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Summary - CCEA Unit A2 1 - Physiology and Ecosystems - Coordination and control
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Summary notes of CCEA A21 Biology specification in regards to co-ordination and control section.
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CO ORDINATION AND CONTROL IN PLANTSZone of division: Where mitosis occurs only at the tip
Zone of elongation- Where cells lengthen
Plant growth substances:
Auxins- Apical meristem (tip) – causes cell elongation (in the zone of elongation) (flexibility)
Cytokinins – Apical meristem (tip) – causes mitosis in the tip (zone of division)
Gibberelins – Mainly in leaves (but also stem) – Causes cell elongation in the stem (internodal
region) (some plants show growth in internodal regions due to gibberleins to prevent leaves from
shading each other.)
Control of flowering
Flowering is controlled by the length of daylight (photoperiod)
Long day plants- only flower when period of daylight is longer than a critical length.
Short day plants- Only flower when period of daylight is shorter than critical length.
Light sensitive pigment found in leaves – Phytochrome
- Phytochrome 660 – absorbs red light
- Phytochrome 730 – absorbs far red light
It is the length of continuous darkness that is the key to the P 730 level:
- Summer=short night=high P730
- Winter=long night=time to break down P 730 to P660
Required photoperiod Required P730 Levels Effect of P730
Long day plant Short night (long day) High P730 Stimulates flowering
Short day plant Long night (short day) Low P730 Inhibits flowering
, CO ORDINATION AND CONTROL IN MAMMALS
Central nervous system – the brain and spinal cord
Peripheral nervous system – the nerves that are attached to the brain and spinal cord.
Nerve is a bundle of neurones
Structure of a neurone:
Cell body – contains nucleus and other organelles
Dendrons/dendrites – transmit impulse to the cell body
Axon – transmit impulses way from the cell body. Axon terminates in synaptic knobs (bulbs).
Sensory neurone conducts impulse from receptor to CNS.
Motor neurone conducts impulse from CNS to effector (muscle)
Nerve Impulses
Resting Potential/Polarisation
- Approx. -70mV potential difference
- More negative inside the axon membrane
- Membrane impermeable to the diffusion of ions
Action Potential/Depolarisation
- Approx. 40mV potential difference
- More positive inside axon membrane
-Sodium channel proteins open
- Membrane now permeable to positive ions
- Influx of sodium ions
Repolarisation
- Re-establish resting potential
- more negative inside axon membrane
- positive (sodium) ions pumped/diffuse out of axon
- Refractory period where membrane becomes too negative, so action potential cannot be
generated (ensures one way system)
Threshold Stimulus is any stimulus strong enough to initiate an impulse.
- Weak stimulus causes no action potential/impulse as threshold is not reached. Increasing stimulus
strength (above threshold) increases number of action potentials)
All or nothing law: If depolarisation is not great enough to reach threshold, an action potential and
impulse will not be generated. (Stimulus reaches threshold- impulse of +40mV)
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