NCERT Solutions for Class 10 Science Chapter 6: Control and Coordination (NCERT 2026–27)

These Class 10 Science Chapter 6 solutions cover Control and Coordination with step-by-step answers to every in-text question and every end-of-chapter exercise. The chapter explains how the nervous system and hormones work together to control and coordinate activities in animals, and how plants respond to stimuli through movements and chemical signals — all matched exactly to the NCERT textbook for session 2026–27.

Class: 10 Subject: Science Chapter: 6 Title: Control and Coordination Branch: Biology Session: 2026–27
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Class 10 Science Chapter 6 Solutions – Overview

Chapter 6, Control and Coordination, studies the two systems that keep a multicellular body working as one unit. In animals these are the nervous system (fast, electrical messages along neurons) and the endocrine system (slower, chemical messages through hormones). The chapter explains how receptors in sense organs detect stimuli, how a nerve impulse travels along a neuron and crosses a synapse, and how reflex arcs in the spinal cord give very quick responses. It describes the three regions of the human brain — fore-brain, mid-brain and hind-brain — and their functions, and how the brain and spinal cord are protected. It then turns to plants, which respond without nerves or muscles, through immediate movements (the sensitive plant) and growth movements called tropisms (phototropism, geotropism, hydrotropism, chemotropism) coordinated by plant hormones such as auxin. Finally it covers animal hormones — adrenaline, thyroxin, growth hormone, insulin, testosterone, oestrogen — and the feedback mechanism that keeps their secretion precise.

Key Concepts & Definitions

Stimulus: any change in the environment to which an organism responds (heat, light, touch, smell).

Receptor: a specialised cell or nerve ending in a sense organ that detects a stimulus — e.g. gustatory receptors (taste), olfactory receptors (smell), photoreceptors (light).

Neuron: the structural and functional unit of the nervous system, specialised to conduct electrical impulses; its parts are the dendrites, cell body, axon and nerve endings.

Synapse: the tiny gap between the axon ending of one neuron and the dendrite of the next, where the electrical impulse is changed into a chemical signal.

Reflex arc: the short pathway receptor → sensory neuron → spinal cord → motor neuron → effector (muscle) that produces a quick, automatic reflex action.

Central nervous system (CNS): the brain and spinal cord, which receive and integrate information.

Tropism: a directional growth movement of a plant part in response to a stimulus — towards (positive) or away from (negative) it.

Hormone: a chemical messenger secreted in tiny amounts by an endocrine gland, carried in the blood (animals) or by diffusion (plants), that acts on a target organ.

Feedback mechanism: a self-regulating control in which the level of a substance (such as blood sugar) regulates the amount of hormone secreted.

Direction of a nerve impulse: Dendrite → Cell body → Axon → Axon ending → (synapse, chemical) → next dendrite / muscle / gland.

Reflex arc pathway: Receptor → Sensory (afferent) neuron → Spinal cord (relay) → Motor (efferent) neuron → Effector muscle.

Three regions of the brain: Fore-brain (thinking, sensation, hunger), Mid-brain + Hind-brain (involuntary actions); Hind-brain has the cerebellum (posture, balance, precision) and medulla (blood pressure, salivation, vomiting).

In-text Questions — Answers

These are the in-text “Questions” boxes from the NCERT chapter, reproduced verbatim and answered in order.

Page 102

1. What is the difference between a reflex action and walking?

ANSWER A reflex action is a sudden, automatic and involuntary response to a stimulus (e.g. pulling the hand back from a flame). It is controlled by a reflex arc in the spinal cord, is very fast, and does not need conscious thinking by the brain. Walking is a voluntary action that we decide to perform. It is controlled by the fore-brain (with the cerebellum maintaining balance and posture), involves conscious thought, and is comparatively slower and deliberate.

2. What happens at the synapse between two neurons?

ANSWER At the synapse, the electrical impulse arriving at the axon ending of one neuron triggers the release of chemical substances (neurotransmitters). These chemicals diffuse across the tiny gap (synapse) and start a fresh electrical impulse in the dendrite of the next neuron. Thus the synapse converts an electrical signal into a chemical signal and back, and ensures the impulse travels in one direction only.

3. Which part of the brain maintains posture and equilibrium of the body?

ANSWER The cerebellum, a part of the hind-brain, maintains posture and equilibrium (balance) of the body and ensures precision of voluntary actions such as walking in a straight line or riding a bicycle.

4. How do we detect the smell of an agarbatti (incense stick)?

ANSWER The smell is detected by olfactory receptors in the lining of the nose. These receptors pick up the chemical molecules of the smell and set off a nerve impulse. The impulse travels through nerves to the olfactory area of the fore-brain, where it is interpreted, so that we recognise the smell of the agarbatti.

5. What is the role of the brain in reflex action?

ANSWER Reflex actions are completed by the reflex arc in the spinal cord, so the response does not wait for the brain. However, the same sensory information also travels up to the brain, which becomes aware of the action afterwards. So the brain does not control the reflex itself but receives the information and registers what has happened.

Page 108

1. What are plant hormones?

ANSWER Plant hormones (phytohormones) are chemical compounds that help to coordinate growth, development and responses to the environment in plants. They are synthesised at a place away from where they act and simply diffuse to the area of action. Examples are auxin, gibberellins, cytokinins and abscisic acid.

2. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?

ANSWER The folding of leaves of the sensitive plant (touch-me-not) is a quick movement in response to touch; it does not involve growth and is not directional — the movement happens at a point different from the point of touch, caused by cells changing shape through change in water content. The bending of a shoot towards light is a slow, growth-dependent and directional (tropic) movement caused by the hormone auxin. It is permanent, while the leaf movement of the sensitive plant is temporary.

3. Give an example of a plant hormone that promotes growth.

ANSWER Auxin is a plant hormone that promotes growth (by helping cells to grow longer). Gibberellins and cytokinins are other growth-promoting hormones.

4. How do auxins promote the growth of a tendril around a support?

ANSWER When a tendril touches a support, the side of the tendril in contact with the support gets less auxin, so its cells grow slowly, while the side away from the support has more auxin, so its cells grow faster and longer. This unequal growth makes the tendril curve and coil around the support, clinging to it.

5. Design an experiment to demonstrate hydrotropism.

ANSWER Take a wide trough filled with soil and sow some seeds near one edge. Bury a small porous clay pot (or a beaker) of water inside the soil at a distance from the seeds, on the opposite side, and keep the rest of the soil relatively dry. Water only through the buried pot so that moisture spreads on one side. After a few days, carefully dig out the seedlings and observe the roots. The roots will be found bending and growing towards the moist region (the water pot) rather than growing straight down. This bending of roots towards water demonstrates positive hydrotropism.

Page 111

1. How does chemical coordination take place in animals?

ANSWER Chemical coordination in animals takes place through hormones secreted by the endocrine glands. These hormones are released directly into the blood and carried to all parts of the body. They act on specific target organs/tissues and bring about the required response. The timing and amount of each hormone are regulated by feedback mechanisms, so coordination is achieved without nerves.

2. Why is the use of iodised salt advisable?

ANSWER Iodine is essential for the thyroid gland to synthesise the hormone thyroxin, which regulates carbohydrate, protein and fat metabolism for proper growth. If iodine is deficient in the diet, thyroxin cannot be made in sufficient amount, and the person may suffer from goitre (a swollen neck). Iodised salt supplies the needed iodine and prevents this deficiency.

3. How does our body respond when adrenaline is secreted into the blood?

ANSWER Adrenaline is secreted by the adrenal glands directly into the blood and reaches many target organs. The heart beats faster, supplying more oxygen to the muscles. Blood to the digestive system and skin is reduced (by contraction of small arteries there) and is diverted to the skeletal muscles. The breathing rate increases due to contraction of the diaphragm and rib muscles. Together these prepare the body to deal with a stressful situation (“fight or flight”).

4. Why are some patients of diabetes treated by giving injections of insulin?

ANSWER Insulin is a hormone produced by the pancreas that regulates blood sugar level. In some diabetic patients the pancreas does not secrete insulin in proper amounts, so blood sugar rises and causes harmful effects. Such patients are given insulin injections to control and lower their blood sugar level to a normal range.

Exercises — Full Solutions

All questions are reproduced verbatim from the NCERT “Exercises”, in order, and solved fully.

1. Which of the following is a plant hormone? (a) Insulin (b) Thyroxin (c) Oestrogen (d) Cytokinin.

ANSWER (d) Cytokinin. Cytokinin is a plant hormone that promotes cell division. Insulin, thyroxin and oestrogen are all animal hormones.

2. The gap between two neurons is called a (a) dendrite. (b) synapse. (c) axon. (d) impulse.

ANSWER (b) synapse. The synapse is the small gap between the axon ending of one neuron and the dendrite of the next, where the impulse is transferred as a chemical signal.

3. The brain is responsible for (a) thinking. (b) regulating the heart beat. (c) balancing the body. (d) all of the above.

ANSWER (d) all of the above. The fore-brain is responsible for thinking, the medulla (hind-brain) regulates heart beat and other involuntary actions, and the cerebellum (hind-brain) maintains balance — so the brain does all three.

4. What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?

ANSWER Function of receptors: Receptors are specialised cells or nerve endings, usually located in the sense organs, that detect stimuli (information) from the environment such as taste, smell, light, sound, touch, heat and pain. On detecting a stimulus they set off a nerve impulse that is carried to the central nervous system for an appropriate response. If receptors do not work properly: the body cannot detect changes in the environment correctly. For example, if the gustatory receptors of the tongue or olfactory receptors of the nose are damaged, a person cannot taste or smell food properly. If pain or heat receptors of the skin fail, a person may touch a very hot or sharp object without realising it and get seriously injured or burnt. Thus, faulty receptors delay or prevent the proper response and can endanger the body.

5. Draw the structure of a neuron and explain its function.

ANSWER Structure (described in words, as the figure cannot be drawn here): A neuron has three main parts — (i) a cell body (cyton) containing the nucleus and cytoplasm, with many fine branching dendrites arising from it; (ii) a long fibre called the axon extending from the cell body; and (iii) nerve endings at the tip of the axon. The dendrites receive information; the axon carries the impulse away from the cell body. Function: Information is acquired at the tip of a dendrite, where it sets off a chemical reaction that creates an electrical impulse. This impulse travels from the dendrite to the cell body and then along the axon to its end. At the axon ending the impulse causes the release of chemicals that cross the synapse and start a similar impulse in the next neuron, muscle or gland. Thus the neuron conducts information rapidly from one part of the body to another.

6. How does phototropism occur in plants?

ANSWER Phototropism is the directional growth movement of a plant part in response to light. It is brought about by the plant hormone auxin, which is synthesised at the shoot tip. When light falls on one side of the shoot, auxin diffuses towards the shady side (away from light). The higher concentration of auxin on the shady side makes the cells there grow longer, while the cells on the lit side grow less. As a result the shoot bends towards the light (positive phototropism), whereas roots bend away from light (negative phototropism).

7. Which signals will get disrupted in case of a spinal cord injury?

ANSWER The spinal cord carries nerves that connect the body to the brain and also forms reflex arcs. In a spinal cord injury, the signals that get disrupted are: (i) the reflex actions whose reflex arcs pass through the injured region, and (ii) the communication between the brain and the body — both the sensory (information going up to the brain) and the motor (instructions coming down to the muscles) signals. So coordination between the affected parts of the body and the brain is lost.

8. How does chemical coordination occur in plants?

ANSWER Plants have neither a nervous system nor muscles, so coordination is carried out only by chemicals called plant hormones. These hormones are synthesised at one place (for example, auxin at the shoot tip) and simply diffuse to the region where they act. Different hormones perform different roles: auxin promotes cell elongation and controls tropic movements, gibberellins help in the growth of the stem, cytokinins promote cell division (more in fruits and seeds), and abscisic acid inhibits growth and causes wilting of leaves. By varying their concentration, these hormones coordinate the growth, development and responses of the plant to the environment.

9. What is the need for a system of control and coordination in an organism?

ANSWER A multicellular organism is made up of many different organs and tissues that must work together as a single, well-functioning body. A system of control and coordination is needed so that the organism can: (i) detect changes (stimuli) in its environment and respond appropriately to use them to its advantage or to protect itself; (ii) keep the activities of all body parts integrated and in harmony; and (iii) maintain a stable internal environment (e.g. control blood sugar, blood pressure) through nervous and hormonal regulation. Without it, the body parts would act independently and survival would be impossible.

10. How are involuntary actions and reflex actions different from each other?

ANSWER
Reflex actionInvoluntary action
A sudden, quick response to a stimulus (e.g. withdrawing the hand from a flame).An ongoing internal action over which we have no thinking control (e.g. heartbeat, breathing, digestion).
Controlled mainly by the spinal cord through a reflex arc.Controlled mainly by the mid-brain and hind-brain (medulla).
Usually triggered by an external stimulus.Goes on continuously without any external stimulus.
It is a momentary, one-time response.It is a continuous process essential for life.

11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.

ANSWER
Nervous mechanismHormonal (chemical) mechanism
Information is carried as electrical impulses along neurons.Information is carried by chemical hormones through the blood.
Response is very fast.Response is comparatively slow.
Reaches only the cells connected by nerves.Can reach all cells of the body, regardless of nerve connections.
Effect is usually short-lived.Effect usually lasts longer.
A cell needs time to reset before sending a new impulse.Can act steadily and persistently.
Similarity: both systems serve to control and coordinate body activities so the organism can respond suitably to its environment, and the two often work together.

12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?

ANSWER
Movement in a sensitive plantMovement in our legs
Happens in response to a stimulus (touch) but is not under the plant’s control.A voluntary action under our conscious control.
No nervous or muscle tissue; cells change shape by changing their water content (swelling/shrinking).Brought about by muscle cells that change shape using special proteins, on receiving a nerve impulse.
Information passes by electrical-chemical means but through no specialised conducting tissue.Information passes as electrical impulses through specialised nervous tissue (nerves).
Movement occurs at a point different from the point of stimulus.Movement occurs in the muscle that receives the motor signal.

Extra Practice Questions

Short Answer Type Questions

Q1. Name the parts of the central nervous system.

ANSWERThe central nervous system consists of the brain and the spinal cord.

Q2. Why is the brain protected inside a bony box and a fluid-filled balloon?

ANSWERThe brain is a very delicate and vital organ. The bony box (skull) protects it from external injury, and the fluid (cerebrospinal fluid) around it acts as a cushion that absorbs shocks and protects the brain from jerks.

Q3. What is geotropism? Give an example.

ANSWERGeotropism is the directional growth of a plant part in response to gravity. Roots grow downwards (positive geotropism) and shoots grow upwards (negative geotropism).

Q4. Which gland secretes growth hormone, and what happens if it is deficient in childhood?

ANSWERThe pituitary gland secretes growth hormone, which regulates growth and development. Its deficiency in childhood leads to dwarfism (very short stature).

Q5. How is the secretion of insulin regulated by feedback?

ANSWERWhen the blood sugar level rises, it is detected by the cells of the pancreas, which respond by producing more insulin. As the blood sugar level falls back to normal, insulin secretion is automatically reduced. This self-regulation is the feedback mechanism.

Long Answer Type Questions

Q1. With the help of the reflex arc, explain how a reflex action takes place when you touch a hot object.

ANSWERWhen the hand touches a hot object, the heat receptors in the skin detect the stimulus and set off a nerve impulse. The impulse travels along a sensory (afferent) neuron to the spinal cord. There, instead of going all the way to the brain first, the impulse is passed directly to a motor (efferent) neuron through a relay neuron. The motor neuron carries the impulse to the effector muscle of the arm, which contracts and quickly pulls the hand away. This whole pathway — receptor → sensory neuron → spinal cord → motor neuron → muscle — is the reflex arc. Because the response is generated in the spinal cord without waiting for the brain to think, it is extremely fast and protects the body from harm. The information also reaches the brain afterwards, so we become aware of the action.

Q2. Describe the structure of the human brain and the functions of its main parts.

ANSWERThe human brain has three major regions — the fore-brain, mid-brain and hind-brain. The fore-brain is the main thinking part; it has sensory areas that receive impulses for hearing, smell, sight, etc., association areas where information is interpreted, motor areas that control voluntary muscles, and a centre that controls the sensation of hunger (feeling full). The mid-brain and hind-brain control many involuntary actions. In the hind-brain, the medulla controls involuntary actions such as blood pressure, salivation and vomiting, while the cerebellum is responsible for precision of voluntary movements and for maintaining posture and balance of the body. The brain is connected to the rest of the body by the peripheral nervous system (cranial and spinal nerves) and is protected by the skull and cerebrospinal fluid.

Q3. Explain how plants coordinate their responses without a nervous system, with examples of different tropic movements.

ANSWERPlants have no nervous system or muscles, so they coordinate responses through electrical-chemical signals and mainly through plant hormones that diffuse from their site of synthesis to the site of action. Plants show two kinds of movement. The first is an immediate movement independent of growth, such as the quick folding of the leaves of the sensitive plant on touch, caused by cells changing shape through change in water content. The second is growth-dependent directional movement called tropism, controlled by hormones like auxin. Examples are phototropism (shoots bend towards light, roots away from it), geotropism (roots grow down towards gravity, shoots grow up), hydrotropism (roots grow towards water) and chemotropism (growth in response to a chemical, e.g. pollen tube growing towards the ovule). In this way plants sense their environment and respond suitably even without nerves.

MCQs & Assertion–Reason

1. The structural and functional unit of the nervous system is the:

(a) nephron    (b) neuron    (c) axon    (d) synapse

2. Information is acquired in a neuron at the:

(a) axon    (b) cell body    (c) dendrite    (d) synapse

3. Reflex arcs are formed in the:

(a) fore-brain    (b) cerebellum    (c) spinal cord    (d) medulla

4. The part of the brain that controls blood pressure, salivation and vomiting is the:

(a) cerebellum    (b) medulla    (c) fore-brain    (d) mid-brain

5. The bending of a shoot towards light is due to the hormone:

(a) cytokinin    (b) abscisic acid    (c) auxin    (d) insulin

6. Growth of roots towards water is called:

(a) phototropism    (b) geotropism    (c) hydrotropism    (d) chemotropism

7. The hormone secreted during a frightening or stressful situation is:

(a) thyroxin    (b) adrenaline    (c) insulin    (d) oestrogen

8. Deficiency of iodine in the diet may cause:

(a) diabetes    (b) dwarfism    (c) goitre    (d) gigantism

9. The plant hormone that inhibits growth and causes wilting of leaves is:

(a) auxin    (b) gibberellin    (c) cytokinin    (d) abscisic acid

10. Blood sugar level in the body is regulated by:

(a) thyroxin    (b) insulin    (c) adrenaline    (d) growth hormone

Answer key: 1-(b), 2-(c), 3-(c), 4-(b), 5-(c), 6-(c), 7-(b), 8-(c), 9-(d), 10-(b).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: A reflex action is faster than a voluntary action.

Reason: A reflex action is completed by a reflex arc in the spinal cord without waiting for the brain to think.

A-R 2. Assertion: Roots of a plant show positive geotropism.

Reason: Roots grow downwards in response to the pull of gravity.

A-R 3. Assertion: Hormonal coordination is faster than nervous coordination.

Reason: Hormones are carried by the blood to all parts of the body.

A-R 4. Assertion: Iodised salt should be used in the diet.

Reason: Iodine is necessary for the thyroid gland to make thyroxin.

A-R 5. Assertion: The cerebellum maintains posture and balance of the body.

Reason: The cerebellum is the main thinking part of the brain.

Answer key: 1-(A), 2-(A), 3-(D), 4-(A), 5-(C).

Common Mistakes to Avoid

Watch out for these

  • Saying reflex actions are controlled by the brain — they are controlled by the spinal cord (the brain only becomes aware afterwards).
  • Confusing involuntary actions (heartbeat, breathing — mid/hind-brain) with reflex actions (sudden response — spinal cord).
  • Writing that nerve impulses jump across the synapse as electrical signals — they cross as chemical signals.
  • Mixing up the cerebellum (balance, posture) with the medulla (blood pressure, vomiting, salivation).
  • Calling the movement of the sensitive plant a growth movement — it is due to a change in water content of cells, not growth.
  • Stating that auxin accumulates on the lit side of a shoot — it diffuses to the shady side.
  • Mislabelling animal hormones as plant hormones (insulin, thyroxin, oestrogen are animal hormones).

Exam Tips

How to score full marks in this chapter

Learn the reflex arc sequence (receptor → sensory neuron → spinal cord → motor neuron → effector) and the direction of a nerve impulse (dendrite → cell body → axon → synapse) — these are frequent diagram and one-mark questions. For the brain, remember the function of each part: fore-brain = thinking and sensation, cerebellum = balance and posture, medulla = involuntary actions. Make a quick table of hormone – gland – function (growth hormone/pituitary, thyroxin/thyroid, insulin/pancreas, adrenaline/adrenal, testosterone/testes, oestrogen/ovaries) and memorise the four tropisms. When a question asks to “draw and explain”, label the parts and explain function in points. State definitions precisely — many marks come from correct keywords like synapse, reflex arc, tropism and feedback mechanism.

Frequently Asked Questions

What is Class 10 Science Chapter 6 Control and Coordination about?

Chapter 6 explains how living organisms control and coordinate their activities. In animals this is done by the nervous system (fast electrical impulses through neurons and reflex arcs) and the endocrine system (hormones), while plants respond through immediate movements and growth movements called tropisms, coordinated by plant hormones such as auxin.

What is a reflex arc?

A reflex arc is the pathway followed by a nerve impulse during a reflex action: receptor → sensory neuron → spinal cord → motor neuron → effector muscle. Because it works through the spinal cord without waiting for the brain, it produces a very quick, automatic response.

What is the difference between phototropism and geotropism?

Phototropism is the growth movement of a plant part in response to light (shoots bend towards light, roots away from it), while geotropism is the growth movement in response to gravity (roots grow downwards, shoots grow upwards). Both are directional growth movements controlled by hormones like auxin.

Are these Class 10 Science Chapter 6 solutions free?

Yes. All ClearStudy NCERT Solutions for Class 10 Science are free and follow the official NCERT textbook for session 2026-27, with every in-text question and exercise solved step by step.

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