Answers to all in-text and exercise questions of Chapter 6, Control and Coordination (NCERT Class 10 Science, 2026-27 reprint): reflex actions and the synapse, parts of the brain, the structure of a neuron, plant hormones and tropisms, hydrotropism experiment, endocrine glands, iodised salt, adrenaline and insulin. All 26 questions are answered, with the key answer highlighted.
Free NCERT solutions by Notes Bazar · www.notesbazar.in/ncert-solutions/class-10-science/chapter-6-control-and-coordination
Animals coordinate through the nervous system (fast electrical impulses carried by neurons, with chemical signals across the synapse) and hormones (chemicals made by endocrine glands and carried by blood). Plants have no nervous system: they respond through plant hormones such as auxins, gibberellins, cytokinins and abscisic acid, and through changes in water content of cells.
The synapse is the tiny gap between the nerve ending of one neuron and the dendrite of the next. When the electrical impulse reaches the end of the axon, it releases a few chemicals (neurotransmitters). These cross the gap and start a new electrical impulse in the dendrite of the next neuron. This way the message passes in one direction only.
The electrical impulse releases chemicals that cross the gap and start a similar impulse in the next neuron.
How do we detect the smell of an agarbatti (incense stick)?
Solution
Molecules of the smoke and scent spread through the air and enter our nose. The olfactory receptors in the nose detect them and send nerve impulses to the forebrain, where the information is interpreted, and we recognise the smell.
Olfactory receptors in the nose detect the scent molecules and send impulses to the forebrain, which identifies the smell.
A reflex action is controlled by the spinal cord, so the brain is not needed for the response itself. But the information also travels up to the brain, so we become aware of what happened (e.g. that the object was hot). The brain can learn from it and, in some cases, override or modify the reflex.
The response is made by the spinal cord; the brain receives the information so we become aware of it.
Plant hormones (phytohormones) are chemical substances made by plants that coordinate growth, development and responses to the environment. They are made in one part and act in another. Examples: auxins (growth of stem tips, bending towards light), gibberellins (stem growth), cytokinins (cell division), and abscisic acid (inhibits growth, causes wilting of leaves).
Chemicals made in plants that control and coordinate their growth and responses, e.g. auxins and gibberellins.
How is the movement of the leaves of the sensitive plant different from the movement of a shoot towards light?
Solution
Leaves of the sensitive plant (touch-me-not)
Shoot bending towards light
Not related to growth
Growth movement (phototropism)
Very quick
Slow
Caused by cells quickly changing shape as water moves out of them
Caused by auxin, which makes cells on the shaded side grow faster
Not directional: the leaves fold whichever side is touched
Directional: depends on the direction of light
The sensitive plant's folding is a fast, non-growth movement due to loss of water from cells; bending towards light is a slow, directional growth movement due to auxin.
How do auxins promote the growth of a tendril around a support?
Solution
When a tendril touches a support, auxin moves to the side away from the support. The cells on that side grow faster than those in contact with the support. So the tendril bends towards and coils around the support.
Auxin collects on the side away from the support, which grows faster, so the tendril curls around the support.
Fill a wide glass trough or box with moist soil. Put a porous clay pot filled with water in one corner, so that the soil around it becomes wet while the rest stays fairly dry.
Sow a few germinating seeds (such as gram or pea) in the soil some distance from the pot.
Do not water the soil directly for a few days.
Carefully remove the soil and observe the roots. They will have bent and grown towards the porous pot, i.e. towards water.
(Hydrotropism means growth in response to water; roots show positive hydrotropism.)
Seedlings grown in soil kept moist only near a porous pot of water send their roots towards the pot.
How does chemical coordination take place in animals?
Solution
It takes place through hormones. Endocrine glands (such as the pituitary, thyroid, pancreas and adrenals) release hormones directly into the blood. The blood carries them all over the body, and each hormone acts only on specific target cells or organs that have the right receptors. The timing and amount of release are controlled by feedback mechanisms.
Endocrine glands secrete hormones into the blood, which carries them to target organs where they act.
The thyroid gland needs iodine to make the hormone thyroxin, which regulates carbohydrate, protein and fat metabolism. Too little iodine in the diet causes goitre (a swollen neck). Iodised salt is an easy way to get enough iodine.
Iodine is needed to make thyroxin; lack of it causes goitre.
Why are some patients of diabetes treated by giving injections of insulin?
Solution
Insulin, made by the pancreas, regulates the level of sugar in the blood. In some diabetic patients the pancreas does not make enough insulin, so the blood sugar level rises and harms the body. Insulin injections supply the missing hormone and bring the blood sugar level down.
Because their pancreas does not make enough insulin, which is needed to control the blood sugar level.
What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Solution
Receptors are specialised cells, usually in the sense organs, that detect stimuli from the environment (light, sound, smell, taste, touch, heat) and start nerve impulses that carry the information to the brain or spinal cord.
If receptors do not work properly, the body cannot detect the stimulus or respond to it. For example:
damaged skin receptors: we may not feel a hot object and get burnt;
damaged olfactory receptors (as in a cold): we cannot smell food or a gas leak;
damaged receptors in the eye or ear: problems with seeing or hearing, and danger cannot be noticed in time.
Receptors detect stimuli and send messages to the nervous system; if they fail, we cannot respond to dangers or changes in time.
Draw the structure of a neuron and explain its function.
SolutionStructure of a neuron (nerve cell)
Dendrites receive the stimulus (information) and start a chemical reaction that creates an electrical impulse.
The impulse travels through the cell body, which contains the nucleus, to the axon.
The axon carries the impulse to its end, the nerve ending, where chemicals are released into the synapse to pass the message to the next neuron or to a muscle or gland.
The neuron is the unit of the nervous system: dendrites pick up messages, which travel as electrical impulses through the cell body and axon to the nerve endings.
Phototropism is the bending of a plant part in response to light. When light falls on a shoot from one side, auxin made at the shoot tip moves to the shaded side. The cells on the shaded side grow longer than those on the lighted side, so the shoot bends towards the light. (Roots bend away from light.)
Auxin moves to the shaded side of the shoot, making its cells grow faster, so the shoot bends towards light.
Plants coordinate through plant hormones. They are made in one part (often a growing tip) and spread by diffusion to other parts, where they control growth and responses:
Auxins make cells grow longer and cause bending towards light;
Gibberellins help the stem grow;
Cytokinins promote cell division, mostly in fruits and seeds;
Abscisic acid inhibits growth and causes wilting of leaves.
Through plant hormones such as auxins, gibberellins, cytokinins and abscisic acid, which diffuse to their target cells.
What is the need for a system of control and coordination in an organism?
Solution
An organism is made of many organs that must work together in a proper sequence. It must also respond quickly to changes in its surroundings, such as danger or food. Control and coordination make sure that all body activities happen at the right time and to the right extent, that the internal conditions stay balanced, and that the organism can survive.
To make all organs work together smoothly and to respond correctly to changes around it.
How are involuntary actions and reflex actions different from each other?
Solution
Involuntary actions
Reflex actions
Actions of internal organs that go on continuously without our will, e.g. heart beat, breathing, peristalsis
Sudden, automatic responses to a stimulus, e.g. knee jerk, withdrawing the hand from a hot object
Controlled mainly by the medulla and midbrain (and the autonomic nervous system)
Controlled mainly by the spinal cord
Usually slow and continuous
Very quick, happen once in response to a stimulus
Involuntary actions are continuous activities of internal organs controlled by the brain; reflexes are quick responses to a stimulus controlled by the spinal cord.
Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Solution
Nervous mechanism
Hormonal mechanism
Messages are electrical impulses (with chemicals at synapses)
Messages are chemicals (hormones)
Carried by nerve fibres (neurons)
Carried by blood
Very fast
Slower
Effect is short-lived
Effect usually lasts longer
Reaches specific organs that are wired to the nerves
Reaches every cell, but acts only on target organs
Similarity: both carry information and coordinate the body's activities and responses.
Both coordinate the body; nervous control is fast and electrical through nerves, hormonal control is slower, chemical and longer lasting, through blood.
What is the difference between the way movement takes place in a sensitive plant and the movement of our legs?
Solution
Sensitive plant: when touched, the cells at the leaf base quickly lose water and change shape, so the leaves fold. There are no nerves or muscles; the message spreads from cell to cell by electrochemical means.
Our legs: the movement is voluntary. The brain sends nerve impulses to the leg muscles, whose cells contain special proteins that change shape and arrangement, making the muscle contract and move the bones.
The plant's leaves fold because cells lose water (no nerves or muscles); our legs move because nerves make muscles contract.
