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The Vault
RowQ
The Vault
CBSE Class 10 Biology · 11 questions · 26 marks
From the instant a hand jerks away from something hot to the slow bending of a sunflower toward light, living organisms constantly sense their surroundings and respond to them. This chapter explores two coordination systems working together in animals — the fast, wire-like nervous system and the slower, chemical hormonal system — as well as how plants coordinate growth using hormones without any nerves at all. Along the way you will trace the exact path a nerve impulse takes during a reflex action.
Which hormone is often called the 'fight or flight' hormone because it prepares the body to deal with emergencies?
Answer
Adrenaline is correct — secreted by the adrenal glands, it increases heartbeat, breathing rate, and blood supply to muscles during stress or danger.
The tiny gap across which a nerve impulse passes from one neuron to the next is called a:
Answer
Synapse is correct — the electrical impulse triggers release of chemical neurotransmitters that cross this gap to stimulate the next neuron.
Which plant hormone mainly promotes cell division and is used to delay the ageing of leaves?
Answer
Cytokinin is correct — it is found in high concentration in growing tissues like fruits and seeds and promotes cell division.
Deficiency of iodine in the diet leads to under-production of thyroxine and causes:
Answer
Goitre is correct — iodine is essential for thyroxine synthesis, and its deficiency causes an enlarged thyroid gland.
Assertion (A): The knee-jerk and similar reflex actions occur very quickly, before we consciously realise what has happened. Reason (R): Reflex actions are controlled directly by the spinal cord through a reflex arc, so the signal does not have to wait for processing by the brain.
Answer
Both A and R are true and R is the correct explanation of A — the reflex arc allows a rapid motor response via the spinal cord, even though the brain is informed of the action shortly after.
What is a synapse and what role does it play in the transmission of a nerve impulse?
Answer
A synapse is the small gap between the axon terminal of one neuron and the dendrite of the next neuron (or an effector organ). When an electrical impulse reaches the end of a neuron, it triggers the release of chemical messengers called neurotransmitters into the synapse; these diffuse across the gap and generate a new electrical impulse in the next neuron, ensuring the signal travels in one direction only.
Differentiate between nervous coordination and hormonal coordination in animals.
Answer
Nervous coordination uses electrical impulses carried along neurons; it acts very rapidly, produces an immediate but short-lived response, and is generally targeted to specific muscles or glands. Hormonal coordination uses chemical messengers (hormones) released into the bloodstream by endocrine glands; it acts more slowly since hormones must travel through blood, but produces a longer-lasting, more widespread effect on target organs throughout the body.
Explain phototropism with a suitable example.
Answer
Phototropism is the directional growth movement of a plant part in response to light. Shoots typically show positive phototropism, bending toward the light source, because auxin accumulates on the shaded side of the shoot, causing cells there to elongate more than on the illuminated side — for example, a potted plant kept near a window gradually bends its stem toward the light.
Explain, step by step, the pathway of a reflex arc when a person accidentally touches a sharp pin.
Answer
When the finger touches a sharp pin, receptors in the skin detect the painful stimulus and generate an electrical impulse. This impulse travels along a sensory neuron to the spinal cord. Inside the spinal cord, the sensory neuron passes the signal to a relay (connector) neuron, which immediately relays it to a motor neuron. The motor neuron carries the impulse to an effector — the muscles of the arm — causing them to contract and quickly withdraw the hand, all without waiting for the brain to process the pain. This entire pathway (receptor to sensory neuron to spinal cord to motor neuron to effector) is called the reflex arc; it allows a very fast protective response, while a slightly delayed signal also travels up to the brain so the person becomes consciously aware of the pain.
Describe the location and function of any four human endocrine glands and the hormones they secrete.
Answer
The pituitary gland, located at the base of the brain, secretes growth hormone, which regulates growth of the body; its deficiency in childhood causes dwarfism and excess causes gigantism. The thyroid gland, in the neck, secretes thyroxine, which regulates carbohydrate, fat, and protein metabolism in the body; it requires iodine for synthesis. The pancreas secretes insulin, which lowers blood glucose level by promoting its conversion to glycogen for storage; insufficient insulin secretion causes diabetes. The adrenal glands, located above the kidneys, secrete adrenaline, which increases heartbeat, breathing rate, and blood flow to muscles to prepare the body for emergency situations.
A student accidentally places her hand on a hot vessel while cooking. Her hand jerks away almost instantly, and only a moment later does she feel the sensation of pain and shout out. Based on this situation, explain why the withdrawal of the hand happens before the pain is consciously felt, and name the structure primarily responsible for this rapid response.
Answer
The withdrawal of the hand is a reflex action, controlled by a reflex arc that operates through the spinal cord rather than the brain. As soon as heat receptors in the skin detect the harmful stimulus, the signal travels via a sensory neuron directly to the spinal cord, where it is relayed to a motor neuron that instructs the arm muscles to contract and pull the hand away — this happens within a fraction of a second. The sensation of pain, however, is felt only when a separate signal reaches the cerebrum in the brain, which takes slightly longer, so the hand is withdrawn before the pain is consciously registered. The spinal cord is the structure primarily responsible for this rapid protective response.
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