Survival, Response to Stimuli and Neurones

Question 1

Describe the effect of IAA on the shoots (6)

Answer 1

1. IAA synthesised in shoot tips
2. IAA diffuses into growing region
3. Light causes movement of IAA from light side to shaded side
4. Proportionally more IAA on shaded side
5. Causes directional growth as there is greater cell elongation on shaded side
6. Shaded side grows faster and causes shoot to bend towards light

Question 2

Describe the effect of IAA on the roots (6)

Answer 2

1. IAA synthesised in root tips
2. IAA diffuses into growing region
3. IAA moves towards shaded side
4. Inhibits cell elongation
5. Uneven growth
6. Causes directional growth away from light and towards gravity

Question 3

Describe what is meant by the term taxis (1)

Answer 3

1. Moves towards or away from directional stimulus

Question 4

Describe what is meant by the term kinesis (1)

Answer 4

1. Movement is random
   OR
2. Insect isn’t moving towards a particular stimulus

Question 5

Compare and contrast taxis and tropisms (2)

Answer 5

1. Both are directional responses to stimuli
2. Taxis involves the movement of the entire organism whereas tropism is the movement of part of an organism

Question 6

Explain the advantage of simple reflex arcs (3)

Answer 6

1. Rapid
2. Protect against damage to body tissue
3. Doesn’t have to be learnt
4. Help escape from predators
5. Enable homeostatic control

Question 7

As a neurone transmits an impulse, its rate of oxygen consumption increases. Explain why (2)

Answer 7

1. ATP required for active transport
2. Na+ moved out only at nodes in myelinated

Question 8

Describe how a resting potential is maintained in a neurone (4)

Answer 8

1. Active transport of Na+
2. Out of neurone
3. Differential permeability to K+ and Na+
4. Membrane more permeable to K+

Question 9

The potential across the membrane is reversed when an action potential is produced. Describe how (2)

Answer 9

1. Na+ channels open
2. Na+ diffuse in

Question 10

Describe the sequence of events leading to the release of acetylcholine and its binding to the post synaptic membrane (6)

Answer 10

1. Depolarisation of presynaptic membrane
2. Ca2+ channels open and Ca2+ enter
3. Synaptic vesicles fuse with presynaptic membrane and release acetylcholine
4. Acetylcholine diffuses across synaptic cleft
5. Binds to receptors on post synaptic membrane
6. Na+ enter leading to depolarisation

Question 11

When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob. Describe how (3)

Answer 11

1. Causes Ca2+ channels to open
2. Ca2+ enter by facilitated diffusion
3. Causes vesicles to fuse with presynaptic membrane

Question 12

Give two reasons why transmission across a cholinergic synapse is unidirectional (2)

Answer 12

1. Presynaptic neurone releases acetylcholine
2. Only post synaptic neurone has receptors

Question 13

The binding of GABA to receptors on postsynaptic membranes causes negatively charged chloride ions to enter postsynaptic neurones. Explain how this will inhibit transmission of nerve impulse by postsynaptic neurones (3)

Answer 13

1. Neurone becomes hyperpolarised
2. More Na+ required
   OR
3. Not enough Na+ enter to reach threshold
4. For depolarisation

Question 14

Describe how the speed of the conduction could be increased in the neurone (2)

Answer 14

1. Axon is myelinated
2. Shows saltatory conduction
   OR
3. Axon has large diameter
4. Less resistance to flow of ions

Question 15

Myelination affects the rate of conduction of a nerve impulse. Explain how. (2)

Answer 15

1. Impulse jumps from node of ranvier to node of ranvier
2. Fewer jumps to travel length of axon

Question 16

Describe how the inhibition of acetylcholinesteraase affects the action of synapses (2)

Answer 16

1. Acetylcholine not broken down
2. Na+ enter / depolarisation

Question 17

Describe what is meant by the term refractory period (4)

Answer 17

1. Limits number of impulses per second
2. Maximum frequency of impulse transmission
3. Period of time between threshold and resting potential membrane
4. When maximum frequency reached, no further increase

Question 18

Describe spatial summation (3)

Answer 18

1. Different neurones converge at a single synapse
2. Causes release of enough neurotransmitter to reach threshold
3. Causes action potential in post synaptic membrane

Question 19

Describe temporal summation (3)

Answer 19

1. Impulse arrive in rapid succession
2. Giving cumulative effect
3. Sufficient to depolarise post synaptic membrane

Question 20

Explain how a resting potential is maintained across the axon membrane in a neurone (3)

Answer 20

1. Na+ diffuse in and K+ diffuse out
2. Membrane more permeable to K+ leaving than Na+ entering
3. Na+ actively transported out and K+ in

Question 21

Explain why the speed of transmission of impulses is faster along a myelinated axon
than along a non-myelinated axon (3)

Answer 21

1. Myelination provides insulation
2. In myelinated, saltatory conduction
3. In non-myelinated depolarisation occurs along length of axon

Question 22

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)

Answer 22

1. Less ATP produced
2. Less active transport
3. No net movement of Na+ and K+