BIOL5

Question 1

What is the role of ATP in myofibril contraction?

[2 marks]

Answer 1

1. (Reaction with ATP) breaks/allows binding of myosin to actin/ actinomyosin bridge;
2. Provides energy to move myosin head;

Question 2

The mice that were not able to produce creatine were homozygous for a recessive allele of a gene. Mice that are heterozygous for this allele are able to produce forces similar to those of normal mice that are homozygous for the dominant allele of the same gene.
Explain why the heterozygous mice can produce forces similar to those of normal mice.
[2 marks]

Answer 2

1. (Heterozygous) have one dominant/normal allele (for creatine production);
2. (This) leads to production of enough/normal amount of creatine;

Question 3

The desired gene in Figure 4 was from an insect. In stage 6, the plant containing this gene was able to use it to synthesise an insect protein.
The plant is able to synthesise the insect protein. Explain why this is possible.
[3 marks]

Answer 3

1. Genetic code is universal/triplets in DNA always code for same amino acid;
2. It/insect DNA can be transcribed;
3. Can be translated (process/mechanism same in all organisms/cells);

Question 4

Scientists investigated the effect of diabetes on the control of heart rate in response to changes in blood pressure in rats.
The scientists found the mean changes in heart rates of healthy rats and rats with diabetes in response to rises or falls in blood pressure.
Diabetes can damage the nervous system. The response of the rats with diabetes is different from the response of the healthy rats. Use your knowledge of the control of heart rate by the nervous system to suggest an explanation for these results.
[4 marks]

Answer 4

1. Damage to autonomic (nervous) system in diabetic rats;
2. (Could be) pressure receptors/baroreceptors (in arteries/aorta/carotid body) don’t work as well;
3. Damage to medulla
   OR
   Change in (number of) impulses to/from
   medulla;
4. (When pressure drops damage to) sympathetic system, so doesn’t speed up (enough);
5. (When pressure rises damage to) parasympathetic system, so doesn’t slow down (enough);

Question 5

Name the process by which the base sequence of a spacer is lost from a DR region.
[1 mark]

Answer 5

Deletion mutation;

Question 6

Explain how the use of DNA probes produced the results in Figure 7.
[3 marks]

Answer 6

1. Probes are single stranded / have a specific base sequence;
2. Complementary base sequence on (specific) spacer
   OR
3. Complementary/specific to (particular) spacer;
4. (In white squares probe) binds (to single-stranded spacer) and glows/produces light/fluoresce;

Question 7

Multiple sclerosis (MS) is a condition caused when the body’s own immune system attacks the myelin sheath around axons. The cell bodies of the neurones themselves can also be damaged or destroyed. People with MS usually have periods of time when their MS gets no worse, followed by relapses when it gets worse.
Scientists investigated the effects on neurones of damage to myelin. The scientists obtained a modified antigen from the myelin sheath of humans and injected it into mice. After a number of days, this injection of antigen resulted in the myelin sheaths in the mice being damaged. Some cell bodies of neurones were also damaged.
Suggest how the injection of the antigen resulted in the myelin sheaths being damaged.

Answer 7

1. Antigen stimulates immune response / activates B/T cells;
2. B/T cells divide OR antibodies produced;
3. Antibodies/T cells attack myelin sheaths;

Question 8

Suggest how the scientists found the percentage of mitochondria with the unusual ultrastructure.
[3 marks]

Answer 8

1. Took photographs/areas at random;
2. Counted total number (of normal) and number of unusual mitochondria;
3. Divided number of unusual mitochondria by total number and multiply by 100;

Question 9

One form of muscle disease is caused by a mutated allele of a gene. This leads to production of myosin molecules that are unable to bind to other myosin molecules.
if myosin molecules are unable to bind to other myosin molecules, this prevents muscle contraction.
Use Figure 1 and your knowledge of how muscles contract to suggest why. [3 marks]

Answer 9

1. Can’t form myosin/thick filaments;
2. Can’t pull/can’t move actin/slide actin past / (myosin) have to be joined/fixed to pull actin;
3. Myosin moves /if attached doesn’t move;
4. Can’t move actin towards each other/middle of sarcomere/between myosin/
   can’t shorten sarcomere/can’t pull Z lines together;

Question 10

Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. This stimulates the cancer cells to divide.
Scientists have produced a monoclonal antibody that stops this stimulation.
Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour.
[3 marks]

Answer 10

1. Antibody has specific tertiary structure/binding site/variable region;
2. Complementary (shape/fit) to receptor protein/GF/ binds to receptor protein/to GF;
3. Prevents GF binding (to receptor);

Question 11

For each student, the scientists also determined how much methylation was present within the specific gene. DNA methylation is the attachment of substances called methyl groups to cytosine or adenine. This prevents transcription.
Suggest how methylation of DNA can prevent expression of a gene. [3 marks]

Answer 11

1. Prevent binding of transcription factor;
2. Prevents RNA polymerase binding/working;
3. Prevents complementary/specific base-pairing;
4. (No transcription, so) no (pre)mRNA made;
5. No/less translation (of mRNA);

Question 12

Describe how a Pacinian corpuscle produces a generator potential when stimulated. [3 marks]

Answer 12

1. (Increased pressure) deforms/changes stretch-mediated sodium (ion) channel;
2. (Sodium channels open and) sodium ions flow in;
3. Depolarisation (leading to generator potential);

Question 13

Cannabinoids include substances found in cannabis that can enter brain tissue. Scientists are developing artificial cannabinoids that can enter neuromuscular junctions but cannot enter brain tissue.
Suggest why these artificial cannabinoids would be better to use than cannabis when
treating someone with MS.
[2 marks]

Answer 13

1. They won’t affect synapses in brain;
2. They won’t cause problems with the brain’s function/won’t damage brain;
3. (So only the) muscle/neuromuscular junctions treated/affected;

Question 14

Scientists investigated the control of blood glucose concentration in mice. They kept a group of normal mice without food for 48 hours. After 48 hours, the blood glucose concentrations of the mice were the same as at the start of the experiment.
[3 marks]

Answer 14

1. Release of glucagon;
2. Leads to formation of glucose in liver (cells);
3. From non-carbohydrates/amino acids/fatty acids;

Question 15

The scientists wanted to know on which chromosome the gene with alleles R and r was located. From the flies with genotype RR, they obtained cells that were in mitosis and added a labelled DNA probe specific for allele R. They then looked at the cells under an optical microscope.
Explain why they used cells that were in mitosis.
[2 marks]

Answer 15

1. (Cells in mitosis) chromosomes visible;

2. (So) can see which chromosome DNA probe attached to;

Question 16

explain why scientists used the same restriction endonuclease enzymes on each DNA sample. (2)

Answer 16

1. Cut (DNA) at same (base) sequence/(recognition) sequence;

2. (So) get required gene;

Question 17

What is the role of phosphocreatine (PC) in providing energy during muscle contraction?
[2 marks]

Answer 17

1. (Phosphocreatine) provides phosphate/phosphorylates;

2. To make ATP;

Question 18

The scientists used the polymerase chain reaction (PCR) to produce copies of the cDNA. They added a DNA probe for allele A to the cDNA copies. This DNA probe had a dye attached to it. This dye glows with a green light only when the DNA probe is attached to its target cDNA.
Explain why this DNA probe will only detect allele A. [2 marks]

Answer 18

1. Probe (base sequence) complementary (to DNA of allele A/where A is);
2. (Probe) binds by forming base pairs/hydrogen bonds;
3. So (only) this DNA labelled/has green dye/gives out (green) light;

Question 19

The scientists calculated the mean rate of carbon dioxide production of the leaves using measurements of carbon dioxide release in the dark.
Explain why they did not use measurements taken in the light.
[2 marks]

Answer 19

1. (In the light) photosynthesis/in the dark no photosynthesis;
2. (In light,) carbon dioxide (from respiration) being used/taken up (by photosynthesis);

Question 20

Describe two ways in which the mean rate of respiration in soil under trees is different from soil not under trees.
[2 marks]

Answer 20

(Between 06.00 and 12.00, (No Mark))
Respiration higher in soil under tree, (No mark)
1. Tree roots carry out (a lot of) respiration;
2. More/there are roots under tree;
OR
3. More food under trees;
4. So more active/greater mass of/more organisms (carrying out respiration);
OR
Soil not under trees respiration increases (No mark)
5. Soil in sunlight gets warmer;
6. Enzymes (of respiration) work faster;

Question 21

Describe the part played by each of the following in myofibril contraction.
Tropomyosin [2 marks]

Answer 21

1. Moves out of the way when calcium ions bind;

2. Allowing myosin to bind (to actin)/crossbridge formation;

Question 22

Describe the part played by each of the following in myofibril contraction.
myosin [2 marks]

Answer 22

1. Head (of myosin) binds to actin and moves/pulls/slides actin past;
2. (Myosin) detaches from actin and re-sets/moves further along (actin)
3. This uses ATP;

Question 23

suggest and explain one advantage of: the number of capillaries supplying slow muscle fibres. [2 marks]

Answer 23

1. (Glycogen broken down) gives (lots of) glucose for glycolysis/anaerobic respiration;
2. Glycolysis/anaerobic respiration not very efficient/only yields 2 ATP per glucose;

Question 24

suggest and explain one advantage of: the high glycogen content of fast muscle fibres [2 marks]

Answer 24

1. (Many capillaries) give high concentration/lots of oxygen/ shorter diffusion pathway for oxygen/large surface area for oxygen exchange/diffusion;
2. Good glucose supply with little glycogen present;
3. Allows high rate of/more aerobic respiration OR prevents build-up of lactic acid/(muscle) fatigue;

Question 25

In this investigation, the higher the concentration of sucrose in a rat’s mouth, the higher the frequency of nerve impulses from each taste receptor to the brain. If rats are given very high concentrations of sucrose solution to drink, the refractory period makes it impossible for information about the differences in concentration to reach the brain. Explain why. [2 marks]

Answer 25

1. (Refractory period) leads to discrete/separate nerve impulses/time when another nerve impulse can’t happen; OR (Refractory period) limits number of impulses per second/frequency of nerve impulses; 2. When maximum frequency reached/exceeded, no further increase in information/all (higher) concentrations of sucrose seem the same;

Question 26

In humans, when the stomach starts to become full of food, receptors in the wall of the stomach are stimulated. This leads to negative feedback on the desire to eat. Suggest why this negative feedback is important. [3 marks]

Answer 26

1. (Negative feedback) stops desire/wish to eat/appetite; 2. (This) limits amount eaten/stops eating; 3. Prevents/reduces risk of obesity/too much energy intake;

Question 27

To make the DNA probe, the geneticist had to find the base sequence of the normal gene. Once he had copies of the gene, what methods would he use to find the base sequence of the gene? [2 marks]

Answer 27

1. Restriction mapping/described; | 2. DNA/base sequencing (of fragments)/ description/name of method;