Control and Coordination Class 10: Notes and Board Questions

What Control and Coordination is about

Weightage: This chapter is part of Unit II, World of Living, which carries 25 of the 80 theory marks together with Life Processes, How do Organisms Reproduce? and Heredity.Source: CBSE Science syllabus 2026-27, Unit II World of Living

In real board papers: asked in 21 of the 21 board papers we hold (2023 to 2026), on average 5.7 marks per paper. See the questions

Key concepts

Receptors, neurons and the synapse

NCERT section 6.1 Animals – Nervous System

Every response begins with detecting a change. The specialised tips of some nerve cells do this job, and they are called receptors. Most of them sit in sense organs such as the inner ear, nose and tongue. Gustatory receptors detect taste and olfactory receptors detect smell.

A neuron carries the message in a fixed order. The information is picked up at the dendritic tip. There it sets off a chemical reaction that produces an electrical impulse. The signal moves through the dendrite and the cell body, then runs down the axon.

When the signal reaches the axon's tip, it triggers the release of a chemical messenger. This chemical crosses a tiny gap called the synapse. On the other side, it starts a fresh electrical impulse in a dendrite of the next neuron. A similar junction passes the message from a neuron to a muscle cell or a gland.

Remember this pattern: the signal is electrical inside a neuron and chemical across the synapse. Nervous tissue is an organised network of neurons, specialised for carrying information quickly from one part of the body to another.

Worked example

(3 marks) In a neuron, name the part where:
(i) information is acquired,
(ii) information travels as an electrical impulse,
(iii) the impulse is converted into a chemical signal.
Also explain what happens at the synapse between two neurons.

Try it first, then show the solutionSolution

1. (i) Dendrite (the dendritic tip) acquires the information. (½ mark)
2. (ii) The impulse travels from the dendrite through the cell body and along the axon. (½ mark)
3. (iii) At the end of the axon, the electrical impulse causes chemicals to be released. (½ mark)
4. At the synapse, these chemicals cross the gap between the two neurons. (1 mark)
5. They start a similar electrical impulse in a dendrite of the next neuron, so the message moves on. (½ mark)

Answer: Dendrite; axon (via the cell body); end of the axon. At the synapse, chemicals released from the axon end cross the gap and start a new electrical impulse in the next neuron's dendrite.

Reflex action and the reflex arc

NCERT section 6.1.1 What happens in Reflex Actions?

A reflex action is a sudden response to a change in the environment, made without thinking about it. Pulling your hand back from a flame is a reflex.

Why do we need reflexes? Thinking is a complex job. It needs many impulses from many neurons in the thinking part of the brain. If the signal from a hot object had to travel up to the brain, be thought about, and then travel back to the arm muscles, you could be burnt before you moved.

The body solves this with a short cut. The nerves that detect heat (input) are linked to the nerves that move muscles (output) by a much simpler connection, called a reflex arc. It is formed in the spinal cord, because this is the first place where the incoming (sensory) and outgoing (motor) nerves lie close together.

The information still goes on to the brain, so you become aware of the event afterwards. Reflex arcs evolved because the brain's thinking process is not fast enough. Many animals have very little thinking network at all. Even in animals with a complex brain, reflex arcs remain the more efficient way to make quick responses.

Worked example

(1 mark)
Assertion (A): When you touch a very hot object, you pull your hand away before you have thought about the pain.
Reason (R): In a reflex arc, the nerves that detect heat are connected to the nerves that move muscles in the spinal cord.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

Try it first, then show the solutionSolution

1. A is true: withdrawing the hand is a reflex action, done without thinking.
2. R is true: reflex arcs are formed in the spinal cord, where input and output nerves first meet.
3. R explains A: because the connection skips the slow thinking process of the brain, the hand moves before you think. (1 mark)

Answer: (a) Both A and R are true and R is the correct explanation of A.

Human brain and its protection

NCERT section 6.1.2 Human Brain; 6.1.3 How are these Tissues protected?

The brain and spinal cord together form the central nervous system (CNS). They receive information from all parts of the body and integrate it. The peripheral nervous system is the set of nerves that leave the brain (cranial nerves) and the spinal cord (spinal nerves) and reach the rest of the body, linking it with the CNS.

The brain has three regions.

• Fore-brain: the main thinking part. It has areas that receive sensory impulses for hearing, smell, sight and so on. Association areas interpret this by combining it with other inputs and stored information. A decision then goes to the motor areas, which control voluntary muscles. A separate centre in the fore-brain is linked to hunger and tells you when you are full.
• 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. The cerebellum gives precision to voluntary actions and maintains posture and balance.

This delicate organ is well protected. The brain sits inside a bony box, cushioned in a fluid-filled balloon that absorbs shocks. The spinal cord is protected by the vertebral column, or backbone.

Worked example

(3 marks) After an accident, a patient shows two problems.
(i) He cannot walk in a straight line or pick up a pencil precisely.
(ii) He has trouble with control of his blood pressure and salivation.
Name the part of the brain affected in each case, with the region it belongs to. Which part of the brain would he still need in order to decide to get up from his chair?

Try it first, then show the solutionSolution

1. (i) Cerebellum, a part of the hind-brain. It is responsible for precision of voluntary actions, posture and balance. (1 mark)
2. (ii) Medulla, a part of the hind-brain. It controls involuntary actions such as blood pressure and salivation. (1 mark)
3. Deciding to get up is a voluntary action. The decision is made in the fore-brain and sent to its motor areas, which control the voluntary muscles. (1 mark)

Answer: (i) Cerebellum (hind-brain); (ii) medulla (hind-brain); the decision needs the fore-brain, the main thinking part, acting through its motor areas.

Voluntary, involuntary and reflex actions

NCERT section 6.1.2 Human Brain

The responses of the nervous system fall into three groups. Learn them as a set, with the controlling part and the reason.

• Voluntary actions are based on deciding what to do next. Writing, talking, moving a chair and clapping at the end of a programme are examples. The fore-brain decides and sends messages through its motor areas to the muscles. The cerebellum makes these actions precise.
• Involuntary actions happen without our thinking control. You cannot easily control them even if you try. Examples are the heartbeat, breathing, digestion, blood pressure, salivation and vomiting. Many are controlled by the mid-brain and hind-brain, and the medulla controls blood pressure, salivation and vomiting.
• Reflex actions are sudden, quick responses to a particular stimulus, such as pulling back from a flame or a change in the size of the pupil. They work through a reflex arc and are often protective.

Why does the difference matter? A voluntary action needs thinking, so it is slower but flexible. Involuntary actions keep the body running without attention. Reflexes trade thinking for speed when there is danger.

Worked example

(3 marks) Classify each action as voluntary, involuntary or reflex. Give one reason or the controlling part for each.
(i) Your heart beating while you sleep
(ii) Writing an answer in the exam
(iii) Your pupil becoming smaller when a bright torch shines in your eye

Try it first, then show the solutionSolution

1. (i) Involuntary action. (½ mark)
2. It happens without thinking control; many such actions are controlled by the mid-brain and hind-brain. (½ mark)
3. (ii) Voluntary action. (½ mark)
4. It is decided by the fore-brain, which sends messages to muscles; the cerebellum gives it precision. (½ mark)
5. (iii) Reflex action. (½ mark)
6. It is a sudden, automatic response to bright light through a reflex arc, without thinking. (½ mark)

Answer: (i) Involuntary – controlled by the mid-brain and hind-brain; (ii) voluntary – fore-brain, with cerebellum for precision; (iii) reflex – quick automatic response through a reflex arc.

How muscles cause movement

NCERT section 6.1.4 How does the Nervous Tissue cause Action?

The nervous tissue collects information, sends it around, processes it and makes decisions. But the final job, the actual movement, is done by muscle tissue.

A nerve impulse reaches a muscle through a junction similar to a synapse. The simplest idea of movement at the cell level is that muscle cells change their shape so that they become shorter.

How do they change shape? Muscle cells contain special proteins. When nervous electrical impulses arrive, these proteins change both their shape and their arrangement inside the cell. The new arrangement gives the muscle cell a shorter form, and this shortening pulls on the body part and moves it.

You met voluntary and involuntary muscles in Class IX. Voluntary muscles, such as leg muscles, receive messages from the motor areas of the fore-brain. Involuntary actions such as the heartbeat go on without our thinking control.

Compare this with plants. Plant cells also change shape to move, but they have no such special proteins. They change the amount of water inside them instead. Keep this contrast in mind for comparison answers.

Worked example

(3 marks) Explain how muscle cells move when they receive a message from the brain. How is this different from the way the leaves of a sensitive plant move?

Try it first, then show the solutionSolution

1. The brain's message travels as an electrical impulse along a nerve and is passed to the muscle cell at a junction similar to a synapse. (1 mark)
2. Special proteins in the muscle cell change their shape and their arrangement in response to the impulse. (1 mark)
3. The new arrangement makes the muscle cell shorter, which produces movement. (½ mark)
4. In the sensitive plant there are no such proteins; plant cells change shape by changing the amount of water in them, swelling or shrinking. (½ mark)

Answer: Muscle cells shorten because special proteins change shape and arrangement in response to nerve impulses; plant cells change shape by gaining or losing water.

Immediate response to stimulus in plants

NCERT section 6.2.1 Immediate Response to Stimulus

Plants have neither a nervous system nor muscles, yet they respond to stimuli. They show two kinds of movement: one that does not depend on growth and one that does.

Take the sensitive plant (chhui-mui, or touch-me-not, of the Mimosa family). When you touch its leaves, they fold up and droop very quickly. No growth is involved, so the plant must actually move its leaves.

Notice that the leaves move at a point different from where they were touched. So the information that a touch has happened must be communicated from cell to cell. Plants do this by electrical-chemical means, but unlike animals they have no specialised tissue for conducting information.

For movement, some cells must change shape. Plant cells do this by changing the amount of water in them. Gaining water makes them swell and losing water makes them shrink. This change in shape folds the leaves.

The key contrasts for the exam: this movement is fast, does not involve growth, and is not directed towards or away from the stimulus. Tropic movements, which you meet next, are slow and caused by growth.

Worked example

(3 marks) Give three differences between the folding of the leaves of a touch-me-not plant and the bending of a shoot towards light.

Try it first, then show the solutionSolution

1. Growth: leaf folding involves no growth; bending towards light is caused by growth and stops if growth is prevented. (1 mark)
2. Speed: leaf folding is very quick; bending towards light is slow, over days. (1 mark)
3. Mechanism: in the touch-me-not, cells change shape by changing their water content; in the shoot, auxin makes cells on the shady side grow longer. (1 mark)
4. (Also accepted: the stimulus is touch in one case and light in the other; the shoot's growth is in a direction related to the stimulus.)

Answer: Any three: no growth versus growth-dependent; quick versus slow; water-content change versus auxin-driven unequal growth; touch versus light as stimulus.

Tropic movements in plants

NCERT section 6.2.2 Movement Due to Growth

Most plant responses are slow. The plant grows in a particular direction, and because the growth is directional, it looks as if the plant is moving. These directional growth movements are called tropic movements. They can be towards the stimulus or away from it.

• Phototropism (light): shoots bend towards light, roots bend away from it. This lets the shoot grow out into the sunshine.
• Geotropism (gravity): roots grow downwards and shoots usually grow upwards, away from the earth.
• Hydrotropism (water): growth of a plant part in response to water.
• Chemotropism (chemicals): for example, a pollen tube grows towards the ovule.

Note that the same stimulus can produce opposite responses in the root and the shoot.

Tendrils are a related growth movement. In a pea plant, tendrils are sensitive to touch. The part of the tendril touching a support grows more slowly than the part away from it. The faster-growing outer side makes the tendril coil round the support and cling to it.

In Activity 6.2, germinating bean seeds on a wire mesh over a flask of water, kept in a box open to light on one side, show shoots bending towards light and roots away from it.

Worked example

(3 marks) In Activity 6.2, the bean seedlings have grown with shoots bent towards the window light and roots bent away from it. The flask is now turned so that the shoots point away from the light and the roots point towards it, and is left for a few days.
(a) Will the old, already-bent parts of the shoot and root change direction? Give a reason.
(b) In which direction will the new growth of the shoot and the root be?
(c) What do you conclude from this activity?

Try it first, then show the solutionSolution

1. (a) No. These movements are caused by growth, and the old parts have already grown, so their bent shape stays. (1 mark)
2. (b) New growth of the shoot bends towards the light again, and new growth of the root bends away from the light. (1 mark)
3. (c) Shoots grow towards light and roots grow away from it; this phototropic movement depends on growth and is directional. (1 mark)

Answer: (a) No, the old parts stay as they are; (b) new shoot growth turns towards light, new root growth turns away; (c) phototropism is a growth movement in which shoots and roots respond oppositely to light.

Plant hormones (introduction)

NCERT section 6.2.2 Movement Due to Growth

Why do plants and animals need chemical messages at all? Electrical impulses are fast, but they have two limits. They reach only cells joined by nervous tissue, and a cell needs time to reset before it can send another impulse. A chemical released by a cell instead diffuses all around it. Any cell with special molecules on its surface to detect it can respond. This is slower, but it can reach all cells and work steadily.

Plant hormones coordinate growth, development and responses to the environment. A plant hormone is produced in one part of the plant and spreads to another part, where it has its effect. You need four examples (introduction only).

• Auxin: made at the shoot tip, helps cells grow longer. When light comes from one side, auxin diffuses towards the shady side. Cells there grow longer, so the shoot bends towards light.
• Gibberellins: like auxins, help the stem grow.
• Cytokinins: promote cell division, so they are found in greater amounts where cells divide rapidly, such as fruits and seeds.
• Abscisic acid: inhibits growth; its effects include wilting of leaves.

The first three promote growth. Abscisic acid gives the signal to stop.

Worked example

(1 mark) A seedling in a box receives light only from its left side. Where will auxin collect in the shoot, and which way will the shoot bend?
(a) On the left side; the shoot bends to the right
(b) On the right side; the shoot bends to the left
(c) On the right side; the shoot bends to the right
(d) On the left side; the shoot bends to the left

Try it first, then show the solutionSolution

1. Light comes from the left, so the right side of the shoot is the shady side.
2. Auxin made at the shoot tip diffuses towards the shady (right) side.
3. Cells on the right side grow longer than cells on the left.
4. The longer right side makes the shoot curve to the left, towards the light. (1 mark)

Answer: (b) On the right side; the shoot bends to the left.

Hormones in animals and feedback

NCERT section 6.3 Hormones in Animals

Animal hormones form the endocrine system, the second way of control and coordination. Endocrine glands secrete hormones directly into the blood, which carries them to target organs. Unlike nerve impulses, they can reach all cells.

In a scary situation, the body must prepare to fight or run. Adrenaline from the adrenal glands makes the heart beat faster, sending more oxygen to muscles. Muscles around small arteries of the digestive system and skin contract, diverting blood to skeletal muscles. Breathing rate rises as the diaphragm and rib muscles contract.

Other hormones control growth and balance:

• Thyroxin (thyroid) regulates carbohydrate, protein and fat metabolism. The thyroid needs iodine to make it; lack of iodine can cause goitre (swollen neck).
• Growth hormone (pituitary) regulates growth; deficiency in childhood causes dwarfism.
• Testosterone (testes) and oestrogen (ovaries) bring the changes of puberty.
• Insulin (pancreas) regulates blood sugar; too little raises blood sugar, as in diabetes.

Amounts are controlled by feedback. When blood sugar rises, pancreas cells detect it and release more insulin; as sugar falls, insulin release drops.

Worked example

(5 marks)
(a) A squirrel suddenly sees a dog. Name the hormone that prepares its body to fight or run, and the gland that secretes it. Describe how this hormone reaches its targets and three changes it brings about, saying how each helps. (3 marks)
(b) Why is it advisable to use iodised salt? (2 marks)

Try it first, then show the solutionSolution

1. (a) Adrenaline, secreted by the adrenal glands. (1 mark)
2. It is secreted directly into the blood and carried to target organs such as the heart. (½ mark)
3. The heart beats faster, so more oxygen reaches the muscles. (½ mark)
4. Muscles around small arteries of the digestive system and skin contract, so blood is diverted to the skeletal muscles. (½ mark)
5. Breathing rate increases due to contraction of the diaphragm and rib muscles; together these changes ready the body for action. (½ mark)
6. (b) Iodine is needed by the thyroid gland to make thyroxin. (½ mark)
7. Thyroxin regulates carbohydrate, protein and fat metabolism to give the best balance for growth. (½ mark)
8. If iodine is lacking, a person may suffer from goitre, seen as a swollen neck because the thyroid gland lies in the neck. (1 mark)

Answer: (a) Adrenaline from the adrenal glands, carried by blood; faster heartbeat, blood diverted to skeletal muscles, faster breathing. (b) Iodine is needed to make thyroxin; its lack can cause goitre.

Science in real life: Control and Coordination

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Topics in this chapter

• Nervous System and Neuron StructureComing soon
• Reflex Action and Reflex Arc
• Human Brain and Its Protection
• Coordination in Plants and Tropic MovementsComing soon
• Plant HormonesComing soon
• Hormones in Animals

Control and Coordination: formulas and key facts

Path of a nerve impulse

1. 1.Dendritic tip
2. 2.cell body
3. 3.axon
4. 4.end of axon
5. 5.synapse
6. 6.dendrite of next neuron

Use for any 'trace the path' or neuron diagram question. Electrical inside the neuron, chemical across the synapse.

Synapse

What	the gap between two neurons
Signal	chemicals released at the axon end cross it
Result	a new impulse starts in the next dendrite

A one-mark definition. Never say the electrical impulse jumps across.

Receptors

$Specialisedtipsofnervecellsthatdetectinformation,mostlyinsenseorgans;gustatory=taste,olfactory=smell$

Use in questions on smell, taste or what happens when receptors fail.

Central and peripheral nervous system

$CNS=brain+spinalcord;PNS=cranialnerves(frombrain)+spinalnerves(fromspinalcord)$

Useful in assertion-reason items on how the brain talks to muscles.

Reflex arc

Input nerve detecting the stimulus connected to output nerve moving the muscle, in the spinal cord

Quote this when asked why reflexes are fast or where they are controlled. Information still reaches the brain.

Fore-brain

Main thinking part: sensory areas (hearing, smell, sight), association areas, motor areas for voluntary muscles, hunger centre

Answer for thinking, deciding, voluntary actions and feeling full.

Hind-brain: medulla

Controls involuntary actions such as blood pressure, salivation and vomiting

Do not mix it up with the cerebellum; the medulla is for automatic body functions.

Hind-brain: cerebellum

Precision of voluntary actions; posture and balance of the body

Answer for walking straight, riding a bicycle, picking up a pencil.

Protection of the CNS

Brain: bony box + fluid-filled balloon for shock absorption; spinal cord: vertebral column

Short 2-mark question; mention both the bone and the fluid for the brain.

Types of tropism

$Phototropism=light;geotropism=gravity;hydrotropism=water;chemotropism=chemicals(pollentubetoovule)$

Shoots go towards light and away from the earth; roots go away from light and towards the earth.

Plant hormones

Auxin and gibberellins: stem growth; cytokinins: cell division (fruits, seeds); abscisic acid: inhibits growth, wilting of leaves

Introduction only. Learn one function each and be ready to say which promote growth and which inhibits it.

Auxin and phototropism

1. 1.Light from one side
2. 2.auxin diffuses to shady side
3. 3.shady-side cells grow longer
4. 4.shoot bends towards light

In a 3-mark explanation, write the four links in this order.

Gland and hormone list

Pituitary: growth hormone; thyroid: thyroxin; pancreas: insulin; testes: testosterone; ovaries: oestrogen; adrenal: adrenaline

Also learn the deficiency links: iodine lack → goitre; growth hormone lack in childhood → dwarfism; low insulin → high blood sugar.

Feedback mechanism

1. 1.Rise in blood sugar
2. 2.pancreas releases more insulin
3. 3.blood sugar falls
4. 4.insulin release reduced

Use for any question on how the amount and timing of a hormone are regulated.

Nervous versus hormonal control

Signal	nervous electrical vs hormonal chemical via blood
Speed	nervous fast vs hormonal slower
Reach	nervous only cells connected by nerves vs hormonal all cells
Persistence	nervous cells need time to reset vs hormonal steady and persistent

The basis for every 'compare and contrast' question on control in animals.

Control and Coordination: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the board asks Control and Coordination

The question patterns to expect, and the method that works for each.

Tricks to remember Control and Coordination

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Order of a neuron

  'Do Cats Always Sleep?' = Dendrite, Cell body, Axon, Synapse.

  Use it when: Tracing the path of an impulse or labelling the neuron in the right order.

• Two hind-brain parts

  Cerebellum = Cycle (balance, posture, precise movements). Medulla = Must-run jobs: blood pressure, salivation, vomiting.

  Use it when: Brain MCQs and case-based symptom questions where these two are swapped.

• Auxin is shy of light

  'Auxin runs to the shade, the shade side grows, the shoot bows to the light.'

  Use it when: Any phototropism explanation or MCQ on which side grows faster.

• Plant hormones: go and stop

  'AGC go, ABA no' = Auxin, Gibberellins, Cytokinins promote growth; Abscisic acid stops it (wilting leaves).

  Use it when: Picking the growth inhibitor or promoter in one-mark questions.

• Tropism prefixes

  Photo = light, Geo = earth (gravity), Hydro = water, Chemo = chemicals. Root and shoot always respond oppositely to light and gravity.

  Use it when: Naming a tropism from a description or a case passage.

• Speed check for control systems

  Nerves = wires (fast, only where connected). Hormones = broadcast through blood (slow, reach everyone, keep going).

  Use it when: Writing compare-and-contrast answers on nervous versus hormonal control.

Control and Coordination: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section E style)

Read the situation, then answer every part. In the board paper this is a 6-mark question split into 1 + 1 + 2 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Control and Coordination

The slips examiners see most often, and what to write instead.

• ✗Mistake: Saying the brain controls a reflex action

  Students know the brain controls everything, so they write it automatically.

  Wrong working

  When we touch a hot object, the brain thinks quickly and tells the hand to move away.

  Right working

  The reflex arc is formed in the spinal cord, where the input nerve is connected to the output nerve. The hand moves without thinking; the information also reaches the brain, so we feel it later.

  ✓Do this: For any reflex, write 'spinal cord, reflex arc, no thinking', and add that the brain receives the information afterwards.

  Usually costs: 1 mark in an MCQ or assertion-reason item; 1 to 2 marks in a 3-mark answer.

• ✗Mistake: Swapping cerebellum and medulla

  Both are in the hind-brain and sound similar.

  Wrong working

  The medulla maintains posture and balance of the body.

  Right working

  The cerebellum maintains posture and balance and gives precision to voluntary actions. The medulla controls involuntary actions such as blood pressure, salivation and vomiting.

  ✓Do this: Link cerebellum to riding a bicycle and medulla to salivation; check the function word before answering.

  Usually costs: The full 1 mark in an MCQ; ½ to 1 mark in a case-based part.

• ✗Mistake: Putting auxin on the lit side of the shoot

  Students assume light 'pulls' growth towards it, so the lit side must grow more.

  Wrong working

  Auxin collects on the side facing light, so those cells grow and the shoot bends to light.

  Right working

  Auxin diffuses to the shady side. The cells on the shady side grow longer, so that side becomes longer and the shoot bends towards light.

  ✓Do this: Picture the outside of a bend: the longer side is always away from the direction of bending, which is the shady side.

  Usually costs: 1 to 1½ marks in a 3-mark phototropism answer, or the full mark in an MCQ.

• ✗Mistake: Calling the touch-me-not movement a tropism or growth movement

  All plant movements are lumped together as 'tropisms'.

  Wrong working

  The leaves of the sensitive plant fold due to thigmotropism, as growth occurs on one side.

  Right working

  The folding of sensitive-plant leaves is an immediate response with no growth. Cells change shape by changing their water content. Tropic movements are slow and caused by directional growth.

  ✓Do this: Ask: is it quick and without growth? Then it is not a tropism. Use water content as the mechanism.

  Usually costs: 1 to 2 marks in a difference or comparison question.

• ✗Mistake: Saying the electrical impulse crosses the synapse

  Students learn that nerves are electrical and forget the chemical step.

  Wrong working

  At the synapse, the electrical impulse jumps from one neuron to the next.

  Right working

  At the end of the axon, the electrical impulse causes chemicals to be released. These chemicals cross the synapse and start a new electrical impulse in the dendrite of the next neuron.

  ✓Do this: Write the three words 'electrical, chemical, electrical' for one neuron, the gap, and the next neuron.

  Usually costs: 1 mark in a 2- or 3-mark question on the synapse.

• ✗Mistake: Leaving out the blood when describing hormones

  Students write which gland makes which hormone but not how it travels.

  Wrong working

  Adrenaline is made by the adrenal gland and makes the heart beat faster.

  Right working

  Adrenaline is secreted by the adrenal glands directly into the blood and carried to target organs such as the heart, which then beats faster, supplying more oxygen to the muscles.

  ✓Do this: In any hormone answer, include the chain: gland, secreted into blood, target organ, effect.

  Usually costs: ½ to 1 mark in a 3- or 5-mark answer.

NCERT exercise guide: Control and Coordination

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

Control and Coordination: previous year questions

• Asked in 21 of the 21 board papers we hold (2023 to 2026), on average 5.7 marks per paper; 65 questions in all, counting OR alternatives. In 4 of 4 sample papers.

Counted from the real papers on our previous year papers page, not estimated. Average marks are over every board paper we hold, with an OR pair counted once. Chapter tags are ours.

Solved board questions from Control and Coordination

Real questions from recent papers. Try each one first, then open our step-by-step solution with marks per step.

Every Control and Coordination question, by year

Practice questions on Control and Coordination

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQHarder board level

   Consider these statements about plant hormones:
   (I) Auxin is synthesised at the root tip.
   (II) Cytokinins are present in greater concentration in fruits and seeds.
   (III) Abscisic acid causes wilting of leaves.
   (IV) Gibberellins inhibit the growth of the stem.
   Which statements are correct?
   (a) I and II
   (b) II and III
   (c) III and IV
   (d) I and IV

   Hint

   Check each statement separately: where auxin is made, and whether gibberellins promote or stop growth.

   Answer

   (b) II and III. Auxin is made at the shoot tip, not the root tip, and gibberellins help stem growth rather than inhibit it.

2. Q2 · 1 mark · MCQBoard level

   The peripheral nervous system is made up of:
   (a) the brain and spinal cord
   (b) cranial nerves and spinal nerves
   (c) the brain and cranial nerves
   (d) the spinal cord and spinal nerves

   Hint

   The brain and spinal cord together form a different system.

   Answer

   (b) Cranial nerves and spinal nerves. The brain and spinal cord form the central nervous system.

3. Q3 · 2 marks · Very short answerBoard level

   Name the hormones responsible for the changes of puberty in boys and in girls, and the gland that secretes each. (2 marks)

   Hint

   One gland is found only in males and the other only in females.

   Answer

   Boys: testosterone, secreted by the testes. Girls: oestrogen, secreted by the ovaries.

4. Q4 · 3 marks · Short answerBoard level

   Give two limitations of electrical impulses in coordination. How does chemical communication overcome them? (3 marks)

   Hint

   Think about which cells an impulse can reach, and what a cell needs after sending one.

   Answer

   1. Impulses reach only cells connected by nervous tissue. 2. After an impulse, a cell needs time to reset, so it cannot send impulses continually.

   A chemical released by cells diffuses around them. Other cells detect it with special molecules on their surfaces. It can reach all cells regardless of nerve connections and act steadily and persistently, though more slowly.

5. Q5 · 5 marks · Long answerBoard level

   (a) Name four plant hormones and state one function of each.
   (b) Where are plant hormones made and how do they reach their place of action?
   (c) Why are cytokinins found in greater concentration in fruits and seeds? (5 marks)

   Hint

   Three of the four hormones promote growth; one stops it.

   Answer

   (a) Auxin: helps cells grow longer, so shoots bend towards light. Gibberellins: help in stem growth. Cytokinins: promote cell division. Abscisic acid: inhibits growth and causes wilting of leaves.

   (b) Each is produced in one part of the plant and spreads by diffusion to another part, where it has its effect.

   (c) Fruits and seeds are areas of rapid cell division, and cytokinins promote cell division.

6. Q6 · 3 marks · Short answerBoard level

   A friend shines a bright torch into your eyes. Trace the sequence of events in the reflex that follows, and say why you cannot prevent it by thinking. (3 marks)

   Hint

   The response is a change in pupil size. Follow it from receptor to muscle.

   Answer

   Receptors in the eye detect the bright light. Impulses travel along input nerves and are passed directly to output nerves through a reflex connection, without waiting for thought. The output nerves make the muscles of the eye reduce the size of the pupil, protecting the eye.

   It is a reflex, so it happens without thinking or conscious control. The information still reaches the brain, but only after the response.

7. Q7 · 3 marks · Short answerHarder board level

   You decide to pick up a pencil and write your name neatly. Explain how the brain, nerves and muscles work together in this action. (3 marks)

   Hint

   Include a decision, a precision controller and what the muscle cells do.

   Answer

   The fore-brain decides to act, and its motor areas send messages through the peripheral nervous system to voluntary muscles of the hand. The cerebellum in the hind-brain gives precision to this voluntary action.

   When the impulses reach the muscle cells, special proteins change their shape and arrangement, so the cells become shorter and the fingers move.

8. Q8 · 3 marks · Short answerBoard level

   (a) What do the terms hydrotropism and chemotropism mean? Give one example of chemotropism.
   (b) In geotropism, how do the root and the shoot respond? (3 marks)

   Hint

   'Hydro' means water and 'chemo' refers to chemicals.

   Answer

   (a) Hydrotropism: directional growth of a plant part in response to water. Chemotropism: directional growth in response to chemicals. Example: the pollen tube grows towards the ovule.

   (b) Roots grow downwards, towards the pull of gravity. Shoots grow upwards, away from the earth.

9. Q9 · 3 marks · Case-basedHOTS / competency

   Imagine a doctor sees three patients:

   • X, an adult who is very short and had a hormone deficiency as a child.
   • Y, who has a swollen neck and whose diet lacks iodine.
   • Z, whose blood sugar stays high.

   For each, name the hormone and the gland involved. For which patient would iodised salt help, and why? (3 marks)

   Hint

   Match each symptom to the job of a hormone: growth, metabolism, blood sugar.

   Answer

   X: growth hormone, from the pituitary (dwarfism). Y: thyroxin, from the thyroid (goitre). Z: insulin, from the pancreas.

   Iodised salt would help Y, because iodine is essential for the thyroid to make thyroxin. Lack of iodine can cause goitre.

10. Q10 · 3 marks · Short answerHOTS / competency

    A classmate says: 'Humans have a highly developed brain that can think, so reflex arcs are useless to us.' Do you agree? Justify your answer. (3 marks)

    Hint

    Compare how long thinking takes with how fast a dangerous situation needs a response.

    Answer

    No. Thinking involves complex interactions of many nerve impulses in the brain, so it takes time. In danger, such as touching a flame, we could get burnt before thinking finishes.

    Reflex arcs in the spinal cord connect input and output nerves directly, so the response is quick. Even after complex brains evolved, reflex arcs stay more efficient for quick responses, and the information still reaches the brain afterwards.

11. Q11 · 1 mark · Assertion-reasonHarder board level

    Assertion (A): When adrenaline is released, less blood flows to the skin and the digestive system.
    Reason (R): Adrenaline is secreted directly into the blood.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

    Hint

    Ask what actually narrows the blood supply to these organs, not just how adrenaline travels.

    Answer

    (b) Both A and R are true but R is not the correct explanation of A. Blood to the skin and digestive system falls because muscles around their small arteries contract; R only tells how adrenaline travels.

12. Q12 · 5 marks · Long answerHarder board level

    Suppose a student is waiting backstage before a speech. Her heart pounds and she breathes fast.
    (a) Name the hormone responsible and the gland that secretes it.
    (b) How does this hormone reach the heart?
    (c) Describe three changes it causes in the body and how each prepares her for action.
    (d) Why could nerve impulses alone not bring about such wide-ranging changes? (5 marks)

    Hint

    Think heart, blood supply and breathing; then compare how far nerves and blood can reach.

    Answer

    (a) Adrenaline, secreted by the adrenal glands. (1)

    (b) It is secreted directly into the blood, which carries it to target organs such as the heart. (1)

    (c) The heart beats faster, so more oxygen reaches the muscles. Muscles around small arteries of the skin and digestive system contract, so blood is diverted to the skeletal muscles. Breathing rate rises as the diaphragm and rib muscles contract. (2)

    (d) Nerve impulses reach only cells connected by nervous tissue, so only a limited set of tissues could be instructed. A hormone in the blood reaches all cells and brings about the wide-ranging changes needed. (1)

13. Q13 · 3 marks · Short answerHarder board level

    Compare the movement of the leaves of a sensitive plant with the movement of your legs on three points: how the information is carried, how the cells change shape, and what controls the movement. (3 marks)

    Hint

    Plants have no nerves, no muscles and no special proteins for movement.

    Answer

    Information: in the sensitive plant it passes from cell to cell by electrical-chemical means with no specialised tissue; in the leg, impulses travel along neurons, a specialised nervous tissue.

    Cell shape: plant cells swell or shrink by changing their water content; leg muscle cells shorten because special proteins change their shape and arrangement.

    Control: the plant responds directly to touch with no brain; leg movement is a voluntary action decided by the fore-brain and made precise by the cerebellum.

14. Q14 · 3 marks · Short answerHarder board level

    Think about receptors that do not work properly.
    (a) If a person's olfactory receptors were damaged, what two problems would arise while eating, and why?
    (b) If the heat-detecting receptors in a person's fingers stopped working, why would touching a hot vessel be dangerous? (3 marks)

    Hint

    Every response, including a reflex, begins at a receptor.

    Answer

    (a) The person could not smell the food, because olfactory receptors detect smell. The food would also taste dull, because the fore-brain combines smell information with taste information from the tongue when it interprets food.

    (b) The heat would not be detected, so no impulse would start in the input nerve. The reflex arc would never be triggered, the hand would not be pulled away, and the person could get burnt without noticing.

15. Q15 · 3 marks · Short answerHarder board level

    After an injury to his cerebellum, a man can still solve problems and plan his day clearly, but he can no longer ride a bicycle. Explain this using the functions of different parts of the brain. (3 marks)

    Hint

    Different parts of the brain handle different inputs and outputs.

    Answer

    Different parts of the brain are responsible for different jobs. Thinking, deciding and planning happen in the fore-brain, the main thinking part, which is not injured, so he still thinks clearly.

    Riding a bicycle needs balance, posture and precise voluntary movements, which are controlled by the cerebellum in the hind-brain. With the cerebellum injured, he can decide to ride but cannot keep his balance or control the movements precisely.

16. Q16 · 5 marks · Long answerHarder board level

    (a) Describe how a message travels through a neuron and across a synapse to the next neuron.
    (b) How does a nerve impulse finally make a muscle move? Explain what happens inside the muscle cell.
    (c) State how plant cells change shape instead. (5 marks)

    Hint

    Electrical, then chemical, then electrical; then think of proteins in muscle and water in plant cells.

    Answer

    (a) Information is picked up at the dendritic tip, where it sets off a chemical reaction that creates an electrical impulse. The impulse passes through the cell body and along the axon. At the axon's end it triggers the release of chemicals, which cross the synapse and start a new electrical impulse in a dendrite of the next neuron. (2)

    (b) A similar junction passes the impulse from a neuron to a muscle cell. Special proteins in the muscle cell change their shape and arrangement in response, giving the cell a shorter form, and this shortening moves the body part. (2)

    (c) Plant cells have no such proteins; they change shape by changing the amount of water in them, swelling or shrinking. (1)

17. Q17 · 3 marks · Short answerHarder board level

    How are involuntary actions and reflex actions different? Give two examples of each and name what controls them. (3 marks)

    Hint

    Both happen without thinking; ask what triggers each and where it is controlled.

    Answer

    Involuntary actions, such as the heartbeat and breathing, keep the body running without our thinking control. Many are controlled by the mid-brain and hind-brain, and the medulla controls blood pressure, salivation and vomiting.

    Reflex actions, such as pulling the hand from a flame or the pupil narrowing in bright light, are sudden responses to a particular stimulus. They work through a reflex arc and are often protective.

    Both happen without thinking, but a reflex is a quick response set off by a specific stimulus, while involuntary actions go on as part of the body's normal working.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.What is the gap between two neurons called?Show answer

   The synapse.

2. 2.Where are reflex arcs formed?Show answer

   In the spinal cord.

3. 3.Which part of the brain maintains posture and balance?Show answer

   The cerebellum, in the hind-brain.

4. 4.Name three involuntary actions controlled by the medulla.Show answer

   Blood pressure, salivation and vomiting.

5. 5.What makes up the peripheral nervous system?Show answer

   Cranial nerves from the brain and spinal nerves from the spinal cord.

6. 6.Which plant hormone inhibits growth?Show answer

   Abscisic acid; its effects include wilting of leaves.

7. 7.Which hormone needs iodine to be made, and by which gland?Show answer

   Thyroxin, made by the thyroid gland.

8. 8.What does lack of growth hormone in childhood cause?Show answer

   Dwarfism.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you trace an impulse from the dendritic tip to the next neuron and say where it turns chemical?
• ☐Can you explain why a reflex arc is in the spinal cord and what the brain's role is?
• ☐Can you name the CNS and PNS and the nerves that form the PNS?
• ☐Can you give the job of the fore-brain, medulla and cerebellum with one example each?
• ☐Can you classify any action as voluntary, involuntary or reflex and name its controlling part?
• ☐Can you explain how muscle cells shorten and how plant cells change shape?
• ☐Can you give three differences between touch-me-not movement and phototropism?
• ☐Can you explain phototropism using auxin and the shady side, step by step?
• ☐Can you list four plant hormones with one function each, and name the inhibitor?
• ☐Can you match six animal hormones to their glands and explain the insulin feedback loop?

Control and Coordination: frequently asked questions