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WORKBOOK ANSWERSOCR A-level Biology ACommunication, homeostasis and energy (Topic 8)Genetics, evolution and ecosystems

This Answers document provides suggestions for some of the possible answers that might be given for the questions asked in the workbook. They are not exhaustive and other answers may be acceptable, but they are intended as a guide to give teachers and students feedback.

Module 5 Communication, homeostasis and energyTopic 8 Respiration

Respiration is important1 It traps very small amounts of energy; it traps energy quickly and readily and releases it

equally readily; by conversion of ADP + Pi to ATP when energy is available and ATP to ADP + Pi when the stored energy is needed; described as the energy currency of the cells; ATP cannot be transported between cells — it must be released within each cell as it is needed; as small amounts of energy are involved there is little energy loss during the conversion.

© Jenny Wakefield-Warren 2017 Hodder Education 1

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3 Photosynthesis is how sunlight energy is trapped and used as chemical energy. This chemical energy is used by plants and other organisms for energy release during respiration.

4 In microorganisms energy is needed for protein synthesis, cell division, growth and to drive chemical processes.

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Name of the process Function

Active transport Pump mechanisms, such as the movement of molecules through cell membranes against their concentration gradients: uptake of many food molecules in the

gut uptake of some ions in the kidney Na+/K+ pump mechanism in nerve cells

to establish a resting or action potential

Activation Energy is required for the activation of molecules

Exocytosis When large molecules are secreted or released out of a cell

Endocytosis When large molecules are taken into a cell

Protein synthesis Building up polypeptides and proteins from amino acids

DNA synthesis, cell division Replicating DNA for cell division

The process of cellular respiration1 It does not use or need any oxygen and occurs in both aerobic and anaerobic conditions.

It occurs in the cytosol (so all the enzymes necessary to convert glucose into pyruvate are found there).

2 Both occur in the matrix of the mitochondria, where pyruvate is converted to acetate.


3 They are highly folded so a large surface area is provided. They carry all the enzymes and carrier molecules needed for the electron transport. These are embedded within the membrane, along with ATP synthase. ATP synthase is where ATP is synthesised through the phosphorylation of ADP.

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a PhosphorylationMain reactions: one ATP molecule is hydrolysed for each step:1 glucose to glucose 6-phosphate2 fructose 6-phosphate to fructose 1,6-bisphosphateSo two ATPs are used upWhat happens: glucose is activated and energy levels raised by adding phosphate to form glucose 6-phosphate and later a second phosphate is added to fructose 6-phosphate to form fructose 1,6-bisphosphate.Energy and Pi are released for each of these steps.

b IsomerisationMain reaction: fructose 6-phosphate is formed.What happens: glucose 6-phosphate is converted to fructose 6-phosphate.

c Splitting the 6-carbon molecule Main reaction: two molecules of 3-carbon triose phosphate (TP) are formed.What happens: fructose 1,6-bisphosphate is split into two molecules, each one of three carbons and with a single phosphate attached.

d OxidationMain reactions: triose phosphate is oxidised and reduced NAD is formed.What happens: two hydrogen atoms are removed to oxidise triose phosphate. Dehydrogenase enzymes are used with the coenzyme NAD acting as the hydrogen acceptor.

e Substrate-level phosphorylationMain reactions: two molecules of reduced NAD are formed and enough energy to reform two ATP molecules.What happens: enough energy is released to allow an ATP molecule to form directly, when a substrate molecule (in this case triose phosphate) is modified by an enzyme-controlled reaction.

f Formation of pyruvateMain reactions: a TP molecule is converted to pyruvate.Two more ATP molecules form.What happens: each triose phosphate molecule is converted to 3C pyruvate by enzyme-controlled reactions.Phosphorylation of two more ADP molecules forms two more ATP molecules by substrate-level phosphorylation.


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6 Two molecules of reduced NAD. (The NAD coenzymes have been reduced by the acceptance of hydrogen atoms.)

Two ATP molecules as a net gain. (Four are actually made but two are used up during phosphorylation of glucose.)

Two molecules of pyruvate.

7 In the absence of oxygen pyruvate molecules are used in fermentation — either lactate fermentation in animal cells or ethanol fermentation in yeast and some bacteria.

8 Decarboxylation: a carboxyl group is removed from pyruvate using pyruvate decarboxylase. The carboxyl group forms carbon dioxide.

Dehydrogenation: the enzyme pyruvate dehydrogenase removes hydrogen atoms — accepted by (coenzyme) NAD to form reduced NAD.

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a The products of the two molecules of pyruvate entering the link reaction: two reduced NAD, two carbon dioxide molecules and two acetyl coenzyme A molecules.

b Acetyl (a 2-carbon molecule) is the final product. Accepted by coenzyme A to form acetyl coenzyme A. The 2-carbon acetyl group is carried as acetyl coenzyme A into the Krebs cycle.

10 Release of coenzyme A: acetate drives the cycle with a series of enzyme-controlled reactions, and releases coenzyme A to join oxaloacetic acid and form a 6C molecule.

Decarboxylation: citrate is oxidised to release two molecules of carbon dioxide.

Dehydrogenation: the citric acid molecule is oxidised by releasing eight hydrogen atoms. Six of the hydrogen atoms are accepted by NAD and three molecules of reduced NAD are formed. Two of the hydrogen atoms are accepted by FAD to form a single molecule of reduced FAD.

Substrate-level phosphorylation: enough energy is released to form one molecule of ATP directly.

Reformation of oxaloacetate: at the end of these steps, a 4C molecule is dehydrogenated to reform oxaloacetate and continue the cycle again.

11 The products of two turns of Krebs cycle are: six reduced NAD, two reduced FAD, four carbon dioxide molecules and two ATP molecules produced directly.


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Coenzymes13 Coenzymes are non-protein organic molecules. They bind to the enzyme’s active site.

Some of them help in enzymatic oxidation and reduction reactions because the enzyme needs a hydrogen acceptor or donor for the hydrogen atoms that it has removed.

The coenzyme becomes reduced when a pair of hydrogen atoms (which will later be divided into protons and electrons) are accepted, and becomes oxidised when the hydrogen is passed on.

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a NAD (nicotinamide adenine dinucleotide): a hydrogen acceptor molecule; manufactured in the body from vitamin B3; nicotinamide accepts a pair of hydrogen atoms and so becomes reduced; it is oxidised when it loses the hydrogen atoms; an important molecule involved in all stages of respiration.

b FAD (flavine adenine dinucleotide) (similar to NAD, but): contains the vitamin B2 riboflavin with adenosine and two phosphate groups; acts as a hydrogen acceptor but it is tightly bound to the dehydrogenase enzyme embedded in the inner mitochondrial membrane; therefore it does not pump the hydrogen atoms into the intermembranal space; returns them to the matrix instead.

c Coenzyme A (CoA): organic molecule made from vitamin B complex (pantothenic acid), adenosine and three phosphate groups and the amino acid cysteine; carries acetate made from pyruvate in the link reaction into the Krebs cycle; also carries acetate groups made from fatty acids and some from amino acids to the Krebs cycle; therefore is an important entry point for other respiratory substrates.

15 Phosphorylation is the addition of phosphate to a molecule. (For example, in the process of ATP formation, using small amounts of energy to add inorganic phosphate to ADP and form ATP.) In oxidative phosphorylation, the final acceptor is oxygen. When the final electron acceptor is oxygen, the proton (hydrogen ion) rejoins the electron, and reduces the oxygen to form water. Substrate-level phosphorylation and photophosphorylation are ATP formation but without oxygen as the final acceptor. Photophosphorylation involves trapping light energy.


Chemiosmosis16 Electrons flow along the carrier molecules and release energy; (the reduced coenzymes

are oxidised); some of the energy is used to pump the protons into the intermembranal space; protons build up here and a proton and electrochemical gradient forms; no ATP is used for this pump — energy comes from the electron flow or electromotive force; the inner membrane is impermeable to ions (including protons); so ions cannot move across the membrane but flow through ion channels (within the membrane) down the proton gradient; the ion channels are part of ATP synthase; protons flow down the ion channel of ATP synthase and the rotating part of the ATP synthase enzyme turns, with energy released; used to build one ATP molecule from ADP and Pi.

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Stage Location Substrate molecule

Product molecules

Number of ATP molecules

Type of respiration

Glycolysis Cytosol 6C glucose

2 × 3C pyruvate2 × ATP2 × reduced NAD

2 directly Aerobic and anaerobic

Link reaction Matrix of mitochondria

Pyruvate AcetateReduced NAD and CO2

Aerobic

Krebs cycle Matrix of mitochondria

Acetate and CoA

Oxaloacetic acid recycled2 × CO2

1 × ATP6 × reduced NAD 2 × reduced FAD

2 directly (for two turns of cycle)

Aerobic

Oxidative phosphorylation

Cristae of mitochondria

Reduced NAD and ADP

H2O and26 x ATP

26–28 Aerobic

Total 30–32

Mitochondria18

a Outer membraneFeature: protein channels and carriers Function: passage of molecules (pyruvate and reduced NAD from glycolysis) into the mitochondrion


b MatrixFeature: enzymes in matrix; 4C oxaloacetate; reduced coenzyme NAD; mitochondrial DNA and ribosomes (70s)Function: catalyse the link and Krebs reactions; accepts acetate from the link reaction to form a 6C molecule; carries H2 to the electron transport chain;synthesises the proteins and enzymes needed

c Inner membrane — cristaeFeature: a lipid inner membrane that is different from the outer membrane; highly folded structure; electron carrier complexes; coenzyme FAD; cofactors; large molecules of ATP synthase enzyme protruding into the matrix

Function: membrane is impermeable to ions, including H+ ions, so these are prevented from passing through; increases surface area for more electron carriers and enzymes, such as ATP synthase; each carrier is an enzyme and a cofactor, arranged in a chain to allow the electron transport chain reaction to proceed; bound to dehydrogenase enzyme within the cristae and reduced by accepting H atoms (these H are pumped out to the matrix – not to the intermembranal space); haem- or iron-containing groups (Fe2+) become reduced (to Fe3+) when accepting an electron and oxidised (to Fe2+) when the electron is donated to the next carrier (an example of a redox reaction)Protons pass through down proton gradient from intermembranal space to matrix —this rotates ATP synthase and allows ATP to be formed from ADP and Pi using energy from the process called chemiosmosis

d Intermembranal spaceFeature: small space between inner and outer membranes

Function: protons are actively pumped into this space — they build up in this space as they can enter through the outer membrane but cannot pass on through the inner membrane; creates a proton gradient as the source of potential energy

Anaerobic respiration1 Lactate fermentation (e.g. in the muscle cells of animals) where pyruvate acts as the

hydrogen acceptor for the hydrogen from reduced NAD.

Ethanol or alcohol fermentation (e.g. in fungi such as yeast, and in plants and some bacteria) where ethanal acts as a hydrogen acceptor to remove the hydrogen atoms from reduced NAD. Ethanol is first produced from pyruvate.

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Molecules and substances involved in fermentation

Lactate fermentation Ethanol fermentation

Pyruvate Remains unchanged until it accepts H

Loses a molecule of carbon dioxide and becomes ethanal

Intermediate molecule None Ethanal reduced to ethanol

H Pyruvate Ethanal


Molecules and substances involved in fermentation

Lactate fermentation Ethanol fermentation

Enzyme Lactate dehydrogenase Pyruvate decarboxylaseEthanol dehydrogenase

NAD Oxidised Oxidised

End product Lactic acid (lactate) Ethanol (alcohol)

Number of molecules reduced NAD

2 2

Number of CO2

molecules0 2

Net gain of ATP molecules

2 2

Respiratory substrates3

a Glucose is most commonly respired in most human tissues.

b Red blood cells cannot respire any other substrate because they have no mitochondria. Brain cells only respire glucose as only glucose can cross the blood/ brain barrier.

c Fat and proteins/amino acids and other molecules can also be used as respiratory substrates. Most animals eat different food, so their tissues use a variety of substrates.

The respiratory quotient4

a RQ = 5.0/6.0 = 0.83

b This value suggests a mixture of respiratory substrates, but with more fat than carbohydrate or protein because the value is lower than 0.9.

RQ protein = 0.9, RQ carbohydrates = 1.0, RQ fats = 0.7

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a The bubble can move in either direction so that if there is more or less CO2 released than O2 uptake the difference can be calculated.

b From 0 to 4 minutes RQ = 1. At 6 minutes and 8 minutes RQ = 0.9. At 10 minutes RQ = 0.95. (With sodium hydroxide the CO2 produced is removed, so the figures in this column represent O2 uptake.)

c 0.33 mm−1 g−1 min–1 or 0.005 mm−1 g−1 s–1

d An accurate value could be obtained by calculating the volume of gas in the capillary tube.


Exam-style questions1 For active transport, for the uptake of mineral ions against their concentration gradient

from the soil; for the secondary pump required in the transport of food molecules by translocation; for the light-independent stage of photosynthesis (although the ATP for this is derived from the light-dependent stage).

2 B

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a i Oxidative phosphorylation: the cristae/inner membrane

ii The Krebs cycle: the matrix

iii Decarboxylation: the matrix

iv Electron transport chain: the cristae/inner membrane

b Codes for proteins/enzymes required in respiration.

c NAD or FAD

d The protons are actively pumped into the intermembranal space; using energy from some of the oxidised coenzymes; no ATP used at this step; proton gradient built up; electrochemical gradient also built up; protons flow down this gradient via ion channels; ion channels associated with ATP synthase; as the protons flow through the ion channel of ATP synthase the enzyme is rotated; this releases energy; used to build an ATP molecule.

e When electron flow stops chemiosmosis stops; no ATP produced; lack of ATP means muscles cannot contract; actin and myosin cannot slide past each other/no active movement of the myosin head; muscles fail to contract; breathing movements stop/intercostal muscles/diaphragm muscles stop breathing movements.

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a Glycolysis

b In the cytosol

c Pyruvic acid/pyruvate

d 4 ATP, but since two are used up early in the process there is a net gain of only 2 ATP.

e Lactate production occurs in actively respiring cells, e.g. muscles; glycolysis results in ATP, reduced NAD and pyruvate; the pyruvate acts as the H+ acceptor to recycle the NAD; lactate dehydrogenase catalyses the reduction of pyruvate to lactate and the oxidation of NAD.

Whereas, in yeast, alcohol fermentation; glycolysis results in ATP, reduced NAD and pyruvate as for lactate fermentation; pyruvate loses CO2; catalysed by enzyme pyruvate decarboxylase and coenzyme; forms ethanal; ethanal acts as hydrogen acceptor from reduced NAD; now NAD oxidised and ethanal reduced to ethanol; catalysed by enzyme ethanol dehydrogenase.


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a A: Glycolysis

B: Lactate fermentation/anaerobic respiration

C: Aerobic respiration/Krebs cycle and oxidative phosphorylation

b Pathway C

c Pathway A

d Alcohol and CO2


Module 6 Genetics, evolution and ecosystemsTopic 1 Cellular control1 Genetic variation may give rise to a new allele of a gene that gives a selective advantage

to the organisms and allows a species to adapt to a changing environment.

2 Alleles of genes that result in undesirable features will be selected against and either fall to a very low frequency in, or be eliminated from, the population.

Types of gene mutation3 A change in the DNA base sequence of a gene.

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Type of gene mutation What is it? What is the impact?

Substitution A nucleotide with a different base from the original is incorporated into a developing strand of DNA

Causes a change in only one of the base triplets, which might not change the coded amino acid and so have an effect on the coded polypeptide

Insertion One or more nucleotides are added to the DNA

Causes a change to all the base triplets that follow the insertion, i.e., causes a frameshift

Deletion Loss of one or more nucleotides from the DNA

Causes a change to all the base triplets that follow the insertion, i.e. a frameshift mutation

Stutter The same nucleotide triplet is repeated, usually many times

Causes the organism to malfunction, e.g. Huntington’s disease

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a Because most amino acids are encoded by more than one base triplet.

b Because the code is degenerate, a change in one base may result in a triplet that still codes for the same amino acid.


6 A genetic code based on just pairs of letters would give 16 possibilities (42). This is insufficient for 20 amino acids.

7 The new allele may be recessive and masked by a dominant allele. The gene may be only one of a number involved in the expression of the characteristic and so the impact of the new allele is reduced. Another gene may actively suppress the expression of this gene — an effect called epistasis.

The effect of mutations on protein production and function

Beneficial mutations8 The intensity of sunlight is too low in northern Europe to penetrate the skin, reducing the

ability of humans to synthesise vitamin D. A mutation that lowered the concentration of melanin in the skin would enable humans to produce more vitamin D and so avoid rickets.

Neutral mutations9 A mutation causing a change in eye colour is neutral because a change in eye colour is

unlikely to result in a selective advantage or selective disadvantage.

Regulatory mechanisms that control gene expression10

a One of the DNA strands is used as a template for the production of mRNA.

b Pre-mRNA is edited by removal of the introns and splicing the exons back together.

c A newly formed polypeptide chain is processed in the Golgi apparatus.


Transcriptional level11

Method Process Regulatory roleMethylation Methyl groups are added to

DNA nucleotides with an enzyme to catalyse the reaction

Stabilises cells so they can no longer act as stem cells

Creates epigenetic effect

May prevent expression of retroviral DNA, so helps to control disease

Acetylation Transfer of acetyl group to histone proteins; causes chromosome to change shape

When the chromosome changes shape, the gene becomes more or less accessible

The accessibility determines the expression of that gene

12 It is a short sequence of nucleotides close to, and upstream from, the gene. When one or

more transcription factors bind to the promoter region, it allows RNA polymerase to bind to the gene and begin transcription.

13 Oestrogen binds to a receptor on the surface of target cells and, being lipid soluble, diffuses through the cell surface membrane. It diffuses to the nucleus where it binds to an oestrogen receptor within a protein complex. This receptor is a transcription factor that binds to the gene promoter regions for lots of different genes and initiates transcription. Once it is attached the oestrogen changes the receptor shape and leaves the protein-complex, binds to the promoter region for one of the target genes and attracts cofactors. The oestrogen receptor and cofactors allow RNA polymerase to bind and transcription of that gene begins.

The lac operon14 The lac operon is a functioning unit of the DNA containing a group of genes all involved (in

some way) in the digestion of lactose. They all are under the control of one promoter.

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a Region where the protein CRP (or cyclic AMP repressor protein) binds. Helps bind the enzyme RNA polymerase to the promoters to allow transcription of the genes. If cyclic AMP (cAMP) is present the CRP attaches to the DNA and allows RNA polymerase to bind.

b RNA polymerase attaches here if CRP–cAMP join with the DNA at the CRP site. RNA polymerase cannot attach if this site is covered by the repressor and so DNA transcription stops and no mRNA is produced for protein synthesis.

c Located next to the structural gene. This is where the repressor binds. The region acts as a switch, allows transcription and translation of structural genes. This gene codes for the three enzymes if there is no inhibitor. When the repressor binds to the operator site transcription and translation are stopped.


d In the lac operon there are three structural genes, alongside each other. These code for β-galactosidase, lactose permease and another enzyme. All three can be transcribed to mRNA together when the promoter and operator are switched on.

Post-transcriptional level

Editing of primary mRNA and removal of introns16 Each gene of a eukaryote contains sequences of non-coding DNA, called introns. During

translation, these introns are copied to molecules of pre-mRNA; the editing removes these intron regions from the mRNA and splices together the coding regions (exons).

17 Both are nucleotide sequences within a molecule of DNA/pre-mRNA (comparison for 1 mark).

Exons code for amino acid sequences but introns do not (contrast for 1 mark).

18 There are some introns that code for specific proteins themselves or can be further processed to create non-coding RNA molecules that may have a gene regulatory function.

Post-translational level

Activation by cAMP19 It is a derivative of ATP, formed by the action of an enzyme, adenylyl cyclase. It acts as a

secondary messenger for many processes such as hormone activation, cell transport, and activation and regulation of ion channels.

Genetic control of the development of body plans20 The sequence is determined by transcription factors (sequence specific DNA-binding

factors). These are proteins that bind to specific DNA sequences and control the rate of transcription for those gene sequences into mRNA.

Homeobox gene sequences in plants, animals and fungi21

a Homeobox genes code for transcription factors. They are a sequence of 180 bases (60 amino acids of a protein). They regulate transcription by the protein binding to the DNA at one point and regulating transcription of genes further along the DNA. Homeobox sequences are the same whatever organism they are found in, because they all have the same function of coding for transcription factors. Homeobox genes act as master genes controlling other genes and when they will function at different stages

b The homeobox controlling early development in animals, plants and fungi, by turning specific genes on and off in the correct order.

Homeobox sequences give the basic body pattern by controlling segmentation pattern (of insects and mammals) and the identity for the sections (what each will become and which organs will be present). They determine the polarity of the organism (i.e. the head and tail) and development of wings and limbs.

22 There are nine homeobox genes in the fruit fly, Drosophila melanogaster, which are involved in control of development in the embryo in the correct sequence: head, thorax and abdomen. The same genes are found in four Hox clusters in humans.


Role of Hox genes in controlling body plan development23

a They are in organised groups known as Hox clusters.

b Some organisms only have one or two Hox clusters. For example, roundworms have just one Hox cluster whereas vertebrates have four clusters, each with 9–11 genes, found on different chromosomes.

24 The hox clusters contain genes in a linear order that is directly related to the order of the regions they affect and when they affect the region. (For example, head–tail axis develops first followed by segmentation in the embryo; when and where the legs, antennae and wings will develop.)

If only a single mutation occurs, this will cause changes in the gene cluster, which in turn will cause similar changes in all the regions under its control. Some Hox genes will activate genes initiating apoptosis and control development by causing cell death in some areas. (In Drosophila there is a Hox gene that activates a gene, called Rpr (meaning reaper), that causes cell death in areas of the head lobes separating the maxillary and mandibular head lobes.) The same idea is seen in finger and toe development.

The importance of the mechanisms of mitosis and apoptosis25 Breakdown of the cell cytoskeleton; DNA becoming denser and more tightly

packed/condensation of the chromatin; breakdown of the nuclear envelope; biochemical changes in the cytosol; formation of vesicles containing hydrolytic enzymes; finally, phagocytosis by phagocytes.

26 Destroying the harmful self-targeting T lymphocytes during development of the immune system, to prevent attack on the self body cells. Has a protective mechanism against cancer — under the influence of the tumour-suppressor genes apoptosis destroys and removes any genetically damaged cells (with damaged DNA) as they could give rise to cancer. Role in embryonic development—by destoying unwanted cells during development to ensure the final structure is correct. Role in maintaining healthy adult tissues by destroying damaged or genetically deformed cells.

Response of genes to internal and external stimuli27

Process Factors in process Outcome

Internal cell signalling Cytokines, hormones, growth factors, nitric oxide

Controls cell division and apoptosis. Without control apoptosis is reduced and cell division is uncontrolled so tumours may arise. Or if too much apoptosis occurs degeneration of tissues or organs results.


Process Factors in process Outcome

External factors (e.g. pathogens or pollutants)

A protein —cyclin D—is produced by cells when they are affected by external factors.

An upset in the mitosis/apoptosis balance.Cyclin D sets off a chain effect—an enzyme cascade. Genes are activated that produce cyclins A and B.For the cell cycle to proceed cyclins A, B and D must be produced.

External factors (e.g. those increasing stress)

The mechanism of cell signalling is disrupted.The microbiome of the body is disrupted.

The cell signalling no longer effectively controls the mitosis/apoptosis balance.An imbalance of the microbiome has been linked to a wide variety of illnesses in humans, such as inflammatory bowel disease, Crohn’s disease, some of the autoimmune diseases and anxiety

Epigenetic effects Changes in gene expression (epigenetics)

The DNA code itself is not affected, although acetylation of methylation will mean it is presenting differently.

Exam-style questions1 Level 3 (5–6 marks) Provides a comprehensive discussion of the mechanisms, with an

understanding of both. Well-developed line of reasoning that reads well is clear and logical and uses scientific terminology where appropriate. All information is relevant and in continuous prose. Reference to controlled by cyclins, cyclin-dependent kinases or CDKs and other control measures, e.g. protooncogenes genes, which stimulate cell division, and tumour suppressor genes which reduce cell division. Cyclins are the regulators and the CDKs act as the catalysts once they are activated by the cyclins. When cyclins activate the CDKs they catalyse phosphorylation of certain target proteins, which has the effect of activating or inactivating them. This allows the cell cycle to move from one phase to the next.

Apoptosis is programmed cell death. Also developmental changes in the embryo are orchestrated so that cells are produced (by mitosis) where they are needed but later are destroyed (by apoptosis) in areas where they are not needed. So here destruction is part of the developmental process in organisms—for example—fingers and toes initially are formed as a whole but then partially destroyed to allow them to separate.

Level 2 (3–4 marks) Describes some (a few) of the mechanisms, with some indication of understanding both. A line of reasoning that is presented with some structure and use of scientific terminology. Mostly relevant information.

Level 1 (1–2 marks) Describes some aspects of the mechanisms. The information has only a little structure and lacks scientific terminology.

2 It is a section of DNA that carries genes coding for those enzymes needed to hydrolyse lactose, which are only produced when lactose is needed and is available for use.


There are two mechanisms that both ensure glucose is used, if available, before any hydrolysis of lactose.

In the normal situation for the operon the enzymes needed for lactose hydrolysis are prevented from being transcribed by the lac repressor. If there is no lactose this lac repressor stops transcription of the genes, in the lac operon group, coding for the enzymes that hydrolyse lactose.

If glucose is present (even when lactose is also in the medium) the activator protein, needed for the enzymes’ production, stays inactive and the third enzyme lactose permease is also not produced to stop lactose transport into the cells.

3 A role in polypeptide manufacture: when bound to cAMP receptor protein, it causes the binding of RNA polymerase to gene promoter regions, activating transcription.

The activation of protein kinases: in eukaryotic cells, it works by activating protein kinase A (PKA), an inactive or precursor enzyme. Once activated it is the enzyme phosphorylase kinase. This enzyme is responsible for activating a number of proteins.

cAMP activates some proteins directly, e.g. exchange proteins are activated by cAMP with a similar mechanism to the PKA mechanism.

Another mechanism involves control of translation involving siRNA (small interfering RNA). These are short lengths of double-stranded RNA attached to protein complexes and the mRNA targeted for breakdown. Therefore the siRNA controls whether certain proteins are synthesised and so controls the gene expression.


Topic 2 Patterns of inheritancePhenotypic variation1 Phenotypic variation refers to differences in the observable or measurable characteristics

of an organism. Genotypic variation refers to the combination of the different alleles of each gene that an organism possesses.

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Feature Continuous variation Discontinuous variationNumber of genes involved Polygenic—many genes,

each with two or more alleles, are involved in the inheritance

Few—usually one or two, each with two or more alleles

Effect on phenotype The features show a gradual change as there are many intermediates

The features are in discrete categories—either present or absent

Effect on genotype Environmental factors have a significant effect

Environment has little influence

Environmental factors3 Poor diet may limit growth due to a lack of essential amino acids/protein so full potential of

height, for example, may not be realised unless the diet is well balanced and offers all the essential nutrients and amino acids/protein.

4 Plants kept in the dark will become yellow and etiolated (over-long and weakly growing) due to the action of the plant growth substance auxin. They will be unable to produce chlorophyll if the chloroplasts are not subjected to light. However, once in the light chlorophyll is produced and etiolation is slowly reversed and normal growth resumes. Although the genes are present in the plants they cannot be expressed due to the environmental conditions.

Genetic factors 5 The albino plant has a mutant gene that prevents production of chlorophyll. This is very

different from the environmental effect seen in question 4 because the plant cannot produce any chlorophyll at all due to the lack of the necessary gene. The gene for chlorophyll synthesis is expressed only in the light.

Genetic variation6 Variation is increased by sexual reproduction because parents produce genetically

different gametes and fertilisation of these gametes occurs at random.

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a Changes the combination of the alleles of the genes on each chromosome.

b The two gametes carry chromosomes with different alleles. Two different sources of genetic information are brought together, so new combinations are possible. Fertilisation is a random process with many sperm being possible fertilisers.


c Introduces new variants or changes in the genetic material, which may or may not be harmful, e.g. non-disjunction, occurring during meiosis.8 The chiasmata are points at which chromatids from homologous chromosomes become

entangled, break and rejoin. They help variation because parts of chromatids are exchanged, leading to new combinations of alleles of the genes on each chromosome.

Genetic diagrams showing patterns of development

Monogenic inheritance9 A (monohybrid) monogenic cross is the inheritance of a single pair of alleles of a single

gene. If one allele is dominant and the other is recessive, the expected phenotypic ratio is 3 : 1.

10 Parents: GG (green) × gg (yellow)

Gametes: G g

F1 : All Gg (green)

F1 Gametes: G or g × G or g

Punnett square showing genotypes of F2

G g G GG Gg

g Gg gg

F2 phenotype 3 green : 1 yellow

Codominance11 The resulting phenotypic ratio is 1 : 2 : 1 ratio.

Explanation: When two alleles are codominant neither is dominant and so both are expressed in the phenotype. When both alleles appear together the phenotype is a mixture of both. This may be clarified with an example, e.g. red and white flowers producing a pink flower if it is heterozygous.

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a There are two identical alleles for a gene coding for a characteristic.

b The alleles for a gene coding for a characteristic are different.

c Two alleles of a gene are neither dominant nor recessive so when they appear together the phenotype will show the effects of both alleles.

d A normal chromosome other than a sex chromosome.

e Two or more genes are found on the same chromosome.

f An allele that is shown in the phenotype only if it is present in the homozygous condition.


g An allele always expressed in the phenotype even when another allele is also present.

Dihybrid inheritance 13 Dihybrid; linked; crossing over; alleles; variation

14 Use T = tall, t = dwarf, C = cut-leaves, c = potato-leaves.

The F1 plants must have a heterozygous genotype because they have a range of different phenotypes in their offspring in the F2 . So the F1 genotype = TtCc

The F1 cross is therefore = TtCc × TtCc

The gametes for both are: TC Tc tC tc

TC Tc tC

tc

TC TTCC TTCc TtCC TtCc

Tc TTCc TTcc TtCc Ttcc

tC TtCC TtCc ttCC ttCc

tc TtCc Ttcc ttCc ttcc

So the expected ratio is 9 : 3 : 3 : 1

Observed = 944 + 278 + 284 + 102 = 1608 1608/16 = 100.5

Therefore, expected = 904.5, 301.5, 301.5, 100.5, which is close to 9 : 3 : 3 : 1 ratio (need a χ2 test to confirm)

Multiple alleles15 Antigens; ABO; monohybrid; multiple allelic; two.

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Blood Groups of the ABO system Possible genotypes

A IAIA or IAIO

B IBIB or IBIO

AB IAIB

O IO IO

Use of phenotypic ratios and linkage

Autosomal linkage17

a A normal body chromosome—not a sex chromosome.

b 3 : 1 (or 1 : 2 : 1) — the same ratio as for monogenic inheritance.


c Crossing over at meiosis I can give rise to new combinations of alleles, so in a population a small number will show a new linked combination.

Sex linkage 18 A carrier female has one X chromosome with the recessive allele for colour blindness and

one X chromosome with the dominant allele for colour vision. A male has a 1 in 2 chance of inheriting the X chromosome carrying the allele for colour blindness so you might expect half the woman’s sons to be colour blind. Whichever of her X chromosomes they inherit, all the woman’s daughters will inherit their father’s X chromosome carrying the allele for colour vision. Consequently, none of them will be colour blind.

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a XB Xb

b As males only have one X chromosome they can only have a genotype of XB Y or Xb Y, so cannot be tortoiseshell.

c

Parental phenotypes: Black female × Ginger male

Parental genotypes: Xb Xb XB Y

Parental gametes: Xb or Xb XB or Y

Punnet Square:

F1 phenotype: (% of tortoiseshell cats): 50%

Epistasis20 When two or more genes interact they all influence the expression of the same

characteristic, because the genes are involved in an enzyme pathway. In this case each gene usually codes for (a polypeptide) an enzyme. If one of the genes has an allele coding for a non-functioning enzyme the metabolic pathway stops and the characteristic cannot be expressed.


XB Y

Xb XB Xb Xb Y

Xb XB Xb Xb Y

21

a The ratio is close to a 9 : 4 : 3 ratio and both parental genotypes are PpRr.

b Since the F1 ratio is close to a 9:3:3:1 ratio, the genes must be unlinked. Of the 16 possible genotypes:

9 will contain at least one dominant allele of both genes, so will have purple leaves

3 will have at least one dominant allele of gene A but will be homozygous recessive for gene B and so will have red leaves

4 will be homozygous recessive for gene A and so will have white leaves.

Use these in the following Punnett square for a student check.

PR Pr pR pr

PR PPRR PPRr PpRR PpRr

Pr PPRr PPrr PpRr Pprr

pR PpRR PpRr ppRR ppRr

pr PpRr Pprr ppRr pprr

Chi squared test 22 It is used on categorical data/data in categories to see if there is a significant difference

between the expected data and the observed data.

23

a The null hypothesis was ‘there is no difference between the observed and the expected data’.

b

Category O E O – E (O – E)2 (O – E)2 / E

Red uneven fruit 97 109 12 144 1.32

Red round fruit 48 36 12 144 4.00

Orange uneven fruit 45 36 9 81 2.25

Orange round fruit 4 12 8 64 5.33

χ2 = 12.90

c 4 – 1 = 3

d p < 0.01

e The probability that the difference between the observed results and the expected results occurred by chance is less than 0.01. Since this is less than the accepted


0.05 probability level, we can conclude that the difference was not due to chance and can reject the null hypothesis.

Factors affecting evolution of a species24

a Maximum population size that a specific habitat is able to support indefinitely.

b A combination of all the biotic and abiotic factors that limit any increases in population size.

c Any factor that affects the ability of some members of the population to survive and reproduce.

25

Factor Effect on population Example

Stabilising selection A population remains stable for a characteristic if selection removes the extremes.The optimum (mode) is maintained.

Stabilisation of human birth mass around the optimum.

Directional selection The characteristic will slowly change in one direction. If an environment changes any individuals with features better suited to the new environment will be selected and survive to breed.

Ground finches on the Galapagos with larger beaks survived at the expense of those with smaller bills when the available seeds became larger.

Genetic drift A random change in allele frequencies that occurs in small populations.

Red poppies over white spotted marmots

Genetic bottleneck A change in allele frequencies that follows a drastic reduction in population size.

Hawaiian goose (ne ne), northern elephant seal, giant panda

Founder effect The population shows low genetic diversity because the founding population contained only a small sample of the gene pool of the population from which it came.

Tibial muscular dystrophy—an inherited mutant allele (TTN) in Finland.A Pacific island with high numbers of an inherited eye defect present as a recessive mutant allele in just one of the original colonisers.

Hardy-Weinberg equation for allele frequencies26 The sum of all the alleles for a specific gene in the population.


27

a p + q = 1 refers to the relative frequencies of the alleles for a specific gene in the population. p is the frequency of the dominant allele and q is the frequency of the recessive allele for the gene. 1 represents the whole population.

b p2 + 2pq + q2 =1 refers to the genotypic frequencies for the alleles for a characteristic. Here p2 represents the frequency of the homozygous dominant genotype, q2 the frequency of the homozygous recessive genotype and 2pq the frequency of the heterozygous genotype.

28

There are no genetic changes in the population.

There is no migration (either emigration or immigration).

There is no selection.

There is no gene mutation.

The population is large and can breed randomly and freely within the population with no limit on success.

There is no genetic drift.

Isolating mechanisms in evolution of new species 29

a Populations become separated by a geographical barrier and so become reproductively isolated. In the absence of gene flow, selection can result in these isolated populations accumulating genetic differences that establish them as separate species.

b Sub-populations are not separated by a geographical barrier but by spatial/temporal/behavioural differences. In the absence of gene flow, selection can result in these isolated populations accumulating genetic differences that establish them as separate species.

The principles of artificial selection 30 Maintaining a resource of organisms; providing a source of wild type which show more

genetic variation; increased milk yield in dairy cattle; variety and range of dog breeds useful to man, all bred from grey wolves; improvement in bread wheat; larger-sized fruit e.g. tomatoes, and other plants used for human consumption.

Ethical issues with artificial selection 31 Level 3 (5–6 marks) Provides a comprehensive discussion of the ethical issues with an

understanding of both sides of the argument. Well-developed line of reasoning that reads well, is clear and logical and uses scientific terminology where appropriate. All information is relevant and in continuous prose.

Level 2 (3–4 marks) Describes some (a few) of the issues with some indication of both sides of the argument being at least considered. A line of reasoning that is presented with some structure and use of scientific terminology. Mostly relevant information.


Level 1 (1–2 marks) Describes some aspects of the issues. The information has only a little structure and lacks scientific terminology.

Exam-style questions

1 Child 1 could have either Mr X or Mr Y as the male parent since the M could come from the mother and N from either of the male fathers. Mr Y may have a recessive IO.

Child 2 must have Mr X as their father since the father must contribute an M antigen as child 2 has two M alleles (Mr Y has no M to contribute) and for the ABO system the allele IO will come from both parents to give an O group.

Child 3 cannot be the child of Mr X since neither Mr X nor Mrs X has antigen A to contribute. This must have come from another father—likely to be Mr Y.

2 B = black, b = brown, S = short hair, s = long hair

F1 = BbSs × BbSs so F1 gametes = BS Bs bS bs

BS Bs bS bs

BS BBSS BBSs BbSS BbSs

Bs BBSs BBss BbSs Bbss

bS BbSS BbSs bbSS bbSs

bs BbSs Bbss bbSs bbss

So 9 black, short hair (B_S_) : 3 black, long hair (B_ss): 3 brown, short hair (bbS_): 1 brown, long hair (bbss)

3

a F1 = BbAa × bbAA, so F1 gametes for black agouti = Ba bA and for brown agouti = bA

bA

Ba BbAa

bA bbAA

So the F2 ratio is 1 : 1

b The two genes are linked so there is no independent assortment of the two alleles for the two genes.

c This is a lethal gene, which halts development or causes death. Epistasis is where one gene or allele masks the phenotypic expression of other genes or alleles in the interaction. (needs the idea of masks)


4

Albinism can only occur by having two recessive alleles for albinism (aa). Therefore, the frequency of the homozygous recessive (q²) must be 0.0001 (since 1 in 10 000 people is affected). So:

q = = 0.01

Using p + q = 1: p = 1 – 0.01 = 0.99

Now use 2pq (from the second equation p2 + 2pq + q2 = 1):

2 × 0.99 × 0.01 = 0.02 (to 2 d.p.). So the frequency of carriers of albinism is 0.02.


Topic 3 Manipulating genomes

The uniqueness of the genome1 Its genome

2 E. coli has a single circular loop of DNA, with relatively few protein coding genes (4288) mostly organised into operons and in smaller loops called plasmids. There are also some ribosomal RNA and transfer RNA genes. Homo sapiens has rod-shaped chromosomes (23 pairs), each carrying 20 000 to 25 000 genes, and loops of DNA in the mitochondrial matrix.

3 The study and application of genetic and molecular biology techniques to gene mapping and gene sequencing (on the chromosomes or for an entire organism).

4

a Any three from: structural genes; non-structural; ribosomal RNA and transfer RNA genes; regulatory genes; promoters; hypervariable sequences; junk DNA. (Allow introns and exons.)

b Mitochondrial DNA (mtDNA) within the mitochondria or chloroplast DNA within chloroplasts (ctDNA).

The principles of DNA analysis5 Any two from: PCR (polymerase chain reaction); gel electrophoresis; DNA sequencing;

DNA profiling.

Polymerase chain reaction (PCR)6 The sequence of bases in the primer must match (by complementary base pairing) the

DNA sequence just beyond the region of DNA being copied/amplified. Different DNA has different base sequences.

Gel electrophoresis7 The DNA sample is treated with restriction enzymes to ‘cut’ it into small sections or

fragments are amplified using PCR; a dye or a radioactive label is added and the fragments are loaded into the wells in the gel.


8

DNA sequencing and new sequencing techniques

The principles of DNA profiling9 Basic principle—DNA contains a variable number of short tandem repeats; they are

unique to each individual.

Method—amplify fragments containing short variable repeats, separate by electrophoresis, match bands between samples of DNA.

10 Minisatellites (variable number tandem repeats or VNTRs) are small sections (10–100 bps) of DNA in structural genes or in the non-structural DNA and are inherited from both parents. These are repeated at various points along the chromosome and can be cut by restriction enzymes.

Microsatellites (STRs) are much shorter sequences of nucleotides (2–5 nucleotides long but repeated 10–30 times) which may be in the non-coding DNA between the structural genes. These are easily identified and more unique as there is more variation between individuals and they are less likely to degrade. Also, only a short length is needed, so DNA profiling works well on a small sample.

11 The greater the number of STRs in the gene for the protein huntingtin, the greater the risk of developing the symptoms of Huntington’s disease in later life.

Use in detecting disease12 It is a variation in one nucleotide. A change in a single base will not affect the gene

reading frame so protein synthesis can still occur and a protein can still be produced. It may be the same protein if the nucleotide change still codes for the same amino acid or it


may be a different variation of a protein. Role: act as biological markers of disease; form a large proportion of genetic variation in humans; occur more frequently than mutations.

Bioinformatics13 The genes involved in development in Drosophila are similar in some ways to those found

in other animals including humans. This can be given as a percentage figure of degrees of similarity, which is useful in uncovering evolutionary relationships and ancestry.

The principles and techniques of genetic engineering14

a An enzyme that forms phosphodiester bonds. Can be used to join a gene to a plasmid.

b A structure used to deliver a gene into the host organism as part of genetic engineering.

c A bacterial artificial chromosome.

d A vesicle surrounded by plasma membrane.

e recombinant DNA, formed when DNA from one organism is combined with the DNA of another.

15

Applications Role in genetic engineering

Restriction enzymes Cuts DNA at specific base sequences

Ligase enzymes Anneals or seals the DNA cut ends and forms a phosphodiester bond between them

Reverse transcriptase enzymes Makes cDNA from RNA

Plasmids Is used to transfer DNA into the bacterial cells

Viruses/liposomes May be used to transfer genes into human cells

16 It cuts across the DNA at a specific recognition sequence, comprising a short palindromic sequence of bases.

17 This is an unpaired ‘overhanging’ sequence of bases on one of the polynucleotide chains. It allows the annealing of another ‘overhanging’ sequence of complementary bases.

Humulin18 The differences, although in only a few nucleotide base pairs, create a slightly different

protein. This difference triggers the human immune system and an immune response.

1. The mRNA produced from the gene for insulin is extracted from β cells in the pancreas and converted to DNA using reverse transcriptase.

2. Sticky ends are added to the cDNA.

3. A plasmid from E. coli is extracted and cut using a restriction enzyme.

4. The cut plasmids are mixed with the cDNA with complementary sticky ends.


5. A ligase enzyme anneals the cDNA and cut plasmid.

6. Plasmids are added to new bacteria treated with calcium followed by a cold shock.

7. Transformed bacteria are identified and pure continuous cultures of them are set up.

8. Insulin, produced in large quantities by the transformed bacteria, is harvested.

GM crops and ethics20 Any two valid answers, for example golden rice that provides increased levels of vitamin A

precursors or GM bananas that act as a vaccine for hepatitis B.

21 Advantages: resistance to disease pests, drought and herbicides improves crop production and reduces losses; an increase in nutritional value; production of medicines/vaccines; allows production of crops that allow for climate change faster than traditional selection processes; allows large-scale food production to keep pace with the increase in human population growth.

Objections: may be too expensive for farmers in developing countries; possible transfer of antibiotic-resistant genes or herbicide-resistant genes into other organisms; could lead to antibiotic-resistant pathogens or weeds super resistant to herbicides; the genomes of crop plants may be altered by introduction of foreign genes; mutations in foreign genes could cause unknown effects in crop plants; possible creation of new pathogenic viruses; loss of genetic diversity; no economic advantage to farmers as they still need to use herbicides and pesticides and cannot keep seed for replanting as the crops do not breed true.

GM animals and ethics 22 Unspecified public concerns regarding use of GM animals; full effect of GM on the whole

genome of the animals is unknown; effect of GM animals in the food chain untested; lack of public trust of scientists.

GM microorganisms and pathogens and ethics23

GM organism Use in genetic engineering Application

Mouse Production of monoclonal antibodies

Detection and directed cancer treatment

Virus Modified to carry and deliver genes

Gene therapy

The principles of gene therapy24

a Inserting genes into cells of an organism to correct or repair a genetic problem. Usually a dominant allele is added into the cells where an individual has two recessive alleles for the gene.

b Somatic gene therapy: a gene is inserted into body cells of an organism so only those cells benefit. Usually this must be repeated at regular intervals as the cells will die and not pass on the gene. If inserted into a stem cell it may offer longer-term treatment.


Germ-line germ therapy: a gene is inserted into reproductive cells of an organism. In this case the gene will be passed on to the gametes and so to any offspring.

Exam-style questions1 Level 3 (5–6 marks) provides a comprehensive discussion of the issues, with an

understanding of both benefits and drawbacks of the argument. Well-developed line of reasoning that reads well, is clear and logical and uses scientific terminology where appropriate. All information is relevant and in continuous prose.

Level 2 (3–4 marks) Describes some (a few) of the benefits with some indication of drawbacks being at least considered. A line of reasoning that is presented with some structure and use of scientific terminology. Mostly relevant information.

Level 1 (1–2 marks) Describes some aspects of the issues and not well balanced at all. The information has little structure and lacks scientific terminology).

2

a i Fluorescent markers, which can be detected by laser scanners.

ii A type of gel electrophoresis is used. The DNA migrates through this gel to the anode (in a similar way to the gel electrophoresis technique.

b Their phosphate groups give DNA fragments a negative charge, so DNA fragments migrate to the anode of an electric field. Pores in the agarose gel allow fragments to migrate, with the smaller fragments moving faster, and so further, than the larger fragments.

c The DNA fragments are detected as they migrate through agarose gel in capillary tubes, so there is no need to wait until the end of electrophoresis to begin analysis. There are many capillary tubes—96 is the number frequently used—so more ‘runs’ can be performed at the same time. Analysis is by direct feed into a computer, so the output is faster.

3

a A retrovirus contains a core of RNA instead of DNA and an enzyme called reverse transcriptase.

b The virus infects the organism’s cells. Its RNA and enzyme enter the nucleus where DNA is manufactured from viral RNA suing the host cell’s mechanism and the enzyme. The resulting DNA is incorporated into the host DNA where it can lie dormant for many years before becoming activated.


Topic 4 Cloning and biotechnologyCell division1

Type of cell division

Feature

Mitosis Meiosis

Number of nuclear divisions 1 2 (meiosis I and meiosis II)

Number of daughter cells produced

2 4

Chromosome sets in each daughter cell

Same as parent cell Half the number as the parent cell

May involve crossing over No Yes

Results in genetic variation No Yes

2

a Cells that can divide to renew themselves and to produce a small variety of other cells.

b Cells that can divide and differentiate into any type of body cell and into extra embryonic cells.

c Cells that can divide and differentiate into any type of body cell but not into extra embryonic cells.

3 Meristematic tissue — found at the tips of shoots or roots (apical meristems), in axillary/lateral buds and between the xylem and phloem within vascular bundles (enabling secondary thickening).


Cloning in plantsNatural cloning4

Vegetative reproduction Type of tissue Reproductive features

Runners Horizontal stems Stem grows over the soil surface. New roots and leaves and, later, new plants form at the nodes.

Stolons Thin, underground stems Potato tubers are stolons that swell with stored starch at the tips. These eventually produce shoots from the lateral buds (‘eyes’ of the potato) and new plants.

Bulbs Thick, short stems; often disc-like.

The leaf bases are swollen with stored food, e.g. onion. New plants grow in the early spring.

Root tubers Swollen root The root is swollen with food. New stems and new plants grow from the tuber in the spring.

Artificial cloning

5 Advantages: rapid growth, easy to establish; all plants will be of same reliable quality because they are genetically identical; so identical crops such as cereals—rice, maize, wheat and various fruits such as apples, pears and raspberries will all be of the same quality; plants will breed true, which does not always happen from seed; plants may be produced that are not weather dependent.

Disadvantages: all plants are genetically identical, so in the case of disease or pests all will be equally susceptible; loss of variation and diversity; build-up of pests and diseases, especially viruses.

6 Cloning in plants involves using tissue from the original parent such as a vegetative structure, storage organ, cuttings, tissue cultures. As a result all the clones are genetically identical. Formation of dog breeds is not cloning as they are not genetically identical. They result from selective breeding over successive generations. So it is also a slow process.

7 The most commonly used plant growth substance is auxin (IAA, indoleacetic acid); at appropriate concentrations it stimulates mitosis and the formation of adventitious roots.

8

a Concentration of abscisic acid; concentration of gibberellin; temperature at which seeds germinated; time for germination.

b Age/variety/source of seeds used; pH of solutions; volumes of all liquids; concentration of oxygen in Petri dishes; space between seeds.


c Temperature affects enzyme reaction rate and 25oC is optimum / suitable temperature for seed germination OR to remove temperature as a confounding variable;

d Gibberellins stimulate germination; because in the absence of abscisic acid (water only) there is a strong correlation between concentration of gibberellin and percentage germination/reference to data; abscisic acid inhibits germination/has an antagonistic effect on gibberellin; because in the presence of abscisic acid there is no germination (whatever the concentration of gibberellin).

e Any two of: encouraging root growth of cuttings; encouraging growth in length of stem; discouraging growth in length of stem; discouraging growth of lateral buds; inducing flowering; inducing fruit formation; stimulating fruit ripening; delaying fruit ripening.

9 Callus: explants are removed by cutting leaves, stems or roots (all are differentiated cells); stimulated to divide by mitosis into an undifferentiated mass—callus; callus is subdivided to increase number of plantlets; cultured on a medium with plant hormones added; equal concentrations of auxin and cytokinins give best growth; some cells isolated from the callus may be cultured in a suspension.

Meristem: meristems are cut from axillary buds or apex of the stem; then cultured in same way as for callus growth to promote mitosis.

Commercial value: numerous new plants can be cultivated each year from one original callus or meristem, e.g. chrysanthemum apical meristem may produce 1 million new plants in a year; all genetically identical so quality and desirability are known and reliable; importance in fruit crops as rapid and reliable growth with reliable resulting fruit crop; also in cereal crops; named examples such as apples, pears, rice, wheat; resistance to known pathogens, diseases and pests is assured.

Commercially good as cost is lower; idea of less care needed when compared to seeds (easier).

Disadvantages: mainly loss of variation and loss of genetic diversity; risk of loss of adaptability in the case of environmental changes or new pathogens; build-up of pests and diseases possible in cloning, especially viruses.

Cloning in animalsNatural Cloning

10 Identical twins are genetically identical and have same epigenetic imprinting since produced from the same fertilised egg. Therefore scientific studies can focus on the environmental effects as genetics is known. Epigenetics may be a result of environmental changes. Non- identical twins are NOT genetically identical only as similar as any other sibling.


Artificial Cloning

11

12 In embryo cloning a single fertilised egg is cloned into two embryos—artificial identical twins. So cloning involves the germ cell. The embryos are then implanted into surrogate mothers.

In cloning of adult cells (somatic cell nuclear transfer) the nucleus is removed from the adult somatic cell. The nucleus is also removed from an egg (cell) and is replaced by the nucleus from the adult somatic cell, e.g skin or gut lining. The technique may involve injecting the nucleus, using an electric current to fuse the somatic cell and the enucleated egg cell. Cloning of the embryos may then also occur before implantation into a surrogate mother. This may involve a surrogate of the same species OR of another, similar species in the case of rare animals.

13 Level 3 (5–6 marks) Provides a comprehensive discussion of the ethical issues relating to artificial cloning, with an understanding of both sides of the argument. Well-developed line of reasoning that reads well, is clear and logical, and uses scientific terminology where appropriate. All information is relevant and in continuous prose.

Level 2 (3–4 marks) Describes some (a few) of the issues, with some indication of both sides of the argument being at least considered. A line of reasoning that is presented with some structure and use of scientific terminology. Mostly relevant information.

Level 1 (1–2 marks) Describes some aspects of the issues. The information has little structure and lacks scientific terminology.


Biotechnology and microorganisms14 Use of living organisms to produce useful products, e.g. drugs or food, or to carry out a

useful service, such as sewage disposal.

15 Primary metabolites are any compounds produced by the metabolic activity of an organism during normal growth. Secondary metabolites are any compounds produced by an organism after it has stopped growing.

Use in human food production16

a It is an enzyme used to tenderise the meat.

b Papain is a protease that digests/hydrolyses protein fibres and any fibrous tissue.

c Re-used for more brewing; used as yeast extract; used in cattle feed.

d pH 3.5–4.5

Use in drug production17 With batch-fed fermentation, food such as maize supplements the glucose and lactose

nutrients as they are being used up, and this stimulates the production of the antibiotic that would not be produced or produced in small amounts with only glucose supplied. With batch fermentation the only nutrients added are those at the start of the reaction, so the quantity of product reduces as time progresses.

18

Use in bioremediation19 The bacteria metabolise the hydrocarbons in the oil. The products are carbon dioxide and

water as well as biomass, which are harmless to the environment.


Culturing microorganisms and aseptic techniques20 Sources of carbon, energy, nitrogen, mineral salts, water and growth factors. (All prepared

under sterile conditions.)

21 Disinfection of surrounding areas before and after work to remove bacteria from work surfaces; the agar/nutrient culture medium must be autoclaved to kill any bacteria it contains; using protective clothing and gloves to reduce risk of transmission of bacteria between self and culture; all apparatus to be sterilised in an autoclave or similar at over 120oC for 15–20 minutes to kill all bacteria on and in it; medium to be sterilised and poured under sterile conditions; transfer of microbes to be with a flamed loop or pipette to kill bacteria in/on it; flame loop after inoculation/place wet pipette into disinfectant after inoculation since it is contaminated by the inoculum; lift lid of Petri dish as little as possible to reduce risk of airborne bacteria falling on agar surface; have lighted Bunsen burner on bench to create upward current away from culture.

22 Batch: production continues until substrate is used up; waste products accumulate; the product must then be separated from enzyme and waste products; limited operation time; reactor must be cleaned and sterilised before starting up again.

Fed-batch: operation time continued for longer as substrate is fed into fermenter at regular intervals; production stops when waste products build up; temperature and pH constantly monitored; product must be separated from enzyme and waste products.

Continuous: product is continuously collected from fermenter; pH and temperature conditions are constantly monitored and substrate is added to enzyme continuously; production can continue for long periods until reaction rate slows due to enzyme damage/denaturing.

23

Condition How the condition is controlled

Reason for control

Temperature Using a thermostatically controlled heater

Enzymes work best at an optimum temperature

pH Use buffers to maintain optimum pH

Enzymes have an optimum pH

Carbon source Add a supply of carbohydrate, e.g. monosaccharide/disaccharide or polysaccharide; CO2 for autotrophs

To enable microorganisms to produce organic molecules

Nitrogen source Add amino acids, peptides nitrates in autotrophic organisms

To enable microorganisms to produce amino acids /polypeptides /proteins/ nucleotides

Using immobilised enzymes 24 An enzyme that is entrapped in an inert matrix or compound but remains active.

25 No need to keep adding enzyme because it can be re-used; no cost of separating enzyme from final products because the enzyme remains in the fermenter.


Exam-style questions1 Packed-bed continuous flow is the best for industry because a stream of substrate is

passed over it and the product can be continually collected. There is no ‘down time’. Immobilised enzymes will not form part of the product and so there is no costly separation needed after the reaction. As they are trapped they will remain in the reactor for reuse unlike soluble enzymes. Immobilised enzymes have greater thermostability as they remain 78% active at 70oC and 55% active at 80oC, unlike soluble enzymes. A thermostable enzyme can be used at higher temperatures giving a faster rate of reaction; products will be formed quicker and the yield per unit time is greater.

2 The smooth surfaces are easier to clean; reduces contamination; non-corrosive and inert, so not affecting flavour; strong, so resists pressure build up; temperature control is easier; can be made into large containers more easily than other materials.

3 Level 3 (5–6 marks) Provides a comprehensive discussion of the advantages AND disadvantages of using microorganisms, with an understanding of both sides of the argument. Well-developed line of reasoning that reads well, is clear and logical, and uses scientific terminology where appropriate. All information is relevant and in continuous prose.

Level 2 (3–4 marks) Describes some (a few) of the issues with some indication of both sides of the argument being at least considered. Possibly not well balanced, with one side better argued. A line of reasoning that is presented with some structure and use of scientific terminology. Mostly relevant information.

Level 1 (1–2 marks) Describes some aspects of the issues. Possibly only one side considered. The information has only a little structure and lacks scientific terminology.


Topic 5 Ecosystems 1

a The variety of life. This can be considered by the number of different ecosystems or by the number of different species within them or by the genetic variation within each of the species.

b A measure of how close the numbers of organisms of each species are to each other in a particular environment.

c The number of different species present in an area.

2 Species richness only considers the number of different species present whilst species diversity considers both the number of different species present and the relative abundance of each of them.

3 Photoautotrophic organisms (such as green plants) synthesise complex organic compounds using light energy. Heterotrophic organisms (such as animals) obtain organic compounds from other organisms.

Sampling techniques for studying distribution and abundance4 An abundance scale is a method of estimating the relative abundances of different species

against a known but subjective scale. Examples: DAFOR (Dominant, Abundant, Frequent, Occasional and Rare) or ACFOR (Abundant, Common, Frequent, Occasional and Rare) or the Braun-Blanquet scale (+ for less than 1% to 4 for between 51 and 75% coverage)

5 Longworth mammal traps/pitfall traps/light traps to trap animals; mark, release, recapture; cameras for catching sight of wandering large animal; sweep nets for assessing pond/stream animals.

6

a Set out a suitable grid; generate random numbers for coordinates; devise method for locating coordinates e.g paired working procedure; OR a line transect and method of position quadrats along the line at suitable intervals; quadrat size selected; identification of species; method of recording percentage cover for each species; method of replication suggested; sampling for each slope.

b For the south-facing slope N=46. For the north-facing slope N=41.

Species South-facing slope

(n/N)2 North-facing slope (n/N)2

Calluna vulgaris (heather)

14 0.092 9 0.048

Deschampsia caespitosa (grass)

12 0.067 9 0.048

Trifolium repens (clover)

9 0.038 6 0.021

Holcus lanatus (grass)

6 0.017 3 0.005

Juncus effusus (rush)

5 0.012 1 0.001

Achillea millefolium 0 0 6 0.021


Species South-facing slope

(n/N)2 North-facing slope (n/N)2

(yarrow)

Anthriscus sylvestris (cow parsley)

0 0 4 0.010

Epilobium hirsutum (great willowherb)

0 0 3 0.005

N = 46 41∑(n/N)2 = 0.226 ∑(n/N)2 = 0.159

c Carry out replicates in each site / repeat the investigation at another time.

Biotic factors7

Biotic factor Example Relative benefits to populations involved

Intraspecific competition

An example of plant or animal species

Successful organisms gain water, nutrients, space, shelter, light and a suitable mate

Intraspecific cooperation

Social species, e.g. termites, ants or honey bees

Work together for benefit of whole group

Interspecific cooperation

Mutualism, e.g. corals and zooxanthellae, lichen, mycorrhiza

Algae are protected from consumers or gain nitrogen from nitrogenous waste or gain carbon dioxide from coral respiration; coral gains carbohydrates

In lichen, fungi gain sugars and nutrients. Algae gain a foothold and are protected from water lossIn mycorrhiza, fungi gain sugars, nutrients and protection; plant gains ions

Predation Carnivores Carnivores gain food prey species suffer loss of population members

Diseases Parasites, e.g. tapeworms, flukes, plasmodium, ichneumon wasp

Infectious diseases, e.g. influenza

Only the parasite benefits, with the host suffering to a varying degree

Causes harm to host and spreads to other individuals

Abiotic factors8

a Any abiotic factor related to the climate, e.g. wind exposure, temperature range, rainfall/ precipitation.


b Any abiotic factor related to the soil, e.g. air (oxygen concentration), pH, soil texture, soil type, soil depth, humus content, mineral ion concentration, water content/ water table level.

c Any physical factor such as aspect, gradient, drainage, altitude, topography, soil erosion.

9 Soil type or crumb type/texture, moisture content, mineral ion content, humus content, pH, compactness, temperature, soil air/oxygen.

Energy and biomass transfer10 A measure of the organic and inorganic matter, excluding water, present in an organism or

in a trophic level.

11 Photoautotrophic and chemoautotrophic organisms. Accept green plants and chemoautrophs,

12 Photoautotrophs fix carbon dioxide using light energy. Chemoautrophs fix carbon dioxide using energy derived from the oxidation of inorganic substances.

13 A photoheterotrophic organism uses light energy but obtains carbon as complex carbon compounds. A chemoheterotrophic organism obtains energy from complex carbon compounds already built up by organisms in a lower trophic level.

14

Efficiency of energy transfer

15

a (44090/7.1 × 106) × 100 = 0.62%

b (8760/44090) × 100 = 19.87%

c 3960 – 2300 = 1660

(1660/8760) × 100 = 18.94%


Recycling in the ecosystem

Recycling of carbon16 They have acted as a sink for carbon, which is now being released when fossil fuels are

combusted.

17 Level 3 (5–6 marks) Provides a comprehensive discussion of the number of different producers. An understanding of the producer feeding relationship in the ecosystem / trophic level. An understanding of the process of carbon fixation. Well-developed line of reasoning that reads well is clear and logical and uses scientific terminology where appropriate. All information is relevant and in continuous prose.

Level 2 (3–4 marks) Describes some (a few) of the issues with some indication that both the producer role within the ecosystem and carbon fixation as a process are being at least considered. A line of reasoning that is presented with some structure and use of scientific terminology. Mostly relevant information.

Level 1 (1–2 marks) Describes some aspects of the producer issue or of the carbon fixation process. Unlikely to be both but if it is then very patchy and superficial for both. The information has little structure and lacks scientific terminology.

Recycling of nitrogen18 Nitrogen is fixed in the form of nitrates (nitrification). Nitrate ions are taken up by

autotrophs, to be used to make amino acids. Amino acids are used to synthesise proteins or used as amino groups for synthesis of purines and pyrimidines. Primary consumers eat the autotrophs, hydrolyse the proteins to amino acids that are absorbed and reused in protein synthesis. In turn, these new proteins are consumed by secondary consumers and decomposers. Consumers may metabolise some amino acids into the Krebs cycle or break down unwanted amino acids for conversion to glucose or glycogen.

Nitrogen fixation19 Nitrosomonas—converts ammonia (NH3) or ammonium ions (NH4

+) to nitrite ions (NO2–);

Nitrobacter—converts nitrite ions (NO2–) to nitrate ions (NO3

–); Azotobacter—nitrogen fixation; Rhizobium—nitrogen fixation.

20 Ammonia (NH3) or ammonium ions (NH4+); dinitrogen/nitrogen gas (N2); nitrite ions (NO2

-) nitrate ions (NO3

-)

Succession21 Ecological succession describes the series of changes (called seral stages) occurring over

time, in which each community changes the abiotic conditions, enabling other communities to develop. Features common to all types of succession include:

loss of members of earlier communities through competition with populations in the later communities

eventual development of a relatively stable climax community

progression from pioneer species that colonise the environment to the climax community, associated with an increasing number of populations, an increase in the complexity of the food webs, an increase in total biomass and an increase in the stability of the community


Primary succession22 Primary succession begins in a barren environment, such as new land exposed by

volcanic activity, water collecting in a hanging lake or land exposed by glacial retreat.

Secondary succession begins in an environment that was previously colonised but has become bare due to damage, e.g. a forest fire or a dried up pond. In this case the environment might not be completely free of organisms, for example seeds or resistant spores from the previous community might remain.

23 Marram grass and sedge are the pioneer species—only they can tolerate the harsh conditions of the bare sand. Their death and decomposition adds humus to the sand, changing its humus content and pH. This allows heather to colonise the developing soil. The death and decay of the dominant plants in each community lowers the pH still further and adds yet more humus to the soil, changing its colour. Eventually a climax community, dominated by oak, develops.

Deflected succession24 Chalk grassland, heathland, lawns and playing fields: grazing or human intervention such

as mowing keeps the seral stage an early stage—called plagioclimax. Agriculture: ploughing, crop growth and harvesting cause deflected succession. In this case no plagioclimax forms as the harvesting prevents this.

Exam-style questions1

Abiotic factor Effect on plant distribution

Temperature Temperature determines species e.g. cool temperatures: temperate plants; hotter climes: tropical plants. In any ecosystem an increase in temperature causes a rise in metabolism of organisms, e.g. an increase in the rate of photosynthesis.

Light intensity An increase in light intensity increases the rate of photosynthesis in some plants but is harmful to those that are adapted to shaded environments.

Oxygen concentration Low oxygen concentration is rare in ecosystems in which plants are able to photosynthesise rapidly. In aquatic environments that are polluted by organic waste, bacterial respiration might reduce the oxygen to such a low concentration that plants will not survive.

pH pH is a critical factor in determining the niche of a species. Some need a neutral pH and others survive best in alkaline or in acidic conditions

Wind speed High wind speeds increase the rate of transpiration from plant leaves as well as reducing the local temperature. Woody xerophytes, such as pine, survive well in these conditions but more fragile, herbaceous plants seldom do.


2

a Dry mass, wet mass and carbon mass. (For dry mass, the biological material is weighed, dried at a temperature high enough to evaporate the water but not so high that it will burn the organic matter, and reweighed until its mass is constant.)

b Dry mass is an easy way to measure biomass, but the organisms must be destroyed. Wet mass is easy to measure but includes water that is variable in quantity and is not a component of assimilation. Carbon mass is a good comparator as carbon is a key component of all assimilated organic compounds, but it is very difficult to determine/does not measure nitrogen content does not measure inorganic/mineral content.

c Harvest the production from a known area. Burn the harvested material in such a way that it heats a known volume of water/in a bomb calorimeter. Use the value of the specific heat of water to calculate the energy needed to cause the measured rise in water temperature. The units will be a unit of energy and a unit of area, e.g. kJ m–2. To calculate productivity over a period, the units would include time, e.g. kJ m–2 year–1.

3 Level 3 (5–6 marks) Provides a comprehensive discussion of the relationship between energy and the ecosystem. Well-developed line of reasoning that reads well, is clear and logical, and uses scientific terminology where appropriate. All information is relevant and in continuous prose.

Level 2 (3–4 marks) Describes some (a few) of the issues with some indication of both energy and ecosystem being at least considered. A line of reasoning that is presented with some structure and use of scientific terminology. Mostly relevant information.

Level 1 (1–2 marks) Describes some aspects of the issues. The information has little structure and lacks scientific terminology.


Topic 6 Populations and sustainabilityFactors determining population size1

a All the individuals of the same species living in the same area at the same time.

b All the organisms of all the populations living in the same area at the same time.

2 Limiting factors are those factors that are closest to the minimum required and so will limit the growth (in this case) of the population. There are a number of different abiotic and biotic factors that affect population growth.

3 Members of the same species occupy the same niche and so will be competing for the same resources, whilst those of different species have a different niche and are unlikely to have identical requirements to support life.

4 Lag Description: the growth is very slow and shows little increase as the organisms become accustomed to the environment. Explanation: In some cases specific enzymes must be manufactured in order to make use of the available nutrients. Reproduction in the population is slow because the initial numbers are low.

Log Description: this is the stage of exponential growth, so the curve is very steep. Explanation: reproduction and growth are rapid and exceed death rate, resources are freely available and not limiting growth.

Stationary Description: the curve levels off and flattens. Explanation: reproduction has slowed and now is equal to death rate. Resources are limiting, so only a set number of organisms can be supported (environmental resistance). The fermenter has reached carrying capacity.

5 The curve will drop and eventually may become zero. This is because resources have been used up and/or toxic waste products have accumulated.

6

a The maximum population size / density that an ecosystem can support.

b A precise description of the range of abiotic and biotic factors in which organisms of a single population can survive.

c When different species avoid direct competition by occupying different niches within the same habitat.

d When two species have the same niche but the more competitively successful species eliminates the less successful species in competition.

Interaction between populations

Predator–prey relationships7


a Between day 4 and 14 the two populations fluctuate, with the predator cycle lagging a little behind that of the prey. As the predator populations rises in number the prey population falls to a low point (of 26 at day 10). In turn this causes the predator number to fall (26 at day 12). Prey population now increases as there are few limiting factors once the food increases. This rise provides the predator with more food so their number rises.

b At A the prey numbers reach a peak due to few limiting factors. Predator numbers reach a peak 2 days later. The predator numbers increase above the prey numbers briefly.

c ParameciumDay 1: 162/15 cm3 of mediumDay 16: 162/15 cm3 of mediumChange = 0

SaccharomycesDay 1: 75/0.1 cm3 of mediumDay 16: 75/0.1 cm3 of mediumChange = 0

8 The predator population is also likely fall, a little after the fall in the prey population. However, the fall is not large because alternative food sources will also provide for immediate food needs. Some organisms do not exist on one source of food.

9 Interspecific competition is between members of different species. Intraspecific competition is between members of the same species.

10

a For example, between grey (or black) and red squirrels or American bluebells and English bluebells, or any suitable suggestion.

b For example, between male robins or stags for a mate or territory, or any suitable suggestion.

Conservation of biological resources11 Conservation is the management of biodiversity and sustainability of habitats and species

whilst at the same time allowing managed use by humans. Preservation is protection of ecosystems, habitats and species without allowing any human use.

12

Biological resource Human use Reason Sustainability

Timber Use as construction material for buildings/homes and for paper

Economic value Managing both natural and plantation forests, e.g. coppicing in woodlands

Fish As a protein source (food) and a vitamin source

Economic value Managing fish stocks in oceans by controlling fishing methods, volumes and areas


13 Banning fishing in certain areas (exclusion zones can be set up), limiting the number of fishing boats; limiting the size of catch for each boat or the number of certain species; banning fishing during the spawning season; regulation of the type of fishing gear, e.g. the size of fishing net, to allow young fish to escape and breed and restocking. Vital for inspections to ensure all these points are enforced.

14 Protected by the Antarctic Treaty, which protects the area for science and conserves marine life. This is a pioneering ecological approach, which means looking at population dynamics but also at reducing the chances of harm, e.g. by reducing visitors, preventing introduction of alien plant and animal species, long-term monitoring of species present (e.g. Adele penguin) and especially reducing catches of krill. Setting up complete exclusion zones is part of this. Standard methods do not monitor or aim to control ecologically but use mainly population dynamics and monitoring.

15

Management of timber

Method of removal of timber Effect of management

Clear felling Removal of trees of same age over an area and so removing the canopy.

Economic advantage but is destructive because biodiversity is affected and soil is exposed and likely to erode.

Selective felling Removal of mature, diseased and unwanted trees. Canopy is mostly preserved.

Economically less advantageous but less destructive to ecosystem. Trees left in place allow continued biodiversity and natural regeneration.

Strip felling Removal of small areas or strips. Strips are replanted and adjacent strips are only felled once these have grown to a reasonable size.

Less disruptive with reduced damage to biodiversity. Little or no soil erosion.

Coppicing Cutting trees to ground level but leaving the stump to re-grow, with several stems developing from lateral buds. These grow very rapidly because roots are well established. Can be carried out in rotation.

Wood is important for charcoal, fencing poles and posts. Can be used for paper or burning in power stations. Can be repeated indefinitely and a range of trees are suitable.

The effects of humans on environment16 For example:

Ecosystem Specific interest Possible human damage

Masai Mara in Kenya Large mammal populations of the savanna

Tourism; increase in local human population; big game hunters illegally killing animals enticed out of the reserves


Ecosystem Specific interest Possible human damage

Terai region in Nepal Bengal tiger, one-horned rhino and Indian elephant

Reducing numbers to critical levels through illegal hunting for ivory or tusks or other body parts for Chinese medicine; poaching by game hunters; habitat reduction

Peat bogs Acidic soil caused by constant leaching out of bases increases abundance of moss (Sphagnum sp.), heather, deergrass, bog myrtle, so it is unique; provides a habitat for red deer and rare birds

Measures to ‘improve’ the soil using drainage or afforestation; use of conifers that are not native; reducing the natural habitat

Snowdonia National Park Scenic areas with mountain and local species

Invasion by alien plants; tourism including climbers

Antarctica Penguins and marine life Invasion by alien plants and animals; overfishing of krill

Galapagos islands Many endemic species Alien species and tourism

17 Invading the areas and showing strong and vigorous growth that out-competes the natural vegetation. In some areas river and stream banks have become overcrowded and choked. Habitat change occurs and river flow is obstructed – leading to changes in the freshwater species.

18 These are established and protected links that join up separated areas such as parks and game reserves. They allow many animals to move from one to the other in a protected way and take advantage of much larger spaces they need to search for food, mates and places to live and survive. It is important they are maintained for these reasons.

19 Krill populations are important as a food source for a large variety of marine life such as birds, seals, some whale species and many species of fish. Krill are at the primary consumer level (trophic level) of feeding relationships with an important link to other consumers. When numbers decline, other organisms have too little food and numbers of all marine life decline. Krill feed on phytoplankton. With low numbers of primary consumers, phytoplankton numbers will not be controlled so they will increase in numbers and upset the balance of gases—oxygen and carbon dioxide—in the seas, eventually causing large-scale death and decline. This will impact on the carbon levels in the atmosphere as phytoplankton in the seas are the largest carbon sink on earth.

20 Measures to ‘improve’ the soil led local authorities to drain soil and plant trees (e.g. non-native conifers) in an afforestation program funded by grants. This has reduced the natural habitat including natural vegetation such as moss (Sphagnum sp.) heather, deergrass, bog myrtle and cottongrass, which die as the soil is dried out. Animal species, such as red deer and rare birds (e.g. golden plovers, golden eagles, greenshanks and dunlins) are declining. It is a unique habitat.

Efforts to conserve the areas include reducing the use of non-native conifers and replanting with native species, reducing the soil drainage program and removal of the tax breaks that encouraged the process. Other actions include protecting the areas (e.g. the RSPB has taken steps to prevent further development). Blocking drains and removing


non-native trees helps to restore the areas. Protection also includes setting up nature reserves( e.g. at Forsinard Flows) and protecting areas by citing them as Sites of Special Scientific Interest (SSSIs).


21

a Bengal tiger, one-horned rhino and Indian elephant.

b Rhinos and elephants illegally hunted for horns and ivory, and tigers for body parts for Chinese jewellery/artefacts and medicine. Poaching by game hunters. All cause reduction in numbers to critical levels. Habitat reduction causes a reduction in other species as well.

c National parks, conservation units such as the Tiger Conservation Units and policing/patrolling of these areas and game reserves units provided by the government and the army.

Exam-style questions1 Level 3 (5–6 marks) Provides a comprehensive discussion of the conflict issues, with an

understanding of both sides of the argument. Well-developed line of reasoning that reads well, is clear and logical, and uses scientific terminology where appropriate. All information is relevant and in continuous prose.

Level 2 (3–4 marks) Describes some (a few) of the issues with some indication of both sides of the argument being at least considered. A line of reasoning that is presented with some structure and use of scientific terminology. Mostly relevant information.

Level 1 (1–2 marks) Describes some aspects of the issues. The information has only a little structure and lacks scientific terminology.

2

a A non-living environmental factor that affects the ecosystem and distribution of organisms.

b Biotic = any other stream-living organism, e.g. shrimps, sticklebacks, minnows. Abiotic = pH of water, flow rate of water, temperature of water, salinity etc.

c Oxygen concentration is much lower than at the other sites; allow paired and comparative data quotes that illustrate this point because high BOD of organic pollutants or bacterial action decomposing pollutants; high numbers of tube worms at site B and tube worms survive in/are indicator species of low oxygen concentration; absence of species such as mayflies or stoneflies at B and these can only survive in/are indicator species of unpolluted water.

d Presence of limiting factors; competition between individuals within the same species (intraspecific); the carrying capacity has been reached for that ecosystem.

e Runoff of the manure fertiliser into stream at B; leads to eutrophication/or an explanation of this; decomposers (aerobic bacteria) increase in number; as a result use the oxygen; reduction in certain freshwater/aquatic species.

f Protection of biodiversity by the conservation area; compromised by the farm activity; educational facilities of trust affected; any research may be affected; effect on fund raising; visual appearance may be affected; farmer interested in increasing milk yield; and financial impact of moves/directives for change or alternative wording; possibility of enforcement or protection legislation/a named reserve designation.


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