiliser on the amounts of straw and grain produced by wheat plants.
Amount of fertiliser
added/g m–2Dry mass of straw
(= stems and leaves)/
g m–2
Dry mass of grain/
g m–2Total dry mass ofstraw plus grain/
g m–2
0 458 252 710
2.8 465 250 715
5.6 475 247 722
11.2 497 238 735
16.8 520 223 743
(a) (i) Calculate the percentage increase in the total dry mass of straw plus grain when the
amount of fertiliser was increased from 5.6 to 16.8 g m–2. Show your working.
............................................... %(2)
(ii) Use the data in the table to describe the effect of increased application of fertiliser on the growth of wheat plants.
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(b) (i) Explain how fertiliser applied to the land could enter streams and rivers.
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(ii) Explain how pollution of river water with fertiliser can cause the death of fish.
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(Total 8 marks)
21. The table shows some results from a study of the transfer of energy in some primary consumers in a grassland ecosystem. All figures are in arbitrary units.
Amount of energy Type of organism
mammals insects
consumed in food (C) 25.00 4.00
absorbed from the gut (A) 12.50 1.60
in faeces (F) 12.50 2.40
in new body mass (P) 0.25 0.64
lost in respiration (R) 12.25 0.96
(a) (i) The ratio of the amount of energy lost in respiration to the amount of energy consumed in food in the mammals is 0.49 : 1. Calculate the ratio of the amount of energy lost in respiration to the amount of energy consumed in food in the insects.
Answer ......................................(1)
(ii) Suggest an explanation for the difference between these two ratios.
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(b) Use the letters C, F and P to complete the equation
R = ..............................................................................................................................(1)
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(c) A higher proportion of the energy consumed in food is absorbed from the gut in secondary consumers than in primary consumers. Suggest an explanation for this.
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(Total 5 marks)
22. Read the following passage.
Early settlers used a technique known as ‘slash and burn’ to clear land for growing crops. Trees were cut down and burned and seeds of crop plants were scattered on the cleared land. After a few years, crop growth was usually so poor that people would move on and repeat the process. At low human population densities there was no long-term damage to the forest as the cleared areas of land had a chance to recover once people had left.
With an increase in human population, and over periods of time, large areas of forest have been destroyed. Modern developments have made possible greater yields from an area of land and farming has become more intensive. To maintain soil fertility, farmers now add fertilisers to the soil.
Use information from the passage and your own knowledge to answer the following questions.
(a) Explain how the process of ‘slash and burn’ would affect the availability of carbon in the atmosphere.
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(b) Explain how bare, cleared land could once again become forest.
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(c) Fertiliser, such as manure, contains ammonium compounds. Explain how the presence of soil bacteria and the use of manure improve crop yield.
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(d) Explain the advantages of conserving a forest ecosystem.
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(Total 15 marks)
38
23. The adult whitefly and its larva feed on the leaves of crop plants. A parasitic wasp lays its eggs inside the whitefly larva. When the wasp larvae hatch, they feed on the internal organs of the whitefly larva. The wasp can be released into glasshouses to act as a biological control for the whitefly.
(a) How would the whitefly reduce the yield of a crop plant?
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(b) (i) Give two reasons why biological control might be better than the use of chemical pesticides for controlling whitefly.
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(ii) Give two reasons why the use of chemical pesticides might be better than biological control of the whitefly.
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(Total 6 marks)
39
24. The graph shows the effect of nitrogen fertiliser on the yield of maize.
1 4
1 3
1 2
11
1 0
9
8
7
60 5 0 1 0 0 1 5 0 20 0 2 5 0
A m o u n t o f n itro g e nfer tilise r / k g h a –1
–13Yie ld /m h a
(a) Calculate the percentage increase in the yield of maize when the fertiliser application was
increased from 10 to 60 kg ha–1. Show your working.
Answer ....................................... %(2)
(b) The percentage increase in yield of maize decreases at higher fertiliser applications. Suggest two reasons why.
1 ..................................................................................................................................
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2 ..................................................................................................................................
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(Total 4 marks)
40
25. Some ways of clearing forest for agriculture are described as sustainable. The diagram shows one way in which agriculture can continue indefinitely on infertile forest soils.
P r im ary fo res t
R iv e r
C u ltiv a te d fie ldH u ts
N e xt se aso n 's f ie ld s.S eco n d ary fo res t c lea redan d b u rn t. S o m e n itro g en -co n ta in in g su b s ta n ceslo s t in sm o k e
A b an d o n edfie ld s
S ec on d a ry fo res treg ro w s. N u trien tlev e ls res to re d in8 -10 y ears .
(a) One way to catch flying insects is to trap them on a sticky surface.
(i) Describe how you could use sticky traps to compare the diversity of flying insects in the primary forest and in a cultivated field.
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(ii) Describe and explain how the diversity of insects in the primary forest would differ from the diversity of insects in the cultivated field.
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(b) Use your knowledge of nitrogen cycling to explain
(i) why crops can be grown in the cleared field for only two or three years;
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(ii) how the concentration of nitrates in the soil is restored 8 - 10 years after cultivation is abandoned.
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(Total 15 marks)
42
43
26. Two fields, A and B, were used to grow the same crop. The fields were divided into plots. Different masses of fertiliser containing sodium nitrate were applied to these plots. After six weeks, samples of crop plants from each plot were collected and their mass determined. The results are shown in the table.
Mass of fertiliser Mass of crop/kg m–2
added/kg ha–1 Field A - used for grazing cattlein previous year
Field B - used for same crop inprevious year
0 14.5 6.4
10 16.7 9.8
20 17.4 12.9
30 17.5 16.2
40 17.5 17.1
50 17.5 17.1
60 17.5 17.1
(a) (i) Describe the pattern shown by the data for field B.
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(ii) Explain the change in the mass of crop produced from field B when the mass of
fertiliser added increases from 0 to 20 kg ha–1.
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(iii) Explain why the mass of crop produced stays the same in both fields when more than 40 kg of fertiliser is added.
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(b) In the previous year, field A had been used for grazing cattle. Field B had been used to grow the same crop as this year. When no fertiliser was added, the mass of crop from field A was higher than from field B. Explain this difference.
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(c) Explain two advantages and one disadvantage of an inorganic fertiliser such as sodium nitrate compared with an organic fertiliser such as manure.
Advantage 1 ...............................................................................................................
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Advantage 2 ...............................................................................................................
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Disadvantage .............................................................................................................
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(Total 10 marks)
27. (a) Insecticides are pesticides which kill insects. A low concentration of insecticide was sprayed on the leaves of rose plants to kill greenfly which were feeding on the plants. Ladybirds eat greenfly. One month after spraying, the concentration of insecticide in the tissues of ladybirds was found to be higher than the concentration sprayed on the rose plants. Explain why.
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45
(b) Spotted knapweed is a common weed in the USA. Two methods, chemical control and biological control, have been used to reduce the numbers of spotted knapweed plants.The table shows the results of an investigation comparing the effectiveness of these two methods.
Month Mean number of spotted knapweed plants per m2
Chemical control Biological control
February 2 2
March 15 3
April 3 3
May 20 5
June 3 4
July 16 3
August 2 2
(i) Describe the pattern of plant numbers resulting from the use of
chemical control; ........................................................................................................
.....................................................................................................................................(1)
biological control. .......................................................................................................
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(ii) Explain how chemical control leads to the changes in the number of spotted knapweed plants from March to June.
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46
(c) Explain why the spotted knapweed plants were never completely eliminated when using
(i) chemical control;
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(ii) biological control.
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(Total 10 marks)
28. The diagram shows the transfer of energy through a cow. The figures are in kJ × 106 year–1.
C = 91 .3 4
R = 3 0 .5 1
A = 3 4 .2 8
P = .. .. .. .. .U = 0 .0 3F = 5 7 .0 6
Key: A = energy absorbed from the gutC = energy consumed in foodF = energy lost in faecesP = energy used in production of new tissueR = energy lost by respirationU = energy lost in urine
(a) (i) Complete the following equation for the energy used in the production of new tissue. Use only the letters C, F, R and U.
P = ...........................................................................................................................(1)
47
(ii) Calculate the value of P.
P = ................................... kJ × 106 year–1
(1)
(b) It has been estimated that an area of 8100 m2 of grassland is needed to keep one cow. The
productivity of grass is 21 135 kJ m–2 year–1. What percentage of the energy in the grass is used in the production of new tissue in one cow? Show your working.
Answer ....................................... %(2)
(c) Keeping cattle indoors, in barns, leads to a higher efficiency of energy transfer.Explain why.
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(Total 5 marks)
29. The soybean is a leguminous plant. The effect of nitrate fertiliser and of the nitrogen-fixing bacterium, Rhizobium, on the growth of soybeans and on the growth of one species of grass was investigated. The soybeans and grass seeds were sown together in pots of soil in five different proportions. They were then treated with different combinations of nitrate fertiliser and Rhizobium bacteria, as follows:
Batch A: no Rhizobium, no nitrate fertiliserBatch B: Rhizobium added, no nitrate fertiliserBatch C: no Rhizobium, nitrate fertiliser addedBatch D: Rhizobium added, nitrate fertiliser added
48
The dry masses of the soybean plants and of the grass were determined after 6 months of growth. The results are shown in the graphs.
0
0
0
0
1
1
1
1
2
2
2
2
3
3
3
3
4
4
4
4
S o y b ean
S o y b ean
S o y b ean
S o y b ean
N u m b er o f g ra ss seed s
N u m b er o f g ra ss seed s
N u m b er o f g ra ss seed s
N u m b er o f g ra ss seed s
8
8
8
8
6
6
6
6
4
4
4
4
2
2
2
2
0
0
0
0
N u m b er o f so y b ean s
N u m b er o f so y b ean s
N u m b er o f so y b ean s
N u m b er o f so y b ean s
G rass
G rass
G rass
G rass
6 0
5 0
4 0
3 0
2 0
1 0
0
6 0
5 0
4 0
3 0
2 0
1 0
0
6 0
5 0
4 0
3 0
2 0
1 0
0
6 0
5 0
4 0
3 0
2 0
1 0
0
D rym ass / g
D rym ass / g
D rym ass / g
D rym ass / g
A : n o , n o n itra teR h izob iu m
C : n o , + n itra teR h izob iu m
B : + , n o n itra teR h izob iu m
D : + , + n itra teR h izob iu m
(a) Did Rhizobium bacteria have any effect on the growth of the grass? Give evidence from graphs C and D for your answer.
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49
(b) Can the soybean make use of nitrogen supplied in the form of nitrate fertiliser?Give evidence from the graphs for your answer.
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(c) Describe and explain the effect of Rhizobium bacteria on the growth of soybeans.
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(Total 6 marks)
30. (a) Fertilisers are added to soils to replace the nutrients lost when crops are harvested.Give two advantages of using
(i) an organic fertiliser such as farmyard manure;
1 ...................................................................................................................….
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2 ......................................................……...........................................................
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(ii) an inorganic fertiliser.
1 ....................…………...........................................................................…......
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(b) The table shows the effects of adding manure or inorganic fertiliser to some crops grown in plots.
Yield of crop / tonnes per hectare
Crop Control plot Farmyard manure only
Inorganic fertiliser only
Sugar beet 3.8 15.6 15.6
Mangold 3.8 22.3 30.9
Wheat 2.1 3.5 3.1
(i) How should the control plot be treated?
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(ii) Suggest why inorganic fertiliser improved the yield of the mangold crop more than the sugar beet crop.
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(Total 7 marks)
31. Phytoplankton are microscopic photosynthesising organisms which live in water. In favourable environmental conditions they have a very high rate of reproduction. They are eaten by microscopic animals called zooplankton. In an investigation, samples of water were removed from a lake at intervals over a twelve-month period and the biomasses of these organisms were determined. The results are shown in the graph.
51
B io m a ss
Z o o p lan k to n
P h y to p la n k to n
Jan F eb M ar A p r M ay Ju n Ju l A u g S ep O c t N o v D e c
M o n th
52
The diagram shows the relationship between the biomass of the phytoplankton and the biomass of the zooplankton for one of the months during this investigation.
Z o o p lan k to n
P h y to p lan k to n
(a) Use the graph to give one month in which this relationship would have been found.
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(b) Explain why the biomass of the primary consumers is less than the biomass of the producers in most communities.
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(c) Explain why the biomass of the phytoplankton in the lake could be less than that of the zooplankton, as shown in the diagram.
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(Total 5 marks)
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32. (a) Substances found in fallen leaves contain the elements carbon and nitrogen.Explain how the activities of decomposers and nitrifying bacteria recycle the substances in fallen leaves for re-use by the trees.
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(b) Explain how the felling and burning of trees on a large scale could affect the concentration of carbon dioxide in the atmosphere.
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(c) Both rapidly-growing softwood trees and slow-growing hardwood trees grow in tropical rainforests. The seeds of both kinds of tree lie dormant on the floor of a mature forest and only germinate when exposed to light and warmth. However, the seedlings of many hardwood species grow more successfully beneath the protective canopy of the softwood trees.
When a small area of trees has been cut down, it can return naturally to tropical rainforest. Suggest and explain how re-establishment of the rainforest ecosystem may occur in such areas.
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(Total 15 marks)
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33. Since 1965 there has been a steady rise in the phosphate concentration in the water of Lake Windermere. Scientists have monitored the phosphate concentration and plant biomass over a period of time. The results are shown in the graphs.
3 0
2 0
1 0
0
3 0
2 0
1 0
0
1 9 5 5
1 9 5 5
1 9 6 5
1 9 6 5
1 9 7 5
1 9 7 5
1 9 8 5
1 9 8 5
1 9 9 5
1 9 9 5Yea r
P h o sp h a teco n cen tra tio n /g d m – 3
P lan tb io m ass /a rb itra ryu n its
(a) Suggest one source of the phosphate in the lake.
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(b) Calculate the percentage decrease in plant biomass between 1985 and 1995.Show your working.
Answer ............................................(2)
56
57
(c) From these graphs, a student concluded that changes in phosphate concentration caused changes in plant biomass. Explain why this conclusion may not be valid.
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(d) Between 1982 and 1992 the number of fish in the lake decreased. Explain how the change in phosphate concentration may have resulted in this decrease in the fish population.
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(e) (i) One plant which has grown in the lake is blanket weed. It could be controlled by the use of herbicides. Give two disadvantages of this method of control.
1 .......................................................................................................................
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(ii) Small freshwater shrimps could be added to eat the blanket weed. They would act as a biological control. Suggest one reason why adding the shrimps would not clear the lake of blanket weed.
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(Total 15 marks)
34. The herring is a fish found in the North Sea. In the food chain below, the figures represent
biomass. The units are g m–3.
P h y to p lan k to n Z o o p la n k to n H e rrin g
4 .0 2 1 .0 1 .7
(a) Sketch and label a pyramid of biomass to represent this food chain.
(1)
(b) In this food chain, the phytoplankton reproduce very rapidly. Suggest why this rapid rate of reproduction is essential to sustain the food chain.
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(Total 3 marks)
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35. (a) Explain how large-scale deforestation for agriculture would lead to a decrease in the diversity of organisms in the area.
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(b) Explain how large-scale deforestation could
(i) increase the concentration of carbon dioxide in the atmosphere in the area;
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(ii) decrease the concentration of carbon dioxide in the atmosphere in the area.
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(Total 5 marks)
36. (a) The table shows the effect of different concentrations of inorganic nitrogen fertiliser on the yield of spinach plants.
Nitrogen fertiliser applied / kg ha–1 40 110 160 210 260 310 360
Yield / tonnes ha–1 8 13 18 22 24 26 26
(i) Describe and explain the effect of adding inorganic nitrogen fertiliser on the yield of spinach.
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(ii) Give two advantages of using an inorganic fertiliser, rather than manure.
1 .......................................................................................................................
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2 .......................................................................................................................
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(b) Fertilisers may leach out of farmland into freshwater streams and lakes. Explain how this can be harmful to the environment.
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A laboratory investigation was carried out into the relationship between a population of glasshouse whitefly and its wasp parasite. The results are shown in the graph.
61
N u m b er p e r u n ita rea
0 5 1 0 1 5 2 0G en e ra tio n s
P a ra s ite
G lassh o u se w h ite fly
62
(c) (i) Explain the changes which took place in both populations between generations 6 and 13.
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(ii) The wasp parasite could be used as a biological control agent for the glasshouse whitefly. What is biological control?
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(Total 15 marks)
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37. A food chain found in oak woodland is shown below.
Organism Oak Tree Aphid Hoverfly Great tit Parasitic mite
Trophic level A B C D E
The pyramid of numbers and pyramid of biomass representing this food chain are shown in the diagram.
E
D
C
B
A
T ro p h icle v e l
P y ram id o fn u m b ers
P y ram id o fb io m ass
65
(a) Not all the light energy entering the leaves of the oak tree is used in photosynthesis. Give one reason for this.
.....................................................................................................................................
.....................................................................................................................................(1)
66
(b) Give two ways in which energy is lost between trophic levels A and B.
1 .................................................................................................................................
....................................................................................................................................
2 .................................................................................................................................
....................................................................................................................................(2)
67
(c) Explain the difference between the shapes of the two pyramids at trophic levels D and E.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(Total 5 marks)
68
38. Deforestation often involves clearing large areas of forest for use as agricultural land.
(a) Deforestation reduces the diversity index of an area cleared in this way. Explain why.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
69
(b) Because the forest soil is often nutrient-poor, nitrogen-containing fertilisers may be applied to ensure good crop yields. Use your knowledge of the nitrogen cycle to explain the potential benefit of applying a fertiliser containing ammonium nitrate rather than one containing potassium nitrate.
.....................................................................................................................................
.....................................................................................................................................
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(Total 5 marks)
70
39. Detritivorous insects feed on the dead remains of plants. Some students estimated the numbers of detritivorous insects at two different sites in an ecosystem. They also obtained data about the net primary production of the sites to see if this influenced the numbers of insects present. Net primary production is a measure of plant biomass formed per year. The results are shown in the table.
SiteNumber of insects
per m2Net primary production /
g m–2 y–1
A 316 1440
B 90 550
71
(a) Explain how the students could use the mark-release-recapture technique to estimate the numbers of insects.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(4)
72
(b) The students used the chi-squared (χ2) test to test the hypothesis that there was no significant difference between the numbers of insects per square metre at sites A and B.
The value they obtained was 125.8. They checked this value in χ2 tables.
(i) How many degrees of freedom should they check against?
...........................................................................................................................(1)
73
(ii) What level of probability is normally used to judge whether a difference is statistically significant?
...........................................................................................................................(1)
74
(iii) The value of χ2 for the 0.001 level of probability for this number of degrees of freedom is 10.8. What does the value obtained by the students suggest about the difference in numbers of the insects per square metre between the two sites?Explain your answer.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(2)
75
(c) (i) Explain why the net primary production of an area does not represent the total amount of plant biomass formed per year by photosynthesis.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(2)
76
(ii) Suggest how the difference in net primary production of sites A and B might explain the difference in the number of insects between the sites.
...........................................................................................................................
...........................................................................................................................(1)
77
(iii) Explain the role of bacteria in making carbon in dead plant remains available to plants.
...........................................................................................................................
...........................................................................................................................
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...........................................................................................................................
...........................................................................................................................
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(Total 15 marks)
78
40. Purple loosestrife is a plant which grows in Europe. It was introduced into the USA where it became a pest.
(a) Suggest why purple loosestrife became a pest when it was introduced into the USA, but is not a pest in Europe.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
79
(b) A European beetle was tested to see whether it could be used for the biological control of purple loosestrife in the USA. In an investigation, beetles were released in an area where purple loosestrife was a pest. The table shows some of the results.
Time after releasing
beetles / years
Mean number of purple loosestrife stems per
square metre
Mean number of beetles per square
metre
1 22 5
2 8 40
3 6 68
4 7 62
Are the beetles effective in controlling purple loosestrife? Give evidence from the table to support your answer.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
80
(c) Fire-ants are a serious pest in parts of the USA. An investigation was carried out to find the best way to control the fire-ant population. The graph shows the results of this investigation.
0 1 2 3
1 2 0
1 0 0
8 0
6 0
4 0
2 0
0
In sec tic id e o n ly
In sec tic id e fo llo w ed b yb io lo g ica l co n tro l
T im e a fte r trea tm en t w ith in sec tic id e / y ea rs
P e rcen tag eo f in itia lp o p u la tio n
In sec tic id eap p lied
81
(i) Describe the effect of using insecticide followed by biological control.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(2)
82
(ii) Explain the change in fire-ant population over the period when they were treated with an insecticide alone.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(3)
(d) Give the advantages and disadvantages of using biological control.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
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.....................................................................................................................................(6)
(Total 15 marks)
83
41. Phytoplankton and zooplankton were both found in a lake. Phytoplankton are unicellular protoctistans. Zooplankton are small animals that feed on the phytoplankton.
The biomass of the phytoplankton and zooplankton per cubic metre of water was estimated on several occasions over a period of three months. These data were used to calculate the productivity of the phytoplankton and zooplankton. In this instance, productivity was described as the amount of biomass produced per cubic metre per day.
(i) What calculation would have to be made to find the productivity of the phytoplankton?
.....................................................................................................................................
.....................................................................................................................................(1)
(ii) The ratio of productivity of phytoplankton to productivity of zooplankton per year in this lake was 9.2 : 1. How is this figure consistent with the principles of energy transfer through an ecosystem?
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(Total 3 marks)
84
42. When fertilisers are applied to fields next to a lake, nitrogen-containing substances from the fertilisers get into the lake.
(a) (i) Describe how the nitrogen-containing substances get into the lake.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(1)
(ii) It takes longer for the nitrogen-containing substances to get into the lake when an organic fertiliser is used than when an inorganic fertiliser is used. Explain why it takes longer when an organic fertiliser is used.
...........................................................................................................................
...........................................................................................................................(2)
(b) Describe how the presence of nitrates in a lake may eventually lead to the death of fish.
.....................................................................................................................................
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.....................................................................................................................................(4)
(Total 7 marks)
85
43. In the activated sludge method of sewage treatment, organic matter in untreated sewage supplies nutrients to bacteria in the treatment tank. These bacteria include decomposers and nitrifying bacteria. The bacteria are eaten by ciliated protoctistans, which are, in turn, eaten by carnivorous protoctistans.
(a) (i) Sketch and label a pyramid of energy for the organisms found in the treatment tank.
(1)
86
(ii) Explain what causes this pyramid of energy to be this shape.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(2)
(b) (i) Explain the roles of the decomposers and the nitrifying bacteria in converting nitrogen in organic compounds in the sewage into a soluble, inorganic form.
...........................................................................................................................
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...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(3)
(ii) Nitrifying bacteria are one kind of bacteria that are important in the nitrogen cycle; nitrogen-fixing bacteria are another kind. Describe the part played by nitrogen-fixing bacteria in the nitrogen cycle.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(2)
87
(c) The organic matter in untreated sewage consists of small particles, which are suspended in water. Activated sludge consists of solid lumps (flocs) of organic matter and bacteria. When the two are mixed in the treatment tank, bacteria from the flocs become dispersed in the water and feed on the suspended organic matter, converting it to flocs. Different types of ciliated protoctistans feed on the bacteria.
Free-swimming protoctistans are able to move throughout the tank.
Crawling protoctistans can only move over the surface of the flocs.
The diagram shows the change in the nature of the organic matter in the treatment tank and the changes in the numbers of the different types of organisms present.
N u m b er o fb ac te ria
N u m b er o fp ro to c tis tan s
F ree sw im m in g
C raw lin g
D isp e rsed b ac te riaB ac te ria o n flo ck s
N a tu re o fo rg an icm a tte r intan k
T im e
M ain ly su sp en d ed M ain ly flo ck s
88
(i) Explain the changes in the numbers of dispersed bacteria and the numbers of free-swimming protoctistans.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(3)
(ii) Explain how the changes that occur in the treatment tank illustrate the process of succession.
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...........................................................................................................................
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...........................................................................................................................(4)
(Total 15 marks)
89
44. Ions of metals such as zinc often pollute rivers. The effect of zinc ions on gas exchange and respiration in fish was investigated. Fish were kept in tanks of water in a laboratory.
The fish in one group (X) had a solution of a zinc compound injected directly into their blood and were then put in a tank of zinc-free water. A second group (Y) was not injected but had the solution of the zinc compound added to the water in the tank.
The partial pressure of oxygen in the blood of both groups of fish was then monitored. The results are shown in the graph.
0 3 6 9 1 2 1 5 1 8 2 1 2 4 2 7
1 2
1 0
8
6
4
2
0
P artia l p re ssu reo f o x y g en inb lo o d leav in gth e g as ex ch an g esu rface / k P a
G ro u p Z in c in b lo o d
X
G ro u p Z in c in w a te r
Y
Z in cg iv en
T im e / h
(a) During this investigation, the water temperature in the tanks was kept constant. Explain why changes in the water temperature might lead to the results of the investigation being unreliable.
.....................................................................................................................................
.....................................................................................................................................(1)
90
(b) The results from the two groups were compared using a statistical test.
(i) Suggest a null hypothesis that could be tested.
...........................................................................................................................(1)
(ii) Explain why it is important to use a statistical test in analysing the results of this investigation.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(2)
(c) Two suggestions were made to explain the results shown in the graph.
A Zinc ions reduce the rate at which oxygen is taken up from the water and passes into the blood.
B Zinc ions reduce the ability of haemoglobin to transport oxygen.
Which of these suggestions is the more likely? Explain the evidence from the graph that supports your answer.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(d) During the investigation, the pH of the blood was also monitored. It decreased in group Y. Suggest an explanation for this decrease in pH.
.....................................................................................................................................
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.....................................................................................................................................
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.....................................................................................................................................
.....................................................................................................................................(3)
91
(e) Leaves were collected from sycamore trees growing in a polluted wood and the concentration of some metal ions in samples of these leaves was measured. Woodlice were then fed with the leaves. After 20 weeks, the concentration of the ions in the bodies of the woodlice was measured. Some of the results are shown in the table.
Concentration of ions / µg g–1
Copper Cadmium Zinc Lead
Leaves 52 26 1430 908
Woodlice 1130 525 1370 132
(i) Which of the elements shown in the table is concentrated most by the woodlice? Use suitable calculations to support your answer.
(2)
(ii) Suggest what happens to most of the lead ions in the leaves eaten by the woodlice.
...........................................................................................................................
...........................................................................................................................(1)
(iii) Explain the difference in the copper ion concentration between the leaves and the woodlice.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(2)
(f) Yorkshire fog is a species of grass. Two varieties of Yorkshire fog were studied. One variety was tolerant to arsenic, while the other variety was not. In a series of investigations, it was found that
Arsenic-tolerant plants grow in soil which contains a high concentration of arsenic.
Arsenic-tolerant plants growing in soil containing high concentrations of arsenic and phosphorus-containing compounds have very low concentrations of arsenic in their cells. They also have low concentrations of phosphates in their cells. Arsenic and phosphorus are chemically similar.
Plants that are not tolerant to arsenic grow poorly on soil which has a high concentration of both arsenic and phosphorus-containing compounds.
Tolerance to arsenic in Yorkshire fog is caused by a single gene with the allele, a, for tolerance recessive to the allele, A, for non-tolerance.
92
(i) What caused the allele for tolerance to first arise?
...........................................................................................................................
...........................................................................................................................(1)
(ii) Give two functions of phosphates in plant cells.
1 ........................................................................................................................
...........................................................................................................................
2 ........................................................................................................................
...........................................................................................................................(2)
(iii) Arsenic-tolerant Yorkshire fog plants are very rare in areas with low concentrations of arsenic in the soil, even where the soil has a high concentration of phosphate. Explain why they are unable to compete in these conditions with plants that are not tolerant to arsenic.
...........................................................................................................................
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...........................................................................................................................(3)
(Total 20 marks)
45.
F irs ttro p hic
lev e l
S e co n dtro p h ic
lev e l
T h irdtro p h ic
le v e l
6 9 1 0 0 0 0
7 7 0 0 0
1 2 5 0 0E n erg y lo s t
E n erg y los t
S o la r en erg y n o t u sedin p h o to sy n th e s is
9 0 0 0 0
To ta lso la ren erg y7 0 0 0 0 0 0
(A ll u n its a re in k ilo jo u le s p e r sq u are m etre p er y ea r)
93
(a) Suggest two reasons why not all of the solar energy can be used in photosynthesis.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................(2)
(b) (i) Calculate the amount of energy available to the third trophic level.
..............................(1)
(ii) Describe one way in which energy is lost from the first trophic level.
...........................................................................................................................
...........................................................................................................................(1)
(iii) Suggest one reason why the energy loss from the first trophic level is greater than that from the second trophic level.
...........................................................................................................................
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(Total 5 marks)
94
46. Dieldrin is an organochlorine pesticide. It was used to treat wheat grain before planting. An investigation was carried out to find the effect of treated wheat grain on the dieldrin concentration in the tissues of mice living in wheat fields. Mice were trapped before and after the treated wheat was planted. One line of traps was in the grass border of the field. Another was in the area planted with wheat.
Period Locationof traps
Number of mice
caught
Number of miceanalysed
Mean dieldrincontent of mice /
ppm
Beforesowing
In grassborder
11 9 0.15
Beforesowing
In plantedarea
15 4 0.23
Aftersowing
In grassborder
18 2 6.49
Aftersowing
In plantedarea
18 7 10.96
(a) (i) Calculate the percentage change in mean dieldrin concentration in the tissues of mice from each of the two areas. Show your working.
P erc en tag e ch an g e ing ra ss b o rd er
P erc en tag e ch an g e inp lan ted a rea% %
(2)
(ii) Suggest one explanation for the different dieldrin content of mice trapped in the two areas after sowing.
...........................................................................................................................
...........................................................................................................................(1)
(b) Suggest one reason why the results of the investigation might be unreliable.
....................................................................................................................................
....................................................................................................................................(1)
95
(c) Suggest an explanation for the fact that the use of dieldrin is now banned in this country.
....................................................................................................................................
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....................................................................................................................................(2)
(Total 6 marks)
47. (a) The diagram shows part of a food web in a marine ecosystem.
P h y to p la n k to n B a rn ac le la rv a
S an d e e l
H e rrin g C o rm o ra n t
7 0 % o f d i e t
2 1 % d ie t
Draw and label a pyramid of numbers for the food chain.
Phytoplankton Barnacle larva Herring - Cormorant.
(1)
(b) Explain, in terms of energy, why food chains with the fewest steps are most efficient.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
96
(c) If the barnacle population were to decrease as a result of pollution. explain how the herring population may be affected.
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.....................................................................................................................................(2)
(Total 5 marks)
48. The expanding human population places increasing demands on limited resources to satisfy food production. Farmers employ a variety of methods to eliminate crop-destroying pests in order to increase food production. In the short term, chemical sprays have proved an effective method. However, the use of chemicals, particularly ‘broad spectrum’ compounds, has caused problems. For this and other reasons alternative methods of controlling pests are now being used. Integrated pest management utilises chemical and biological control methods, together with a number of agricultural practices, e.g. crop rotation and planting pest-resistant varieties. Pest-resistant varieties have been produced by many years of selective breeding and more recently by genetic engineering.
(a) Explain what is meant by ‘biological control’, and describe one example of how biological control has been used to control a specific pest.
.....................................................................................................................................
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97
(b) Explain the advantages and disadvantages of using biological methods, rather than chemicals, to control pests.
.....................................................................................................................................
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.....................................................................................................................................(4)
(c) Briefly describe the process of genetic engineering and suggest one advantage it has compared to selective breeding.
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(Total 12 marks)
98
49. The rhinoceros beetle is a pest which damages coconut palms growing on South Pacific islands. One method of control is to introduce a virus which kills the beetles. The virus was first used on the island of Tonga in 1971. The table shows the results of surveys of rhinoceros beetle damage to palm trees carried out at two sites in 1971 and 1978.
Site 1971 1978
Number of palmtrees examined
Number of palmtrees damaged
by beetles
Number of palmtrees examined
Number of palmtrees damaged
by beetles
A 289 48 302 23
B 226 34 278 28
(a) The virus was introduced at sites A and B. At site A the virus was introduced as part of an integrated pest management scheme.Was the introduction of the virus more successful at site A or at site B?Support your answer with suitable calculations from the data in the table.
.....................................................................................................................................
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.....................................................................................................................................(3)
(b) (i) Suggest two techniques which could be combined with the introduction ofthe virus to produce effective pest management schemes.
1. ........................................................................................................................
............................................................................................................................
2. ........................................................................................................................
............................................................................................................................(2)
(ii) Explain the benefits of an integrated pest management scheme.
............................................................................................................................
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............................................................................................................................(2}
99
(c) Introduction of the virus is an example of biological control.
Explain two possible limitations of biological control methods.
1. .................................................................................................................................
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2. .................................................................................................................................
.....................................................................................................................................(2)
(Total 9 marks)
50. (a) Why do plants need ions which contain nitrogen?
.....................................................................................................................................
.....................................................................................................................................(1)
(b) (i) Explain why it is necessary for farmers to apply fertilisers to land that is used annually to grow a cereal crop.
..........................................................................................................................
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..........................................................................................................................
..........................................................................................................................(2)
(ii) Explain what is meant by the law of diminishing returns with respect to the application of artificial fertilisers.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(2)
100
(c) The graph shows the relationship between nitrate application to farmland and the concentration of nitrate in a nearby reservoir.
2 5
2 0
1 5
1 0
5
0
1 2 5
1 0 0
7 5
5 0
2 5
0
N itra teap p lic a tion tofa rm lan d/k g p er h ec ta rep er y ear
N itra teco n c en tra tio nin re se rv o ir/m g p er litre
1 9 6 0 1 9 6 5 1 9 70 19 7 5 1 9 8 0 1 9 8 5 19 9 0Year N itra te ap p lic a tio n
to fa rm la n dN itra te co n ce n tra tio nin re se rv o ir
(i) Explain why there was an overall increase in the concentration of nitrate of nitrate in the reservoir between 1960 and 1990.
..........................................................................................................................
..........................................................................................................................(1)
(ii) Suggest one explanation for the large fall in nitrate concentration in the reservoir between 1982 and 1984.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(2)
101
(d) Explain why there is concern at the amount of nitrates being leached into rivers, lakes and reservoirs.
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(Total 12 marks)
51. The flow chart summarises what happens to the energy in food eaten by a cow. The figures on the right-hand side of the diagram refer to the percentage of the total amount of energy in the food.
E n erg y in fo o d
X
E n e rg y fo r m etab o lism
N et en erg y av a ilab lefo r fo rm a tio n of
n ew tissu e
F a ece s
G ases re lea se dd u ring d ige s tio n
U rin e
E n erg y fo rm o v e m e nt,h ea t,e tc
3 0
8
4
2 3
3 5
1 0 0
(a) (i) What is represented by Box X?
...........................................................................................................................
...........................................................................................................................(1)
(ii) Write a simple equation summarising the relationship between energy for metabolism (M), net energy (N) and energy from respiration (R).
...........................................................................................................................102
(1)(b) Higher yields can be produced from cows if they are kept in heated sheds rather than
allowed to live outside. Use the information in the flow chart to suggest one explanation for this.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(c) The amount of beef that can be produced from a given area of land is less than the amount of a plant crop such as wheat. Use your knowledge of food chains to explain why.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(1)
(Total 5 marks)
52. The diagram represents the cycling of nitrogen on a dairy farm. The width of the arrows represents the relative amount of nitrogen.
G ra ssc ro p C a ttle M ilk
N itra te sin so il
L o ss fro m so il
F ertilise r
(a) Not all of the nitrate is taken up by the grass crop. Some is lost from the soil.Give two ways in which nitrate may be lost from the soil.
1...................................................................................................................................
2...................................................................................................................................(1)
103
(b) Use information from the diagram to explain why it is necessary for a farmer to add fertiliser in order to maintain production of milk.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(c) Complete the flow chart below to show the pathway by which nitrogen in the urine and faeces of cattle is converted into a form suitable for uptake by the grass crop.Indicate on your flow chart the type of bacterium responsible for each step.
N itro ge n inu rin e a n d fa ece s
(2)(Total 5 marks)
104
53. The graph shows the nitrate concentration in a river over a period of one calendar year.
5 0
4 0
3 0
2 0
1 0
C o nc en tra tio no f n itra teio n s/m g d m – 3
J F M A M J J A S O N D
M o n th
(a) (i) Describe the variation in nitrate concentration shown in the graph.
..........................................................................................................................
..........................................................................................................................(1)
(ii) Suggest two possible explanations for a rise in nitrate concentration in the river.
1. .......................................................................................................................
2. .......................................................................................................................(2)
(b) Explain how each of the following could account for falling nitrate concentration.
(i) algal growth
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(2)
105
(ii) biological denitrification
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..........................................................................................................................(2)
(Total 7 marks)
54. Sand shrimps are crustaceans which live and feed in the surface layers of sand and mud in estuaries. The graph (Figure 1) shows the range of temperature and salt concentration in which these sand shrimps can survive.
3 0
2 0
1 0
00 1 2 3 4 5
S alt co n ce n tra tio n /%
Tem p era tu re /ºC
R a n g e inw h ich sa n dS h r im p s su r-v ive
F ig u re 1
106
Figure 2 shows a sketch map of a tropical estuary where sand shrimps live. The salt concentration varies as the tide goes in and out, and as different volumes of sea water mix with the fresh water from the river. Below the map is a graph which shows the maximum and minimum salt concentrations at different points along the estuary.
K e y A rea w h eresan d shr im p sa re fo u n d
R iv er
A rea s ex p o seda t lo w tid e
P erm an e n tflo w o f w a te r
C B A
O p e nse a
F u r th e s tp o in t rea ch ed
b y tid e
4
3
2
1
0
S a ltco n ce n tra tio n /%
D is ta n ce
F ig u re 2
M a x im u m
M in im u m
(a) Use the information given to explain
(i) the presence of sand shrimps at A;
..........................................................................................................................
..........................................................................................................................
(ii) the absence of sand shrimps at B;
..........................................................................................................................
..........................................................................................................................
(iii) the absence of sand shrimps at C.
..........................................................................................................................
..........................................................................................................................(3)
(b) (i) Another species of crustacean, Y, can tolerate only salt concentrations below 1.5% and temperatures below 20 °C. Mark on the map, with a Y, one place where species Y might live.
(1)
107
(ii) Suggest how having different ranges of tolerance enables both species of crustacean to survive in the same estuary.
..........................................................................................................................
..........................................................................................................................(1)
(c) Suggest two abiotic factors, other than salt concentration and temperature, that you would expect to show significant variation at point A on the map.
1. .................................................................................................................................
2. .................................................................................................................................(2)
(d) The annual biomass production per square metre is much higher in the estuary than on the land around the estuary. The mean length of the food chains in the estuary is also greater. Suggest an explanation for the estuary having longer food chains.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(Total 9 marks)
55. Table A shows the nitrogen input on a dairy farm. Table B shows what happens to this nitrogen.
Table A Table B
Nitrogen input Nitrogen content/kg per hectare
Fate of nitrogen Nitrogen content/kg per hectare
Inorganic fertiliserand manure
259 In plants 112
Animal food 60 In milk and meat 67
Fixation 19 Leaching 56
Total 338 Denitrification 55
Released to air as ammonia 48
Total 338
(a) Calculate the percentage of the total nitrogen input incorporated into milk and meat.
...................%(1)
108
(b) (i) Use the data to explain why dairy farmers use fertilisers.
...........................................................................................................................
...........................................................................................................................
........................................................................................................................... (1)
(ii) A farmer plants clover, which is a leguminous plant, in the fields used for grazing cattle. Explain how the clover might affect the amount of fertiliser that the farmer needs to use.
...........................................................................................................................
........................................................................................................................... (1)
(ii) Explain how environmental damage may arise from leaching of fertiliser.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................(4)
(Total 7 marks)
109
56. In an investigation of food chains in an area of grassland, an experimental plot was treated with a solution containing radioactive phosphate. The phosphate was taken up by the plants and their tissues became radioactive.
The bar chart shows the concentrations of radioactive phosphate in the tissues of the plants, the herbivores and the carnivores in the plot over the next six weeks.
C o n ce n tra tionof ra d ioa c tiv eph o sp h a tein tis su es
1 2 3 4 5 6Tim e/w eek s
K ey
P la n tsH erb iv o re sC arn iv o res
(a) The radioactive phosphate was absorbed by the plant and incorporated into organic compounds. Name two phosphorus-containing organic compounds and describe their importance in plants.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(4)
(b) (i) Describe and explain the changes in the concentrations of radioactive phosphate in the tissues of the plants and the herbivores over the six–week period.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
.......................................................................................................................... (4)
110
(ii) Suggest one way in which microorganisms are involved in recycling phosphorus contained in the tissues of dead carnivores.
..........................................................................................................................
..........................................................................................................................
.......................................................................................................................... (1)
(c) If radioactive carbon had been used for this investigation, a much lower proportion would be passed on to the organisms in the next trophic level. Suggest why.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(3)
(Total 12 marks)
57. Over most of the last 2000 years, agricultural practices in Britain have resulted in an increase in the number of species compared to the original climax forest. Modern intensive agriculture, however, is leading to a reduction in the number of invertebrate species such as insects.
(a) Explain how each of the following activities associated with modern farming might reduce the number of species of invertebrate animal.
(i) the use of herbicides
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(ii) using large areas for the growth of single crops
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(4)
111
112
(b) Intensive agricultural production in the European Community resulted in a surplus of some crops. One solution to this has been to pay farmers to ‘set-aside’ some of their land by neither planting crops nor grazing animals on it. Describe what will happen to an area of land which is set aside and not returned to agriculture.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(4)
(Total 8 marks)
58. (a) Describe how one named parasite or predator is used successfully in the biological control of a named pest.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(b) Most cases of successful biological control using parasites have involved
1 the search for parasites of the pest in the country of origin, especially in areas with a similar climate to the planned area of release;
2 the study of the effect of the parasite on other organisms under laboratory conditions;
3 release of large numbers of parasites which results in a decline in the pest population;
4 the stable existence together of both pest and parasite at low population densities.
113
Explain the importance of each of the above steps in achieving successful biological control of a pest.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(8)
(c) Suggest two advantages of using biological control rather than pesticides.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(Total 12 marks)
59. In an investigation of growth in nettles, nettle seeds were planted in soil taken from two woods where no nettles were growing. Before the seeds were planted, various mineral nutrients were added to samples of the soils from each wood. When the nettle plants had grown, their mean dry mass was measured. The results are shown in the table.
S o u rce o f so il
M ean d ry m ass o f n e ttle p lan ts /m g
N oN u tr ie n ts
a dd e d
P h o sp h atead d e d
N itra tead d ed
P h o sp h a tean d n itra te
ad d ed
A ll essen tia ln u tr ie n ts ex ce p tp h o sp h a te a d d ed
W o o d A
W o o d B
6
1
92
2 4 8
5
1
1 2 5
2 8 1
5
1
114
(a) Which mineral nutrient was a limiting factor in the soils taken from the two woods?
.....................................................................................................................................
Explain the evidence from the table for your answer.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(b) Phosphate can be a serious pollutant of rivers and lakes.
(i) Give two major sources of phosphates that may pollute rivers and lakes.
1..........................................................................................................................
2..........................................................................................................................(2)
(ii) Explain how fish in a lake may be killed as a result of pollution by phosphates
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(3)
(Total 7 marks)
115
60. The energy value of the biomass synthesised by the producers in an ecosystem is a measure of the productivity of the ecosystem. The table shows the estimated annual mean energy value of the biomass synthesised in ecosystems in a country and the sea beside it.
Ecosystem Estimated mean energy value of biomass
synthesised by producers/kJ m–2y–1
Deep oceanShallow seaAlluvial plain – farmlandAlluvial plain – woodlandMountain grasslandDesert
3 00010 20029 00035 000 3 500 2 200
(a) Explain how energy is transferred into biomass by producers.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(3)
(b) (i) Suggest why the deep ocean has a lower productivity than the shallow sea.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(2)
(ii) Suggest one reason why the productivity of the farmland on the alluvial plain is lower than that of the woodland. Explain your answer.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(2)
116
(c) In which ecosystem would you expect there to be the smallest number of animal species? Explain your answer.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(Total 9 marks)
61. A glasshouse modifies the physical environment of a crop and enables factors that limit photosynthesis to be controlled. The diagram shows a glasshouse.
B lin d
G lass
Ven tila to r
(a) Each of the labelled parts is involved in controlling the physical environment of a glasshouse. What is the role of each of these parts?
(i) Glass..................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(ii) Blinds.................................................................................................................
.....................................................................................................................................
(iii) Ventilator...........................................................................................................
.....................................................................................................................................(4)
117
(b) Large commercial glasshouses use automatic water sprinklers to maintain the optimum water content in the soil. Explain why the rate of photosynthesis falls if there is a shortage of water in the soil.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(Total 6 marks)
62. (a) The graph shows the yield of a crop when different amounts of a nitrogen-containing fertiliser are applied.
5
4
3
2
1
00 5 0 1 0 0 1 50 2 0 0
A m o u nt o f fe rtilise r a pp lied /k g n itro g en pe r he c ta re
Y ie ld /to n n esp e r h e c ta re
A
BC
(i) Explain the effect of the amount of fertiliser applied on the yield of the crop for each of the labelled sections of the curve.
A........................................................................................................................
...........................................................................................................................
B.......................................................................................................................
..........................................................................................................................
C.......................................................................................................................
..........................................................................................................................(3)
(ii) A fertiliser costs 120p per kg nitrogen and the crop sells for £200 per tonne. Use the graph to calculate whether applying 125 or 150 kg nitrogen per hectare would be more profitable. Show your working.
(2)
118
(b) Give one advantage and one disadvantage of using inorganic fertilisers instead of manure.
Advantage...................................................................................................................
.....................................................................................................................................
Disadvantage...............................................................................................................
.....................................................................................................................................(2)
(Total 7 marks)
63. One type of aphid is a pest of cucumbers grown in glasshouses. The aphid invades glasshouses in large numbers during April and breeds rapidly. It can be controlled by chemicals, although secondary infestations often occur which are difficult to remove with chemicals. Two methods have been tested for keeping a parasite of the aphid in the crop before the aphids invade.
Method 1Maize planted between the cucumbers.The maize is infested with a type of aphidthat is not damaging to cucumbers.These aphids are host to the aphid parasite.The maize needs an irrigation system.
Method 2The aphid parasite is released atweekly intervals during the periodwhen the cucumber crop is atrisk
To investigate the effectiveness of each technique, cucumber aphids were released onto crops of cucumbers in glasshouses.The table shows the results.
Time fromintroducingaphids/ days
Number of cucumber aphids per leaf
Untreated Method 1 Method 2
0 0 0 0
7 60 30 30
21 1500+ 140 80
35 1500+ 55 25
49 1500+020 6
119
(a) Which of the two methods would you consider to be more economical? Use the information above to support your answer.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(b) What are the advantages and disadvantages for a grower of cucumbers of using biological control instead of chemicals for controlling aphids.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
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.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(4)
(Total 6 marks)
64. The diagram summarises the flow of energy through agricultural production systems.
S ola r e n erg y
A gr ic u ltu ra lp ro d u c tio n
sy ste m s
H e at e ne rg y
E n e rg y in h arv es ted c ro p
E n e rg y in w as te p ro d uc ts
D irec t e n ergy in pu t
( la b o u r a n d fu e l)
In d irec t e n ergy in p ut
120
(a) Suggest what is meant by an indirect energy input.
.....................................................................................................................................
.....................................................................................................................................(1)
(b) (i) The energy efficiency of the system is the energy in the harvested crop divided by the total energy input, expressed as a percentage. The energy efficiency of rice production in the United States is 1.55%. The energy efficiency of rice production in Indonesia is 7.08%. Explain the difference between these figures.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(2)
(ii) Solar energy is used more efficiently by plants grown in modern intensive agricultural systems than in subsistence agricultural systems. Suggest a reason for this.
..........................................................................................................................
..........................................................................................................................(1)
(c) An African village which relied on subsistence agriculture grew thirty species of crop plant. Explain why this would have resulted in a higher total food yield than would have been obtained from growing a single species.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................(2)
(Total 6 marks)
121
65. The table shows the energy relationships for three animals living in grassland. The figures refer to percentages of the energy in the food consumed by the animal.
Animal
Energyabsorbed intotissues /% (A)
Energyincorporatedinto new tissue /% (P)
Energyin faeces /%
(F)
Efficiency =
A
100P
Small mammalfeeding on plants
Insect feeding onplants
Small mammalfeeding on animals
50
40
80
1.5
16
2
50
60
20
..........
..........
..........
(a) (i) Complete the table to show the efficiency.(1)
(ii) Explain what happens to the energy that is absorbed into tissue but not used in the growth of new tissue.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................(2)
(iii) Suggest one reason why the percentage of energy in faeces is much higher in mammals that feed on plants than in those that feed on animals.
............................................................................................................................
............................................................................................................................(1)
(b) Explain why efficiency is lower in
(i) the small mammal that feeds on plants than the insect that feeds on plants;
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................(2)
122
(ii) the small mammal that feeds on animals than the small mammal that feeds on plants.
............................................................................................................................
............................................................................................................................(1)
(Total 7 marks)
66. The Everglades in Florida is a very large area of natural swamp which contains many important and endangered species. The director of Florida’s drug control policy has suggested spraying the Everglades with a fungus to reduce illegal cannabis growing. The fungus suggested is Fusarium oxysporum which infects a number of species of plant. Researchers have developed a variety of the fungus which they claim will attack only the cannabis plant. Environmentalists have strongly protested against using this fungus.
(a) Suggest and explain two reasons why this method of biological control might be preferable to using a chemical spray to kill the cannabis plants.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................(4)
(b) Suggest two reasons why environmentalists would object to using the fungus for controlling cannabis.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................(2)
(Total 6 marks)
123
67. (a) Explain two ways in which the expanding human population is placing increasing demands on natural communities.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................(2)
(b) Under natural and suitable conditions, bare soil would eventually become covered by a woodland community. Explain how farming practices prevent this from happening.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................(4)
(c) The graph shows the number of species from three insect groups which are thought to be extinct or close to extinction in three different habitats in the UK.
6 0
5 0
4 0
3 0
2 0
1 0
0
N u m b e r o fspe c ies
S o il a t ea r lys tag e o f
c o lo n isa tion
L iv e tre es D ea d tre es
Ty p e o f h ab ita t
B e e tle s
F lies
B u tte rf liesan d m o th s
K e y
124
(i) Farming often produces temporary areas of bare soil on which colonisation may start, but these data show that many species of insect associated with the type of community that develops in this habitat are endangered. Suggest why.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................(3)
(ii) Suggest explanations for the differences between the data for live trees and dead trees.
............................................................................................................................
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............................................................................................................................(3)
(Total 12 marks)
68. (a) (i) Describe one way in which mineral ions are released from rocks into soil.
............................................................................................................................
............................................................................................................................(1)
125
(ii) Describe how detritivores are involved in the recycling of nutrients.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................(3)
(b) The bar chart shows the amounts of nitrate and phosphate in soil from two different areas of grassland, A and B. Both areas are used for grazing.
A re a AN o fe rtilise r o rm a n u re ad d ed .C o n ta in s :2 sp ec ie s o f g rass1 0 o th er sp ec ies o fflo w erin g p lan t
A re a BS p ra y ed y e arly w ithliq u id m an u re .C o n ta in s :3 sp ec ie s o f g rass1 o th e r spe c ies o fflo w erin g p lan t
7
6
5
4
3
2
1
0
A m o u n t o fn itra te an dp h o sp h a te inso il/kg p erh e c ta re
A re a A A rea B
G rass lan d a rea
n itra te
p ho sp h a te
(i) Explain the effect of nitrate and phosphate supply on the diversity of plants.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................(2)
126
(ii) Area B is going to become part of a nature reserve. A proposed change in land management is to stop spraying with liquid manure. Explain the likely effect of this change on the diversity of plants.
............................................................................................................................
............................................................................................................................(1)
(Total 7 marks)
69. The diagram shows changes in the biomass of a cereal crop and of the weeds in a field.
To ta lb io m asso f c e re a lc ro p an dw ee k s ina fie ld
G ro w thw ith o u tfe r tilise r
F e rtilise rad d ed
H erb ic id ea d de d
W e ed s
U n w an tedp art o f c ro p
W a n tedp art o f c ro p(ce rea l g ra in )
(a) Describe and explain the effect of adding fertiliser on the biomass of the plants.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................(2)
(b) Explain why the application of herbicide increases the final yield of the crop.
....................................................................................................................................
....................................................................................................................................(1)
127
(c) Suggest two ways, other than adding fertiliser or herbicide, of ensuring that the maximum amount of grain is harvested.
1..................................................................................................................................
....................................................................................................................................
2..................................................................................................................................
....................................................................................................................................(2)
(d) Explain how selective breeding could result in a reduction in the unwanted part of the crop.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................(2)
(Total 7 marks)
70. Deltamethrin is a synthetic insecticide. The chart shows the minimum lethal dose for different groups of organisms.
F ish
C rab
F ro g
In sec t
M a m m al
B ird
Ty p e o fo rg an ism
0 .0 0 0 1 0 .0 0 1 0 .0 1 0 .1 1 1 0 1 0 0 1 0 0 0M in im u m le tha l d o se o f
D eltam eth rin /pa rts p er m illio n
(a) Use the information in the chart to explain why Deltamethrin
(i) may be used as an insecticide on plants intended for human consumption;
............................................................................................................................
............................................................................................................................
128
(1)(ii) should not be used in areas close to ponds and streams.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................(3)
(b) (i) Systemic insecticides are absorbed by plants and are transported through their tissues. The plant tissues become toxic to insects feeding on them. Explain two advantages of using systemic insecticides rather than other types of insecticide.
1..........................................................................................................................
............................................................................................................................
2..........................................................................................................................
............................................................................................................................(2)
(ii) Suggest how genetic engineering could be used to protect plants from
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................(2)
(Total 8 marks)
71. (a) Give two reasons why much of the sunlight falling on the leaves of a plant grown in a glasshouse is not used in photosynthesis.
1..................................................................................................................................
....................................................................................................................................
2..................................................................................................................................
....................................................................................................................................(2)
129
(b) What measurements could be taken in order to find the rate of photosynthesis?
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................(2)
(c) Outline how you would investigate the effect of temperature on the yield of a crop of plants grown in a glasshouse.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
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....................................................................................................................................
....................................................................................................................................(3)
(Total 7 marks)
72. The diagrams show a pyramid of biomass and a pyramid of energy for the same aquatic habitat.
P y ra m id o f b io m a ss
P y ra m id o f en erg y
D e co m p o se rs4 0 gm
D e co m p o se rs9 2 6
–2
– 2
– 2
– 2
–2
F o u rth tro p h ic le ve l 1 .5 g m
F o u r th tro p h ic lev e l 0 .4
T h ird tro p hic lev e l 11 g m
T h ird tro p h ic le v e l 11
S ec on d tro p h ic lev e l 3 7 g m
S e co n d tro p h ic lev e l 1 4 2
F irs t tro p h ic lev e l 8 0 7 g m
F irs t trop h ic lev e l 86 6 2
130
(a) Suggest suitable units for the measurement of energy flow in the pyramid of energy.
.....................................................................................................................................(1)
(b) Calculate the percentage of biomass transferred from the first trophic level to the fourth trophic level. Show your working.
Percentage ...........................................(2)
S (c) (i) Most of the organisms in the first trophic level are single-celled protoctists.How do these organisms obtain their energy?
..........................................................................................................................
..........................................................................................................................(1)
(ii) All of the energy in these protoctists is eventually transferred to the environment.Explain how.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(3)
(Total 7 marks)
73. (a) Explain what is meant by
(i) nitrification;
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
131
(ii) denitrification.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(2)
(b) Explain how the leaching of nitrates from farmland into rivers may lead to a large increase in biochemical oxygen demand (BOD).
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................(5)
(Total 7 marks)
74. (a) Describe and explain the effects of monoculture on the environment.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
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...................................................................................................................................(4)
132
(b) Polychlorinated biphenyls (PCBs) are pesticides which were widely used in the countries surrounding the Baltic Sea. PCBs are non-biodegradable.
(i) Chemical analyses show that gulls, which feed on fish from the Baltic Sea, have very high concentrations of PCBs in their body tissues.Suggest an explanation for this.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(2)
S (ii) Suggest, in terms of molecular structure, why some pesticides are non-biodegradable.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(2)
S (iii) In some populations of pests there are individuals which are resistant to pesticides. Explain why the proportion of pesticide-resistant pests may rise in populations that are sprayed with insecticide.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(3)
(Total 11 marks)
75. Shrubs and small trees cover large areas of northern Canada. In winter there is deep snow for several months. Few species of mammal are adapted to survive in these conditions. The commonest primary consumer is the snowshoe hare, which feeds on the young leaves and shoots of the shrubs and small trees. When a shrub is damaged by grazing it produces toxins in the leaves and shoots. These toxins make the leaves and shoots too unpleasant for the hares to eat. Several mammalian predators feed on the hares.
133
The graphs show changes in the relative biomass of the shrubs, hares and predators over a period of 10 years. The measurements of biomass were taken at the beginning of each winter.
5 0 0 0 0
2 5 0 0 0
R e la tiv eb io m ass /a rb itra ryu nits
S h ru b s
1 0 0 0
8 0 0
6 0 0
4 0 0
2 0 0
0
R e la tiv eb io m ass /a rb itra ryu nits H are s
1 .0 0
0 .7 5
0 .5 0
0 .2 5
0 .0 0
R e la tiv eb io m ass /a rb itra ryu nits P re d a to rs
0 1 2 3 4 5 6 7 8 9 1 0Tim e / y e ars
(a) (i) Calculate the ratio of the biomass of the hares to the biomass of the predators in year 5. Show your working.
Ratio = .....................................................................(2)
134
(ii) Use your knowledge of energy transfer to explain the difference in biomass between the hares and their predators.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(2)
(b) (i) Describe how the pattern of change in biomass over the ten years for the predators differs from the pattern for the hares.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................(2)
(ii) Use the information in the passage and the graphs to explain the changes in the biomass of the hares over the ten years.
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(Total 9 marks)
135
76. Potato plants originate from the Andes mountains in South America. They are adapted for survival in a cool climate. The potatoes we eat are food storage organs, called tubers, and are produced on underground stems.
The graph shows the rates of photosynthesis and respiration for one variety of potato plant.
R ate
0 5 1 0 1 5 2 0 2 5 30Tem p era tu re / ºC
P h o to sy n th es is
R e sp ira tio n
(a) Between which temperatures is there a net gain in energy by the potato plant?
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S (b) When this variety was grown in a hot climate, with a mean daytime temperature of23.5 °C, it failed to produce tubers.
Use information in the graph to explain why no tubers were produced.
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S (c) Suggest what causes the rate of photosynthesis to decrease above 21°C.
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136
(d) Describe how the temperature of the soil around developing tubers could be measured throughout their growing period.
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(Total 7 marks)
77. The graph shows the effect of carbon dioxide concentration, light intensity and temperature on the rate of photosynthesis of a crop plant.
0 1 2 3 4L ig h t in ten s ity / k ilo lu x
X
R a te o fp h o to sy n th es is
0 .1 2 % c arb o n d io x id e a t 2 0 ºC
0 .0 3 % c arb o n d io x id e a t 3 0 ºC
0 .0 3 % c arb o n d io x id e a t 2 0 ºC
(a) Which factor is limiting the rate of photosynthesis at point X? Explain your answer.
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137
(b) In a glasshouse in winter, the mean carbon dioxide concentration is 0.03%, the temperature is 20 °C and the light intensity is 3 kilolux.
Using the graph, predict whether increasing the carbon dioxide concentration to 0.12 % or the temperature to 30 °C would result in the greater increase in growth. Using your knowledge of photosynthesis, give an explanation for your answer.
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(c) Explain why it is not advisable to increase the temperature in a glasshouse on a dull winter day.
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S (d) Little of the sunlight falling on the leaves of a plant grown in a glasshouse, even under optimum conditions, is used in photosynthesis. Give two explanations.
1 ..................................................................................................................................
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(Total 7 marks)
138
78. The diagram shows the flow of energy through trees in a woodland ecosystem. The numbers
represent mean inputs and outputs of energy in kJ m–2 day–1.
P lan t re sp ira tio n6 2
Av ailab le to co n su m e rsan d d e co m p o se rs
6 3
E n erg y n o t u sed5 0 2 5
P h oto sy n the tic p ro d u c ts1 2 5
S o la r rad ia tio n5 1 5 0
(a) Use information in the diagram to
(i) give the amount of energy incorporated into tree biomass;
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(ii) calculate the percentage of solar energy that is fixed by photosynthesis.
Answer ............................. %(2)
(b) Not all the solar radiation reaching the leaves of the tree is used in photosynthesis. Give two explanations for this.
1 ..................................................................................................................................
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2 ..................................................................................................................................
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139
(c) The graph shows the rate of photosynthesis and the rate of respiration in tree leaves at different temperatures.
0
R ate
0 1 0 2 0 3 0 4 0L eaf tem p era tu re / ºC
R e sp ira tio n
P h o to sy nth es is
Give the range of temperatures over which the leaves will show the greatest increase in biomass. Explain your answer.
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(Total 7 marks)
79. The diagram shows a simplified food web in an aquatic ecosystem.
S tic k le b ack s
D ra g o n fly n y m ph s
D a p hn id s M ay fly n y m p h s C ilia tes O ligo c h ae tes
U n ic e llu la r a nd filam en to us a lg ae
(a) In this food web, which organisms feed as tertiary consumers?
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140
(b) The biomass of organisms in an ecosystem can change during the year. In this aquatic ecosystem, the biomass of primary consumers is temporarily greater than that of the producers during the early summer.
(i) Sketch the pyramids of biomass in early summer and autumn for this ecosystem. Name the trophic levels.
Early summer Autumn
(2)
(ii) Suggest suitable units to represent biomass in these pyramids.
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(c) Explain why food chains rarely have more than five trophic levels.
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(Total 6 marks)
141
80. The numbers of species of woody plants in samples from 227 hedges of different ages were counted. The results are shown in the graph. The size of the solid circles shows the number of hedges in each category.
1 0
9
8
7
6
5
4
3
2
1
0
N u m b er o fsp e c ie s o fw o o d y p lan tsin 3 0 m o fh ed g e
K e y
1 - 4 h ed g e s
5 - 1 4 h ed g e s
1 5 - 3 0 h ed g e s
0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 1 0 0 0 11 0 0 1 2 0 0
A g e o f h e d g e / y ea rs
(a) (i) Suggest the age range of the hedges which are likely to support the most complex food webs. Explain your answer.
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(ii) Explain how the complex food webs maintained by these hedges may be of benefit to farmers.
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142
(b) (i) Calculate the maximum percentage of hedges which are 1000 years old or over in this sample. Show your working.
Answer ............................. %(2)
(ii) Many hedges have been removed from arable land in recent years. Explain two advantages to farmers of removing hedges.
1 .......................................................................................................................
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2 .......................................................................................................................
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(Total 9 marks)
81. This questions should be answered in continuous prose, where appropriate.Quality of Written Communication will be assessed in these answers.
S (a) The availability of nitrogen-containing compounds in the soil is often a limiting factor for plant growth. Explain two ways in which a shortage of nitrogen-containing compounds could limit plant growth.
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143
(b) Farmers apply nitrate fertilisers to improve crop growth.
S (i) Explain why plants may fail to grow if high concentrations of nitrate are applied to the soil.
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(ii) Streams and rivers running through farmland can also be adversely affected by application of high concentrations of nitrate fertiliser. Fish cannot survive when the oxygen levels of water are reduced. Explain how high concentrations of nitrate applied to farmland may result in the reduction of the numbers of fish present in aquatic ecosystems.
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144
S (c) Malonate is a substance that inhibits the enzymes of the Krebs cycle. In an investigation, plant roots were placed in a solution containing nitrate and malonate. The solution had air bubbled through it. Explain why these plant roots took up nitrate more slowly than those in a control solution which contained nitrate but no malonate.
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(Total 14 marks)
82. Spider mites are a major pest of cucumbers. An investigation was carried out to compare the effectiveness of two methods of controlling this pest. Two plots of cucumber plants infested with spider mites were used. One plot was treated with a chemical pesticide; a biological control agent was used on the other plot. Figures 1 and 2 show the results. The arrows show when the chemical pesticide was applied (Figure 1) and when the predator was introduced(Figure 2).
2 5
1 5
5
0F eb M a r A p r M ay Ju n Ju l A u g
M o n th
N u m b e r o fsp id er m ite sp er 5 cm 2
C h em ica lc o ntro l
Figure 1
0
5
F eb M a r A p r M ay Ju n Ju l A u g
M o n th
N u m b e r o fsp id er m ite sp er 5 cm 2
B io lo g ica lc o ntro l
Figure 2
145
(a) Using evidence from the graphs, give two advantages of biological control over chemical control.
1 ..................................................................................................................................
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2 ..................................................................................................................................
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(b) Describe two features that a predator must have if it is to be a successful biological control agent.
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(Total 4 marks)
83. (a) Clover is a leguminous plant. A clover plant has root nodules, which contain nitrogen-fixing bacteria.
Describe the nutritional advantage gained as a result of this relationship by
(i) the clover plant;
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(ii) the nitrogen-fixing bacteria.
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146
(b) Cereals may be grown in rotation with other crops, including clover. No fertiliser is added. Alternatively, cereals may be grown every year in the same field and supplied with fertiliser.
Explain two advantages of growing cereal crops in rotation with clover instead of growing them every year in the same field and applying fertiliser.
1 ..................................................................................................................................
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(Total 6 marks)
84. (a) The diagram compares the transfer of energy through a herbivore and through a carnivore of similar size. The width of each arrow is proportional to the energy value.
E n erg y re lea sedin resp ira tio n E n erg y re lea sed
in resp ira tio n
E n ergy s to redin tissu es E ne rg y sto re d
in tis su es
E n erg y lo s tin fae ces
E n e rg y lo s tin faec es
H erb ivo re C a rn iv o re
To ta len erg yin tak e
Tota len erg yin tak e
(i) Use the diagram to calculate the percentage of energy lost in faeces by each animal. Show your working.
Herbivore Carnivore
............................................ % ............................................ %(2)
147
(ii) Suggest an explanation for the percentage of energy lost in faeces for the herbivore being larger than that for the carnivore.
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S (b) Explain why small mammals have a higher rate of respiration than larger mammals.
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(Total 6 marks)
85. In an attempt to control the huge numbers of an insect pest, low doses of a pesticide were sprayed on a lake. After spraying, the concentration of pesticide in the lake water was 14 parts per billion. After spraying, diving birds which fed on small fish in the lake were found to be dying. The concentration of the pesticide in these birds was more than 1 part per thousand.
(a) Explain why the pesticide was in such a high concentration in the diving birds.
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148
S (b) The lake was sprayed three times. The first spraying killed almost all of the insects, as did a second application five years later. When the lake was treated for a third time it was found that some insects were resistant to the pesticide.
Explain how resistance to the pesticide evolved in the insect population.
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S (c) This pesticide is able to pass easily through cell membranes. Suggest why.
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(Total 8 marks)
86. Answers should be written in continuous prose, where appropriate.
A large lake is surrounded by fields. These fields are separated from each other by hedges. One hundred years ago the lake was a habitat for many plants, invertebrates and fish. Today the lake has no fish and few plants or invertebrates.
(a) Explain how increased use of inorganic fertilisers on the fields may have led to these changes.
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149
.....................................................................................................................................(5)(b) Explain how the removal of hedges near the lake would increase the impact of fertilisers
on the aquatic ecosystem.
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(Total 7 marks)
87. Tomato growers have increased the yield of fruit from 100 to 400 tonnes per hectare by growing the tomato plants in automatically heated glasshouses and enhancing the carbon dioxide concentration. To control the nutrient supply to the roots, the plants are grown without soil in plastic troughs, as shown in the diagram.
To m a to p la n t
P las tic tro ug h
R o o t m at
2 to 3 m m de p th o fn u tr ie n t so lu tio n
P u m p
Tan k c o n ta in in gn u tr ie n t so lu tio n
(a) Explain how enhancing the carbon dioxide concentration helps to increase the yield.
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150
(b) Maintaining a high temperature in a glasshouse in winter, when the light intensity is low, may reduce the yield. Explain how.
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S (c) Tomato fruits have a high percentage of water. When making tomato ketchup, it is more economical to use fruits which have a low percentage of water. Growers can reduce the water content of the fruit by adding sodium chloride to the nutrient solution in the plastic trough.
Explain how adding sodium chloride can reduce the water content of the fruit.
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(Total 6 marks)
88. Over a million tonnes of salmon per year are produced in fish farms. The salmon are grown in large cages in sheltered waters, such as off the west coast of Scotland. The cost of these farmed salmon is much lower than that of wild salmon.
(a) Give two reasons why farmed salmon are cheaper than wild salmon.
1 ..................................................................................................................................
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2 ..................................................................................................................................
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S (b) Large amounts of waste food and faeces fall through the bottom of the cages. This results in a much reduced diversity of marine organisms below and around the cages.Explain how the organic matter in the water causes this reduction in diversity.
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151
152
S (c) Farmed salmon are fed on pellets made from small fish. About five tonnes of small fish are required for each tonne of salmon produced. Give two reasons why this high ratio is needed.
1 ..................................................................................................................................
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(Total 6 marks)
89. A popular lake in the United States was affected by large swarms of midges (small biting insects) in the summer. The lake was sprayed with insecticide to kill the midges. The effect of spraying on the following food chain in the lake was investigated.
Plant plankton sunfish western grebe
(a) Shortly after spraying the concentration of insecticide in the water of the lake was
2 × 10–5 g dm–3. After four weeks the concentration in the plant plankton was equivalent
to 5 × 10–3 g dm–3.
By how many times was the insecticide concentrated?
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(b) After a few months the concentration of insecticide in the grebes was more than six times the concentration in the sunfish. Explain why.
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(c) Another lake, which contained dead trout, was found to be contaminated by waste containing mercury ions.
(i) In an investigation, the lethal concentration of mercury ions for trout was 42 parts per billion over four days. Explain what is meant by lethal concentration.
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153
S (ii) Explain how heavy metal ions are toxic to animals.
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(Total 7 marks)
90. The graph shows the mean biomass of heather plants of different ages growing on a moor.
1 2 0 0
1 0 0 0
8 0 0
6 0 0
4 0 0
2 0 0
00 2 4 6 8
A g e / y ea rs
M eanb io m ass/g m – 2
×
×
×
×
×
×
×
×
154
(a) (i) When completely burned, 1 g of heather releases 22 kJ of energy. Use the graph to calculate the mean amount of energy stored as heather biomass per year.
Answer .......................................... kJ m–2
(1)
(ii) The total amount of light energy falling on the leaves of heather plants per year is 3
150 000 kJ m–2. The chlorophyll in the leaves of the heather absorbs only 45 % of this energy.
Calculate the percentage of the total amount of energy absorbed by the chlorophyll per year which is stored as heather biomass. Show your working.
Answer ................................................. %(2)
(iii) Only a small percentage of the light energy absorbed by the chlorophyll is stored as biomass. Suggest two explanations for this.
1 ................................................................................................................…….
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2 ................................................................................................................…….
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155
(b) Explain why only a small percentage of the energy in the heather biomass is transferred to the biomass in the next trophic level.
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(Total 8 marks)
91. In autumn when there is no crop, farm land may be used to grow mustard. The mustard absorbs nitrates which otherwise can leach out of the soil at this time of the year.The mustard is ploughed back into the soil just before sowing of the main crop in the spring.
(a) Nitrogen compounds in the mustard plants are made available for the main crop after ploughing in spring. Describe the role of microorganisms in this process.
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(b) Explain why it is important for the farmer to reduce the leaching of nitrates.
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156
S (c) Plants absorb a number of other nutrients from the soil including phosphates.Describe why phosphates are needed by a growing plant.
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(Total 11 marks)
92. When sewage is discharged into a river, the river becomes polluted with small particles of organic material. The population density of animals and the biochemical oxygen demand (BOD) were recorded from a river immediately upstream from a sewage outlet and at different distances downstream. Figures 1 and 2 show the results.
Asellus is an invertebrate animal that feeds on dead organic matter and is able to live in water mildly polluted by organic waste.
B O D o rco n cen tra tio n
K ey
O x y g en co n cen tra tio n
B O D
D istan ce d o w n stream
D isch a rg e o f sew ag e
Figure 1
P o p u la tio nd en sity
O th e r in v e rteb ra tean im a ls
D is tan ce d o w n stream
D isch a rg e o f sew ag e
A se llu s
Figure 2
157
(a) On Figure 1 continue the line for oxygen concentration to show how this would be expected to change downstream from the point of discharge of sewage.
(1)
(b) Explain the decrease in biochemical oxygen demand with distance downstream from the sewage outlet.
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(c) Suggest an explanation for the changes in the population density of Asellus with distance downstream from the sewage outlet.
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(Total 7 marks)
93. (a) Farmers who grow wheat sometimes leave a field fallow for a year by not growing a crop in it. The concentration of nitrate ions in the soil decreases when a field isleft fallow.
(i) When grass is grown in the field, fewer nitrate ions are lost than when the field is left with bare soil. Explain why.
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158
(ii) A crop of leguminous plants such as clover may be grown in the field and then ploughed in. Explain why less fertiliser would be needed for the wheat crop in the following year.
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(b) The table gives information about the yield and profitability of a wheat crop grown using different amounts of fertiliser.
Nitrogenfertiliserapplied /
kg ha–1
Grainyield /
tonnes ha–1
Grainprotein / %
Valueadded by
using fertiliser /
£ha–1
Cost ofusing
fertiliser /
£ha–1
Benefit : costratio
0 2.4 11.7 – – –
25 2.5 12.5 19 11 1.7 : 1.0
50 2.5 12.9 25 22 1.1 : 1.0
75 2.5 13.3 31 33 0.9 : 1.0
100 2.5 13.5 37
(i) Describe the effects of increasing fertiliser application on the yield and protein content of the grain produced.
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......................................................................................................................….(2)
(ii) Use the data in the table to estimate the benefit : cost ratio for a fertiliser application
of 100 kg ha–1. Write your answer in the table.(1)
(Total 6 marks)
159