Survival, Response To Stimuli And Neurones

Question 1

Explain the advantages of simple reflex arc
5points

Answer 1

Rapid
Protect against damage to body tissues
Do not have to be learnt
Help escape from predators
Enable homeostatic control

Question 2

As a neurone transmit an impulse it’s rate of oxygen consumption increases. Exalting why

Answer 2

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

Question 3

Describe how a resting potential is maintained in a neuron
4 points

Answer 3

Higher concentration of K+ in and higher concentration of Na+ out
Membrane more permeable to K+
Na+ actively transported out and K+ in

Question 4

the potential across the membrane is reversed when an action potential is produced
explain how

Answer 4

sodium ion gates open
Na+ rapidly diffuse in

Question 5

describe the sequence of events leading to the release of acetylcholine and its binding to the post synaptic membrane
6 points

Answer 5

depolarization of presynaptic membrane
ca2+ channels open and calcium ions enter synaptic knob
synaptic vesicles move to fuse with presynaptic membrane and release acetylcholine
which then diffuses across synaptic cleft
acetylcholine then binds to receptors on the post synaptic membrane
sodium ions enter leading to depolarization

Question 6

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

Answer 6

Nerve impulse causes Ca2+ channel protein to open
Ca2+ enter by facilitated diffusion
Causes vesicles to fuse with presynaptic membrane

Question 7

The binding of GABA to receptors on the presynaptic membranes causes negatively charged chloride ions to enter postsynaptic neurones.
Explain how this will inhibit transmission of nerve impulses by post synaptic neurones

Answer 7

Neurone becomes more negative- hyper polarised
More sodium ions required to reach threshold
For action potential

Question 8

Describe how the speed of the conduction could be increased in a neurone.

Answer 8

Axon is myelinated
So impulse jumps from node of ranvier to node of ranvier
Axon has a larger diameter
So less resistance to flow of ions

Question 9

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

Answer 9

Impulse jumps from node of ranvier to node of ranvier
Fewer jumps

Question 10

Describe how the inhibition of acetylcholinesterase affects the action of synapses

Answer 10

Acetylcholine not broken down
Na+ ions continue to enter

Question 11

Describe what is meant by the term refractory period

Answer 11

Refractory period limits the number of impulses per second
Maximum frequency of impulse transmission
Period of time between threshold and resting membrane potential
When maximum frequency reached stimuli seem the same

Question 12

Draw structure of myelinated motor neurone

Answer 12

Go Google one

Question 13

Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non myelinated axon

Answer 13

Myelination provides insulation
Depolarisation occurs at nodes
In non myelinated depolarisation occurs along the entire length of axon

Question 14

Describe the effect of IAA on shoot growth

Answer 14

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

Question 15

Describe the effect of IAA on root growth

Answer 15

IAA synthesised in root tips