2

Question 1

Describe the process of glycolysis (4)

Answer 1

1. Phosphorylation of glucose using ATP;
2. Oxidation of triose phosphate to pyruvate;
3. Net gain of ATP (4 produced, 2 used);
4. NAD reduced;

Question 2

Malonate inhibits a reaction in the Krebs cycle.

Explain why malonate would decrease the uptake of oxygen in a respiring cell (2)

Answer 2

1. Less/no reduced NAD/coenzymes
   OR
   Fewer/no hydrogens/electrons removed (and
   passed to electron transfer chain);
2. Oxygen is the final/terminal (electron) acceptor;

Question 3

Explain how a resting potential is maintained across the axon membrane in a neurone (3)

Answer 3

1. Higher concentration of potassium ions inside
   and higher concentration of sodium ions outside
   (the neurone)
   OR
   potassium ions diffuse out
   OR
   sodium ions diffuse in;
2. (Membrane) more permeable to potassium ions
   (leaving than sodium ions entering)
   OR
   (Membrane) less permeable to sodium ions
   (entering than potassium ions leaving);
3. Sodium ions (actively) transported out and
   potassium ions in;

Question 4

Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon (3)

Answer 4

1. Myelination provides (electrical) insulation;
2. (In myelinated) saltatory (conduction)
   OR
   (In myelinated) depolarisation at nodes (of
   Ranvier);
3. In non-myelinated depolarisation occurs along
   whole/length (of axon);

Question 5

A scientist investigated the effect of inhibitors on neurones. She added a respiratory inhibitor to a neurone. The resting potential of the neurone changed from –70 mV to 0 mV.

Explain why (3)

Answer 5

1. No/less ATP produced;
2. No/less active transport
   OR
   Sodium/potassium pump inhibited;
   02.3
3. Electrochemical gradient not maintained
   OR
   (Facilitated) diffusion of ions causes change to
   0 mV
   OR
   (Results in) same concentration of (sodium and
   potassium) ions (either side of membrane)
   OR
   No net movement of (sodium and potassium)
   ions;

Question 6

In fruit flies, males have the sex chromosomes XY and the females have XX.

In fruit flies, a gene for eye colour is carried on the X chromosome. The allele for red eyes, R, is dominant to the allele for white eyes, r.
Male fruit flies are more likely than female fruit flies to have white eyes.

Explain why (2)

Answer 6

1. Males have one allele;
2. Females need two recessive alleles
   OR
   Females must be homozygous recessive
   OR
   Females could have dominant and recessive
   alleles
   OR
   Females could be heterozygous/carriers;

Question 7

In fruit flies, the genes for body colour and for wing development are not on the sex chromosomes. The allele for grey body colour, G, is dominant to the allele for black
body colour, g. The allele for long wings, L, is dominant to the allele for short wings, l.

A geneticist carried out a cross between fruit flies with grey bodies and long wings
(heterozygous for both genes) and fruit flies with black bodies and short wings.

Table 2 shows the results of this cross.

Table 2

Phenotype of offspring Number of offspring
Grey body and long wings 223
Black body and short wings 218

Explain the results in Table 2 (3)

Answer 7

1. The (two) genes are linked
   OR
   Autosomal linkage;
2. Accept that the
   genes are on the
   same chromosome.
3. No crossing over (occurs)
   OR
   (Linked) genes are close together;
4. No Gl and no gL (gametes produced)
   OR
   No Ggll and no ggLl (offspring produced)
   OR
   Only GL and gl (gametes produced);

Question 8

Neonatal diabetes is a disease that affects newly born children. The disease is caused by a change in the amino acid sequence of insulin. This change prevents insulin binding to its receptor.
Explain why this change prevents insulin binding to its receptor (2)

Answer 8

1. Changes tertiary structure;
2. No longer complementary (to receptor);

Question 9

Using your knowledge of the kidney, explain why glucose is found in the urine of a person with untreated diabetes (3)

Answer 9

1. High concentration of glucose in blood/filtrate;
2. Not all the glucose is (re)absorbed at the
   proximal convoluted tubule;
3. Carrier/co-transport proteins are working at
   maximum rate
   OR
   Carrier/co-transport proteins/ are saturated;

Question 10

Describe a method that could be used to determine the mean percentage cover of algae on a coral reef.

Do not include information on the difficulties of using your method underwater (3)

Answer 10

1. Method of randomly determining position
   (of quadrats) e.g. random numbers
   table/generator;
2. Large number/sample of quadrats;
3. Divide total percentage by number of
   quadrats/samples/readings;

Question 11

Explain how succession results in a wide variety of fish living on coral reefs.
Do not describe the process of succession in your answer (2)

Answer 11

1. Increase in variety/diversity of
   species/plants/animals;
   OR
   Increase in number of species/populations;
2. Provides more/different habitats/niches
   OR
   Provides greater variety/types of food;

Question 12

Ecologists investigated the effect of two fish species, the redband parrotfish and the ocean surgeonfish, on algal growth on an artificial reef. They made this artificial reef by submerging many large concrete blocks at a depth of 16–18 metres off the coast of Florida. They attached four large wire cages, A, B, C and D, to each block and populated the cages as shown.

A – No fish
B – Two redband parrotfish
C – Two ocean surgeonfish
D – One redband parrotfish and one ocean surgeonfish.

After 34 weeks, the ecologists measured the mean percentage cover of all algae within each set of wire cages. The ecologists used a statistical test to find out whether the mean for each set of cages was significantly lower than the mean for set A.

Table 3 shows the probability (P) values that the ecologists obtained using this statistical test.

Table 3
Set of cages P value
B =0.841
C <0.001
D =0.634
Using all the information, evaluate the effect of the two fish species on algal growth on coral reefs (5)

Answer 12

1. Significant (difference/decrease) with C
   (compared with A);
2. No significant (difference/decrease) with B
   and D (compared with A);
3. Reference to less than 5%/0.05
   probability that difference is (less likely) due
   to chance
   OR
   Reference to more than 95%/0.95
   probability that difference is not due to
   chance;
4. Species of algae not known
   OR
   Species of algae may differ (on other reefs);
5. Only done off (coast of) Florida
   OR
   Not done on other reefs;
6. Only done at 16 to 18 metres
   OR
   Not done (on reefs) at other depths;
7. Only 34 weeks;
8. Concrete/artificial reef could affect
   results/growth
   OR
   Natural reef results/growth may differ;
9. Cage may allow other fish/animals to enter;

Question 13

Lake Malawi in East Africa has more species of fish than any other lake in the world. Many of these species have evolved from a common ancestor. Lake Malawi is one of the largest lakes in the world and was formed several million years ago. Since then, the water level has fluctuated greatly. As a result, what is now a large lake was at one time many smaller, separate lakes. The country of Malawi has a total area of 118 000 km2. The actual land area is only 94 080 km2, because approximately one-fifth of the country is Lake Malawi. In December 1990, forests covered 41.4% of the actual land area of Malawi. In December 2016, forests covered 26.4% of the actual land area of Malawi.

Deforestation and farming along the shores of Lake Malawi have caused
increased soil erosion and loss of nutrients into the lake. This has resulted in a decrease in some fish populations. The mark-release-recapture method can be used to estimate the size of a fish population. However, this method can produce unreliable results in very large lakes.

Use the information in the passage and your own knowledge to answer the following questions.
Lake Malawi in East Africa has more species of fish than any other lake in the world
(line 1).

Suggest and explain how this speciation may have occurred (4)

Answer 13

1. Variation/differences due to mutation/s;
2. (Reference to) allopatric (speciation);
3. Smaller/different lakes have different
   environmental conditions
   OR
   Smaller/different lakes have different
   selection pressures;
4. Reproductive separation/isolation
   OR
   No gene flow
   OR
   Gene pools remain separate;
5. Different alleles passed on/selected
   OR
   Change in frequency of allele/s;
6. Eventually different species/populations
   cannot breed to produce fertile offspring;

Question 14

Suggest and explain how the interaction between the muscles labelled in Figure 1 could cause the pupil to constrict (narrow) (2)

Answer 14

1. Circular muscle contracts;
2. Radial muscle relaxes;

Question 15

The retina of an owl has a high density of rod cells.

Explain how this enables an owl to hunt its prey at night.

Do not refer to rhodopsin in your answer (3)

Answer 15

1. High (visual) sensitivity;
2. Several rods connected to a single neurone;
3. Enough (neuro)transmitter to reach/overcome
   threshold
   OR
   Spatial summation to reach/overcome threshold;

Question 16

Steroid hormones are hydrophobic.
Explain why steroid hormones can rapidly enter a cell by passing through its cell-surface membrane (2)

Answer 16

1. Lipid soluble;
2. (Diffuse through) phospholipid (bilayer);

Question 17

In the cytoplasm, testosterone binds to a specific androgen receptor (AR). An AR is a protein.

Suggest and explain why testosterone binds to a specific AR (2)

Answer 17

1. Has a (specific) tertiary structure/shape;
2. (Structures are) complementary;

Question 18

The binding of testosterone to an AR changes the shape of the AR. This AR molecule now enters the nucleus and stimulates gene expression.

Suggest how the AR could stimulate gene expression (2)

Answer 18

1. (AR is) a transcription factor;
2. Binds to DNA/promoter;
3. (Stimulates) RNA polymerase;

Question 19

The light absorbed by chlorophyll is used in the light-dependent reaction.

Name the two products of the light-dependent reaction that are required for the light-independent reaction (2)

Answer 19

1. ATP;
2. Reduced NADP;

Question 20

Describe the sequence of events involved in transmission across a cholinergic synapse.

Do not include details on the breakdown of acetylcholine in your answer (5)

Answer 20

1. Depolarisation of presynaptic membrane;
2. Calcium channels open and calcium ions enter (synaptic knob);
3. (Calcium ions cause) synaptic vesicles move to/fuse with presynaptic membrane and release acetylcholine / neurotransmitter;
4. Acetylcholine/neurotransmitter diffuses across (synaptic cleft);
5. (Acetylcholine attaches) to receptors on the postsynaptic membrane;
6. Sodium ions enter (postsynaptic neurone) leading to depolarisation;

Question 21

The scientist determined the dry mass of the spinach plants. First, he heated each sample at 80 °C for 2 hours.

Suggest what the scientist should do to ensure that he has removed all the water from the sample (2)

Answer 21

1. Weigh and heat;
2. (Until) mass is constant;

Question 22

Alport syndrome (AS) is an inherited disorder that affects kidney glomeruli of both men and women. Affected individuals have proteinuria (high quantities of protein in their urine).

Suggest how AS could cause proteinuria (2)

Answer 22

1. Affects/damages basement membrane
   OR
   More protein channels/carriers in basement membrane;
2. Proteins can pass into the (glomerular)
   filtrate/tubule;

Question 23

The scientists carried out further work to investigate how the transplanted stem cells
developed after transplantation.
* The scientists transplanted stem cells from wild type male mice into
AS female mice.
* After 20 weeks, they found that the quantity of protein in the urine of these female mice had significantly decreased.
* They examined cells from glomeruli in the female mice. Some of these cells
contained a Y chromosome.
Suggest how the transplanted stem cells reduce proteinuria (2)

Answer 23

1. (Transplanted stem cells) differentiate/specialise;
2. Reduce loss of protein at the glomerulus
   OR
   Prevents protein moving into filtrate;

Question 24

A scientist produced transgenic zebrafish. She obtained a gene from silverside fish. The gene codes for a growth hormone (GH). She inserted copies of this GH gene into plasmids. She then microinjected these recombinant plasmids into fertilised egg cells of zebrafish.

Describe how enzymes could be used to insert the GH gene into a plasmid (2)

Answer 24

1. Restriction endonucleases/enzymes cuts
   plasmid;
   OR
   Restriction endonucleases/enzymes produces
   ‘sticky ends’;
2. Ligase joins gene/DNA and plasmid
   OR
   Ligase joins ‘sticky ends’;

Question 25

Microinjection of DNA into fertilised egg cells is a frequent method of producing transgenic fish. However, the insertion of the transferred gene into nuclear DNA may be delayed. Consequently, the offspring of transgenic fish may not possess the desired characteristic. Suggest and explain how delayed insertion of the GH gene could produce offspring of transgenic fish without the desired characteristic. (2)

Answer 25

1. Cell division has occurred (before gene added); 2. (Cells producing) gametes do not receive the gene;

Question 26

North American black bears can hibernate for up to 7 months without food or water. The bears survive using the fat stores in their bodies. The bears build up the fat stores during the summer. During hibernation, the heart rate of black bears decreases from a summer mean of 55 beats per minute to 14 beats per minute. Their metabolic rate falls by 75%. In many mammals, ‘uncoupling proteins’ help to maintain a constant body temperature during hibernation. Uncoupling proteins are found in the inner mitochondrial membrane and act as proton channels during chemiosmosis. However, these proton channels do not generate ATP. In the mountains of North America, when winter changes into spring, the coat colour of snowshoe hares changes from white to brown. Climatic changes have caused the snow to melt earlier. This has reduced the survival rate of snowshoe hares in these habitats. The change in coat colour occurs when new fur replaces old fur. This is called moulting. Recent research has shown that snowshoe hares within a population moult at different times. Moulting at different times could be a major factor in ensuring the survival of snowshoe hare populations. Use the information in the passage and your own knowledge to answer the following questions. Black bears can hibernate for up to 7 months without food or water (lines 1−2). Suggest and explain how (3)

Answer 26

1. Fat (store) used in respiration /metabolism; 2. Less energy/food (store) is required due to low respiration/metabolism OR Less energy/food (store) is required due less movement; 3. Gluconeogenesis; 4. Low SA:V reduces heat loss OR Fat (layer/insulation) reduces heat loss; 5. Long loop of Henle so less water lost; 6. Water provided from respiration; 7. Reduced/no urination; 8. Less evaporation;

Question 27

During hibernation, the heart rate and the metabolic rate of black bears decrease (lines 3−5). Use your knowledge of the nervous control of heart rate to describe how these are linked (4)

Answer 27

1. (Lower metabolism so) less/low CO2 (in blood); 2. (Detected by) chemoreceptors; 3. (Chemoreceptors) located in aorta/medulla OR (Chemoreceptors) located in carotid artery; 4. Fewer impulses to cardiac centre; OR Fewer impulses to medulla (oblongata); 5. (More) impulses along parasympathetic/vagus pathway/neurones/nerve OR Fewer impulses along sympathetic pathway/neurones/nerve; 6. (To) SAN;

Question 28

In many mammals, ‘uncoupling proteins’ help to maintain a constant body temperature during hibernation (lines 6−7). Suggest and explain how (2)

Answer 28

1. Allow passage of protons/H+; 2. (Energy) released as heat;

Question 29

During photosynthesis, plants produce (1) compounds which contain carbon, such as carbohydrates, lipids and proteins. Most of the sugars synthesised by plants are used by the plant in (2). The rest are used to make other groups of biological molecules. These biological molecules form the biomass of the plants. Biomass can be measured in terms of mass of (3) per given area per given time. The chemical energy store in dry biomass can be estimated using (4) . Write the correct biological term beside each number below, that matches the space in the passage (2)

Answer 29

1. Organic 2. Respiration 3. Carbon 4. Calorimetry

Question 30

Describe the light-independent reaction of photosynthesis (6)

Answer 30

1. Carbon dioxide combines/reacts with ribulose bisphosphate/RuBP 2. Produces two glycerate (3- carbon) phosphate/GP using (enzyme) Rubisco; 3. GP reduced to triose phosphate; 4. Using reduced NADP; 5. Using energy from ATP; 6. Triose phosphate converted to glucose / hexose / RuBP / ribulose bisphosphate/named organic substance

Question 31

Farming cattle for humans to eat is less efficient than farming crops because of energy transfer. Explain why (2)

Answer 31

1. Energy lost between/at trophic/feeding levels; 2. Energy lost via respiration /excretion/faeces;

Question 32

Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. The reaction requires 16 molecules of ATP for each molecule of nitrogen that is reduced. When ammonia inhibits nitrogenase activity, nitrogen-fixing bacteria may benefit. Explain how (2)

Answer 32

1. Less/no ATP/energy required/used OR More ATP/energy available; 2. ATP/energy can be used for growth/synthesis/replication OR Lower (rate of) respiration required OR ATP for phosphorylation;

Question 33

The scientists concluded that the observed frequencies of the four phenotypes differed significantly from the expected frequencies. Use your knowledge of the Hardy–Weinberg principle to suggest two reasons why (2)

Answer 33

1. Selection (against/for a blood group/phenotype/allele); 2. (High rate of) mutation; 3. Immigration/emigration; 4. No random mating.

Question 34

Give two reasons why transmission across a cholinergic synapse is unidirectional (2)

Answer 34

1. (Only) the presynaptic neurone/knob/membrane releases/has neurotransmitter/acetylcholine; 2. (Only) the postsynaptic neurone/membrane has receptors OR No receptors in the presynaptic neurone/membrane;

Question 35

Myasthenia gravis (MG) is an autoimmune disease caused when antibodies bind to the sarcolemma (postsynaptic membrane) of neuromuscular junctions. This can weaken the contraction of muscles. Mestinon is a drug that inhibits the enzyme acetylcholinesterase. Mestinon can help in the treatment of MG. Suggest and explain how MG can weaken contraction of muscles. Do not include details of myofibril or muscle contraction in your answer (2)

Answer 35

1. Less/no acetylcholine/neurotransmitter binds to receptor/s; 2. Less/no depolarisation OR Fewer/no action potential(s) OR Fewer/no sodium ions enter to reach threshold;

Question 36

Mestinon can help in the treatment of MG. Explain how (3) (Inhibition of acetylcholinesterase)

Answer 36

1. Less/no acetylcholine/neurotransmitter broken down; 2. (More) acetylcholine attaches to receptors; 3. Depolarisation (of sarcolemma) occurs OR Action potential(s) produced OR (Enough) sodium ions enter to reach threshold OR Fewer/no antibodies attach;

Question 37

Name the part of the body which releases antidiuretic hormone (ADH) into the blood (1)

Answer 37

Posterior pituitary

Question 38

Alcohol decreases the release of ADH into the blood. Suggest two signs or symptoms which may result from a decrease in ADH (2)

Answer 38

1. Dehydration/thirst; 2. Frequent urination OR Increase in volume of urine; 3. Less concentrated urine OR Dilute urine OR Urine paler/lighter in colour;

Question 39

Describe the effect of ADH on the collecting ducts in kidneys (3)

Answer 39

1. (Stimulates) addition of channel proteins into membrane; 2. Increases permeability to water OR (More) water (re)absorbed; 3. By osmosis;

Question 40

Succession occurs in natural ecosystems. Describe and explain how succession occurs (4)

Answer 40

1. (Colonisation by) pioneer species; 2. Pioneers/species/organisms change the environment/habitat/conditions/factors; 3. (Environment becomes) less hostile for other/new species OR (Environment becomes) more suitable for other/new species OR (Environment becomes) less suitable for previous species; 4. Change/increase in diversity/biodiversity; 5. (To) climax community;

Question 41

Light Dependent Reaction

Question 42

Explain how a single base substitution causes a change in the structure of this polypeptide. Do not include details of transcription and translation in your answer (3)

Answer 42

1. Change in (sequence of) amino acid(s)/primary structure; 2. Change in hydrogen/ionic/disulfide bonds; 3. Alters tertiary structure;

Question 43

Explain why the student added glucose solution to each Petri dish of plant shoot (2)

Answer 43

1. For respiration; 2. Provide ATP/energy (for growth);

Question 44

Explain why lids were kept on the Petri dishes containing IAA solution (2)

Answer 44

1. To prevent/reduce evaporation; 2. (Which) alters concentration of (IAA) solution OR (Which) alters water potential;

Question 45

Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of muscle contraction (3)

Answer 45

1. (Less/No) tropomyosin moved from binding site OR Shape of tropomyosin not changed so binding site not exposed/available; 2. (Fewer/No) actinomyosin bridges formed; 3. Myosin head does not move OR Myosin does not pull actin (filaments) OR (Less/No) ATP (hydrol)ase (activation);

Question 46

In muscles, pyruvate is converted to lactate during prolonged exercise. Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration.

Answer 46

1. Regenerates/produces NAD OR oxidises reduced NAD; 2. (So) glycolysis continues;

Question 47

Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose concentration (2)

Answer 47

1. (More) insulin binds to receptors; 2. (Stimulates) uptake of glucose by channel/transport proteins OR Activates enzymes which convert glucose to glycogen;

Question 48

Explain how inhibiting adenylate cyclase may help to lower the blood glucose concentration (3)

Answer 48

1. Less/no ATP is converted to cyclic AMP/cAMP; 2. Less/no protein kinase A is activated; 3. Less/no glycogen is converted to glucose OR Less/no glycogenolysis;

Question 49

What chemicals are needed for the LDR

Answer 49

NADP, ADP, Pi, H2O

Question 50

Describe what happens during photoionisation in the light-dependent reaction (2)

Answer 50

1. Chlorophyll absorbs light OR Light excites/moves electrons in chlorophyll; 2. Electron/s are lost OR (Chlorophyll) becomes positively charged;

Question 51

Explain why the student marked the origin using a pencil rather than using ink (1)

Answer 51

Ink and (leaf) pigments would mix OR (With ink) origin/line in different position OR (With pencil) origin/line in same position OR (With pencil) origin/line still visible;

Question 52

Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin (2)

Answer 52

1. Level of solvent below origin/line; 2. Remove/stop before (solvent) reaches top/end;

Question 53

Describe how you could estimate the size of a population of sundews in a small marsh (5)

Answer 53

1. Use a grid OR Divide area into squares/sections; 2. Method of obtaining random coordinates/numbers e.g. calculator/computer/random numbers table/generator; 3. Count number/frequency in a quadrat/section; 4. Large sample and calculate mean/average number (per quadrat/section); 5. Valid method of calculating total number of sundews, e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in marsh;

Question 54

Suggest and explain how digesting insects helps the sundew to grow in soil with very low concentrations of some nutrients (2)

Answer 54

1. Digestion/breakdown of proteins; 2. Provides amino acids OR (Sundew can) produce a named (organic) nitrogen-containing compound e.g. proteins, amino acids, DNA, ATP; 3. Digestion/breakdown of named (organic) phosphate-containing compound e.g. DNA, RNA; 4. Provides named (organic) phosphate-containing product e.g. nucleotides (1+2 OR 3+4)

Question 55

Exercise causes an increase in heart rate. Describe the role of receptors and of the nervous system in this process (4)

Answer 55

1. Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid/fall in pH OR Baro/pressure receptors detect rise in blood pressure; 2. Send impulses to cardiac centre/medulla; 3. More impulses to SAN; 4. By sympathetic (nervous system for chemoreceptors/CO2) OR By parasympathetic (nervous system for baro / pressure receptors/blood pressure);

Question 56

Sympatric speciation

Answer 56

Same geographical area

Question 57

Allopatric speciation

Answer 57

Different geographical area

Question 58

Explain how chemicals which inhibit the decolourisation of DCPIP could slow the growth of weeds (2)

Answer 58

1. Less/no ATP produced; 2. Less/no reduced NADP produced; 3. Less/no GP reduced/converted to TP;

Question 59

Suggest one way in which an increase in the uptake of phosphate could increase plant growth (1)

Answer 59

Used to produce named phosphate compound in cells; (ATP/DNA/ADP/RNA/RuBP)

Question 60

Suggest one way in which AMF may benefit from their association with plants (1)

Answer 60

Example of a carbon-containing biological compound e.g. carbohydrate/ amino acid/vitamin;

Question 61

Explain why an increase in shoot biomass can be taken as a measurement of net primary productivity (2)

Answer 61

1. Represents dry mass / mass of carbon; 2. Represents gross production minus respiratory losses; 2. NPP = GPP - R (respiratory losses)

Question 62

Phenotype

Answer 62

Expressed characteristics due to genotype and environment

Question 63

Gene pool

Answer 63

All the alleles in a population

Question 64

Lord Howe Island in the Tasman Sea possesses two species of palm tree which have arisen via sympatric speciation. The two species diverged from each other after the island was formed 6.5 million years ago. The flowering times of the two species are different. Using this information, suggest how these two species of palm tree arose by sympatric speciation (5)

Answer 64

1. Occurs in the same habitat / environment / population; 2. Mutation/s cause different flowering times; 3. Reproductive separation/isolation OR No gene flow OR Gene pools remain separate; 4. Different allele/s passed on/selected OR Change in frequency of allele/s; 5. Disruptive (natural) selection; 6. Eventually different species cannot (inter)breed to produce fertile offspring;

Question 65

Describe the roles of calcium ions and ATP in the contraction of a myofibril (5)

Answer 65

1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum; 2. (Calcium ions) cause movement of tropomyosin (on actin); 3. (This movement causes) exposure of the binding sites on the actin; 4. Myosin heads attach to binding sites on actin; 5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend; 6. (Bending) pulling actin molecules; 7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites)

Question 66

The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image of its prey onto the fovea. Explain how the fovea enables an eagle to see its prey in detail. Do not refer to colour vision in your answer (3)

Answer 66

1. High (visual) acuity; 2. (Each) cone is connected to a single neurone; 3. (Cones send) separate (sets of) impulses to brain;

Question 67

Explain how applying pressure to the Pacinian corpuscle produces the changes in membrane potential (3)

Answer 67

1. (Pressure causes) membrane / lamellae to become deformed / stretched; 2. Sodium ion channels in membrane open and sodium ions move in; 3. Greater pressure more channels open / sodium ions enter.

Question 68

When the heart beats, both ventricles contract at the same time. Explain how this is coordinated in the heart after initiation of the heartbeat by the SAN (2)

Answer 68

1. Electrical activity only through Bundle of His / AVN; 2. Wave of electrical activity passes over / through both ventricles at the same time;

Question 69

where is rubisco found

Answer 69

stroma

Question 70

Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain. Explain how this reduces the rate of photosynthesis in weeds (4)

Answer 70

1. Reduced transfer of protons across thylakoid membrane OR Reduced chemiosomotic gradient / proton gradient across thylakoid membrane; 2. (So) less ATP produced; 3. (So) less reduced NADP produced; Reject reduced NAD 4. (So) light-independent reaction slows / stops; OR Less reduction of GP to triose phosphate.

Question 71

Describe the advantage of the Bohr effect during intense exercise (2)

Answer 71

1. Increases dissociation of oxygen; Accept unloading/ release/reduced affinity for dissociation 2. For aerobic respiration at the tissues/muscles/cells OR Anaerobic respiration delayed at the tissues/muscles/cells OR Less lactate at the tissues/muscles/cells;

Question 72

EPO is another performance-enhancing drug. It can increase the haematocrit (the percentage of red blood cells in blood). A heart attack is caused by a lack of glucose and oxygen being delivered to cardiac muscle via the coronary arteries. The overuse of EPO can increase the risk of a heart attack. Suggest how (2)

Answer 72

1. (EPO) causes blood to thicken; Accept descriptions of thickening, eg more viscous 2. (The thickened blood) could block the coronary arteries OR (The thickened blood) slows blood flow OR (The thicker blood) could cause clots;

Question 73

Describe the role of saprobionts in the nitrogen cycle (2)

Answer 73

1. (They use enzymes to) decompose proteins / DNA / RNA / urea; 2. Producing/releasing ammonia/ammonium compounds / ammonium ions

Question 74

Hardy-Weinberg

Answer 74

p + q = 1 (allele frequency) p² + 2pq + q² (genotypic frequency) work out q first

Question 75

Mark Release Recapture

Answer 75

1. Capture/collect sample, mark and release; 2. Ensure marking is not harmful OR Ensure marking does not affect survival; Accept examples e.g., marking should not be toxic. 3. Allow (time for) sample to (randomly) distribute before collecting a second sample; 4. (Population =) number in first sample × number in second sample divided by number of marked fish in second sample / number recaptured;