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NCERT Class 10 Science Control and Coordination: Exercise Solutions

Step-by-step working for every question of End-of-chapter exercises in NCERT's Class 10 Science book, chapter “Control and Coordination”, written by Shishya. Each question is in our own short words; open the NCERT chapter for the exact wording and figures.

1. Exercises Q1

   Which is a plant hormone: (a) insulin (b) thyroxin (c) oestrogen (d) cytokinin?

   1. Insulin is a hormone produced by the pancreas in animals to regulate blood sugar levels.
   2. Thyroxin is a hormone secreted by the thyroid gland in animals that controls metabolism.
   3. Oestrogen is a sex hormone found in animals that regulates reproductive development.
   4. Cytokinin is a plant hormone that promotes cell division and growth in plants.

   Answer: (d) cytokinin

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2. Exercises Q2

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

   1. A neuron consists of a cell body, dendrites, and an axon.
   2. The dendrites receive signals, while the axon transmits them away from the cell body.
   3. When an impulse travels to the end of an axon, it must cross a small space to reach the next neuron.
   4. This specific junction or gap where the signal is passed from one neuron to another is called a synapse.
   5. Therefore, the correct option is (b).

   Answer: (b) synapse

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3. Exercises Q3

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

   1. The cerebrum handles higher functions like thinking, memory, and decision-making.
   2. The medulla oblongata in the brainstem controls involuntary actions such as heart rate and breathing.
   3. The cerebellum coordinates movement and maintains the body's balance and posture.
   4. Since the brain manages thinking, heart rate, and balance, all the listed functions are correct.

   Answer: (d) all of these

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4. Exercises Q4

   What do receptors do in our body? What problems arise if they do not work properly?

   1. Receptors are sensory organs that detect changes in the internal or external environment.
   2. They convert these stimuli into electrical nerve impulses.
   3. These impulses are sent to the central nervous system for processing.
   4. If receptors do not work properly, the body cannot detect important changes like pain or temperature.
   5. This leads to a lack of appropriate responses, which can cause injury or illness.

   Answer: Receptors detect stimuli and convert them into nerve impulses; if they fail, the body cannot sense changes or respond, leading to harm.

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5. Exercises Q5

   Describe the structure of a neuron and explain its function.

   1. A neuron is the basic structural and functional unit of the nervous system.
   2. It has a cell body containing the nucleus and cytoplasm.
   3. Long, thin branches called dendrites extend from the cell body to receive signals.
   4. A single long branch called the axon transmits nerve impulses away from the cell body.
   5. The axon is covered by a myelin sheath with gaps called nodes of Ranvier.
   6. The axon ends in branched terminals called axon terminals or synaptic knobs.
   7. Neurons receive stimuli through dendrites and transmit impulses along the axon to effectors.
   8. This allows the body to respond to changes in the internal and external environment.

   Answer: A neuron consists of a cell body, dendrites, and an axon; it transmits electrical impulses from sensory receptors to the central nervous system and then to effectors.

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6. Exercises Q6

   How does phototropism occur in plants?

   1. Phototropism is the growth of a plant part towards a source of light.
   2. When light falls on one side of the stem, auxin (a plant hormone) accumulates on the shaded side.
   3. The higher concentration of auxin on the shaded side causes the cells there to elongate more than the cells on the lit side.
   4. This unequal growth on the two sides makes the stem bend towards the direction of the light.

   Answer: Phototropism occurs due to the accumulation of auxin on the shaded side of the stem, causing it to grow faster and bend towards the light.

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7. Exercises Q7

   Which signals are disrupted by a spinal cord injury?

   1. The spinal cord acts as a communication highway between the brain and the rest of the body.
   2. It carries motor signals from the brain to muscles and sensory signals from the body to the brain.
   3. A spinal cord injury damages the nerve fibres in this pathway.
   4. This damage blocks the transmission of both motor and sensory signals.
   5. As a result, the brain can no longer control muscles below the injury, and the body cannot send pain or touch signals to the brain.

   Answer: Both motor and sensory signals are disrupted by a spinal cord injury.

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8. Exercises Q8

   How does chemical coordination occur in plants?

   1. Chemical coordination in plants is achieved through the action of plant hormones, also known as phytohormones.
   2. These hormones are simple organic molecules synthesized in one part of the plant and transported to other parts where they exert their effects.
   3. Unlike animals, plants do not have a nervous system, so they rely on these chemical signals to coordinate growth, development, and responses to the environment.
   4. Examples of such hormones include auxins, which promote cell elongation, and gibberellins, which stimulate stem growth.
   5. The movement of these hormones can occur via the vascular tissues (xylem and phloem) or through diffusion in the plant tissues.
   6. This chemical signaling allows the plant to respond to stimuli like light, gravity, and touch in a coordinated manner.

   Answer: Chemical coordination in plants occurs through plant hormones (phytohormones) that are produced in one part and transported to other parts to regulate growth and development.

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9. Exercises Q9

   Why does an organism need a system of control and coordination?

   1. An organism must respond to changes in its internal and external environment to survive.
   2. Different parts of the body need to work together in a precise order for complex activities.
   3. Without coordination, cells and organs would not function in harmony, leading to failure.
   4. A control system ensures that responses are timely and appropriate to specific stimuli.
   5. This regulation maintains homeostasis and allows the organism to adapt to its surroundings.

   Answer: An organism needs a system of control and coordination to maintain homeostasis, ensure proper functioning of organs, and respond effectively to environmental changes for survival.

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10. Exercises Q10

    How do involuntary actions and reflex actions differ?

    1. Involuntary actions are automatic responses controlled by the spinal cord or brainstem without conscious thought.
    2. Reflex actions are a specific type of involuntary response that occur through a reflex arc involving a sensory neuron, relay neuron, and motor neuron.
    3. Involuntary actions can include slow processes like digestion or heartbeat, while reflex actions are typically rapid protective responses.
    4. Reflex actions do not involve the brain for the initial response, whereas some involuntary actions may be regulated by higher brain centers.
    5. The key difference is that all reflex actions are involuntary, but not all involuntary actions are reflexes.

    Answer: Involuntary actions are automatic body functions controlled by the autonomic nervous system, while reflex actions are rapid, specific involuntary responses to stimuli mediated by a reflex arc.

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11. Exercises Q11

    Compare nervous and hormonal mechanisms of control and coordination in animals.

    1. Nervous system uses neurons to transmit electrical impulses for rapid response.
    2. Hormonal system uses endocrine glands to release chemical messengers into the blood.
    3. Nervous control is fast and precise but short-lived.
    4. Hormonal control is slower but has a longer-lasting effect on the body.
    5. Nervous system coordinates immediate actions like muscle contraction.
    6. Hormonal system regulates long-term processes like growth and metabolism.
    7. Both systems work together to maintain homeostasis in animals.

    Answer: Nervous system provides fast, short-term control via electrical signals, while hormonal system provides slow, long-term control via chemical signals in blood.

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12. Exercises Q12

    How does movement in a sensitive plant differ from movement in our legs?

    1. The leaves of the sensitive plant (touch-me-not) fold quickly when touched; this movement is not due to growth.
    2. The plant has no nerves or muscles: the touch is passed from cell to cell as an electrical-chemical signal.
    3. It is controlled by changes in turgor pressure within the cells of the leaflets.
    4. Movement in our legs is a voluntary action controlled by the brain and spinal cord.
    5. This movement in animals is rapid and involves the contraction and relaxation of skeletal muscles.
    6. The leg movement is driven by the sliding of actin and myosin filaments within muscle fibers.

    Answer: In the sensitive plant, cells change shape by changing the amount of water in them (turgor), after an electrical-chemical signal passes cell to cell — no nerves or muscles. In our legs, the brain and spinal cord send nerve impulses to muscles, whose special proteins make the muscle cells contract and relax.

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