Chapter 7: Control and Coordination
NCERT Class 10 Science Exercise Solutions
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Each question block contains a "Show Answer" button. Click it to reveal the detailed answer. Only one answer is shown at a time — opening a new answer will hide the previous one. These solutions are designed to help you understand nervous system, hormones, and plant responses for exam success.
Question 1
Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin
Answer: (d) Cytokinin
Explanation: Cytokinin is a plant hormone that promotes cell division. Insulin and thyroxin are animal hormones (insulin from pancreas regulates blood sugar; thyroxin from thyroid regulates metabolism). Oestrogen is a female sex hormone in animals.
Explanation: Cytokinin is a plant hormone that promotes cell division. Insulin and thyroxin are animal hormones (insulin from pancreas regulates blood sugar; thyroxin from thyroid regulates metabolism). Oestrogen is a female sex hormone in animals.
Question 2
The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
Answer: (b) synapse
Explanation: A synapse is the junction between two neurons where nerve impulses are transmitted chemically via neurotransmitters. Dendrites receive signals, axons conduct impulses away from the cell body, and impulse is the electrical signal itself.
Explanation: A synapse is the junction between two neurons where nerve impulses are transmitted chemically via neurotransmitters. Dendrites receive signals, axons conduct impulses away from the cell body, and impulse is the electrical signal itself.
Question 3
The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
Answer: (d) all of the above
Explanation: The brain coordinates all voluntary and involuntary activities:
• Thinking: Cerebral cortex (forebrain)
• Heartbeat regulation: Medulla oblongata (hindbrain)
• Body balance: Cerebellum (hindbrain)
It also controls emotions, memory, speech, and sensory processing.
Explanation: The brain coordinates all voluntary and involuntary activities:
• Thinking: Cerebral cortex (forebrain)
• Heartbeat regulation: Medulla oblongata (hindbrain)
• Body balance: Cerebellum (hindbrain)
It also controls emotions, memory, speech, and sensory processing.
Question 4
What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Answer:
Function of receptors: Receptors are specialized nerve endings (in sense organs) that detect stimuli from the environment and convert them into electrical impulses. Examples: photoreceptors (eyes), olfactory receptors (nose), gustatory receptors (tongue), auditory receptors (ears), and skin receptors (touch, pain, temperature).
Problems if receptors don't work properly:
1. Vision impairment: Damaged photoreceptors → blindness or blurred vision
2. Hearing loss: Damaged auditory receptors → deafness
3. Loss of smell/taste: Common during colds or COVID-19
4. Numbness: Skin receptors damaged → inability to feel pain/touch (dangerous for burns/injuries)
5. Balance issues: Inner ear receptors damaged → vertigo, dizziness
6. Neuropathy: Diabetic nerve damage → reduced sensation in limbs
Function of receptors: Receptors are specialized nerve endings (in sense organs) that detect stimuli from the environment and convert them into electrical impulses. Examples: photoreceptors (eyes), olfactory receptors (nose), gustatory receptors (tongue), auditory receptors (ears), and skin receptors (touch, pain, temperature).
Problems if receptors don't work properly:
1. Vision impairment: Damaged photoreceptors → blindness or blurred vision
2. Hearing loss: Damaged auditory receptors → deafness
3. Loss of smell/taste: Common during colds or COVID-19
4. Numbness: Skin receptors damaged → inability to feel pain/touch (dangerous for burns/injuries)
5. Balance issues: Inner ear receptors damaged → vertigo, dizziness
6. Neuropathy: Diabetic nerve damage → reduced sensation in limbs
Question 5
Draw the structure of a neuron and explain its function.
Answer:
Structure of a neuron:
1. Dendrites: Branch-like extensions that receive signals from other neurons.
2. Cell body (Soma): Contains nucleus and cytoplasm.
3. Axon: Long fiber that transmits impulses away from cell body.
4. Myelin sheath: Fatty layer around axon that speeds up impulse transmission.
5. Nodes of Ranvier: Gaps in myelin sheath.
6. Axon terminal: End branches that connect to other neurons via synapses.
Function: Neurons are the functional units of the nervous system. They:
• Receive sensory input from receptors
• Process information in the brain/spinal cord
• Transmit motor output to effectors (muscles/glands)
• Enable rapid communication via electrical impulses (action potentials) and chemical transmission at synapses.
[For a diagram, students should draw a neuron with labeled parts: dendrites, cell body, nucleus, axon, myelin sheath, nodes of Ranvier, and axon terminal]
Structure of a neuron:
1. Dendrites: Branch-like extensions that receive signals from other neurons.
2. Cell body (Soma): Contains nucleus and cytoplasm.
3. Axon: Long fiber that transmits impulses away from cell body.
4. Myelin sheath: Fatty layer around axon that speeds up impulse transmission.
5. Nodes of Ranvier: Gaps in myelin sheath.
6. Axon terminal: End branches that connect to other neurons via synapses.
Function: Neurons are the functional units of the nervous system. They:
• Receive sensory input from receptors
• Process information in the brain/spinal cord
• Transmit motor output to effectors (muscles/glands)
• Enable rapid communication via electrical impulses (action potentials) and chemical transmission at synapses.
Question 6
How does phototropism occur in plants?
Answer:
Phototropism is the directional growth response of plants to light.
Mechanism:
1. Auxin redistribution: When light falls on one side of a shoot tip, auxin (plant hormone) accumulates on the shaded side.
2. Differential growth: Higher auxin concentration on shaded side promotes faster cell elongation.
3. Bending: The shaded side grows longer than the illuminated side, causing the shoot to bend toward light (positive phototropism).
4. Root response: Roots show negative phototropism (bend away from light) as auxin inhibits root growth.
Significance: Maximizes light absorption for photosynthesis in shoots; roots grow deeper into soil away from light.
Phototropism is the directional growth response of plants to light.
Mechanism:
1. Auxin redistribution: When light falls on one side of a shoot tip, auxin (plant hormone) accumulates on the shaded side.
2. Differential growth: Higher auxin concentration on shaded side promotes faster cell elongation.
3. Bending: The shaded side grows longer than the illuminated side, causing the shoot to bend toward light (positive phototropism).
4. Root response: Roots show negative phototropism (bend away from light) as auxin inhibits root growth.
Significance: Maximizes light absorption for photosynthesis in shoots; roots grow deeper into soil away from light.
Question 7
Which signals will get disrupted in case of a spinal cord injury?
Answer:
Spinal cord injury disrupts communication between brain and body parts below the injury site:
Disrupted signals:
1. Sensory signals (ascending tracts): Impulses from skin, muscles, organs to brain → loss of touch, pain, temperature sensation below injury.
2. Motor signals (descending tracts): Commands from brain to muscles → paralysis (loss of voluntary movement) below injury.
3. Reflex arcs: Some reflexes may be lost or exaggerated depending on injury level.
4. Autonomic signals: Control of bladder, bowel, sexual function, blood pressure regulation.
Consequences: Paralysis (paraplegia if lower body; quadriplegia if all limbs), loss of sensation, incontinence, and possible respiratory problems if injury is high cervical.
Spinal cord injury disrupts communication between brain and body parts below the injury site:
Disrupted signals:
1. Sensory signals (ascending tracts): Impulses from skin, muscles, organs to brain → loss of touch, pain, temperature sensation below injury.
2. Motor signals (descending tracts): Commands from brain to muscles → paralysis (loss of voluntary movement) below injury.
3. Reflex arcs: Some reflexes may be lost or exaggerated depending on injury level.
4. Autonomic signals: Control of bladder, bowel, sexual function, blood pressure regulation.
Consequences: Paralysis (paraplegia if lower body; quadriplegia if all limbs), loss of sensation, incontinence, and possible respiratory problems if injury is high cervical.
Question 8
How does chemical coordination occur in plants?
Answer:
Chemical coordination in plants is achieved through plant hormones (phytohormones) that regulate growth, development, and responses to stimuli.
Mechanism:
1. Hormone production: Produced in meristematic tissues (shoot/root tips, young leaves).
2. Transport: Diffuse through cells or move via vascular tissues.
3. Target cells: Bind to specific receptors, triggering physiological responses.
Major plant hormones and functions:
• Auxins: Cell elongation, phototropism, apical dominance
• Gibberellins: Stem elongation, seed germination, fruit growth
• Cytokinins: Cell division, delay aging
• Abscisic acid (ABA): Stress response, stomatal closure, seed dormancy
• Ethylene: Fruit ripening, leaf abscission, senescence
Unlike animals, plants lack specialized glands; hormones act where produced or transported.
Chemical coordination in plants is achieved through plant hormones (phytohormones) that regulate growth, development, and responses to stimuli.
Mechanism:
1. Hormone production: Produced in meristematic tissues (shoot/root tips, young leaves).
2. Transport: Diffuse through cells or move via vascular tissues.
3. Target cells: Bind to specific receptors, triggering physiological responses.
Major plant hormones and functions:
• Auxins: Cell elongation, phototropism, apical dominance
• Gibberellins: Stem elongation, seed germination, fruit growth
• Cytokinins: Cell division, delay aging
• Abscisic acid (ABA): Stress response, stomatal closure, seed dormancy
• Ethylene: Fruit ripening, leaf abscission, senescence
Unlike animals, plants lack specialized glands; hormones act where produced or transported.
Question 9
What is the need for a system of control and coordination in an organism?
Answer:
Control and coordination systems are essential for:
1. Responding to stimuli: Environmental changes (light, temperature, touch) require appropriate responses for survival.
2. Maintaining homeostasis: Internal balance of temperature, pH, glucose levels, etc.
3. Integrating body functions: Different organs must work together harmoniously (e.g., during digestion, respiration).
4. Ensuring timely responses: Reflex actions protect from harm (withdrawing hand from fire).
5. Growth and development: Regulated by hormones in plants and animals.
6. Reproduction: Hormonal control of sexual maturation and breeding cycles.
7. Movement and locomotion: Nervous system coordinates muscle contraction.
8. Adaptation: Helps organisms adapt to changing environments.
Without control and coordination, organisms would be unable to function effectively or survive.
Control and coordination systems are essential for:
1. Responding to stimuli: Environmental changes (light, temperature, touch) require appropriate responses for survival.
2. Maintaining homeostasis: Internal balance of temperature, pH, glucose levels, etc.
3. Integrating body functions: Different organs must work together harmoniously (e.g., during digestion, respiration).
4. Ensuring timely responses: Reflex actions protect from harm (withdrawing hand from fire).
5. Growth and development: Regulated by hormones in plants and animals.
6. Reproduction: Hormonal control of sexual maturation and breeding cycles.
7. Movement and locomotion: Nervous system coordinates muscle contraction.
8. Adaptation: Helps organisms adapt to changing environments.
Without control and coordination, organisms would be unable to function effectively or survive.
Question 10
How are involuntary actions and reflex actions different from each other?
Answer:
| Reflex Actions | Involuntary Actions |
|---|---|
| Rapid, automatic responses to specific stimuli | Ongoing regulatory activities not under conscious control |
| Involve spinal cord or lower brain (medulla) | Controlled by midbrain, hindbrain, or autonomic nervous system |
| Purpose: Immediate protection (e.g., blinking, knee jerk) | Purpose: Maintain internal functions (e.g., heartbeat, digestion) |
| Can be somatic (withdrawing hand) or autonomic (pupil constriction) | Mostly autonomic (smooth/cardiac muscle control) |
| Pathway: Reflex arc (receptor → sensory neuron → spinal cord → motor neuron → effector) | Pathway: Complex neural/hormonal regulation |
| Examples: Sneezing, coughing, withdrawing hand from hot object | Examples: Heartbeat, peristalsis, breathing, gland secretion |
Both are automatic but differ in speed, control center, and purpose.
Question 11
Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Answer:
| Aspect | Nervous System | Endocrine System (Hormonal) |
|---|---|---|
| Nature of message | Electrical impulses and neurotransmitters | Chemical hormones |
| Transmission | Through neurons (fast) | Through bloodstream (slow) |
| Speed | Very fast (milliseconds) | Slow (seconds to hours) |
| Duration | Short-lived effects | Long-lasting effects |
| Target | Specific muscles/glands | Multiple organs/tissues |
| Response | Localized, precise | Widespread, generalized |
| Control | Voluntary and involuntary | Mainly involuntary |
| Adaptation | Rapid adjustments | Long-term changes (growth, metabolism) |
| Components | Brain, spinal cord, nerves | Glands (pituitary, thyroid, etc.) |
| Examples | Reflex actions, muscle movement | Growth (GH), metabolism (thyroxin), stress (adrenaline) |
Both systems work together: e.g., hypothalamus links nervous and endocrine systems.
Question 12
What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Answer:
| Sensitive Plant (Mimosa pudica) | Human Leg Movement |
|---|---|
| Type of movement: Nastic movement (non-directional) | Type of movement: Voluntary muscular movement |
| Mechanism: Changes in turgor pressure; loss of water from leaf base cells causes drooping | Mechanism: Contraction and relaxation of skeletal muscles |
| Control: Chemical-electrical signals between cells (no nervous system) | Control: Nervous system (brain → spinal cord → motor neurons → muscles) |
| Speed: Relatively fast (seconds) but slower than animal movement | Speed: Very fast (fraction of a second) |
| Energy: No ATP used directly for movement; osmotic changes | Energy: ATP required for muscle contraction |
| Reversibility: Reversible (leaves regain turgor after some time) | Reversibility: Reversible through opposing muscle actions |
| Purpose: Defense against herbivores/predators | Purpose: Locomotion, manipulation, balance |
| Involvement of growth: No growth involved (immediate response) | Involvement of growth: No growth involved |
Plant movement is due to water changes in cells; animal movement is due to specialized muscle tissues controlled by nerves.