survival, response and nervous coordination Flashcards

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1
Q

Describe the effect of IAA on root and shoot growth.

A
  • 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.
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2
Q

Describe what is meant by the term taxis.

A
  • Moves towards or away from directional stimulus
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3
Q

Describe what is meant by the term kinesis.

A
  • Movement is random/non-directional response
    OR
  • Insect is not moving towards a particular stimulus;
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4
Q

Compare & Contrast taxis and tropism.

A
  • Both are directional responses to stimuli
  • Taxis involves the movement of the entire organism whereas tropism is the movement of part of an organism
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5
Q

Explain the advantages of simple reflex arcs.

A
  • Rapid;
  • Protect against damage to body tissues;
  • Do not have to be learnt;
  • Help escape from predators;
  • Enable homeostatic control;
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6
Q

As a neurone transmits an impulse, its rate of oxygen consumption increases.
Explain why.

A
  • 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;
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7
Q

Describe how a resting potential is maintained in a neurone.

A
  • 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;
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8
Q

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

A
  • Sodium ion gates / channel (proteins) open;
  • Na+ (rapidly) diffuse in;
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9
Q

SYNAPSE:
Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane.

A
  • 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;
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10
Q

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

A
  • (Nerve impulse/depolarisation of membrane) causes Ca2+ channel (proteins) to open;
  • Ca2+ enter by (facilitated) diffusion;
  • Causes (synaptic) vesicles to fuse with (presynaptic) membrane;
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11
Q

Give two reasons why transmission across a cholinergic synapse is unidirectional.

A
  • (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
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12
Q

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.

A
  • (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;
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13
Q

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

A
  • 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;
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14
Q

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

A
  • Impulse jumps from node of Ranvier to node of Ranvier / depolarisation only at node of Ranvier;
  • Fewer jumps / depolarisations to travel length of axon;
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15
Q

Describe how the inhibition of acetylcholinesterase affects the action of synapses.

A
  • Acetylcholine not broken down / stays bound to receptor;
  • Na+ ions (continue to) enter / (continued) depolarisation / Na+ channels (kept) open / action potentials;
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16
Q

Describe what is meant by the term refractory period.

A
  • (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;