Survival, Response To Stimuli & Neurones (6)

Question 1

Describe the effect of IAA on root and shoot growth

Answer 1

• IAA synthesised in shoots tips
• IAA diffuses into growing (cell elongating) region
• Light causes movement of IAA from light to shaded side
• Causes directional growth as there is greater cell elongation on shaded side
• Shaded side grows faster and causes shoot to bend towards light

• IAA synthesised in root tips
• IAA diffuses into growing (cell elongating) region
• IAA moves towards underside/shaded side
• Inhibits cell elongation
• Uneven growth (more elongation on side with less IAA)
• Causes directional growth away from light and downwards towards gravity.

Question 2

Describe what is meant by taxes

Answer 2

Moves towards or away from directional stimulus

Question 3

Describe what is meant by kinesis

Answer 3

A change in movement which is random
/ non-directional
(Due to a change in stimulus)

Question 4

Compare and contrast taxes and trophism

Answer 4

• Both are directional responses to stimuli
• Taxes involves the movement of the entire organism whereas trophism is the movement of part of an organism

Question 5

Explain the advantages of simple reflex arcs

Answer 5

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

Question 6

As a neurone transmits an impulse, it’s rate of oxygen consumption increases. Explain why

Answer 6

• ATP required for active transport
• Na+ actively transported out only at nodes in myelinated / Na+ (actively) moved out along whole length of axon in non-myelinated

Question 7

Describe how a resting potential is maintained in a neurone

Answer 7

• Active transport/pumping of sodium (ions across membrane)
• out of neurone / higher concentration outside
• differential permeability to K+ and Na+
• membrane more permeable to K+ ions

Question 8

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

Answer 8

• Sodium ion channel proteins open;
• Na+ rapidly diffuses in

Question 9

SYNAPSE:

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

Answer 9

• Depolarisation of presynaptic membrane;
• Ca2+ channels open and calcium ions enter (synaptic knob);
• Calcium ions cause synaptic vesicles to fuse with presynaptic membrane and release acetylcholine / neurotransmitter;
• Acetylcholine neurotransmitter diffuses across synaptic cleft;
• Acetylcholine binds to receptors on the postsynaptic membrane;
• Sodium ions enter (postsynaptic neurone) leading to depolarisation.

Question 10

B