survival, response and nervous coordination Flashcards
Describe the effect of IAA on root and shoot growth.
- IAA synthesised in shoots tips.
- IAA diffuses into growing (cell elongating) region.
- Light causes movement of IAA from light side to shaded side.
- Proportionally more IAA on shaded side.
- Causes directional growth as there is greater cell elongation on shaded side.
- Shaded side grows faster and causes shoot to bend towards the 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.
Describe what is meant by the term taxis.
- Moves towards or away from directional stimulus
Describe what is meant by the term kinesis.
- Movement is random/non-directional response
OR - Insect is not moving towards a particular stimulus;
Compare & Contrast taxis and tropism.
- Both are directional responses to stimuli
- Taxis involves the movement of the entire organism whereas tropism is the movement of part of an organism
Explain the advantages of simple reflex arcs.
- Rapid;
- Protect against damage to body tissues;
- Do not have to be learnt;
- Help escape from predators;
- Enable homeostatic control;
As a neurone transmits an impulse, its rate of oxygen consumption increases.
Explain why.
- ATP required for active transport;
- Na+ (actively) moved out only at nodes in myelinated / Na+ (actively) moved out along whole length of axon in non-myelinated;
Describe how a resting potential is maintained in a neurone.
- 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;
The potential across the membrane is reversed when an action potential is produced.
Describe how.
- Sodium ion gates / channel (proteins) open;
- Na+ (rapidly) diffuse in;
SYNAPSE:
Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane.
- Depolarisation of presynaptic membrane;
- Ca2+ channels open and calcium ions enter (synaptic knob);
- (Calcium ions cause) synaptic vesicles move to/fuse with presynaptic membrane and release acetylcholine / neurotransmitter;
- Acetylcholine/neurotransmitter diffuses across (synaptic cleft);
- (Acetylcholine attaches) binds to receptors on the postsynaptic membrane;
Sodium ions enter (postsynaptic neurone) leading to depolarisation;
When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob.
Describe how.
- (Nerve impulse/depolarisation of membrane) causes Ca2+ channel (proteins) to open;
- Ca2+ enter by (facilitated) diffusion;
- Causes (synaptic) vesicles to fuse with (presynaptic) membrane;
Give two reasons why transmission across a cholinergic synapse is unidirectional.
- (Only) the presynaptic neurone/knob/membrane releases/has neurotransmitters/acetylcholine;
- (Only) the postsynaptic neurone/membrane has receptors
OR
no receptors in the presynaptic neurone/membrane
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 impulses by postsynaptic neurones.
- (Inside of postsynaptic) neurone becomes more negative/hyperpolarised;
- More sodium ions required (to reach threshold) OR Not enough sodium ions enter (to reach threshold);
- For depolarisation/action potential;
Describe how the speed of the conduction could be increased in a neurone.
- Axon is myelinated;
- So shows saltatory conduction/impulses jump from node of Ranvier to node of Ranvier;
OR - Axon has a larger diameter;
- So less resistance to flow of ions;
Myelination affects the rate of conduction of a nerve impulse. Explain how.
- Impulse jumps from node of Ranvier to node of Ranvier / depolarisation only at node of Ranvier;
- Fewer jumps / depolarisations to travel length of axon;
Describe how the inhibition of acetylcholinesterase affects the action of synapses.
- Acetylcholine not broken down / stays bound to receptor;
- Na+ ions (continue to) enter / (continued) depolarisation / Na+ channels (kept) open / action potentials;
