6. Organisms Respond to change in environment

Question 1

Explain the effect of myelination on the rate of nerve impulse conduction. (2 marks)

Answer 1

1. myelin insulates
2. saltatory conduction

Question 2

Give one reason why a speed would be an underestimate of
the speed of transmission of an impulse along a neurone. (1 mark)

Answer 2

diffusion across synapse

Question 3

Damage to the myelin sheaths of neurones can lead to problems controlling the
contraction of muscles.
Suggest one reason why. (2 marks)

Answer 3

1. action potentials travel more slowly
2. so delay in muscle contraction

Question 4

A myelinated axon conducts impulses faster than a non-myelinated axon.
Explain this difference. (3 marks)

Answer 4

1.(In myelinated) action potential only at node(s);
2.(In myelinated, nerve impulse) jumps from node to node in saltatory conduction
3.(In myelinated) action potential does not travel along entire length

Question 5

Describe how calcium ions are involved in synaptic transmission. (2 marks)

Answer 5

1. (Nerve impulse causes) Ca 2+ to enter presynaptic neurone/membrane;
2. (Ca 2+ entry) causes fusion of vesicles with presynaptic membrane

Question 6

It is important that a neurotransmitter such as serotonin is transported back out of synapses. Explain why. (2 marks)

Answer 6

1. (If not removed) keeps binding (to receptors);
2. Keeps causing action potentials

Question 7

Sodium and potassium ions can only cross the axon membrane through proteins.
Explain why. (2 marks)

Answer 7

1. can not pass through phospholipid bilayer;
2. because water soluble

Question 8

The scientists then compared the length of time that the control mice and the
trained mice could carry out prolonged exercise. The trained mice were able to
exercise for a longer time period than control mice.
Explain why. (3 marks)

Answer 8

1. (More aerobic respiration) produces more ATP;
2. Anaerobic respiration delayed;
3. Less or no lactate;

Question 9

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. (3 marks)

Answer 9

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

Question 10

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. (3 marks)

Answer 10

1. (Inside of postsynaptic) neurone becomes more
   negative/hyperpolarisation
2. More sodium ions required (to reach threshold)
3. For depolarisation/action potential;

Question 11

Explain why the student removed the shoot tip from each seedling. (2 marks)

Answer 11

1. Tip produces IAA;
2. Affects concentration of IAA

Question 12

Explain why the student added glucose solution to each Petri dish in IAA experiment (2 marks)

Answer 12

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

Question 13

Explain why the lids were kept on the Petri dishes in IAA experiment (2 marks)

Answer 13

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

Question 14

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 14

1. (Less/No) tropomyosin moved from binding site
2. (Fewer/No) actinomyosin bridges formed;
3. Myosin head does not move

Question 15

Damage to the myelin sheath of neurones can cause muscular paralysis. Explain why (3 marks)

Answer 15

1. (Nerve)
   impulses pass
   to other neurones
2. (Nerve) impulses slowed/stopped;

Question 16

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 16

1. No/less ATP produced;
2. No/less active transport
   OR
   Sodium/potassium pump inhibited;
3. Electrochemical gradient not maintained, no net movement of ions

Question 17

Suggest two reasons why the patients had ziconotide injected into their cerebrospinal
fluid rather than taking a pill containing the drug. (2 marks)

Answer 17

1. Rapidly/quickly/directly reaches spinal cord;
2. Too large to be absorbed

Question 18

When the patients recorded the intensity of pain, suggest two reasons why it was
important to use a statistically valid scale. (2 marks)

Answer 18

1. (Sensation of) pain is subjective
2. To ensure that differences (in pain detection)
   were (statistically) significant
   OR
   For (valid) comparison;