population questions

1. Moose are large herbivorous animals.

(a) In a study of one population of moose, 72 animals were trapped and marked with ear tags. They were then released. One month later, fieldworkers examined 120 moose and found that 14 of these had ear tags.

Use these figures to calculate the size of the moose population. Show your working.

Answer:............................(2)

(b) Isle Royale is a large island in Lake Superior. Moose first colonised this island in 1900. At the time they had no predators on the island. Wolves, which are predators of moose, were introduced to the island in 1950. The graph shows the moose population from 1900.

I sla nd co lo n ise db y m o o se

W o lv e sin tro d u ced

3 00 0

2 00 0

1 00 0

019 0 0 1 9 1 0 1 9 2 0 1 9 3 0 1 9 4 0 1 9 50 1 9 6 0 1 9 7 0

D ate

M o o sep o p u la tio n

(i) Suggest an explanation for the changes in the moose population before the introduction of the wolves.

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Sir George Monoux Sixth Form College 1

(ii) Describe the effect of introducing wolves on the moose population.

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(Total 5 marks)

2. Spruce trees produce very large numbers of seeds. Most of these seeds die immediately, releasing nitrogen compounds into the soil. Swedish scientists investigated the effects of this on the growth of pine seedlings, in areas where the forest floor was free of moss plants and in areas where moss plants grew.

(a) Describe the part played by soil bacteria in making the nitrogen in compounds in the dead spruce seeds available to pine seedlings.

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(b) In areas where the forest floor was free of moss plants, the pine seedlings grew better in plots with added spruce seeds than they did in control plots. In areas in which moss plants grew, the difference in growth of the pine seedlings in plots with added spruce seeds was not statistically significant from those in the control plots. Suggest an explanation for the effect of the moss plants on the growth of the pine seedlings.

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(Total 5 marks)


3. The sand shrimp, Crangon septemspinosa, is a member of the community found in a sea-shore ecosystem.

(a) Give the meaning of:

(i) community; .......................................................................................................

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(ii) ecosystem. ........................................................................................................

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(b) The contours on the graph represent 0%, 50% and 100% survival for C. septemspinosa in aerated water over a range of temperatures and salinities (salt content of sea water).

30

25

20

15

10

50 5 10 1 5 2 0 2 5 3 0 3 5 4 0 4 5

1 0 0 % su rv iv a l

0 %su rv iv a l

5 0 % su rv iva l

Tem p era tu re/ °C

P erce n tag e sa lin ity

(i) What are the upper and lower limits of temperature for 100% survival ofC. septemspinosa?

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(ii) Other than the factors shown in the graph, name one biotic and one abiotic factor, which might also limit the survival of C. septemspinosa.

Biotic factor ......................................................................................................

Abiotic factor ....................................................................................................(2)

(Total 5 marks)


4. The diagram shows some of the feeding relationships in a food web for a forest.

S p arro w h aw k F o x

B lu e tit

H ed g eh o g

S p id e r

F ro g

S lu g

E a rth w o rm

G ro u n db e etle

W in ter m o th ,ca te rp illa rs

W o od

W oo d b o rin gb ee tle

G reysq u irre l

G ra sssn ak e

L eav e s F ru itsan d

se ed s

W o o dm o u se

(a) Name an organism that is both a primary and a secondary consumer in this food web.

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(b) Name a group of organisms, not shown in the web, which is needed to recycle nutrients.

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(c) Explain how bare ground may, over a long period of time, become forest.

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(d) With reference to the food web, explain the effect that deforestation has on the species diversity of an area.

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(Total 8 marks)

5. The community present in a roadside ecosystem was investigated.

(a) Explain what is meant by:

(i) community; ......................................................................................................

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(ii) ecosystem. ........................................................................................................

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(b) The diagram shows a section through a road which has a sloping bank and hedge on each side.

H ed g eH e d g e

S ou th -fac in gb an k

N or th - fac in gb a nk

R o ad


The following plant species were found growing on 10-metre lengths of the north-facing and south-facing road banks.

P la n t sp ec ies

W h ite d ea d ne ttle

L esser ce lan d in e

D an d elio n

R ag w or t

C o w p ars ley

T his tle

G ro u n d se l

2 3

1 8

8

1 0

7

5

1 5

0

8

4

0

1 0

1

1 0

In d ex o f d iv ers ity 5 .9 4

S o u th -fa c in gro a d b a n k

N o rth -fa c in gro a d b an k

N u m b er o f p la n ts

(i) Suggest and explain how one abiotic factor might have caused differences in plant growth on the two road banks.

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(ii) Explain why the south-facing road bank is likely to show greater ecological stability than the north-facing road bank.

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(iii) The south-facing road bank would also be expected to have a higher diversity of animals. Suggest one reason for this.

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(c) In order to estimate the population of woodlice living on the north-facing road bank, four pitfall traps were set in the ground at 2-metre intervals and left for 24 hours. All the woodlice that had fallen into the traps were marked on their underside with quickdrying paint and released back into their habitat. The next day the traps were examined again and the numbers of marked and unmarked woodlice were counted. The results are shown in the table.

N u m b e r o f w o o d lic e m a rk ed an d re lease d

N u m b e r o f m ark e d w o o d lic e in 2 n d ca tc h

N u m b e r o f u n m ark ed w o o d lic e in 2 nd ca tc h

1

2

0

5

2

2 8

4

1 7

3

0

0

3

4

1 0

2

11

Tr ap n u m b e r

(i) Use the data to estimate the woodlouse population in this area. Show your working.

Population = .................................................(2)

(ii) Suggest two reasons why it is not possible to make a reliable estimate of the woodhouse population size from these data.

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(Total 12 marks)


6. Limpets are animals which live on rocky sea shores. When the tide is out, a limpet is firmly attached to the rock by a muscular ‘foot’. Taller limpets are more likely to be dislodged by wave action. Variation in the size of limpets was investigated on two shores, A and B. The height and width of each limpet was measured as shown in the diagram.

H eig h t, H

W idth , W

F o o t

S h e ll

The results of the investigation are given in the table.

M e an

S a m p le s iz e

Stan d a rdd ev ia tio n

HW

S h o re A S h o re B

0 .3 3 0 .4 7

0 .0 8 0 .1 2

2 8 3 3


(a) (i) On which shore did the limpets have a greater variation in values of W

H

?Give evidence from the table for your answer.

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(ii) Which shore had limpets that were better adapted to withstand wave action? Use evidence from the table to explain your answer.

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(b) (i) In investigations like this, why is it necessary to collect data from a large number of specimens which are selected at random?

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(ii) Describe how you would select limpets at random.

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(c) Red seaweeds are algae which contain, in addition to chlorophyll, a red pigment called phycoerythrin. Green seaweeds do not contain phycoerythrin. Both phycoerythrin and chlorophyll absorb light energy which can be used in photosynthesis. The graphs show the percentage of light of different wavelengths absorbed by sea water, by chlorophyll and by phycoerythrin.

8 0

6 0

4 0

2 0

04 0 0

4 0 0

50 0

50 0

6 0 0

6 0 0

7 00

7 00

A b so rp tio n b yse aw a te r/%

v io le t b lu e g reen y e llo w o ran g e re d

P h y c o ery th rin

C h lo ro p h y ll

W a v elen g th / n m a n d c o lo u r o f lig h t

A b so rp tio nb y p lan t

p ig m e n ts


Use information from the graphs to explain why red seaweeds are usually found in deeper water (further down the shore) than green seaweeds.

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(Total 15 marks)

7. New Zealand beech trees do not produce seeds every year. A study was carried out on the mice living in an isolated New Zealand beech forest. Because of the location of this forest, biologists could only visit it at monthly intervals and stay approximately 12 hours on each visit.

At the beginning of each visit, they set all the traps they had available. This number varied. At the end of the visit, they collected the traps and released any mice they had captured.

Figure 1 shows the population density of the mice at different times during a New Zealand beech seed year and a non-seed year.

2 5

2 0

1 5

1 0

5

0

N ew Z ea la n d b ee chseed y ear

N o n -seed y earN u m b ero f m iceca p tu redp er 1 0 0trap s

M a y A u g N o v F eb M a yM o n th

Figure 1


(a) Use the information in the question to suggest

(i) why the mark-release-recapture method would have given unreliable results;

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(ii) the advantage of giving the number of mice captured per 100 traps rather than just the number of mice captured.

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(b) (i) A statistical test was carried out on the August figures. The population density of mice in the seed year was found to be significantly different at the p = 0.05 level from the population density in the non-seed year. Explain the meaning of this statement.

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(ii) Suggest why the population density increases in a seed year.

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In a different survey, mice were trapped at various sites in the UK. Figure 2 shows the mean body mass and the standard deviation of the adult males that were among the trapped mice.

1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6

R efr ig e ra ted co ld s to res

F arm s in S co tlan d

F arm s in W a le s

F arm s in N o rthe rn E ng lan d

M ass / g

Figure 2

(c) (i) Explain why the data for only the male mice were plotted in Figure 2.

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(ii) In collecting the raw data in this survey, the investigators also measured the amount of tooth wear shown by the mice. Suggest why.

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(d) (i) Explain the advantage of a large body mass to mice living in a refrigerated cold store.

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(ii) Use the information in Figure 2 to explain what is meant by directional selection.

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(e) The colour of wild mice is grey but in some island populations there are black mice.The difference in colour is caused by a single pair of alleles.

(i) Describe how you could use genetic crosses to show that the allele for black is the recessive allele.

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(ii) Explain how you could find the frequency of the recessive allele in a population of mice living on an island.

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(Total 20 marks)

8. Read the following passage.

Despite its bad press, cholesterol is essential. We cannot manage without it. It is an importantcomponent of plasma membranes. Myelin, the substance surrounding many nerve fibres, isinvolved in the rapid conduction of nerve impulses and myelin is rich in cholesterol.

Being insoluble in water, cholesterol cannot be transported in solution in the blood plasma.5 Instead, it is packaged in lipoprotein particles. The main carrier of cholesterol is low-density

lipoprotein (LDL). Each LDL particle has a cholesterol core protected by an outer coat andtopped by a special protein molecule.


How is LDL-packaged cholesterol taken up by cells? Plasma membranes are studded withbinding sites for this "topping" protein. These LDL receptors are made of protein with some

10 sugar chains attached, and their numbers increase or decrease according to the cell's needs forcholesterol. After latching on to LDL receptors, LDL particles are pulled into the cytoplasmand processed in various ways. This regulatory mechanism, however, cannot controlcholesterol concentrations outside cells when large amounts of cholesterol are present in theblood. The excess cholesterol is eventually deposited in artery walls. This leads to an increased

15 risk of thrombosis.

In the 1980s, researchers purified the LDL receptor molecule and determined the sequence ofits 839 amino acids. They also isolated the LDL receptor gene. Mutation of this gene gives riseto a condition known as familial hypercholesterolemia (FH). All the evidence we have, suchas that all affected individuals have at least one affected parent, and that male to male

20 transmission is possible, indicates that the mutant allele is dominant and located on one of theautosomes.

The FH allele is found in a high frequency in some populations. Among South AfricanAfrikaners, for example, 1 in 100 are FH heterozygotes while 1 in 30 000 are homozygous forthe FH allele. These people are all at risk of premature death from coronary heart disease.

Source: adapted from MANGE and MANGE, Basic Human Genetics (Sinaeur Associates Inc.) 1994

Use information from the passage and your own knowledge to answer the following questions.

(a) Explain how myelin is involved in the rapid conduction of nerve impulses (lines 2-3).

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(b) Describe how negative feedback is involved in controlling the concentration of cholesterol in the cytoplasm of a cell.

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(c) (i) Explain how a mutation of the LDL receptor gene can lead to a high concentration of cholesterol in the blood.

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(ii) Describe how excess cholesterol deposited in artery walls can lead to an increased risk of thrombosis (lines 14-15).

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(d) What is the minimum number of nucleotides in the mRNA molecule that codes for the LDL receptor? Explain how you arrived at your answer.

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(e) All individuals affected with FH have at least one affected parent (line 19).Explain how this shows that the FH allele is not recessive to the normal allele.

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(f) Use the data in the last paragraph to estimate the number of people in the South African Afrikaner population at risk from premature death from coronary heart disease because of FH. Give your answer per 100 000 of the population. Show your working.

Answer .................................... per 100 000(3)

(Total 15 marks)


w9. Read the following passage.

In spite of the ability of animals to eat them, green plants dominate the landscape. Part of thereason for this is that most plants, not just the ones we regard as poisonous, contain toxins.These toxins are found in different amounts in different parts of the plant.

Many different substances act as toxins. The simplest are the non-protein amino acids. These5 substances are chemically similar to the twenty amino acids normally found. in proteins. Thus

-cyanoalanine, NCCH2CHNH2COOH, is clearly similar to alanine, CH3CHNH2COOH.When non-protein amino acids are eaten, they are incorporated into proteins. This results inthe formation of unnatural enzymes that do not function properly. Plants which make thesenon-protein amino acids, however, do not synthesise faulty enzymes. Investigations with lily

10 of the valley have shown why. This plant produces large amounts of azetidine 2-carboxylic acid(ACA). This substance is a non-protein amino acid very similar to the amino acid proline. Inthe lily of the valley, the enzyme which links proline to tRNA does not bind to azetidine2-carboxylic acid.

Another group of toxins has been called the “sugar-shaped weapons of plants” and they inhibit15 enzymes involved in carbohydrate metabolism. One of these is a substance called

swainsonine. It is toxic to cattle and affects the nervous system. This effect results from thebuild-up of mannose-based sugars because the animal’s mannosidase enzymes cannot breakthem down.

Fortunately, many toxic compounds can be made harmless. In mammals, the liver plays an20 important part in this. Poisonous substances are converted into products which are relatively

harmless. These products are excreted either in bile or urine. Molecular size is often the factordetermining the final route of elimination from the body. Only the smaller molecules areremoved in the urine. The selective ability of primary consumers to overcome the chemicaldefences of plants is reflected in the pattern of feeding we see today.

Use information in the passage and your own knowledge to answer the following questions.

(a) -cyanoalanine (line 6) is a non-protein amino acid. Explain why -cyanoalanine is

(i) an amino acid;

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(ii) called a non-protein amino acid.

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(b) (i) Explain why enzymes which contain non-protein amino acids cannot function properly.

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(ii) Explain why enzymes which do not function properly are not synthesised in lily of the valley.

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(c) Would you expect swainsonine (line 16) to be a competitive or a non-competitive inhibitor? Explain the evidence from the passage which supports your answer.

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(d) Explain one way in which the information in the passage can help to explain why different species of primary consumer have different ecological niches.

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(Total 12 marks)


10. Cyanide is a poisonous substance. Cyanogenic clover plants produce cyanide when their tissues are damaged. The ability to produce cyanide is controlled by genes at loci on two different chromosomes. The dominant allele, A, of one gene controls the production of an enzyme which converts a precursor to linamarin. The dominant allele, L, of the second gene controls the production of an enzyme which converts linamarin to cyanide. This is summarised in the diagram.

A lle le

E n zy m e

A

A

A lle le

E n zy m e

L

L

P recu rso r L in am arin C y an id e

(a) Acyanogenic clover plants cannot produce cyanide. Explain why a plant with the genotype aaLl cannot produce cyanide.

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(b) A clover plant has the genotype AaLl.

(i) Give the genotypes of the male gametes which this plant can produce.

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(ii) Explain how meiosis results in this plant producing gametes with these genotypes.

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(c) Two plants, heterozygous for both of these pairs of alleles, were crossed. What proportion of the plants produced from this cross would you expect to be acyanogenic but able to produce linamarin? Use a genetic diagram to explain your answer.

(3)


In an investigation, cyanogenic and acyanogenic plants were grown together in pots. Slugs were placed in each pot and records were kept of the number of leaves damaged by the feeding of the slugs over a period of 7 days. The results are shown in the table.

Undamaged Damaged

Cyanogenic 160 120

Acyanogenic 88 192

(d) A 2 test was carried out on the results.

(i) Suggest the null hypothesis that was tested.

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(ii) 2 was calculated. When this value was looked up in a table, it was found to correspond to a probability of less than 0.05. What conclusion can you draw from this?

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A second investigation was carried out in a field of grass which had been undisturbed for many years. The table shows the population density of slugs and the numbers of cyanogenic and acyanogenic clover plants at various places in the field.

Population density of slugs Number of acyanogenic

clover plants per m2Number of cyanogenic

clover plants per m2

Very low 26 10

Low 17 26

High 0 10

Very High 0 5


(e) Explain the proportions of the two types of clover plant in different parts of the field.

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(Total 15 marks)

11. 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)

12. Mayflies are insects which lay their eggs in streams and rivers. The nymphs which hatch from the eggs live in the water for several years.

Mayfly nymphs were collected by disturbing the gravel of a stream bed. A net placed immediately downstream caught any animals which were washed out of the gravel. Eight samples were collected from shallow, fast-flowing parts of the stream and eight from deeper, slow-flowing parts. Nymphs from two different families of mayfly were found. The results are given in the table.

Family Caenidae Family Baetidae

Shallow water Deep water Shallow water Deep water

Mean number of nymphs 2.38 12.88 24.50 6.00

Standard deviation 1.51 7.92 6.72 1.51


(a) Describe how you would have collected the samples in order to ensure they were representative of the habitats being investigated and could be compared with each other.

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(b) Which one of the four samples showed the greatest variation within the sample? Give evidence from the table for your answer.

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(c) The two families of mayfly nymph occupy different ecological niches.

(i) What is meant by the term ecological niche?

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(ii) Describe the evidence in the table which suggests that the two families of mayflies occupy different ecological niches.

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(iii) Explain the advantage to these two families of mayflies of occupying different ecological niches.

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(Total 8 marks)


13. (a) Explain the meaning of these ecological terms.

Population .…..............................................................................................................

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Community ............………..........................................................................................

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(b) Some students used the mark-release-recapture technique to estimate the size of a population of woodlice. They collected 77 woodlice and marked them before releasing them back into the same area. Later they collected 96 woodlice, 11 of which were marked.

(i) Give two conditions necessary for results from mark-release-recapture investigations to be valid.

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(ii) Calculate the number of woodlice in the area under investigation. Show your working.

Answer ......................................................(2)


(c) Explain how you would use a quadrat to estimate the number of dandelion plants in a field measuring 100 m by 150 m.

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(d) Two similar species of birds (species A and species B) feed on slightly different sized insects and have slightly different temperature preferences. The diagram represents the response of each species to these factors.

S p e c ie s B

S p e c ie s B

S p e c ie s A

S p e c ie s A

Tem p era tu re

To le ra n c e o f in d iv id u a lso f e ac h sp ec ie s

N u m b er o fp re y ite m sea te n b yin d iv id u a lso f e ac hsp ec ie s

S iz e o f fo o d item

1 2

34

5


(i) Which of the numbered boxes describes conditions which represent

the niche of species A; ................

the niche of species B; ................

insects too small for species B and temperature too warm for species A; ................

insects too large for species A and temperature too cool for species B? .................(2)

(ii) These two species are thought to have evolved as a result of sympatric speciation.Suggest how this might have occurred.

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(Total 15 marks)

14. 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


(a) Explain how the students could use the mark-release-recapture technique to estimate the numbers of insects.

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(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)

(ii) What level of probability is normally used to judge whether a difference is statistically significant?

...........................................................................................................................(1)

(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.

...........................................................................................................................

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(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.

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...........................................................................................................................(2)

(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.

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...........................................................................................................................(1)

(iii) Explain the role of bacteria in making carbon in dead plant remains available to plants.

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(Total 15 marks)


15. Tigers inhabit forests where they feed mainly on large prey animals. Over the past fifty years, there has been extensive deforestation in many areas where tigers are found.

The graph shows the relationship between the prey biomass of an area and the tiger population that the area can support.

0 3 0 0 6 0 0 9 0 0 1 2 0 0

3 0

2 0

1 0

0

N u m b er o ftig e rs p e r1 0 0 k m 2

P rey b io m ass / to n n es p e r 1 0 0 0 k m 2

(i) What is meant by the ecological term population?

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.....................................................................................................................................(1)

(ii) Use the graph to explain how deforestation might cause a reduction in the number of tigers in an area.

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(Total 4 marks)


16. The diagram shows some of the components of a pond ecosystem.

HO x y g end isso lv es inp o n d w ate r

IM icro sco p icp h y to p lan k to n

AF ish

BF lo a tin gp lan ts

GR o o tedp lan ts

FS n a ils feed in g o no rg an ism s o n th eb o tto m o f th e p o n d

ED eco m p o se rsin m u d

DM u d

CW ater

(a) (i) What is an ecosystem?

...........................................................................................................................

...........................................................................................................................(1)

(ii) List the letters that represent those components that are part of the pond community.

...........................................................................................................................(1)

(b) New Zealand pygmy weed has been introduced into many garden ponds and has spread to some natural ponds. Here, it competes with naturally occurring plants. Suggest how the introduction of pygmy weed may lead to a reduction in the diversity of the community in a natural pond.

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(Total 5 marks)


17. 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)

(ii) Explain what causes this pyramid of energy to be this shape.

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...........................................................................................................................

...........................................................................................................................(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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(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.

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(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


(i) Explain the changes in the numbers of dispersed bacteria and the numbers of free-swimming protoctistans.

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(ii) Explain how the changes that occur in the treatment tank illustrate the process of succession.

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(Total 15 marks)


18. 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)


(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.

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(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.

.....................................................................................................................................

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(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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(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.

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...........................................................................................................................(1)

(iii) Explain the difference in the copper ion concentration between the leaves and the woodlice.

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(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.


(i) What caused the allele for tolerance to first arise?

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...........................................................................................................................(1)

(ii) Give two functions of phosphates in plant cells.

1 ........................................................................................................................

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2 ........................................................................................................................

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(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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(Total 20 marks)

19. One of the most valuable crops planted by the Forestry Commission is spruce because use its yield of timber is high. Early trial plantings showed that spruce trees grew very slowly when planted on land on which heather was also growing.

(a) Name the type of competition shown between spruce and heather.

....................................................................................................................................(1)

(b) Give two resources for which spruce and heather are likely to be competing.

1. ................................................................................................................................

2. ................................................................................................................................(1)


(c) Further trial plantings on land dominated by heather showed that the growth of spruce was greatly assisted by planting another tree species at the same time. This use of a ‘nurse’ crop is now standard practice. The table shows the results of some of these trial plantings.

Height of spruce after15 years / metres

spruce, heather and Japanese larch 4.5

spruce, heather and Scots pine 3.1

spruce, heather and Corsican pine 3.5

spruce and heather 2.0

(i) Young spruce trees were 50cm high when planted. Calculate the difference in the rate of growth when these trees were grown with Japanese larch compared to the control. Show your working.

Answer...............................(2)

(ii) Suggest one way in which a ‘nurse’ crop may aid the growth of spruce trees.

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(Total 5 marks)

20. The drawing shows plants growing in and around a pond.

A B

CD

E


(a) With reference to the drawing, explain the meaning of the terms

(i) community;

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(ii) population.

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(b) Describe how you could use point quadrats to investigate the distribution of plants at the edge of a pond.

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(Total 6 marks)

21. The number of earthworms in a field may be estimated by using frame quadrats. The quadrats are placed at random on the surface of the area being sampled. The ground is then watered with a very dilute solution of formalin. The earthworms which come to the surface are collected and washed.

(a) (i) Explain why the quadrats should be placed at random.

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(ii) Throwing a quadrat does not ensure a random distribution. Describe a method by which you could ensure that the quadrats would be placed at random.

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(b) Give one advantage of describing the size of the population in terms of biomass rather than as the number of earthworms collected.

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(c) Similar sized populations of earthworms were kept in soils at different temperatures. The earthworms were fed on discs cut from leaves. The table shows the number of leaf discs eaten at each temperature.

Temperature/°C Number of leaf discs eaten

0 0

5 178

10 204

15 174

20 124

Using information in the table, explain how mean soil temperature and feeding activity might affect the size of the earthworm population.

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(Total 7 marks)


22. Blue tits are common British birds. Some aspects of the behaviour of blue tits at different times of the year are summarised below.

March – April Adult birds establish breeding territories.

April – July Breeding season. Eggs laid and young hatch. Adult birds collectfood for their young from within their territories.

July – March Birds form flocks which forage for food over a wide area.

(a) In a study of winter feeding flocks, 36 blue tits visiting a bird table were trapped, and before release each bird was marked by placing a small metal ring round one of its legs. The following day 43 blue tits were trapped. Of these, 21 were ringed. Estimate the size of the blue tit population visiting the bird table. Show your working.

Estimated size of blue tit population:..............................(2)

(b) (i) Give two reasons why the mark-release-recapture technique would not give a reliable estimate of the blue tit population in a wood between April and June.

1. .......................................................................................................................

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2. .......................................................................................................................

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(ii) Suggest how the population of adult blue tits in a wood might be estimated between April and June.

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(Total 6 marks)



Japan may finally swallow the Pill

Three decades after the rest of the industrialised world, Japan has begun its final deliberations on whether to introduce contraceptive pills. Although they are currently banned in Japan, contraceptive pills are expected to be approved by government officials in June. The official explanation for the delay is that there are some concerns that oral contraceptives might encourage people to give up using condoms. However, many observers think that the real reasons behind the delay include the government’s fears of a shrinking population. Women in Japan now have on average only 1.4 children each, one of the lowest rates in the world.

The graphs show projections for the size of the Japanese population and the proportion of the population aged 65 and over.

2 0 0 0 20 1 0 2 0 2 0 2 0 3 0 2 0 4 0 2 05 0Ye ar

1 3 01 2 51 2 011 511 01 0 51 0 0

E stim atedp op u la tio nsiz e /m illio n s

4 03 02 01 0

02 0 0 0 2 0 1 0 2 02 0 2 0 3 0 20 4 0 2 0 50

P e rce nta geo f p o p u la tio nag ed 6 5an d o v e r

Year

(Reproduced with permission from New Scientist magazine RBI Ltd)

(a) Explain how oral contraceptives containing progesterone and oestrogen work.

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(b) Use the information given to evaluate the concerns about introducing oral contraceptives in Japan.

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(c) Assuming that the projected figures shown in the graph are accurate, explain how you would expect the population pyramid for Japan in 2050 to differ from that for 2000.

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(Total 12 marks)

24. An investigation was carried out on competition using two species of Desmodium, which are herbaceous plants. The following plots were set up for each of the species, D. glutinosum and D. nudiflorum, resulting in a total of six plots.

Plot A - small individuals were planted 10 cm from large individuals of the same species.

Plot B - small individuals of one species were planted 10 cm from large individuals of the other species.

Plot C - small individuals of each species were planted at least 3 metres from any other Desmodium plant.


The total increase in leaf length on each of the small plants was measured after four weeks. The results are shown on the bar chart.

1 3 0

4 0

2 0

0D esm o d iu mg lu tin o sum

D e sm o d iu mn u d iflo ru m

In c re ase in lea fle n gth /m m

P lo t

P lo t

P lo t

A

B

C

(a) (i) Name the type of competition in

Plot A...........................................................................................................................

Plot B...........................................................................................................................(1)

(ii) Explain how plot C was used as a control.

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...........................................................................................................................(1)


(b) Use the bar chart to explain how competition affects the growth of these two species.

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(Total 5 marks)

25. The effect of grazing by sheep on the growth and reproduction of heather was investigated. Two areas of moorland were cleared of plants and re-planted with heather seeds. One area was surrounded by a sheep-proof fence, the other was left unfenced.The table shows various measurements of the heather plants taken from these two areas.

Measurement Date Fenced area Unfenced area

Total number of heather seedlings per square metre

Sept 1980April 1981

11095

13273

Percentage cover of heather plants

Aug 1992Aug1993

26.742.3

6.221.5

Mean number of flower-heads

per 0.1 m2 quadrat

Oct 1993 263 50

Mean number of seeds per flower-head

Nov 1993 36.7 25.8

(a) Describe how the percentage cover of heather plants on an area of moorland may be measured.

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(b) Use information in the table to

(i) describe the effect of grazing by sheep on the establishment and initial growth of heather;

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...........................................................................................................................(2)

(ii) calculate the percentage reduction in total seed production resulting from grazing by sheep. Show your working.

Answer.............................%(2)

(Total 7 marks)

26. (a) Explain what is meant by an ecological niche.

.....................................................................................................................................

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(b) Two species of beetle may be found in stored grain. The diagram shows the range of moisture content and temperature that each species can tolerate.

2 4

2 2

2 0

1 8

1 6

1 4

1 2

1 0

8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4Te m p e ra tu re /ºC

M o is tu reco n ten t o fg ra in /%

S p ecies A

S p ecies B

The temperature in different parts of a large grain store ranged from 14 °C to 20 °C.The moisture content of the grain was constant at 16%. Beetles of both species were introduced into the store. What would you expect to happen if

(i) species A were a more successful competitor than species B;

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(ii) species B were a more successful competitor than species A?

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(Total 5 marks)


27. Intercropping involves growing two or more different species of plants together. Maize and beans are intercropped in many tropical regions.

R o w s o fm aize p lan ts

B e an s g row in gb etw ee n ro w so f m aiz e

S o il

Diagrammatic cross-section through a mixed crop of maize and beans

(a) Identify one abiotic factor which would affect the growth of maize plants. Describe how you could measure variation in this factor over a 24-hour period.

Abiotic factor

.....................................................................................................................................

Method of measurement

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.....................................................................................................................................(2)

(b) Describe two ways in which maize plants affect the abiotic environment of the bean plants.

1. .................................................................................................................................

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2. .................................................................................................................................

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(c) The maximum yield which could be gained from a plot in which maize and beansare intercropped would be higher than that which could be gained if either maizeor beans were grown alone. Explain why.

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(Total 6 marks)

28. Great tits are small British birds. During spring and summer, they are found in woodland where they nest in holes in trees. One of their main predators during this time is the weasel, a small mammal which is able to climb trees and enter nest holes. Weasels also prey on mice. The graphs show how three different factors affect the predation of great tits by weasels.

Graph A

5 0

4 0

3 0

2 0

1 0

00 0 .4 0 .8 1 .2 1 .6 2 .0 2 .4 2 .8 3 .2

P op u la tio n d en s ity o f g rea t t its /p a ir s h ec ta re – 1

P red a tio nra te b yw ea se ls o ng rea t tits /%

Graph B

8 0

6 0

4 0

2 0

00 1 0 2 0 3 0 40 5 0 6 0 7 0 80

P re d a tio nra te b yw ea se ls o ng rea t tits /%

9 0 1 0 0 11 0D is tan ce o f g rea t tit n e st fro m n e ares t

n e ig h b o u r/m


Graph C

5 0

4 0

3 0

2 0

1 0

00 1 0 0 1 5 0 2 0 05 0 2 5 0

P o p u la tio n d en s ity o f m ice /n u m b er h ec ta re –1

P red a tio nra te byw e ase ls o ng rea t ti ts /%

(a) Describe how the mark-release-recapture method could be used to estimate the population of mice in the area being studied. What assumptions would you have to make in using this method?

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(b) Using information from the graphs, suggest how predation by weasels acts as a density-dependent factor controlling great tit population size.

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(c) Describe and explain the relationship between the percentage of great tits predated by weasels and the population density of mice shown in Graph C.

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(Total 12 marks)


29. The diagram shows population pyramids for England and Wales in 1901, 1931 and 1956.

1 1

1

1 1

1

1 1

1

0 0

0

1 2/ 1 2/

1 2/

1 2/ 1 2/

1 2/

1 2/ 1 2/

1 2/

1 2/ 1 2/

1 2/

M illio n s M illio n s

M illio n s

P o p u la tio n p y ram id 1 9 0 1 P o p u la tio n p y ram id 1 9 3 1

P o p u la tio n p y ram id 1 9 5 6

M a les

M a les

M alesF em ales

F em ales

F em ales

7 06 05 04 03 02 01 0

1 9 0 1

1 9 5 6

1 9 3 1

8 07 06 05 04 03 02 01 0

908070605040302010

(a) To what extent do the data support the view that there was a decrease in birth rate between 1901 and 1931?

.....................................................................................................................................

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.....................................................................................................................................(2)

(b) Describe and explain the change in life expectancy for 20 year olds which took place between 1901 and 1956.

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(Total 4 marks)


30. The graph shows the changes in the size of the collared dove population in Britain following the introduction of these birds in 1955.

4 0 0 0 0 0

3 0 0 0 0 0

2 0 0 0 0 0

1 0 0 0 0 0

E stim ate dn u m b ers o fad u lt c o lla redd o v es

1 9 5 5 1 9 6 0 1 9 6 5 1 9 7 0 1 9 7 5 1 9 8 0 1 9 8 5 1 9 9 0

Yea r

(a) Describe the pattern of population growth shown in the graph.

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.....................................................................................................................................(2)

(b) Explain how a named density dependent factor might have affected population size in the 1980s.

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(Total 5 marks)


31. Barnacles are animals that live on rocky shores. The adults are fixed to the surface of rocks and do not move. The young larvae can swim freely in the sea. As they get older the larvae settle and attach themselves to a rock surface. Here they develop into adults which feed on microscopic plants and animals in the sea when the tide is in. In Britain two species of barnacle, Chthamalus stellatus and Balanus balanoides, commonly occur together on the same rocky shore.

The diagram shows the typical distribution of the two in relation to the tide levels on a rocky shore.

D istrib u itio n o fC . s te lla tu s

D istrib u itio n o fB . b a la n o id es

A d u lts

A d u lts

S e ttledla rv a e

S ettledla rv ae

M ax im u mh ig h tid elev e l

M in im u mlo w tid elev e l

(a) In both species of barnacle few of the larvae which settle become adults. Explain how intraspecific competition could account for this.

.....................................................................................................................................

.....................................................................................................................................(1)

(b) Suggest how interspecific competition could account for the difference in distribution of the adults of the two species.

.....................................................................................................................................

.....................................................................................................................................(2)

(c) Suggest why there are larvae of C. stellatus above maximum high tide level, but no adults.

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(d) In an investigation, it was found that the presence of adult barnacles stimulated larvae of the same species to settle in the same area of the shore.

(i) Suggest a possible stimulus that encourages the larvae to settle.

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(ii) Suggest an advantage of larvae settling in the same area as the adults.

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(Total 6 marks)

32. The diagrams show the territories occupied by male blackbirds in two successive years. Each letter e.g. W, represents one particular adult blackbird. Letters in brackets, e.g. (F), represent young blackbirds.White areas show territories.Black dots show nest sites.

Year 1 Yea r 2

O

W H(J K )

B

E(F )

C

N

M

OW H

JK

E

C

M


(a) The boundaries of the territories occupied by blackbirds E and H have changed over the two years.Suggest why this happened.

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(b) Explain one advantage to a blackbird of establishing a territory.

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(Total 6 marks)


33. A field is crossed by small ridges and furrows. The distribution in this field of two speciesof buttercup (Ranunculus bulbosus and Ranunculus repens) was investigated, using a transect across the ridges and furrows. The number of buttercup plants in each of a seriesof long narrow strips (15cm × 200cm) at right angles to the transect was counted. The results are shown in the graph.

1 6 0

1 2 0

8 0

4 0

0

N u m b e rof p lan tspe r 15 cm× 2 0 0 cmstrip

D ista nc e a lo n g tran sec t/m

K e y R . rep e n sR . b u lbo su s

0 2 4 6 8 1 0 1 2

F u rro w F urro w

R id g e R idg e

P ro file

(a) (i) Explain what is meant by a transect.

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(ii) Suggest why the counting was done in long narrow strips instead of in square quadrats.

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(b) Describe how the distribution of the two species of buttercup differed.

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(c) In a follow-up experiment, 50 seeds of each species were sown in pots. In half of the pots the soil was able to drain freely. The other pots had no drainage, so the soil was waterlogged. The results are shown in the table.

P o tM ean n u m b er o f seed in g s p er p o t

R a n u n cu lu s b u lb o su s R an u n c u lu s rep en s

F ree -d ra in in g so il

W aterlo g g ed so il

3 2

2

12

12

(i) Using these results, suggest an explanation for the different distributions of R. bulbosus and R. repens in the field.

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(ii) Explain how waterlogging of the soil might affect the rate of growth of a seedling.

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(Total 7 marks)


34. 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

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;

..........................................................................................................................

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(ii) the absence of sand shrimps at B;

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(iii) the absence of sand shrimps at C.

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(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)

(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.

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(Total 9 marks)



The 400 000 hectares of bleak open moorland in the far north of Scotland constitute oneof the finest ‘blanket bogs’ in the world. Although it supports relatively few species, thisoutstanding ecosystem is a wonderful reservoir of wildlife more usually associated withthe Arctic tundra. In the fragile peat grow highly specialised plants that are adapted to

5 survive in the cold, wet, acidic conditions. Over 30 species of sphagnum moss live there,each occupying its own niche within the bog. Other characteristic plants are the sundews,which are insectivorous. They overcome the shortage of nutrients such as nitrates bydigesting small insects that are trapped by long sticky hairs on the leaves. The bog is alsoan important breeding ground for several species of birds, which make use of the vast

10 numbers of insects and other invertebrates that proliferate in early summer. For instance,about 70% of Britain’s population of greenshanks breed here, before migrating to thecoasts further south for the winter.

However, this fragile ecosystem is threatened by extensive afforestation with conifers.Patches of forest already dot the landscape. Drainage work for each patch affects a much

15 wider area than is to be planted, by lowering the water table and thus altering the habitatfor the mosses. Predators such as foxes live in the forest, and few birds nest within a kilometre of a forest patch. Patches of forest are, therefore, much more damaging thanthey might seem. The rate of growth of trees in this harsh habitat is slow, with manycasualties due to fierce gales. Without the tax incentives made available by the

20 government, afforestation in this area might well not be economic.

(a) (i) Explain what is meant by ‘niche’ (line 6).

..........................................................................................................................

..........................................................................................................................(1)

(ii) Explain how drainage work could cause the elimination of some species of moss.

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(b) Suggest why the ecosystem supports ‘relatively few species’ (line 2).

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(c) Suggest the advantage to the greenshank of migrating from its breeding grounds to the coast (lines 11-12).

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(d) Sundew plants are able to digest insects trapped on their leaves. Explain how this is of benefit to the sundews in this environment.

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(e) Evaluate the case for growing trees in this habitat.

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(Total 12 marks)


36. (a) Using one example of each to illustrate your answer, explain the difference between density dependent and density independent factors.

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(b) In 1906 the Kaibab Plateau in the south of the United States was made into a wild-life reserve. At the time a herd of about 4000 deer lived on the plateau. And the aim was to protect these deer. It was estimated that the plateau could support about 30 000 deer. All domestic cattle and sheep were removed, and the coyotes and other predators of the deer were killed.

The graph shows the changes in the size of the deer population over the following 35 years.

1 0 0

7 5

5 0

2 5

0

N u m be ro f d e er/tho u sa nd s

1 9 00 1 9 1 0 1 92 0 1 9 3 0 19 4 0Ye ar


(i) Suggest how ecologists might have estimated that the plateau could support a maximum of about 30 000 deer.

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(ii) Using your knowledge of the factors affecting population size, suggest explanations for the changes in the size of the deer population over the period shown by the graph.

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(Total 12 marks)


37. Mauritius is an island in the Indian Ocean. The graph shows the birth rate and the death rate for its human population between 1890 and 1986.

5 0

4 0

3 0

2 0

1 0

01 8 9 0 1 9 0 0 1 9 10 1 9 2 0 1 9 3 0 1 9 4 0 1 9 5 0 1 9 6 0 1 9 7 0 1 9 8 0 1 9 8 6

R ate p er1 0 0 0

d eath ra te

b irth ra te

1 8 9 0 1 9 0 0 1 9 10 1 9 2 0 1 9 3 0 1 9 4 0 1 9 5 0 1 9 6 0 1 9 7 0 1 9 8 0 1 9 8 6

Yea r

To ta lp o p u la tio n

P o p ula tio nin 1 8 9 0

(a) (i) Using the information in the graph, sketch a curve showing the change in the total population of Mauritius between 1890 and 1986. Sketch your curve on the axes below the graph

(2)

(ii) You would need to know the birth rate and the death rate in order to calculate the population growth in a particular year. What other information would you need?

..........................................................................................................................(1)


(b) Before 1930, many deaths were due to infectious disease. Describe and explain one piece of evidence from the graph which supports this statement.

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(c) Give one way in which the demographic transition shown in this graph differs from that which occurred in the United Kingdom.

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(Total 6 marks)

38. (a) Give the ecological term that best describes each of the following.

(i) all the living organisms in a particular habitat

....................................................................

(ii) the particular set of conditions in a habitat to which a species is adapted

....................................................................

(iii) two species using the same resource in the same habitat

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(iv) movement of a species between two habitats to make use of their resources at different times

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(b) Explain what is meant by succession in a habitat.

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(Total 6 marks)


39. The distribution of two species of plant, greater plantain and white deadnettle, on a roadside verge was investigated. The results are shown in the bar graph.

2 5

2 0

1 5

1 0

5

0

N u m b e ro f p lan tsp er 0 .5 m 2

0 0 .5 1 .0 1 .5 2 .0D is ta n ce fro m ro ad /m

K ey G re a te r p lan ta in W h ite d e ad n e ttle

(a) (i) Describe how the data on distribution could have been obtained.

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.......................................................................................................................... (2)

(ii) Describe what the data show about the distribution of greater plantain.

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.......................................................................................................................... (1)


(b) The drawings show the two species of plant.

G reater p lan ta in

W h ite d ead n ettle1 0 c m

Use evidence from the drawings to suggest a hypothesis that explains the distribution of greater plantain.

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(c) A diversity index for all of the plants growing on this roadside verge was calculated at three-year intervals. The table shows the results.

Year Diversity index

199019931996

6.14.53.1

Explain what these results indicate about the plant community on this verge.

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(Total 7 marks)


40. A population of brown trout in a river was studied over a period of ten years. Each year the size of the population was measured in early summer, when it included the newly hatched young, and again at the end of the summer.The results are shown in the graph.

1 2 0 0

1 0 0 0

8 0 0

6 0 0

4 0 0

2 0 0

0

N u m b e ro f b ro w ntro u t in5 00 mstre tcho f r iv e r

1 2 3 4 5 6 7 8 9 1 0T im e/y ea rs

K e y

E arly su m m e rE nd o f su m m er

It is suggested that the change in population size between early and late summer is due mainly to one or more density dependent factors.

(i) Explain what is meant by a density dependent factor.

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..................................................................................................................................... (1)

(ii) Describe and explain the evidence from the graph which suggests that the change is mainly due to density dependent factors.

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(Total 4 marks)


41. The drawings show the areas of a shallow pond covered by greater reedmace and waterlily in 1973 and 1985. Greater reedmace is a tall plant with long strap-like leaves which are upright and grow out of the water. Waterlilies have broad leaves that float on the surface of the water. Both plants have roots in the muddy bottom of the pond.

Is lan d

Isla nd

P o n d

!9 7 3 1 9 8 5

G rea te rreed m ac e

W ater lily

(a) (i) Calculate the percentage increase between 1973 and 1985 in the area covered by greater reedmace. Show your working.

(2)

(ii) Use information in the drawings to suggest why the area covered by waterlilies decreased.

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.......................................................................................................................... (1)

(b) The pond contains a population of water beetles. The beetles are about 1.5 cm long. Describe one way in which the size of the beetle population could be estimated.

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(c) In a deep lake, only plants that float near the surface can survive. They depend on a supply of mineral nutrients from decomposing matter at the bottom of the lake. The temperature at the bottom of the lake stays almost constant. Explain how differences in the temperature of the water nearer the surface can affect the supply of nutrients from the bottom of the lake.

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(Total 8 marks)

42. Cepaea nemoralis is a species of snail that lives in woods and fields. The snails are preyed on by birds such as thrushes. There are several different colour variations, such as yellow with dark bands and brown with no bands. The drawings show these two forms of the snail.

Yello w, b an d ed B ro w n , u n b an d ed

In an investigation, samples of the snail were collected from two sites, one in a beech wood and the other under a hedge. The results are shown in the table.

C o llec tio n s ite

N u m b e r o f sn a ils co llec ted

Yello w,b a n d ed

B ro w n ,u n b an d ed

To ta l

B eec h w o o d

H e d ge

32

49

8 8

2 6

12 0

7 5

(a) (i) Calculate the percentage of brown, unbanded snails at each collection site.

Beech wood ..........% Hedge ..........%(1)


(ii) A chi-squared test was carried out on the results. Explain the purpose of this test.

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(b) Give one assumption that needs to be made about the method used to collect the snails.

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(c) Suggest a hypothesis to explain the different proportions of brown, unbanded snails found at the two sites.

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(d) Describe how the carbohydrates in the dead leaves in the beech wood would be recycled by the activity of detritivores and microorganisms.

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(Total 12 marks)


43. The diagram shows the percentage of deaths due to different causes in populations with different life expectancy at birth.

1 0 0

5 0

0

P erc en tag eo f p o p u la tio n

4 0 5 0 6 0 70L ife ex p ec tan cy a t b irth /y e ars

O th er ca u se s

Vio len ce

D iseases o f th ec irc u la to ry sy s te m

C an ce rIn fec tio u sd iseases

(a) (i) Sketch a survival curve for a population which has a life expectancy at birth of 40 years.

(1)

(ii) Sketch an age pyramid for a population which has a life expectancy at birth of 70 years.

(1)


(b) Using information from the diagram, explain how the quality of drinking water affects life expectancy at birth.

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.....................................................................................................................................(2)

(c) Suggest an explanation for the change in the percentage of deaths due to cancer shown in the diagram.

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(Total 6 marks)

44. Blue tits are small birds that breed during April and May. The parents feed the young for 2 - 3 weeks, after which the young birds leave the nest.

(a) Explain each of the following observations.

(i) When they leave the nest, young birds from a large brood weigh less than those from a small brood.

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............................................................................................................................(2)

(ii) To grow at the same rate, young birds in large broods need less food than those in small broods.

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............................................................................................................................(2)


(b) The scattergraph shows the results of an investigation into the survival of young birds after leaving the nest.

3 5

3 0

2 5

2 0

1 5

1 0

5

00 1 0 2 0 3 0 9 1 9

M a y Jun eD a te o f h a tch in g

P e rce n ta g esu rv iv in g un tilfo llow in gsp rin g

Suggest two possible explanations for the trend in percentage survival shown in the graph.

1..................................................................................................................................

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....................................................................................................................................(2)

(Total 6 marks)


population questions

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