Control and Coordination
CBSE Class 10 · Science · Notes and practice questions
Control and coordination explains how animals and plants respond to stimuli through the nervous system, the endocrine system, and plant hormones. It covers neuron structure, reflex actions, the brain, plant movements, and the effects of hormonal imbalances.
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Control and coordination in animals is carried out by the nervous system and the endocrine system. The basic unit of the nervous system is the neuron, which transmits impulses along its processes. The brain is the main control centre, and the spinal cord joins it to the rest of the body through nerves. Coordination in plants is mostly chemical because plants do not have a nervous system. This chapter looks at how all these systems work together to produce responses and what happens when regulation goes out of balance.
A neuron has three main parts: dendrites, cell body, and axon. A stimulus generates an electrical impulse that travels from dendrites through the cell body to the axon and then across a synapse. At the synapse, chemical messengers allow the impulse to continue in the next neuron. This pathway, when used for an automatic, rapid response such as touching a hot plate, is called a reflex arc. Reflexes are controlled mainly by the spinal cord, giving a fast response before the brain is fully aware, although the brain later receives the information.
The brain is protected by the cranium (skull) and the spinal cord by the vertebral column. Both are surrounded by membranes called meninges and by cerebrospinal fluid, which cushions shocks. The brain can be divided into the forebrain, midbrain, and hindbrain. The forebrain, especially its cerebrum, is involved in thinking, speech, memory, and voluntary movements. The hindbrain contains the cerebellum, responsible for balance and posture, and other centres controlling breathing and heart rate.
In plants, responses occur as movements and growth changes rather than through a nervous system. Tropic movements are directional growth responses to stimuli such as light and gravity, and they often depend on differential growth caused by auxin. Nastic movements, such as the folding of mimosa leaves when touched, are not based on the direction of the stimulus. Plant hormones—auxins, gibberellins, cytokinins, and abscisic acid—control growth, flowering, ripening, and ageing. In animals, various endocrine glands release hormones into the blood to control metabolism, growth, and homeostasis; if a gland secretes too much or too little of its hormone, specific disorders appear.
Key terms
- Neuron
- The structural and functional unit of the nervous system. It has dendrites that receive impulses, a cell body, and a long axon that conducts impulses away from the cell body.
- Reflex arc
- The pathway taken by a nerve impulse during a reflex action: receptor to sensory neuron to spinal cord or brain, then motor neuron to effector. It allows very quick responses without conscious effort.
- Synapse
- The microscopic gap between the terminal of one neuron and the dendrite of the next neuron or an effector. Impulses cross this gap with the help of chemicals called neurotransmitters.
- Cerebrum
- The largest part of the human brain. It controls voluntary actions, thought, memory, speech and sensations. It is divided into two cerebral hemispheres.
- Hormone
- A chemical messenger secreted by an endocrine gland directly into the blood. Hormones travel to target organs and regulate their activities, including growth, metabolism and reproduction.
- Tropic movement
- The directional growth movement of a plant in response to an external stimulus such as light, gravity, water or touch. The direction of the stimulus determines the direction of the response.
- Nastic movement
- A plant movement that is independent of the direction of the stimulus. It is caused by changes in turgor pressure, bringing about actions such as the folding of mimosa leaves when touched.
- Auxin
- A plant hormone that promotes cell elongation. When light falls unevenly, auxin accumulates on the shaded side and makes that side grow faster, helping the plant bend toward light.
- Insulin
- A hormone produced by the beta cells of the pancreas. It lowers the level of glucose in blood. Deficiency of insulin causes diabetes mellitus, while excess leads to hypoglycemia.
Practice questions with answers
1. What are the three main parts of a neuron and what does each do?
The dendrites receive impulses from other neurons, the cell body contains the nucleus and keeps the neuron alive, and the axon transmits the impulse away to the next neuron, muscle or gland.
2. Describe the path of a reflex action when your finger touches a hot object.
Receptors in the skin send a signal through a sensory neuron to the spinal cord. A motor neuron in the spinal cord carries a response impulse to the muscles of the arm, causing the finger to withdraw. The spinal cord handles this impulse, so the withdrawal happens before the brain registers the pain.
3. How does auxin help a shoot bend towards light?
When light falls from one side, auxin moves to the shaded side of the shoot tip. The shaded side has more auxin and grows faster by cell elongation, so the shoot bends toward the light.
4. A person has high blood sugar, frequent urination and excessive thirst. Name the disease and the gland whose function is disturbed.
The disease is diabetes mellitus. It results from deficient secretion of insulin by the beta cells of the pancreas, as insulin is the hormone that reduces blood glucose by allowing cells to take it up.
5. What are the effects of oversecretion of growth hormone by the pituitary?
If oversecretion occurs before adolescence, the bones grow excessively long and the person becomes a giant — the condition called gigantism. Too little growth hormone in childhood has the opposite effect: growth is stunted and the person remains a dwarf. Both conditions trace back to the pituitary gland, which is why it is called the master gland.
6. Which part of the brain is concerned with balance and posture?
The cerebellum, located in the hindbrain, is responsible for maintaining balance, posture, and coordination of voluntary movements. It makes our body movements smooth and accurate.
7. What is a synapse and how does an impulse cross it?
A synapse is a tiny gap between the axon terminal of one neuron and the dendrite of another neuron (or between a neuron and an effector). When an impulse arrives at the synaptic knob, it triggers the release of chemical neurotransmitters that diffuse across the gap and start a fresh impulse in the next neuron.
8. Why is thyroxine necessary for the normal development of the body?
Thyroxine, made by the thyroid gland, regulates the rate at which the body uses carbohydrates, proteins and fats, and it is essential for normal growth. The thyroid needs iodine to make it, so a diet short of iodine leaves too little thyroxine and the gland swells — the condition called goitre. This is why common salt is iodised. A shortage in childhood also slows physical and mental development, and in adults it shows as tiredness, weight gain and sluggishness.
9. Define nastic movement and give an example.
Nastic movement is a plant response that does not depend on the direction of the stimulus. In the touch-me-not plant (Mimosa pudica), touching the leaves causes them to fold up. This is a nastic movement because the response is independent of where the touch comes from.
10. When sugar level in the blood rises above normal, what does the body do?
The pancreas secretes more insulin into the blood. Insulin then causes the liver and muscles to take up the extra glucose and store it as glycogen, returning the blood sugar level to normal. This is one form of a feedback mechanism in the body.
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