Control and Coordination
What is tested
This domain tests the nervous system and hormones in animals and plants. Expect questions on neurons, reflex arcs, brain parts, spinal cord, endocrine glands, plant growth regulators and tropisms.
Core rules
- A neuron has dendrites, cell body and axon. Impulses pass across a synapse by chemical messengers.
- A reflex arc is a fast, involuntary pathway: receptor → sensory neuron → spinal cord → motor neuron → effector. It often bypasses conscious brain processing.
- Cerebrum controls thinking and memory; cerebellum controls balance and posture; medulla controls involuntary actions such as breathing.
- Hormones are chemical messengers secreted by endocrine glands into blood. Insulin lowers blood glucose; adrenaline prepares the body for emergency.
- Plant hormones include auxin, gibberellin, cytokinin and abscisic acid. Phototropism is growth toward light; geotropism is growth in response to gravity.
Worked example
Touching a hot object: heat receptor in skin → sensory neuron → spinal cord → motor neuron → arm muscle contracts. The hand withdraws before the brain feels pain because the reflex arc is rapid.
Traps
Reflex actions are not controlled consciously by the cerebrum. Cerebellum is not for thinking. Insulin lowers glucose; glucagon raises it. Auxin accumulates on the shaded side and causes bending toward light.