Responses to their environment

Question 1

All the volunteers were given the same food for 3 days.

Suggest and explain one reason why they were given the same food when testing a diuretic

Answer 1

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

Question 2

Furosemide is sometimes used to treat high blood pressure.

Suggest how furosemide would cause a decrease in blood pressure.

Answer 2

Lower volume of blood;

Question 3

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.

Answer 3

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

Question 4

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.

Answer 4

1. (Dopamine) diffuses across (synapse);
2. Attaches to receptors on postsynaptic membrane;
   Ignore name/nature of receptor e.g. cholinergic
3. Stimulates entry of sodium ions and depolarisation/action potential;

Question 5

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.

Answer 5

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

Question 6

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

Answer 6

1. (Inside of postsynaptic) neurone becomes more negative/hyperpolarisation/inhibitory postsynaptic potential;
   Ignore K+
   Accept -75mV or any value below this as equivalent to more negative
   Accept ‘decrease in charge’
2. More sodium ions required (to reach threshold)
   OR
   Not enough sodium ions enter (to reach threshold);
   Accept Na+ for sodium ions
3. For depolarisation/action potential;

Question 7

Red-green colour blindness affects more men than women (lines 7–8).
Explain why.

Answer 7

1. (Gene/allele) is on the X chromosome;

2. Females require two alleles/females can be heterozygous/carriers and males require one allele;

Question 8

People with red-green colour blindness are unable to distinguish between red and green, and also between other colours (lines 8–10)”They have green-sensitive cones but the photoreceptive pigment they contain does not function..”
Explain why.

Answer 8

1. Green sensitive pigment/cones non-functional
   OR
   Cones that detect green light non-functional;
2. Three different types of pigment/cone;
3. Other/different colours (‘seen’) due to stimulation of more than one cone/pigment;

Question 9

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.

Answer 9

1. (iPS cells) divide;

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

Question 10

The acidic pH conditions created by osteoclasts cause the inactive form of the protein osteocalcin to change into the active form of osteocalcin.
Suggest how.

Answer 10

1. (Change in pH) changes / breaks ionic / hydrogen bonds;

2. Changes tertiary structure;

Question 11

Binding of insulin leads to an increase in the rate of respiration in cells such as osteoblasts.
Explain how.

Answer 11

1. (Insulin) leads to more transport proteins / channel (proteins) / carrier (proteins) for glucose;
2. More glucose (for respiration / glycolysis) enters cell;

Question 12

Exercise causes an increase in heart rate.

Describe the role of receptors and of the nervous system in this process.

Answer 12

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 13

Each year, a few people with type I diabetes are given a pancreas transplant. Pancreas transplants are not used to treat people with type II diabetes.
Give two reasons why pancreas transplants are not used for the treatment of type II diabetes.

Answer 13

1. (Usually)Type II produce insulin;
2. Cells / receptors less sensitive / responsive (to insulin)
   OR
   Faulty (insulin) receptors;
3. (Treated / controlled by) diet / exercise;

Question 14

Suggest how transcription factors can reprogramme cells to form iPS cells.

Answer 14

1. Attach to gene / DNA / promoter region;

2. Stimulate / inhibit transcription / RNA polymerase;

Question 15

When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob.
Describe how.

Answer 15

1. (Nerve impulse / depolarisation of membrane) causes Ca 2+ channel (proteins) to open;
2. Ca 2+ enter by (facilitated) diffusion;
3. Causes (synaptic) vesicles to fuse with (presynaptic) membrane;

Question 16

Use your knowledge of how myosin and actin interact to suggest how the myosin molecule moves the mitochondrion towards the presynaptic membrane.
Do not include the roles of calcium ions and tropomyosin in your answer.

Answer 16

1. Myosin head attaches to actin and bends / performs powerstroke;
2. (This) pulls mitochondria past / along the actin;
3. Other / next myosin head attaches to actin (and bends / performs powerstroke);

Question 17

Suggest and explain one advantage of the movement of mitochondria towards the presynaptic membrane when nerve impulses arrive at the synapse.

Answer 17

1. (Mitochondria) supply (additional) ATP / energy;
2. To move vesicles / for active transport of ions / for myosin to move past actin
   OR
   Re-synthesis / reabsorption of neurotransmitter / named neurotransmitter;

Question 18

The image shows glycogen granules present in skeletal muscle.
Explain their role in skeletal muscle.

Answer 18

1.      As a store of glucose
Ignore provide energy
OR
To be hydrolysed to glucose;
2.      For respiration / to provide ATP;

Question 19

During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction.
Suggest how.

Answer 19

1. Low pH changes shape of calcium ion receptors
   Do not accept tropomyosin does not move
2. Fewer calcium ions bind to tropomyosin;
   Accept troponin
3. Fewer tropomyosin molecules move away;
4. Fewer binding sites on actin revealed;
5. Fewer cross-bridges can form
   OR
   Fewer myosin heads can bind

Question 20

Suggest two advantages of simple reflexes.

Answer 20

1. Rapid;
2. Protect against damage to body tissues;
3. Do not have to be learnt;
4. Help escape from predators;
5. Enable homeostatic control.

Question 21

In the nerve pathway in the diagram, synapses ensure that nerve impulses only travel towards the muscle fibre.
Explain how.

Answer 21

1. Neurotransmitter only made in / stored in / released from pre-synaptic neurone;
2. (Neuro)receptors only on the post-synaptic membrane;

Question 22

Axon P was found to conduct impulses much faster than other axons in the nerve pathway shown in the diagram.
Describe and explain one feature of axon P that might cause this difference.

Answer 22

1. Axon P is myelinated;
2. So shows saltatory conduction / impulses jump between nodes of Ranvier
   OR
3. Axon P has a larger diameter;
4. So less resistance to flow of ions.