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1
Q

Describe the process of glycolysis.
[4 marks]

A
  1. Phosphorylation of glucose using ATP;
  2. Oxidation of triose phosphate to pyruvate;
  3. Net gain of ATP;
  4. NAD reduced;
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2
Q

Malonate inhibits a reaction in the Krebs cycle.
Explain why malonate would decrease the uptake of oxygen in a respiring cell.
[2 marks]

A
  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;
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3
Q

Explain how a resting potential is maintained across the axon membrane in a
neurone.
[3 marks]

A
  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;
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4
Q

Explain why the speed of transmission of impulses is faster along a myelinated axon
than along a non-myelinated axon.
[3 marks]

A
  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);
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5
Q

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]

A
  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;
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6
Q

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]

A
  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;
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7
Q

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]

A
  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;
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8
Q

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]

A
  1. Changes tertiary structure;
  2. No longer complementary (to receptor);
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9
Q

Using your knowledge of the kidney, explain why glucose is found in the urine of a
person with untreated diabetes.
[3 marks]

A
  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;
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10
Q

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

A
  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);
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11
Q

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]

A
  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;
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12
Q

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]

A
  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
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13
Q

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]

A
  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;
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14
Q

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

A
  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;
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15
Q

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

A
  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;
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16
Q

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

A
  1. Less chance of recapturing fish
    OR
    Unlikely fish distribute randomly/evenly;
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17
Q

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]

A
  1. High (visual) acuity;
  2. (Each) cone is connected to a single neurone;
  3. (Cones send) separate (sets of) impulses to
    brain;
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18
Q

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]

A
  1. High (visual) sensitivity;
  2. Several rods connected to a single neurone;
  3. Enough (neuro)transmitter to reach/overcome
    threshold
    OR
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19
Q

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

A
  1. Lipid soluble;
  2. (Diffuse through) phospholipid (bilayer);
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20
Q

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]

A
  1. Has a (specific) tertiary structure/shape;
  2. (Structures are) complementary;
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21
Q

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]

A
  1. (AR is) a transcription factor;
  2. Binds to DNA/promoter;
  3. (Stimulates) RNA polymerase;
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22
Q

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]

A
  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;
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23
Q

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

A
  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
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24
Q

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]

A
  1. ATP;
  2. Reduced NADP;
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25
Q

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]

A

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

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26
Q

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]

A
  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;
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27
Q

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

A
  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;
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28
Q

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

A
  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);
  3. (Acetylcholine attaches) to receptors on the
    postsynaptic membrane;
  4. Sodium ions enter (postsynaptic neurone)
    leading to depolarisation;
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29
Q

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

A
  1. Crossing over;
  2. Independent segregation/assortment (of
    homologous chromosomes);
  3. Random fusion of gametes
    OR
    Random fertilisation;
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30
Q

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

A

Codominance;

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31
Q

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]

A
  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;
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32
Q

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]

A
  1. Affects/damages basement membrane
    OR
    More protein channels/carriers in basement
    membrane;
  2. Proteins can pass into the (glomerular)
    filtrate/tubule;
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33
Q

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

A
  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’;
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34
Q

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]

A
  1. Cell division has occurred (before gene added);
  2. (Cells producing) gametes do not receive the
    gene;
35
Q

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

A
  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;
36
Q

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]

A
  1. Change in (sequence of) amino acid(s)/primary
    structure;
  2. Change in hydrogen/ionic/disulfide bonds;
  3. Alters tertiary/30 structure;
37
Q

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]

A
  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);
38
Q

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

A
  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;
39
Q

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

A
  1. For respiration;
  2. Provide ATP/energy (for growth);
40
Q

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

A
  1. To prevent/reduce evaporation;
  2. (Which) alters concentration of (IAA) solution
    OR
    (Which) alters water potential;
41
Q

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]

A
  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)
42
Q

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

A
  1. Regenerates/produces NAD
    OR
    oxidises reduced NAD;
  2. (So) glycolysis continues;
43
Q

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]

A
  1. (More) insulin binds to receptors;
  2. (Stimulates) uptake of glucose by
    channel/transport proteins
    OR
    Activates enzymes which convert glucose to
    glycogen;
44
Q

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

A
  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;
45
Q

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]

A
  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;
46
Q

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

A
  1. Chlorophyll absorbs light
    OR
    Light excites/moves electrons in chlorophyll;
  2. Electron/s are lost
    OR
    (Chlorophyll) becomes positively charged;
47
Q

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

A

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;

48
Q

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

A
  1. Level of solvent below origin/line;
  2. Remove/stop before (solvent) reaches top/end;
49
Q

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

A

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

50
Q

What is a DNA probe?
[2 marks]

A
  1. (Short) single strand of DNA;
  2. Bases complementary (with DNA/allele/gene);
51
Q

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

A
  1. Restriction endonuclease/enzyme;
  2. (Cuts DNA at specific) base sequence
    OR
    (Breaks) phosphodiester bonds
    OR
    (Cuts DNA) at recognition/restriction site;
52
Q

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

A

(So DNA) probe binds/attaches/anneals;

53
Q

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

A
  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;
54
Q

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

A
  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;
55
Q

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

A
  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
56
Q

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

A
  1. (Less/no) ATP;
  2. (Less/no) reduced NADP;
57
Q

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]

A
  1. (Less/no) carbon dioxide (reacts) with RuBP;
  2. (Less/no) GP;
58
Q

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

A
  1. Stroma (of/in chloroplast);
59
Q

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

A

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;

60
Q

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]

A
  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;
61
Q

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]

A
  1. (So the) oxygen is used/absorbed/respired;
62
Q

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

A
  1. Anaerobic respiration produces carbon dioxide;
  2. Increase in pressure/volume (of gas);
63
Q

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]

A
  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;
64
Q

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

A

Large range/difference/increase in numbers;

65
Q

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

A
  1. Decrease/no glucose/substrate
    OR
    Increase in ethanol/carbon dioxide/acidity;
66
Q

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]

A
  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
67
Q

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

A
  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;
68
Q

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]

A
  1. Affects water potential (of blood/body);
  2. Affects volume of urine (produced/removed);
69
Q

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

A

Lower volume of blood

70
Q

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]

A

1.Water potential of filtrate/tubule decreased;

  1. Less water (reabsorbed) by osmosis (from
    filtrate/tubule);
  2. Collecting duct (is where osmosis occurs);
71
Q

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]

A
  1. Small sample size;
  2. Fusion/fertilisation of gametes is random;
  3. Linked Genes;
  4. Epistasis;
  5. Lethal genotypes;
72
Q

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]

A
  1. (Dopamine) diffuses across (synapse);
  2. Attaches to receptors on postsynaptic
    membrane;
  3. Stimulates entry of sodium ions and
    depolarisation/action potential;
73
Q

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]

A
  1. Morphine attaches to opioid receptors;
  2. (More) dopamine released (to provide pain
    relief);
74
Q

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]

A
  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;
75
Q

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

A
  1. (All) the DNA in a cell/organism;
76
Q

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

A
  1. (Transcriptional factor/antibody) has a
    specific/tertiary structure/shape;
  2. Complementary (shape/structure);
77
Q

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

A
  1. DNA, transcription factor and antibod
78
Q

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]

A
  1. Binds to P34 gene/DNA/mRNA
    OR
    Binds to transcription factor gene/DNA
    OR
    Binds to promoter;
79
Q

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

A
  1. Restriction (endonuclease/enzyme) to cut
    plasmid/vector;
  2. Ligase joins gene/DNA to plasmid/vector;
80
Q

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

A
  1. Mass/number of amino acids/polypeptides;
  2. Charge;
  3. R groups (differ);
81
Q

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]

A
  1. Green sensitive pigment/cones non-functional
    OR
    Cones that detect green light non-functional;
  2. Three different types of pigment/cone;
82
Q

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]

A
  1. (iPS cells) divide;
    2.(iPS cells) develop/differentiate into (green
    sensitive) cones;
83
Q

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]

A

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);

Biology Past Paper Questions - KEYWORDS (3 decks)

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