survival and response 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;
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;
sympathetic and parasympathetic
sympathetic increased heart rate
parasympathetic slows down heart rate
