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Control and Coordination

NCERT Class 10 · Science Based on NCERT Class 10 Science textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explains how living organisms respond to changes in their environment through controlled movements. It introduces the nervous system and hormonal system in animals, and plant hormones for coordination. The one big idea is that organisms use electrical impulses (nervous system) and chemical signals (hormones) to detect stimuli, process information, and produce appropriate responses for survival.
Key Concepts (32)
Receptors
Specialised tips of some nerve cells that detect information from the environment, usually located in sense organs.
e.g. Gustatory receptors in the tongue detect taste; olfactory receptors in the nose detect smell.
Neuron
The structural and functional unit of nervous tissue, specialised for conducting information via electrical impulses.
e.g. A nerve cell with dendrites, cell body, and axon that transmits impulses from the skin to the spinal cord.
Synapse
The gap between the axon of one neuron and the dendrite of the next neuron, across which chemical signals transmit the impulse.
e.g. When an electrical impulse reaches the axon end, chemicals are released that cross the synapse to start a new impulse in the next neuron.
Reflex action
A quick, automatic, involuntary response to a stimulus that does not involve conscious thought, mediated by the reflex arc.
e.g. Pulling your hand back immediately after touching a hot flame.
Reflex arc
The neural pathway that connects sensory neurons to motor neurons in the spinal cord, bypassing the brain for rapid response.
e.g. When you touch a hot object, sensory nerves in the hand send impulses to the spinal cord, which directly triggers motor nerves to move the hand away.
Central nervous system (CNS)
The part of the nervous system consisting of the brain and spinal cord, which receives information from all parts of the body and integrates it.
e.g. The brain processes sensory input and sends commands to muscles via the spinal cord.
Peripheral nervous system (PNS)
The network of cranial nerves arising from the brain and spinal nerves arising from the spinal cord that facilitates communication between the CNS and the rest of the body.
e.g. Cranial nerves carry signals from the eyes to the brain; spinal nerves carry signals from the limbs to the spinal cord.
Fore-brain
The main thinking part of the brain, with regions for receiving sensory impulses, interpreting information, and controlling voluntary muscles.
e.g. The fore-brain has separate areas for hearing, smell, sight, and association areas that integrate sensory information with stored memories.
Mid-brain
A part of the brain that controls some involuntary actions and relays sensory information.
e.g. It helps in controlling eye movements and auditory reflexes.
Hind-brain
The part of the brain that controls involuntary actions such as blood pressure, salivation, vomiting, and maintains posture and balance.
e.g. The medulla in the hind-brain controls breathing and heart rate; the cerebellum maintains balance while walking.
Cerebellum
A part of the hind-brain responsible for precision of voluntary actions and maintaining posture and balance of the body.
e.g. Riding a bicycle or picking up a pencil is possible due to the cerebellum.
Medulla
A part of the hind-brain that controls involuntary actions including blood pressure, salivation, and vomiting.
e.g. When you breathe without thinking, the medulla is at work.
Tropic movement (tropism)
Directional growth movements of plants in response to environmental stimuli, either towards or away from the stimulus.
e.g. Shoots bending towards light (phototropism) and roots growing downwards (geotropism).
Phototropism
The directional growth of a plant in response to light; shoots bend towards light, roots bend away from light.
e.g. Sunflower stems grow towards the sun.
Geotropism
The directional growth of a plant in response to gravity; roots grow downwards (positive geotropism), shoots grow upwards (negative geotropism).
e.g. A seed germinating: the root goes down into the soil, the stem goes up into the air.
Hydrotropism
Directional growth of plant roots towards water.
e.g. Roots growing towards a moist area in the soil.
Chemotropism
Directional growth of a plant part in response to chemicals.
e.g. Growth of pollen tubes towards ovules during fertilisation.
Auxin
A plant hormone synthesised at the shoot tip that helps cells grow longer; it diffuses to the shady side, causing the plant to bend towards light.
e.g. When light comes from one side, auxin concentrates on the shady side, making cells there grow longer, bending the shoot towards light.
Gibberellins
Plant hormones that help in the growth of the stem.
e.g. They promote elongation of internodes in plants.
Cytokinins
Plant hormones that promote cell division, present in greater concentration in areas of rapid cell division such as fruits and seeds.
e.g. They help in the growth of new leaves and shoots.
Abscisic acid
A plant hormone that inhibits growth; its effects include wilting of leaves.
e.g. It helps plants respond to stress by closing stomata and stopping growth.
Adrenaline
A hormone secreted from the adrenal glands into the blood that prepares the body for emergency situations (fight or flight).
e.g. When scared, adrenaline increases heart rate, breathing rate, and diverts blood to skeletal muscles.
Thyroxin
A hormone produced by the thyroid gland that regulates carbohydrate, protein, and fat metabolism for body growth; requires iodine for synthesis.
e.g. Iodised salt is needed to prevent goitre, a swelling of the neck due to thyroxin deficiency.
Growth hormone
A hormone secreted by the pituitary gland that regulates growth and development of the body.
e.g. Deficiency in childhood leads to dwarfism; excess leads to gigantism.
Testosterone
A male sex hormone secreted by the testes that brings about changes associated with puberty.
e.g. It leads to deepening of voice, growth of facial hair, etc.
Oestrogen
A female sex hormone secreted by the ovaries that regulates the development of female sex organs and the menstrual cycle.
e.g. It controls the menstrual cycle and secondary sexual characteristics in females.
Insulin
A hormone produced by the pancreas that regulates blood sugar levels.
e.g. Diabetic patients are given insulin injections when their body does not produce enough insulin.
Feedback mechanism
A regulatory mechanism that controls the timing and amount of hormone released based on the body's needs.
e.g. When blood sugar rises, the pancreas secretes more insulin; as sugar falls, insulin secretion is reduced.
Endocrine system
The system of glands that secrete hormones directly into the blood for chemical coordination in the body.
e.g. The adrenal glands, thyroid gland, pancreas, pituitary gland, testes, and ovaries are part of the endocrine system.
Voluntary actions
Actions that are based on conscious thinking and decision-making, controlled by the fore-brain.
e.g. Writing, talking, moving a chair, clapping at the end of a programme.
Involuntary actions
Actions that occur without conscious control, such as heartbeat, breathing, and digestion, controlled by the mid-brain and hind-brain.
e.g. Salivation, vomiting, blood pressure regulation.
Neuromuscular junction
The synapse between a neuron and a muscle cell where the electrical impulse triggers the release of chemicals that cause the muscle to contract.
e.g. When a nerve impulse reaches the muscle, it causes the muscle fibre to shorten.
Formulas & Equations (1)
No specific mathematical formula or chemical equation is present in this chapter.
Reads as: Not applicable.
Variables: Not applicable.
Use when: Not applicable.
⚠ Not applicable.
How It Works
Transmission of nerve impulse across a neuron
  1. Information is acquired at the dendritic tip of a nerve cell, setting off a chemical reaction that creates an electrical impulse.
  2. The electrical impulse travels from the dendrite to the cell body.
  3. The impulse then travels along the axon to its end.
  4. At the end of the axon, the electrical impulse sets off the release of chemicals.
  5. These chemicals cross the gap (synapse) and start a similar electrical impulse in the dendrite of the next neuron.
💡 The impulse is electrical inside the neuron but chemical across the synapse. Students often forget that the signal becomes chemical at the synapse.
Reflex arc mechanism
  1. A stimulus (e.g., touching a hot object) is detected by sensory receptors in the skin.
  2. Sensory neurons carry the electrical impulse to the spinal cord.
  3. In the spinal cord, the sensory neuron connects directly to a motor neuron via a synapse (reflex arc).
  4. The motor neuron carries the impulse to the muscle (effector).
  5. The muscle contracts, causing the hand to be pulled away — all without involving the brain initially.
💡 The reflex arc bypasses the brain for speed, but information also goes to the brain so you feel pain later. Students often think the brain is not involved at all.
How the brain processes information and produces voluntary action
  1. Sensory receptors detect stimuli and send impulses to the fore-brain.
  2. Separate areas of the fore-brain receive sensory impulses for hearing, smell, sight, etc.
  3. Association areas interpret this sensory information by combining it with information from other receptors and stored memories.
  4. A decision is made about how to respond.
  5. The information is passed to motor areas that control voluntary muscles, leading to action.
💡 The fore-brain is the 'thinking part' — it integrates sensory input with memory before deciding on a response.
Movement in sensitive plant (Mimosa pudica)
  1. Touch is detected at a point on the leaf.
  2. Electrical-chemical signals communicate the information from cell to cell (no specialised tissue).
  3. Cells in the leaf change shape by losing water (shrinking) or gaining water (swelling).
  4. This change in water content causes the leaf to fold up and droop.
💡 No growth is involved; movement is due to changes in water content in cells, not muscle proteins.
Phototropism in plants (role of auxin)
  1. Auxin is synthesised at the shoot tip.
  2. When light comes from one side, auxin diffuses towards the shady side of the shoot.
  3. Higher concentration of auxin on the shady side stimulates cells there to grow longer.
  4. The shoot bends towards the light because the shady side grows faster.
💡 Auxin promotes cell elongation on the side away from light, causing bending towards light. Students often think auxin is destroyed by light — it is not, it simply redistributes.
Tendril growth around a support (thigmotropism)
  1. The tendril is sensitive to touch.
  2. When it comes in contact with a support, the part of the tendril in contact with the object does not grow as rapidly.
  3. The part away from the object grows faster.
  4. This differential growth causes the tendril to circle around the object and cling to it.
💡 This is a growth-related movement (tropic), not an immediate response like the sensitive plant.
Adrenaline response (fight or flight)
  1. In a scary situation, the adrenal glands secrete adrenaline directly into the blood.
  2. Adrenaline reaches target organs like the heart, causing it to beat faster.
  3. Blood to the digestive system and skin is reduced due to contraction of muscles around small arteries.
  4. Blood is diverted to skeletal muscles.
  5. Breathing rate increases due to contractions of the diaphragm and rib muscles.
  6. The body is prepared for fighting or running.
💡 Adrenaline is a hormone (chemical signal) that affects many organs simultaneously, unlike nerve impulses which are targeted.
Feedback mechanism for insulin secretion
  1. Blood sugar levels rise after a meal.
  2. Cells of the pancreas detect the rise in blood sugar.
  3. The pancreas responds by producing and secreting more insulin.
  4. Insulin helps cells absorb glucose, lowering blood sugar levels.
  5. As blood sugar falls, insulin secretion is reduced.
💡 This is a negative feedback loop — the response (insulin secretion) reduces the initial stimulus (high blood sugar).
Exam Traps — Don't Make These Mistakes
⚠ Confusing reflex action with voluntary action
✗ Reflex action is a voluntary action that we do without thinking.
→ Reflex actions are involuntary and do not involve conscious thought; voluntary actions are deliberate and involve the fore-brain.
✓ Reflex action is an involuntary, automatic response to a stimulus that does not involve the brain initially, whereas walking is a voluntary action controlled by the fore-brain.
⚠ Thinking the brain is not involved in reflex actions at all
✗ In a reflex action, the brain is not involved at all.
→ While the reflex arc bypasses the brain for speed, information about the stimulus also travels to the brain, so you become aware of the pain later.
✓ In a reflex action, the initial response is mediated by the spinal cord without waiting for the brain, but sensory information also reaches the brain for awareness.
⚠ Confusing auxin's role in phototropism
✗ Auxin is destroyed by light, so the shady side grows less.
→ Auxin is not destroyed by light; it diffuses towards the shady side, where it promotes cell elongation, causing the shoot to bend towards light.
✓ Auxin diffuses towards the shady side of the shoot, where it stimulates cells to grow longer, causing the shoot to bend towards light.
⚠ Mixing up the functions of cerebellum and medulla
✗ The cerebellum controls involuntary actions like heartbeat and breathing.
→ The medulla controls involuntary actions like blood pressure, salivation, and vomiting; the cerebellum controls precision of voluntary actions and balance.
✓ The cerebellum maintains posture and balance and ensures precision of voluntary actions, while the medulla controls involuntary actions such as heartbeat and breathing.
⚠ Thinking plant movements are always growth-related
✗ All plant movements are due to growth.
→ Plants show two types of movement: one dependent on growth (tropic movements) and one independent of growth (e.g., sensitive plant leaf folding due to water loss).
✓ Some plant movements, like the folding of Mimosa leaves, are immediate responses involving changes in water content (no growth), while tropic movements like phototropism are growth-related.
⚠ Confusing hormones with enzymes or nerves
✗ Hormones are electrical signals that travel through nerves.
→ Hormones are chemical signals that travel through the blood, not electrical impulses through nerves.
✓ Hormones are chemical substances secreted by endocrine glands directly into the blood, which carry them to target organs to produce specific effects.
Compare & Contrast
Mode of transmission
Nervous system
Hormonal (endocrine) system
Nervous system uses electrical impulses along neurons for rapid, targeted communication; hormonal system uses chemical messengers (hormones) transported via blood for slower, widespread effects.
Level of control and involvement of brain
Reflex action
Involuntary action
Reflex actions are sudden, automatic responses mediated by the spinal cord (e.g., pulling hand from fire); involuntary actions are ongoing, automatic functions controlled by the brain stem (e.g., heartbeat, breathing).
Nature of movement
Movement in sensitive plant (Mimosa)
Movement of shoot towards light (phototropism)
Sensitive plant movement is immediate, non-growth, due to water loss in cells; phototropism is a slow, growth-related movement due to differential cell elongation caused by auxin.
Effect on plant growth
Auxin
Abscisic acid
Auxin promotes cell elongation and growth; abscisic acid inhibits growth and causes wilting of leaves.
Exam Focus
Marks pattern: 2 MCQs (1 mark each), 1 Very Short Answer (1 mark), 1 Short Answer (3 marks), 1 Long Answer (5 marks). Total approximately 11 marks.
Most asked: Structure and function of neuron · Reflex arc and reflex action · Parts of the human brain and their functions · Plant hormones (auxin, gibberellins, cytokinins, abscisic acid) and tropisms · Endocrine glands and their hormones (adrenaline, thyroxin, growth hormone, insulin, testosterone, oestrogen) · Feedback mechanism (insulin example)
Don't skip: Draw and label the structure of a neuron and explain its function (5 marks).; Explain the reflex arc with a diagram (3-5 marks).; Describe the functions of different parts of the human brain (5 marks).; Compare nervous and hormonal coordination (3-5 marks).; Explain phototropism with the role of auxin (3 marks).; List plant hormones and their functions (3 marks).; Explain the feedback mechanism of insulin (3 marks).
One-Line Revision (read aloud before the exam)
  1. Receptors are specialised nerve endings in sense organs that detect stimuli like taste, smell, touch, light, and sound.
  2. A neuron consists of dendrites, cell body, and axon; it transmits electrical impulses from one part of the body to another.
  3. The synapse is the gap between two neurons where chemical signals transmit the impulse.
  4. A reflex arc is a neural pathway in the spinal cord that enables quick, automatic responses without involving the brain.
  5. The brain has three main parts: fore-brain (thinking), mid-brain (involuntary actions), and hind-brain (balance and vital functions).
  6. The cerebellum maintains posture and balance; the medulla controls involuntary actions like heartbeat and breathing.
  7. The spinal cord is protected by the vertebral column; the brain is protected by the skull and cerebrospinal fluid.
  8. Plant movements are of two types: growth-dependent (tropisms) and non-growth (e.g., sensitive plant leaf folding).
  9. Auxin is a plant hormone that promotes cell elongation; it causes phototropism by diffusing to the shady side.
  10. Gibberellins promote stem growth; cytokinins promote cell division; abscisic acid inhibits growth.
  11. Adrenaline is a hormone that prepares the body for fight or flight by increasing heart rate, breathing rate, and blood flow to muscles.
  12. Thyroxin regulates metabolism and requires iodine; its deficiency causes goitre.
  13. Growth hormone from the pituitary regulates body growth; deficiency causes dwarfism.
  14. Insulin from the pancreas regulates blood sugar levels; diabetes results from insulin deficiency.
  15. Testosterone and oestrogen are sex hormones that bring about changes at puberty.
  16. Feedback mechanisms regulate hormone secretion, e.g., high blood sugar triggers insulin release, which then lowers blood sugar.
  17. The endocrine system uses chemical messengers (hormones) transported via blood for coordination.
  18. Nervous coordination is fast and short-lived; hormonal coordination is slow and long-lasting.
  19. In plants, chemical coordination occurs via hormones that diffuse to target cells.
  20. The fore-brain has separate areas for hearing, smell, sight, and association areas for interpretation.

MCQs — 10 Questions with Answers

Q1. A student accidentally touches a hot stove in the kitchen. Her hand pulls back immediately without her consciously thinking about it. Which of the following best explains why this response is faster than a response involving conscious thought?

  • A. The reflex arc bypasses the brain by using a direct pathway through the spinal cord, reducing the time needed for response ✓
  • B. The hand muscles contract automatically because they are not controlled by the nervous system
  • C. Conscious thought is slower because the brain is located far from the spinal cord
  • D. Heat energy directly triggers muscle contraction without involving nerve impulses

Answer: A — Reflex arcs use a short pathway through the spinal cord that doesn't require input from the brain, making them much faster than conscious responses; option B incorrectly suggests muscles aren't nervous-system controlled, and D falsely claims muscles contract without nerve impulses.

Q2. During a biology practical, a student observes that when she blocks her nose and eats a piece of apple, she cannot distinguish its taste properly, but when she releases her nose, the taste becomes clear. Which concept from the nervous system best explains this observation?

  • A. Gustatory receptors alone cannot detect all components of taste; olfactory receptors in the nose contribute significantly to the perception of flavor ✓
  • B. The taste buds in the mouth are connected directly to the brain, while smell receptors bypass the brain
  • C. Blocking the nose prevents saliva from reaching taste buds, so taste receptors cannot function
  • D. The tongue and nose use different types of neurons that do not communicate with each other

Answer: A — Taste and smell together create the perception of flavor; blocking the nose prevents olfactory input, reducing flavor perception despite gustatory receptors still functioning, while option C incorrectly suggests saliva access is blocked.

Q3. A gardener observes that his sunflower plant bends toward the sunlight over the course of several days. Which statement correctly describes the control mechanism involved in this movement?

  • A. This is a growth response controlled by plant hormones that redistribute due to light direction, not a rapid nervous response like in animals ✓
  • B. The plant's roots detect light and send electrical impulses to the stem to make it bend
  • C. The sunflower has a nervous system similar to animals that allows it to consciously turn toward light
  • D. Light directly causes the cells on the shaded side to contract, bending the plant toward sunlight

Answer: A — Plant movements toward light are slow, growth-based responses mediated by hormones, not rapid nerve-impulse responses; option B incorrectly assigns light detection to roots, and C falsely claims plants have animal-like nervous systems.

Q4. Assertion (A): When a person's hand touches a hot object, the hand is pulled away before the person consciously feels pain. Reason (R): The reflex arc allows a rapid response because sensory and motor neurons communicate directly through the spinal cord without involving the brain. Choose the correct option:

  • 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

Answer: A — The reflex arc does involve the spinal cord as a relay point between sensory and motor neurons, bypassing the brain and allowing faster withdrawal than conscious pain perception; both statements are scientifically accurate and causally related.

Q5. A doctor shines a bright light into a patient's eye and observes that the pupil constricts immediately. Which type of neuron is primarily responsible for detecting the light stimulus in this reflex?

  • A. Sensory receptors (photoreceptors) in the retina of the eye ✓
  • B. Motor neurons in the iris muscle of the eye
  • C. Interneurons located in the spinal cord
  • D. Gustatory receptors in the cornea of the eye

Answer: A — Photoreceptors in the retina detect light stimulus and initiate the reflex arc; motor neurons cause the response (pupil constriction) but do not detect the stimulus, and gustatory receptors detect taste, not light.

Q6. Assertion (A): Electrical impulses in neurons travel from the dendrite through the cell body and along the axon in a single direction. Reason (R): Synapses contain vesicles that release neurotransmitters only from the axon terminal to the next cell. Choose the correct option:

  • 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

Answer: A — The one-way transmission at synapses (neurotransmitter release from presynaptic axon terminal) ensures impulses travel directionally through neurons; both statements are true and the structural feature of synapses explains the directional flow.

Q7. In a laboratory experiment, a student stimulates a frog's leg nerve with an electrical impulse and observes that the leg muscle contracts. If the same electrical impulse is applied directly to the muscle tissue (bypassing the nerve), what would be the most likely outcome?

  • A. The muscle would not contract because muscles require nerve signals to interpret stimuli
  • B. The muscle would still contract because muscle cells can respond directly to electrical stimulation ✓
  • C. The muscle would contract only if the stimulus is stronger than normal nerve impulses
  • D. The muscle would contract, but the response would be slower than when stimulated through the nerve

Answer: B — Muscle cells respond directly to electrical impulses; stimulating muscle directly bypasses the nerve but the muscle still contracts because it can respond to electrical signals independently, making option A incorrect.

Q8. Assertion (A): In a reflex arc, the sensory neuron synapse directly with the motor neuron through an interneuron located in the spinal cord. Reason (R): This arrangement allows the reflex action to occur without sending information to the brain, thereby reducing response time. Choose the correct option:

  • 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

Answer: A — The reflex arc involves sensory-interneuron-motor connections in the spinal cord, enabling rapid responses without brain involvement; the structural arrangement directly explains why reflex actions are faster than conscious responses.

Q9. A student observes that when she chews gum, saliva is produced automatically. Which of the following best explains this response?

  • A. Mechanoreceptors in the mouth detect chewing and trigger a reflex that stimulates salivary glands via the nervous system ✓
  • B. The muscles in the mouth directly secrete saliva without any nervous system involvement
  • C. The brain consciously decides to produce saliva whenever chewing is detected
  • D. Saliva is produced by the teeth grinding together, not by the nervous system

Answer: A — Salivary reflex is triggered by sensory receptors detecting mechanical stimulation (chewing), which activate the nervous system to stimulate salivary glands; option B incorrectly excludes nervous system involvement, and C falsely claims the response is conscious.

Q10. In an experiment, when a student's patellar tendon (just below the kneecap) is tapped with a small hammer, the leg kicks involuntarily. If the student's spinal cord were damaged at the level of the lower back, which of the following would most likely occur?

  • A. The knee-jerk reflex would still occur because the reflex arc can function through the local spinal cord segment, even if higher connections are damaged ✓
  • B. The knee-jerk reflex would be absent because the brain must be involved in all reflex actions
  • C. The knee-jerk reflex would occur but would be slower because signals must now travel through alternative neural pathways
  • D. The knee-jerk reflex would not occur because the hammer tap would not generate enough force to stimulate receptors

Answer: A — The knee-jerk reflex involves a local reflex arc in the spinal cord that operates independently of the brain; damage to higher spinal levels does not affect the reflex because it doesn't require brain involvement, making option B incorrect.

Flashcards

What are receptors and where are they located?

Receptors are specialized tips of nerve cells that detect environmental stimuli and are usually located in sense organs like the inner ear, nose, tongue, and eyes.

What is a synapse?

A synapse is the gap between the axon of one neuron and the dendrite of the next neuron across which chemical signals allow nerve impulses to pass.

Define a reflex action.

A reflex action is a sudden automatic response to an environmental stimulus that occurs without conscious thinking or voluntary control.

What is a reflex arc?

A reflex arc is a simple neural pathway connecting sensory and motor neurons directly through the spinal cord, allowing rapid responses without brain involvement.

Name the three main parts of a neuron and their functions.

Dendrite receives impulses, cell body contains the nucleus, and axon transmits impulses to other neurons or effector cells.

Why are reflex actions faster than conscious responses?

Reflex arcs bypass the brain by connecting sensory neurons directly to motor neurons in the spinal cord, eliminating the time needed for brain processing.

How does an electrical impulse become a chemical signal?

When an electrical impulse reaches the axon terminal, it triggers the release of chemicals (neurotransmitters) that cross the synapse to stimulate the next neuron.

Give an example of a reflex action in humans.

Pulling your hand away from a hot flame instantly without thinking is a reflex action controlled by a reflex arc in the spinal cord.

What is the pathway of a nerve impulse through a neuron?

The impulse travels from the dendrite to the cell body and then along the axon to its terminal end where it is transmitted to the next cell.

Why do we have reflex arcs if our brain can process signals?

Reflex arcs evolved to provide rapid protection in dangerous situations because thinking is complex and slow, and many animals lack advanced brains.

Important Board Questions

Define a synapse. What is its role in transmitting nerve impulses? [2 marks]

State that synapse is a gap between neurons; explain that electrical impulse converts to chemical signal (neurotransmitter) to cross the gap, then becomes electrical again in the next neuron.

Why is the reflex arc considered an efficient mechanism for rapid response? Explain with an example. [3 marks]

Explain that reflex arc bypasses brain by connecting sensory to motor neurons directly in spinal cord; this eliminates brain processing time. Example: touching hot object—hand pulls back before conscious pain is felt because spinal cord controls response while signal still travels to brain.

Describe the complete pathway of a reflex action from stimulus to response. Also explain why this pathway is faster than a response involving the brain's conscious thinking. [5 marks]

Draw or describe: stimulus detected by receptor → sensory neuron → spinal cord synapse → motor neuron → muscle contraction → response. Explain that brain thinking involves complex neuron networks and takes time; reflex arc is simple direct pathway in spinal cord requiring no brain processing. Provide example like pulling hand from flame or eye blinking. Conclude that reflex arc evolved because quick protection matters more than complex thought in dangerous situations.

Assertion-Reason Questions for Control and Coordination

Q1. Assertion (A):

Reflex actions are faster than conscious voluntary actions.

Reason (R):

Reflex arcs in the spinal cord bypass the brain, eliminating the time needed for conscious processing and thinking.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both the assertion and reason are true. Reflex actions are indeed faster because they use reflex arcs in the spinal cord that directly connect sensory neurons to motor neurons without involving the brain. This direct pathway eliminates the delay caused by conscious thought, making the reason the correct explanation for the assertion.

Q2. Assertion (A):

Sensory receptors like gustatory and olfactory receptors are located in sense organs.

Reason (R):

Sense organs contain specialized nerve endings that can generate electrical impulses in response to environmental stimuli.

Answer: B — Both A and R are true, but R is NOT the correct explanation of A — Both the assertion and reason are true statements. Gustatory receptors are in the tongue and olfactory receptors are in the nose. Sense organs do contain specialized receptor nerve endings. However, the reason doesn't explain why receptors are located in sense organs—it only describes what receptors do. The real reason is that sense organs are positioned where they can best detect environmental changes (taste particles in mouth, odor molecules in air).

Q3. Assertion (A):

The electrical impulse in a neuron travels from the dendrite through the cell body to the axon.

Reason (R):

This path ensures that impulses can reach the synapse where they are converted into chemical signals for transmission to the next neuron.

Answer: C — A is true but R is false — The assertion is true—impulses do travel dendrite → cell body → axon. However, the reason is partially misleading. The conversion to chemical signals happens at the axon terminal/synapse of one neuron affecting the dendrite of the next neuron, not during travel through a single neuron. The impulse remains electrical throughout its journey within one neuron; conversion occurs at the synapse between neurons.

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Case-Based Questions (CBQ) for Control and Coordination

Case Study:

A Class 10 student performed an experiment on taste perception with her friends. She asked five friends to eat different foods (sugar, salt, lemon juice, and bitter melon) under two conditions: (1) with nose open and (2) with nose pinched. The friends rated the taste intensity from 1-10 for each food. Results showed that when the nose was pinched, the taste ratings dropped by an average of 60% across all foods. However, the friends could still identify whether the food was sweet, salty, sour, or bitter, though the flavor seemed less intense.

Q1. Why did the taste ratings decrease when the nose was pinched?

  • A. Gustatory receptors stopped functioning
  • B. Olfactory receptors could not detect smell, which contributes to overall flavor perception ✓
  • C. The reflex arc in the spinal cord was blocked
  • D. Taste buds were physically blocked by the nose

Answer: B

Q2. Why could the friends still identify basic tastes (sweet, salty, sour, bitter) even with their nose pinched?

  • A. The brain remembered previous flavors
  • B. Gustatory receptors on the tongue still detected the basic taste qualities ✓
  • C. The pinching stimulated additional taste receptors
  • D. Olfactory receptors in the mouth replaced nasal receptors

Answer: B

Q3. This experiment demonstrates that flavor perception involves:

  • A. Only gustatory receptors working in the brain
  • B. Only olfactory receptors detecting food molecules
  • C. Both gustatory and olfactory receptors working together ✓
  • D. Neither taste nor smell receptors

Answer: C

Q4. If a person has a cold that blocks their nasal passages, they would most likely experience:

  • A. Completely normal taste sensation
  • B. Inability to identify any taste
  • C. Reduced flavor intensity but still ability to detect basic tastes ✓
  • D. Increased sweetness in all foods

Answer: C

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Previous Year Questions (PYQ) for Control and Coordination

Real CBSE board exam questions from past papers — free to attempt.

CBSE 2026 · Set 31/4/1 · 1 mark

Following are the statements about the different parts of the brain. Select the correct statements. (i) The thinking part of the brain is the forebrain. (ii) Centres for smell, hearing, memory, sight are located in forebrain. (iii) Salivation, vomiting, blood pressure are controlled by medulla in the hind brain. (iv) Cerebellum does not control the posture and balance of the body.

  • (i), (ii) and (iii)
  • (ii), (iii) and (iv)
  • (i), (ii) and (iv)
  • (i), (iii) and (iv)

CBSE 2026 · Set 31/4/1 · 2 marks

(A) Varun is diabetic. His latest ultrasound reports showed a blockage in his pancreatic duct. How will this affect the dual functioning of the pancreas?

CBSE 2026 · Set 31/4/1 · 3 marks

Give reasons for the following: (a) Adrenal gland is known as the stress gland of the body. (b) Prenatal sex determination is banned in India. (c) Vegetative propagation is advantageous in some plants.

CBSE 2026 · Set 31/4/1 · 4 marks

Plants exhibit movements in response to various environmental stimuli to adopt and survive in their surroundings. These movements, influenced by external factors such as light, gravity, water and chemicals are regulated by specific plant hormones. For example, the differential growth of plant parts allows them to bend, grow or orient themselves in particular directions. Roots and shoots often show contrasting response to the same stimulus, highlighting the complex mechanisms involved in plant growth and development.

(a) Why is hydrotropism essential for plants?

CBSE 2026 · Set 31/4/2 · 2 marks

(B) Sunil unconsciously touched the hot iron rod and immediately withdrew his hand. Which type of action is involved ? Also define this action. Draw a flow chart to show the path followed for this action.

CBSE 2026 · Set 31/4/3 · 2 marks

Sunil unconsciously touched the hot iron rod and immediately withdrew his hand. Which type of action is involved? Also define this action. Draw a flow chart to show the path followed for this action.

CBSE 2026 · Set 31/5/1 · 1 mark

Identify the endocrine gland that regulates the growth of human body.

  • Pituitary gland
  • Thyroid gland
  • Pancreas
  • Adrenal gland

CBSE 2026 · Set 31/5/2 · 2 marks

[Diagram-based question — skipped] OR (B) Which of the plant hormones are responsible for the following processes ? (i) Promote cell division (ii) Inhibition of growth (iii) Detection of light (iv) Wilting of leaves

CBSE 2026 · Set 31/5/2 · 3 marks

(a) Mention the gland and the hormone secreted by it in scary situation in human beings. (b) Write two responses that enable the human body to be ready to deal with such situation.

CBSE 2026 · Set 31/5/3 · 1 mark

Assertion (A): In case of iodine deficiency in our diet, there is a possibility that we might suffer from goitre. Reason (R): One of the symptoms of goitre is swelling of neck.

  • Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
  • Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
  • Assertion (A) is true, but Reason (R) is false.
  • Assertion (A) is false, but Reason (R) is true.

CBSE 2026 · Set 31/5/3 · 2 marks

[Diagram-based question — skipped]

Observe the given figure and identify the labelled parts P, Q, R and S:

CBSE 2026 · Set 31/2/1 · 1 mark

Identify the type of tropic movement that is responsible for the movement of the pollen tube towards an ovule from the following options.

  • Hydrotropism
  • Geotropism
  • Chemotropism
  • Phototropism

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Class 10 Science Formula Sheet

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