Coordination and response
Coordination and response
This domain tests the nervous system, reflex arcs, synapses, hormones and plant tropisms.
Core rules
- A stimulus is detected by a receptor; a coordinator processes it; an effector responds. Neurones carry electrical impulses.
- Reflex arc: receptor → sensory neurone → relay neurone in spinal cord → motor neurone → effector. Reflexes are rapid and involuntary and protect against harm.
- Synapses are gaps between neurones; a chemical neurotransmitter diffuses across and initiates an impulse in the next neurone. This slows transmission but allows integration.
- Hormones are chemical messengers carried in blood; they act on target organs and are slower but longer-lasting than nerves.
- Blood glucose: insulin lowers glucose by promoting uptake and storage as glycogen; glucagon raises it by releasing glucose from glycogen.
- Tropisms: phototropism is growth towards light; geotropism is growth in response to gravity. Auxin redistributes and causes differential growth.
Worked example
A hand touches a hot object. Temperature receptors in the skin generate impulses along the sensory neurone to the spinal cord; a relay neurone passes the impulse to a motor neurone; the arm muscle contracts and withdraws the hand. The brain may feel pain slightly later. Reasoning: the spinal cord coordinates the reflex without waiting for the brain, which makes the response faster.
Traps
- Reversing sensory and motor neurones.
- Saying synapses are electrical.
- Confusing hormones with nerves in speed and duration.
- Saying auxin causes phototropism by making cells shrink on the dark side.
- Calling a reflex a voluntary action.