survival & response, to stimuli & nervous system 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;
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.
• Sodium ions enter (postsynaptic neurone) leading to depolarisation;
• (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;
Describe what is meant by the term refractory period
• (Refractory period) limits number of impulses per second/frequency of nerve impulses;
• Maximum frequency of impulse transmission
• Period of time between threshold and resting membrane potential.
• When maximum frequency reached/exceeded, no further increase in information/ all (higher) stimuli seem the same;
