Paper 2s

Question 1

Describe the process of glycolysis.
[4 marks]

Answer 1

1. Phosphorylation of glucose using ATP;
2. Oxidation of triose phosphate to pyruvate;
3. Net gain of ATP;
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 marks]

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 marks]

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 marks]

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 marks]

Answer 5

1. No/less ATP produced;
2. No/less active transport
   OR
   Sodium/potassium pump inhibited;
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 marks]

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

The first generation of a population of fruit flies had 50 females.
Calculate how many female fruit flies would be produced from this population in the
fifth generation.
You can assume:
* each female produces 400 offspring each generation
* half the offspring produced each generation are female
* there is no immigration or emigration
* no flies die before reproducing.
Show your working.
Give your answer in standard form.
[3 marks]

Answer 7

1. Correct answer of 8 × 1010 = 3 marks;;;
2. Correct answer not in standard form = 2 marks
   OR
   1.6 × 1013 = 2 mark
   OR
   1.6 × 1011 = 2 mark
   OR
   6.4 × 1011 = 2 mark
   OR
   Shows 8 × 1010 in the working = 2 marks;;
3. 1.28 × 1012 = 1mark
   OR
   3.2 × 1011 = 1 mark
   OR
   8 × 1011 = 1 mark
   OR
   8 × 109 = 1 mark
   OR
   Shows 1.6 × 1011 in the working = 1 mark
   OR
   Shows 2004
   in the working = 1 mark;

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 marks]

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 marks]

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 and explain how the polymerase chain reaction (PCR) is used to amplify a
DNA fragment.
[4 marks]

Answer 10

1. (Requires DNA fragment) DNA polymerase,
   (DNA) nucleotides and primers;
2. Heat to 95 °C to break hydrogen bonds (and
   separate strands);
3. Reduce temperature so primers bind to
   DNA/strands;
4. Increase temperature, DNA polymerase joins
   nucleotides (and repeat method);

Question 11

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 marks]

Answer 11

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 12

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 marks]

Answer 12

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 13

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 marks]

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

Loss of nutrients into Lake Malawi has resulted in a decrease in some fish
populations (lines 12–13).
Explain why.
[4 marks]

Answer 14

1. (Growth/increase of) algae/surface
   plants/algal bloom blocks light;
2. Reduced/no photosynthesis so
   (submerged) plants die;
3. Saprobiotic (microorganisms) aerobically
   respire
   OR
   Saprobiotic (microorganisms) use oxygen in
   respiration;
4. Less oxygen for fish to respire;

Question 15

The mark-release-recapture method can be used to estimate the size of a fish
population (lines 13–14).
Explain how.
[4 marks]

Answer 15

1. Capture/collect sample, mark and release;
2. Ensure marking is not harmful (to fish)
   OR
   Ensure marking does not affect survival (of
   fish);
3. Allow (time for) fish 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;

Question 16

Suggest why the mark-release-recapture method can produce unreliable results in
very large lakes (lines 14–15).
[1 mark]

Answer 16

1. Less chance of recapturing fish
   OR
   Unlikely fish distribute randomly/evenly;

Question 17

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 marks]

Answer 17

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

Question 18

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 marks]

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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 marks]

Answer 20

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

Question 21

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 marks]

Answer 21

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

Question 22

Other than the thermometer, explain how two features of the calorimeter shown in
Figure 2 would enable a valid measurement of the total heat energy released. Parts are: water, sample holder, thermometer, stirer, air
[2 marks]

Answer 22

1. Stirrer distributes heat (energy);
2. Insulation/space/air reduces loss/gain of heat
   OR
   Insulation/space/air reduces
   conduction/convection;
3. Water has high (specific) heat capacity;

Question 23

In natural ecosystems, most of the light falling on producers is not used in
photosynthesis.
Suggest two reasons why.
[2 marks]

Answer 23

1. (Light is) reflected;
2. (Light is) wrong wavelength;
3. (Light) misses chlorophyll/
   chloroplasts/photosynthetic tissue;
4. CO2 concentration or temperature is a limiting
   factor

Question 24

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 marks]

Answer 24

1. ATP;
2. Reduced NADP;

Question 25

Chlorella cells can divide rapidly. A culture of 2000 Chlorella cells was set up in a fermenter. The cells divided every 90 minutes. You can assume that there were no limiting factors and that no cells died during the 24 hours. Calculate the number of cells in the culture after 24 hours. Give your answer in standard form. Show your working. [2 marks]

Answer 25

Correct answer of 1.31/1.3 × 108 (ignoring any subsequent numbers after 1.31) = 2 marks;;

Question 26

Creatinine is produced in muscle tissues. Creatinine diffuses into the blood. box The kidneys then excrete creatinine. A calibration curve can be used to determine the concentration of creatinine in urine. One method of producing a calibration curve needs: * creatinine solution of known concentration * distilled water * creatinine-detecting solution * a colorimeter. Creatinine-detecting solution reacts with creatinine to produce an orange colour. Use the information provided to describe how you could produce a calibration curve for creatinine. Do not include details on the use of glassware in your answer. [4 marks]

Answer 26

1. Use (distilled) water and creatinine solution to produce dilutions (series); 2. Addition of (creatinine-)detecting solution (to each solution); 3. Using a known/specified/constant volume of a solution (e.g. diluted creatinine solution); 4. Record absorbance/transmission of solution/s using a colorimeter; 5. Plot dilution/concentration of (creatinine) solution against absorbance/transmission;

Question 27

Describe how you would determine the concentration of creatinine in a urine sample using your calibration curve. [2 marks]

Answer 27

1. Use same volumes of solutions as used in producing (calibration curve) OR Add (creatinine-)detecting solution (to urine); 2. Read off (creatinine) concentration against absorbance/transmission (value) obtained;

Question 28

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 marks

Answer 28

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 29

Mutation is one cause of genetic variation in organisms. Give two other causes of genetic variation. [2 marks]

Answer 29

1. Crossing over; 2. Independent segregation/assortment (of homologous chromosomes); 3. Random fusion of gametes OR Random fertilisation;

Question 30

Name the relationship between the two alleles that code for flower colour. [1 mark]

Answer 30

Codominance;

Question 31

A population of this species of plant contained 9% of red-flowered plants. Use the Hardy–Weinberg equation to calculate the percentage of pink-flowered plants in this population. Show your working. [2 marks]

Answer 31

1. Correct answer of 42% = 2 marks;; 2. Incorrect answer but shows understanding that 2pq = pink/heterozygous/carriers = 1 mark OR Answer = 0.42 = 1 mark OR Answer = 16.38 / 16.4 = 1 mark;

Question 32

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 marks]

Answer 32

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

Question 33

Describe how enzymes could be used to insert the GH gene into a plasmid. [2 marks]

Answer 33

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 34

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 marks]

Answer 34

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

Question 35

Succession occurs in natural ecosystems. Describe and explain how succession occurs. [4 marks]

Answer 35

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 36

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 marks]

Answer 36

1. Change in (sequence of) amino acid(s)/primary structure; 2. Change in hydrogen/ionic/disulfide bonds; 3. Alters tertiary/30 structure;

Question 37

Haematopoietic stem cell transplantation (HSCT) is a long-term treatment for SCD. In HSCT, the patient receives stem cells from the bone marrow of a person who does not have SCD. The donor is often the patient’s brother or sister. Before the treatment starts, the patient’s faulty bone marrow cells have to be destroyed. Use this information to explain how HSCT is an effective long-term treatment for SCD. [3 marks]

Answer 37

1. Produce healthy (red blood) cells OR Produce (normal) polypeptide/haemoglobin; 2. No sickle/faulty/SCD (red blood) cells (produced) OR No defective polypeptide/haemoglobin; 3. Stem/marrow cells (continuously) divide/replicate OR Less chance of rejection (from brother/sister);

Question 38

Explain why the student removed the shoot tip from each seedling. [2 marks]

Answer 38

1. Tip produces IAA; 2. Affects concentration of IAA OR Affects (shoot) length/growth/elongation; 3. Mitosis/division occurs in shoot tips; 4. Affects (shoot) length/growth/elongation;

Question 39

Explain why the student added glucose solution to each Petri dish. [2 marks]

Answer 39

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

Question 40

Explain why the lids were kept on the Petri dishes. [2 marks]

Answer 40

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

Question 41

Another group of scientists suggested that a decrease in the force of muscle contraction is caused by an increase in the concentration of inorganic phosphate, Pi, in muscle tissues. Their hypothesis is that an increase in the concentration of Pi prevents the release of calcium ions within muscle tissues. Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of muscle contraction. [3 marks]

Answer 41

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 42

Describe the role of glucagon in gluconeogenesis. Do not include in your answer details on the second messenger model of glucagon action. [2 marks]

Answer 42

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

Question 43

Metformin is a dru box g commonly used to treat type II diabetes. Metformin’s ability to lower the blood glucose concentration involves a number of mechanisms including: * increasing a cell’s sensitivity to insulin * inhibiting adenylate cyclase. Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose concentration. [2 marks]

Answer 43

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

Question 44

Explain how inhibiting adenylate cyclase may help to lower the blood glucose concentration. [3 marks]

Answer 44

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

Question 45

A population of fruit flies contained 64% grey-bodied flies. Use the Hardy–Weinberg equation to calculate the percentage of flies heterozygous for gene G. [2 marks]

Answer 45

1. Correct answer of 48% = 2 marks;; 2. Incorrect answer but shows understanding that 2pq = heterozygous/carriers = 1 mark OR Incorrect answer but shows understanding that 1 – (p 2 + q 2 ) = heterozygous/carriers = 1 mark;

Question 46

Describe what happens during photoionisation in the light-dependent reaction. [2 marks]

Answer 46

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

Question 47

Explain why the student marked the origin using a pencil rather than using ink. [1 mark]

Answer 47

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 48

Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin. [2 marks]

Answer 48

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

Question 49

The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves. [1 mark]

Answer 49

(Absorb) different/more wavelengths (of light) for photosynthesis;

Question 50

What is a DNA probe? [2 marks]

Answer 50

1. (Short) single strand of DNA; 2. Bases complementary (with DNA/allele/gene);

Question 51

Describe how the DNA is broken down into smaller fragments. [2 marks]

Answer 51

1. Restriction endonuclease/enzyme; 2. (Cuts DNA at specific) base sequence OR (Breaks) phosphodiester bonds OR (Cuts DNA) at recognition/restriction site;

Question 52

The DNA on the nylon membrane is treated to form single strands. Explain why. [1 mark]

Answer 52

(So DNA) probe binds/attaches/anneals;

Question 53

Describe how you could estimate the size of a population of sundews in a small marsh. [5 marks]

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

Damage to the myelin sheath of neurones can cause muscular paralysis (lines 2–4). Explain how. [3 marks]

Answer 54

1. (Refers to) saltatory conduction OR (Nerve) impulses/depolarisation/ions pass to other neurones OR Depolarisation occurs along whole length (of axon); 2. (Nerve) impulses slowed/stopped; 3. (Refers to) neuromuscular junction OR (Refers to) sarcolemma;

Question 55

Suggest how epigenetics can affect Huntington's disease [ 2 marks]

Answer 55

1. (Increased) methylation of DNA/gene/allele; 2. Inhibits/prevents transcription; 3. Decreased methylation of DNA/gene/allele; 4. Stimulates/allows transcription; OR 5. Decreased acetylation of histone(s); 6. Inhibits transcription; OR 7. Increased acetylation of histone(s); 8. Stimulates/allows transcription

Question 56

Heat stress decreases the light-dependent reaction of photosynthesis. Explain why this leads to a decrease in the light-independent reaction. [2 marks]

Answer 56

1. (Less/no) ATP; 2. (Less/no) reduced NADP;

Question 57

Another effect of heat stress is a decrease in the activity of the enzyme rubisco. A decrease in the activity of an enzyme means that the rate of the reaction it catalyses becomes slower. A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis. Explain why. [2 marks]

Answer 57

1. (Less/no) carbon dioxide (reacts) with RuBP; 2. (Less/no) GP;

Question 58

Where precisely is rubisco found in a cell? [1 mark]

Answer 58

1. Stroma (of/in chloroplast);

Question 59

Describe how alterations to tumour suppressor genes can lead to the development of tumours. [3 marks]

Answer 59

1.(Increased) methylation (of tumour suppressor genes); 2.Mutation (in tumour suppressor genes); 3. Tumour suppressor genes are not transcribed/expressed OR Amino acid sequence/primary structure altered; 4. (Results in) rapid/uncontrollable cell division;

Question 60

A type of malignant tumour cell divides every 8 hours. box Starting with one of these cells, how many tumour cells will be present after 4 weeks? Assume none of these cells will die. Give your answer in standard form. [2 marks]

Answer 60

1. Correct answer of 1.9/1.93 x 1025 = 2 marks;; 2. Incorrect answer but shows 84 = 1 mark OR 28 x 3 = 1 mark OR Incorrect answer but shows 672 divided by 8 = 1 mark;

Question 61

Suggest one reason why it was important that the student left the apparatus for one hour after the yeast culture reached a constant temperature. [1 mark]

Answer 61

1. (So the) oxygen is used/absorbed/respired;

Question 62

During her investigation, the coloured liquid moved to the right. Explain why it moved to the right. [2 marks]

Answer 62

1. Anaerobic respiration produces carbon dioxide; 2. Increase in pressure/volume (of gas);

Question 63

The student found that the coloured liquid moved 1.5 cm in 24 hours. The diameter of the lumen (hole) of the capillary tubing was 1 mm. The volume of a capillary tubing is given by πr 2𝑙, where π is 3.14 and 𝑙 = length. Calculate the volume of gas produced in cm3 hour −1 . Show your working. [2 marks]

Answer 63

1. Correct answer in range of 4.9 x 10-4 to 4.91 × 104 = 2 marks;; 2. Incorrect answer buts shows division by 24 = 1 mark OR Incorrect answer but shows a number from 1175 to 1178 (ignore position of decimal point, standard form and any numbers that follow) = 1 mark; OR Incorrect answer but show the number 49 (ignore position of decimal point, standard form and any numbers after 49) = 1 mark;

Question 64

Explain why a log scale is used to record the number of cells. [1 mark]

Answer 64

Large range/difference/increase in numbers;

Question 65

Many yeast cells die during the death phase. Suggest one reason why. [1 mark]

Answer 65

1. Decrease/no glucose/substrate OR Increase in ethanol/carbon dioxide/acidity;

Question 66

The following equation can be used to make predictions of the growth in the box population of yeast cells under ideal laboratory conditions. Xt = X0 ert Xt = the population after a certain time X0 = the population at the start e = 2.72 (base of natural logarithm) r = growth rate t = time period in hours over which r applies A population of 2000 yeast cells was left for 10 hours. The value for the growth rate was 0.5 Assuming no yeast cells died, calculate the predicted size of the population after 10 hours. Show your working. [2 marks]

Answer 66

1. Correct answer of 298000 or 297766 or 297765.59 or 296826 = 2 marks;; 2. Incorrect answer but working shows 2000 × 2.72 = 1 mark; OR Incorrect answer but working shows 2.720.5 x10 / 2.725 / e 0.5 x10 / = 1 mark

Question 67

Describe how you would determine the mean percentage cover for beach grass on a sand dune. [3 marks]

Answer 67

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 68

All the volunteers were given the same food for 3 days. Suggest and explain one reason why they were given the same food. [2 marks]

Answer 68

1. Affects water potential (of blood/body); 2. Affects volume of urine (produced/removed);

Question 69

Furosemide is sometimes used to treat high blood pressure. Suggest how furosemide would cause a decrease in blood pressure. [1 mark]

Answer 69

Lower volume of blood

Question 70

Furosemide inhibits the absorption of sodium and chloride ions from the filtrate produced in the nephrons. Explain how furosemide causes an increase in the volume of urine produced. [3 marks]

Answer 70

1.Water potential of filtrate/tubule decreased; 2. Less water (reabsorbed) by osmosis (from filtrate/tubule); 3. Collecting duct (is where osmosis occurs);

Question 71

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios. Suggest two reasons why. [2 marks]

Answer 71

1. Small sample size; 2. Fusion/fertilisation of gametes is random; 3. Linked Genes; 4. Epistasis; 5. Lethal genotypes;

Question 72

Dopamine is a neurotransmitter released in some synapses in the brain. The transmission of dopamine is similar to that of acetylcholine. Dopamine stimulates the production of nerve impulses in postsynaptic neurones. Describe how. Do not include in your answer the events leading to the release of dopamine and the events following production of nerve impulses at postsynaptic neurones. [3 marks]

Answer 72

1. (Dopamine) diffuses across (synapse); 2. Attaches to receptors on postsynaptic membrane; 3. Stimulates entry of sodium ions and depolarisation/action potential;

Question 73

Dopamine has a role in numerous processes in the brain including pain relief. The release of dopamine can be stimulated by chemicals called endorphins produced in the brain. Endorphins attach to opioid receptors on presynaptic neurones that release dopamine. Morphine is a drug that has a similar structure to endorphins and can provide pain relief. Explain how. [2 marks]

Answer 73

1. Morphine attaches to opioid receptors; 2. (More) dopamine released (to provide pain relief);

Question 74

GABA is a neurotransmitter released in some inhibitory synapses in the brain. GABA box causes negatively charged chloride ions to enter postsynaptic neurones. Explain how this inhibits postsynaptic neurones. [3 marks]

Answer 74

1. (Inside of postsynaptic) neurone becomes more negative/hyperpolarisation/inhibitory postsynaptic potential; 2. More sodium ions required (to reach threshold) OR Not enough sodium ions enter (to reach threshold); 3. For depolarisation/action potential;

Question 75

What is meant by a genome? box [1 mark]

Answer 75

1. (All) the DNA in a cell/organism;

Question 76

Explain why the antibody binds to the transcription factor. box [2 marks]

Answer 76

1. (Transcriptional factor/antibody) has a specific/tertiary structure/shape; 2. Complementary (shape/structure);

Question 77

Use Figure 8 to explain what ‘precipitated DNA’ consists of. [1 mark]

Answer 77

1. DNA, transcription factor and antibod

Question 78

Soybeans are used in a number of processed foods. However, soybeans contain a protein known as P34 that causes an allergic response in some people. Scientists have created transgenic soybeans that produce single-stranded cDNA, which prevents transcription of the P34 gene. They used recombinant plasmids as vectors to transform soybean cells. After they had screened these cells for production of the P34 protein, they cultured the transformed cells to form soybean plants. Suggest how single-stranded cDNA could prevent transcription of the P34 gene. [1 mark]

Answer 78

1. Binds to P34 gene/DNA/mRNA OR Binds to transcription factor gene/DNA OR Binds to promoter;

Question 79

Describe the roles of two named types of enzymes used to insert DNA fragments into box plasmids. [2 marks

Answer 79

1. Restriction (endonuclease/enzyme) to cut plasmid/vector; 2. Ligase joins gene/DNA to plasmid/vector;

Question 80

Suggest two features of the structure of different proteins that enable them to be separated by gel electrophoresis. [2 marks]

Answer 80

1. Mass/number of amino acids/polypeptides; 2. Charge; 3. R groups (differ);

Question 81

People with red-green colour blindness are unable to distinguish between red and green, and also between other colours (lines 8–10). Explain why. [3 marks]

Answer 81

1. Green sensitive pigment/cones non-functional OR Cones that detect green light non-functional; 2. Three different types of pigment/cone;

Question 82

Current research into the treatment of red-green colour blindness involves the use of induced pluripotent stem cells (iPS cells) (lines 17–19). Suggest how iPS cells could correct red-green colour blindness. [2 marks]

Answer 82

1. (iPS cells) divide; 2.(iPS cells) develop/differentiate into (green sensitive) cones;

Question 83

The use of iPS cells could have advantages over the use of gene therapy to correct box red-green colour blindness (lines 19–20). Using the information from the passage, suggest and explain reasons why. [3 marks]

Answer 83

1 (Use of iPS cells) long-term; 2. (Use of iPS cells) less chance of rejection/immune response; 3. (Use of iPS cells) single treatment; 4. Harm/side effects from using viruses (in gene therapy);