A plant is placed in a completely dark chamber with a single tiny opening that admits light from one side. After 24 hours, the tip of the shoot is cut off and light is again provided from the same direction. What will be observed over the next few hours?

The shoot remains straight with no bending

The shoot bends sharply toward the light

The shoot remains straight with no bending

The shoot bends away from the light

The shoot shows irregular twisting

In a reflex action, the correct sequence of impulse travel is

Sensory neuron → relay neuron → motor neuron

Sensory neuron → motor neuron → relay neuron

Motor neuron → sensory neuron → relay neuron

Sensory neuron → relay neuron → motor neuron

Relay neuron → sensory neuron → motor neuron

Assertion (A): Insulin is secreted by the pancreas. Reason (R): Pancreas is an endocrine gland that also secretes digestive enzymes.

Both A and R are true but R is not the correct explanation of A.

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

Why does a plant shoot exhibit positive phototropism? Explain the hormonal mechanism behind this bending.

Auxin, a plant hormone, accumulates on the shaded side of the shoot, causing those cells to elongate more than cells on the lighted side, which makes the shoot bend toward the light source.

Name the hormone that lowers the blood sugar level in the human body and state the gland that secretes it.

Insulin, secreted by the pancreas (β-cells of islets of Langerhans).

Explain how a feedback mechanism regulates the secretion of thyroxine in the human body.

The hypothalamus releases thyrotropin-releasing hormone (TRH) when thyroxine levels are low. TRH stimulates the pituitary gland to secrete thyroid-stimulating hormone (TSH). TSH then acts on the thyroid gland, prompting it to produce and release thyroxine. As thyroxine concentration in the blood rises, it inhibits the release of TRH from the hypothalamus and TSH from the pituitary. This negative feedback loop ensures that thyroxine levels remain within a normal range.

How does the nervous system help a person to respond to a sudden danger, like seeing a snake? Trace the sequence of events from the sensory input to the motor output, and explain the role of the brain and hormonal system in this situation.

When the eyes see a snake, the visual sensory receptors send signals via sensory neurons to the brain (thalamus → visual cortex). The brain interprets the image as dangerous. Association areas quickly trigger a motor response; motor neurons carry commands to leg muscles, causing the person to run. Simultaneously, the brain (hypothalamus) activates the sympathetic nervous system, which stimulates the adrenal glands to release adrenaline. Adrenaline increases heart rate, breathing rate, and energy availability, preparing the body for a rapid ‘fight or flight’ response.

Trace the pathway of an involuntary action such as breathing, starting from the detection of high carbon dioxide levels in the blood. Include the role of the medulla oblongata, diaphragm, and intercostal muscles. Explain how this reflex arc is different from a spinal reflex.

When carbon dioxide levels in the blood rise, it is detected by chemoreceptors in the medulla oblongata and in the carotid and aortic bodies. The medulla oblongata, located in the hindbrain, contains the respiratory center. It integrates this information and sends nerve impulses via motor neurons to the diaphragm (through the phrenic nerve) and the intercostal muscles (through intercostal nerves). These muscles contract, causing inspiration: the diaphragm flattens, and the rib cage expands, reducing intra-thoracic pressure and drawing air into the lungs. As CO2 levels normalize, the stimulation decreases, and expiration occurs passively or through relaxation. This is an involuntary reflex arc that involves the brain stem, not just the spinal cord. In contrast, a spinal reflex, such as the knee-jerk, bypasses the brain entirely; sensory neuron synapses with motor neuron within the spinal cord, and the response is automatic without involvement of higher brain centers. The breathing reflex involves integration in the medulla, which is part of the brain, making it a cranial reflex, not a simple spinal reflex.

Explain the feedback mechanism that regulates the secretion of thyroxine hormone. How does this mechanism maintain homeostasis?

The secretion of thyroxine is regulated by a negative feedback mechanism involving the hypothalamus and pituitary gland. The hypothalamus secretes thyrotropin-releasing hormone (TRH), which stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH). TSH then acts on the thyroid gland to produce thyroxine (T4) and triiodothyronine (T3). When the level of thyroxine in the blood rises above normal, it inhibits the secretion of TRH from the hypothalamus and TSH from the pituitary. This reduces the stimulation of the thyroid, bringing thyroxine levels back to normal. If thyroxine levels fall too low, the inhibition is removed, and TRH/TSH secretion increases, restoring normal levels. This feedback loop maintains homeostasis by keeping thyroxine within a narrow, optimal range, ensuring stable metabolic rate, growth, and development.

Tetrodotoxin (TTX) is a potent neurotoxin found in puffer fish. It specifically blocks voltage-gated sodium channels on neurons. Sam, a marine biologist, accidentally ingests a small amount of the toxin while handling the fish. He begins to experience numbness and muscle weakness. (1) Briefly describe the sequence of events during the generation of a nerve impulse (action potential) in a typical neuron, highlighting the role of sodium channels. (2) Explain why blocking sodium channels leads to numbness and muscle weakness. (3) Why would TTX poisoning be especially dangerous if it affects motor neurons controlling the diaphragm?

Nerve impulse involves Na+ influx through voltage-gated channels causing depolarization. TTX blocks these channels, preventing impulse generation, causing numbness (no sensory transmission) and muscle weakness (no motor activation). Diaphragm paralysis stops breathing, fatal.

Class 10 Science Chapter 6: Control and Coordination — Important Questions & Sample Paper

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Class 10 Science Chapter 6, ‘Control and Coordination’, explores how organisms detect and respond to changes in their environment. In animals, this is achieved through the nervous system and hormonal (endocrine) system. Students learn about neurons, the structure and function of the brain—cerebrum, cerebellum, and medulla oblongata—and the reflex arc that enables quick, involuntary responses, like withdrawing a hand from a hot object. The chapter also covers chemical coordination via hormones such as adrenaline, thyroxine, and insulin, emphasizing the negative feedback mechanisms that maintain homeostasis. For instance, insulin secretion after a high-carb meal prevents a spike in blood glucose. Plant coordination, though lacking a nervous system, is equally important. The chapter discusses tropic movements: phototropism (growth towards light), geotropism (roots growing downwards), and chemotropism. Experiments, such as covering a plant shoot tip and observing directional growth, illustrate these concepts. Plant hormones like auxin, gibberellin, and cytokinin play key roles. Exam questions from this chapter test both conceptual understanding and application. Students may encounter scenario-based questions on reflex actions, identification of affected brain regions from symptoms, reasoning about hormonal regulation, and experimental analysis of plant movements. A solid grasp of the sequence of events in a reflex arc and the feedback loops is essential. This question bank provides focused practice to help students master these critical topics.

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Science — Control and Coordination

Class 10Time: 3 hrsMax Marks: 80

SECTION A

1.
A plant is placed in a completely dark chamber with a single tiny opening that admits light from one side. After 24 hours, the tip of the shoot is cut off and light is again provided from the same direction. What will be observed over the next few hours?
(a) The shoot bends sharply toward the light(b) The shoot remains straight with no bending(c) The shoot bends away from the light(d) The shoot shows irregular twisting
1
2.
In a reflex action, the correct sequence of impulse travel is
(a) Sensory neuron → motor neuron → relay neuron(b) Motor neuron → sensory neuron → relay neuron(c) Sensory neuron → relay neuron → motor neuron(d) Relay neuron → sensory neuron → motor neuron
1
3.
A seed germinates in soil. As the seedling grows, its roots curve downward irrespective of the seed's orientation. This response is an example of
(a) Positive phototropism(b) Negative geotropism(c) Positive geotropism(d) Negative hydrotropism
1

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In a CBSE exam, this chapter typically contributes questions across the following types. The last column shows how many original questions of each type we have ready in our bank for this chapter:

Question type	Marks each	In our bank
Multiple Choice (MCQ)	1 mark	13
Assertion–Reason	1 mark	6
Short Answer	2 marks	8
Short Answer	3 marks	6
Long Answer	5 marks	5
Case Study	4 marks	6

44 original, exam-style questions in our bank for this chapter — with answers.

Important & sample questions (with answers)

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Q1. A plant is placed in a completely dark chamber with a single tiny opening that admits light from one side. After 24 hours, the tip of the shoot is cut off and light is again provided from the same direction. What will be observed over the next few hours?
1 mark
Multiple Choice (MCQ)
(A) The shoot bends sharply toward the light(B) The shoot remains straight with no bending(C) The shoot bends away from the light(D) The shoot shows irregular twisting
▸ Answer▾ Answer
The shoot remains straight with no bending
Q2. In a reflex action, the correct sequence of impulse travel is
1 mark
Multiple Choice (MCQ)
(A) Sensory neuron → motor neuron → relay neuron(B) Motor neuron → sensory neuron → relay neuron(C) Sensory neuron → relay neuron → motor neuron(D) Relay neuron → sensory neuron → motor neuron
▸ Answer▾ Answer
Sensory neuron → relay neuron → motor neuron
Q3. A seed germinates in soil. As the seedling grows, its roots curve downward irrespective of the seed's orientation. This response is an example of
1 mark
Multiple Choice (MCQ)
(A) Positive phototropism(B) Negative geotropism(C) Positive geotropism(D) Negative hydrotropism
▸ Answer▾ Answer
Positive geotropism
Q4. A patient exhibits irregular and uncontrolled breathing and heartbeat but has intact memory and intellectual function. Based on this, which part of the brain is most likely affected?
1 mark
Multiple Choice (MCQ)
(A) Cerebrum(B) Cerebellum(C) Medulla oblongata(D) Hypothalamus
▸ Answer▾ Answer
Medulla oblongata
Q5. Assertion (A): Insulin is secreted by the pancreas. Reason (R): Pancreas is an endocrine gland that also secretes digestive enzymes.
1 mark
Assertion–Reason
(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▾ Answer
Both A and R are true but R is not the correct explanation of A.
Q6. Why does a plant shoot exhibit positive phototropism? Explain the hormonal mechanism behind this bending.
2 marks
Short Answer
▸ Answer▾ Answer
Auxin, a plant hormone, accumulates on the shaded side of the shoot, causing those cells to elongate more than cells on the lighted side, which makes the shoot bend toward the light source.
Q7. Name the hormone that lowers the blood sugar level in the human body and state the gland that secretes it.
2 marks
Short Answer
▸ Answer▾ Answer
Insulin, secreted by the pancreas (β-cells of islets of Langerhans).
Q8. Explain how a feedback mechanism regulates the secretion of thyroxine in the human body.
3 marks
Short Answer
▸ Answer▾ Answer
The hypothalamus releases thyrotropin-releasing hormone (TRH) when thyroxine levels are low. TRH stimulates the pituitary gland to secrete thyroid-stimulating hormone (TSH). TSH then acts on the thyroid gland, prompting it to produce and release thyroxine. As thyroxine concentration in the blood rises, it inhibits the release of TRH from the hypothalamus and TSH from the pituitary. This negative feedback loop ensures that thyroxine levels remain within a normal range.
Q9. How does the nervous system help a person to respond to a sudden danger, like seeing a snake? Trace the sequence of events from the sensory input to the motor output, and explain the role of the brain and hormonal system in this situation.
3 marks
Short Answer
▸ Answer▾ Answer
When the eyes see a snake, the visual sensory receptors send signals via sensory neurons to the brain (thalamus → visual cortex). The brain interprets the image as dangerous. Association areas quickly trigger a motor response; motor neurons carry commands to leg muscles, causing the person to run. Simultaneously, the brain (hypothalamus) activates the sympathetic nervous system, which stimulates the adrenal glands to release adrenaline. Adrenaline increases heart rate, breathing rate, and energy availability, preparing the body for a rapid ‘fight or flight’ response.
Q10. Trace the pathway of an involuntary action such as breathing, starting from the detection of high carbon dioxide levels in the blood. Include the role of the medulla oblongata, diaphragm, and intercostal muscles. Explain how this reflex arc is different from a spinal reflex.
5 marks
Long Answer
▸ Answer▾ Answer
When carbon dioxide levels in the blood rise, it is detected by chemoreceptors in the medulla oblongata and in the carotid and aortic bodies. The medulla oblongata, located in the hindbrain, contains the respiratory center. It integrates this information and sends nerve impulses via motor neurons to the diaphragm (through the phrenic nerve) and the intercostal muscles (through intercostal nerves). These muscles contract, causing inspiration: the diaphragm flattens, and the rib cage expands, reducing intra-thoracic pressure and drawing air into the lungs. As CO2 levels normalize, the stimulation decreases, and expiration occurs passively or through relaxation. This is an involuntary reflex arc that involves the brain stem, not just the spinal cord. In contrast, a spinal reflex, such as the knee-jerk, bypasses the brain entirely; sensory neuron synapses with motor neuron within the spinal cord, and the response is automatic without involvement of higher brain centers. The breathing reflex involves integration in the medulla, which is part of the brain, making it a cranial reflex, not a simple spinal reflex.
Q11. Explain the feedback mechanism that regulates the secretion of thyroxine hormone. How does this mechanism maintain homeostasis?
5 marks
Long Answer
▸ Answer▾ Answer
The secretion of thyroxine is regulated by a negative feedback mechanism involving the hypothalamus and pituitary gland. The hypothalamus secretes thyrotropin-releasing hormone (TRH), which stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH). TSH then acts on the thyroid gland to produce thyroxine (T4) and triiodothyronine (T3). When the level of thyroxine in the blood rises above normal, it inhibits the secretion of TRH from the hypothalamus and TSH from the pituitary. This reduces the stimulation of the thyroid, bringing thyroxine levels back to normal. If thyroxine levels fall too low, the inhibition is removed, and TRH/TSH secretion increases, restoring normal levels. This feedback loop maintains homeostasis by keeping thyroxine within a narrow, optimal range, ensuring stable metabolic rate, growth, and development.
Q12. Tetrodotoxin (TTX) is a potent neurotoxin found in puffer fish. It specifically blocks voltage-gated sodium channels on neurons. Sam, a marine biologist, accidentally ingests a small amount of the toxin while handling the fish. He begins to experience numbness and muscle weakness.
4 marks
Case Study
1. (i) Briefly describe the sequence of events during the generation of a nerve impulse (action potential) in a typical neuron, highlighting the role of sodium channels.2 marks
2. (ii) Explain why blocking sodium channels leads to numbness and muscle weakness.1 mark
3. (iii) Why would TTX poisoning be especially dangerous if it affects motor neurons controlling the diaphragm?1 mark
▸ Answer▾ Answer
Nerve impulse involves Na+ influx through voltage-gated channels causing depolarization. TTX blocks these channels, preventing impulse generation, causing numbness (no sensory transmission) and muscle weakness (no motor activation). Diaphragm paralysis stops breathing, fatal.

Frequently asked questions

What is a reflex arc?

A reflex arc is the pathway of nerve impulses that produces a reflex action. It typically includes a sensory neuron, relay neuron in the spinal cord, and motor neuron. It enables quick, involuntary responses to protect the body from harm, like withdrawing a hand from heat.

How does auxin control phototropism?

When light shines from one side, auxin moves to the shaded side of the shoot tip, causing cells there to elongate more. This differential growth bends the shoot towards the light.

Which part of the brain regulates involuntary actions like breathing and heartbeat?

The medulla oblongata in the hindbrain controls involuntary vital functions such as breathing, heartbeat, and blood pressure. Damage to this area can be fatal.

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