Class 10 Science · Chapter 6
Control and Coordination
286 Class 10 Science questions on Control and Coordination from the NCERT textbook, NCERT Exemplar and CBSE board papers 2018–2026, each with its answer and a step-by-step solution.
NCERT exercises
NCERT Exemplar exercises
CBSE Class 10 Science previous year papers, with answers →
Questions · page 12 of 15
- Q221 CBSE 2023List two differences between the movement of leaves of a sensitive plant and the movement of a shoot towards light.Step-by-step solution →
Show answer
Leaf folding is a fast, reversible, non-directional movement without growth; shoot bending towards light is a slow, permanent, directional growth movement.
The folding of the leaves of a sensitive plant is not a growth movement: it is caused by a rapid change in the amount of water in the cells at the base of the leaf, so it is very fast and it can be reversed. The bending of a shoot towards light **is** a growth movement: the cells on the shaded side grow longer, so it is slow and permanent. Secondly, the leaf movement has no direction of its own — the leaflets fold the same way wherever they are touched — whereas the shoot always bends towards the side the light comes from. - Q222 CBSE 2023How is an electric impulse created in human nervous system ? Identify the parts of a neuron which helps the nerve impulse to travel
- (i)towards the cell body
- (ii)away from the cell body
Step-by-step solution →Show answer
A chemical reaction at the dendritic tip creates the impulse; the dendrite carries it towards the cell body, the axon away from it.
An electrical impulse is created when information from the environment, acquired at the end of the dendritic tip of a nerve cell, sets off a chemical reaction there; this chemical reaction creates the electrical impulse. (i) The dendrite carries the impulse towards the cell body. (ii) The axon carries it away from the cell body, to its end, where chemicals are released that cross the synapse and start a similar impulse in the next neuron. - Q223 CBSE 2023Where are auxins synthesized in a plant ? Which organ of the plant shows :
- (i)Positive phototropism
- (ii)Negative geotropism
- (iii)Positive hydrotropism
Step-by-step solution →Show answer
Auxins are synthesised at the shoot tip; the shoot shows positive phototropism and negative geotropism, and the root positive hydrotropism.
Auxins are synthesised at the tip (apex) of the shoot, in the growing tip of the stem, and diffuse from there to the region behind the tip. (i) Positive phototropism: the shoot (stem). (ii) Negative geotropism: the shoot (stem). (iii) Positive hydrotropism: the root. - Q224 CBSE 2023What happens at synapse between two neurons? State briefly.Step-by-step solution →
Show answer
At a synapse, a chemical released at the axon end crosses a small gap and starts a fresh impulse in the next neuron.
At a synapse the axon end of one neuron and the dendrite of the next do not touch; a very small gap lies between them. When the electrical impulse reaches the end of the axon it causes the release of a chemical into this gap. The chemical crosses the gap and starts a fresh electrical impulse in the dendrite of the next neuron. Since the chemical is released only on the axon side, the message can cross in one direction only. - Q225 CBSE 2023With the help of an example, explain how does the feedback mechanism regulate the hormone secretion.Step-by-step solution →
Show answer
Feedback adjusts hormone release; for example, a rise in blood sugar makes the pancreas produce more insulin, and as sugar falls, insulin is reduced.
Hormones must be secreted in precise quantities, and the timing and amount of their release are regulated by feedback mechanisms: the change a hormone brings about is itself sensed and used to adjust how much of the hormone is released. Example: if the sugar level in the blood rises, as after a meal, the cells of the pancreas detect it and respond by producing more insulin; insulin helps bring the blood sugar level down, and as the sugar level falls, the secretion of insulin is reduced. - Q226 CBSE 2023Give an example of a plant hormone that promotes growth. Explain how this hormone promotes the growth of tendril around a support.Step-by-step solution →
Show answer
The hormone is auxin; it collects on the free side of the tendril, which elongates faster, so the tendril winds round the support.
Example of a growth-promoting plant hormone: auxin. When the tip of a tendril touches a support, auxin moves away from the side of the tendril that is in contact with the support and collects on the side away from it. The cells on that free side therefore elongate faster than the cells on the side touching the support. This unequal growth on the two sides makes the tendril bend towards the support and wind around it. The response to touch is called thigmotropism. - Q227 CBSE 2023“Pancreas has dual nature.” Justify this statement with an example.Step-by-step solution →
Show answer
The pancreas is both an exocrine gland, sending enzymes through a duct, and an endocrine gland, sending insulin straight into the blood.
The pancreas works both as an exocrine gland and as an endocrine gland, which is why it is said to have a dual nature. As an exocrine gland, it secretes pancreatic juice, which is carried by the pancreatic duct into the duodenum. Pancreatic juice contains trypsin for digesting proteins, amylase for digesting starch and lipase for digesting emulsified fats. As an endocrine gland, the islets of Langerhans in the pancreas secrete the hormones insulin and glucagon directly into the blood, without any duct. Insulin lowers the blood sugar level, and if too little of it is secreted the person suffers from diabetes. Example: the same organ sends lipase down a duct into the small intestine and insulin straight into the blood. - Q228 CBSE 2023Write the sequence of events that involve response of a person when a dust particle is inhaled through the nose by him.Step-by-step solution →
Show answer
Dust in the nose sets off the reflex action of sneezing, which expels the particle through a blast of air.
The response is a reflex action, sneezing, and the events follow the reflex arc: 1. Stimulus: the dust particle irritates the lining of the nose. 2. Receptors: sensory nerve endings in the lining of the nose detect it and produce nerve impulses. 3. Sensory neurons carry these impulses to the brain, to the medulla in the hind-brain. 4. There the impulses are passed on at once, without conscious thought, to motor neurons. 5. Motor neurons carry the impulses to the effectors, the muscles of the chest and the diaphragm. 6. Response: the diaphragm and chest muscles first draw in a deep breath; then the chest muscles contract suddenly and a blast of air through the nose and mouth expels the dust particle: the person sneezes. - Q229 CBSE 2023Name the hormone secreted in scary situations by animals. Write any three responses which enable the animal body to deal with it.Step-by-step solution →
Show answer
Adrenaline is secreted; the heart beats faster, blood is diverted to the skeletal muscles and the breathing rate increases.
Hormone: adrenaline, secreted by the adrenal glands directly into the blood. Three responses: (1) the heart beats faster, so more oxygen is supplied to the muscles; (2) the blood supply to the digestive system and the skin is reduced, because the muscles around the small arteries in these organs contract, and the blood is diverted to the skeletal muscles; (3) the breathing rate increases, because of the contractions of the diaphragm and the rib muscles. All these responses together enable the animal body to be ready to deal with the situation, by fighting or by running away. - Q230 CBSE 2023Name the gland and the hormone secreted by it in scary situations in human beings. List any two responses shown by our body when this hormone is secreted into the blood.Step-by-step solution →
Show answer
The adrenal gland secretes adrenaline, which makes the heart beat faster and the breathing rate rise.
The gland is the adrenal gland — a pair of them, one above each kidney — and the hormone it secretes directly into the blood is adrenaline. Two of the responses it produces are: (i) the heart beats faster and harder, so that more oxygen-rich blood is supplied to the muscles; and (ii) the rate of breathing increases, because of the more frequent contractions of the diaphragm and the rib muscles. (The blood supply to the digestive system and the skin is also reduced, so that more blood goes to the skeletal muscles.) - Q231 CBSE 2023Define geotropism and explain the term positive geotropism and negative geotropism giving one example for each.Step-by-step solution →
Show answer
Geotropism is growth in response to gravity: roots grow downwards (positive) and shoots grow upwards, away from gravity (negative).
Geotropism (gravitropism) is the directional growth movement of a part of a plant in response to the stimulus of gravity. Positive geotropism is growth in the direction of gravity, that is, downwards; its example is the root of a plant, which grows downwards into the soil. Negative geotropism is growth away from the direction of gravity, that is, upwards; its example is the shoot or stem of a plant, which grows upwards, away from the earth. - Q232 CBSE 2023Some plants like pea plants have tendrils which help them to climb up other plants. Explain how is it done. Name the plant hormone responsible for this movement.Step-by-step solution →
Show answer
A tendril grows less on the side touching a support, so it coils round the support (thigmotropism); the hormone responsible is auxin.
Tendrils are sensitive to touch. When a tendril comes in contact with a support, such as the stem of another plant, the part of the tendril in contact with the support does not grow as rapidly as the part away from it. Because the far side grows longer than the near side, the tendril bends towards the support, circles round it and clings to it, and the plant climbs. This is a growth movement in response to touch (thigmotropism). The plant hormone responsible is auxin, which makes plant cells grow longer. - Q233 CBSE 2023In the given diagram
- (i)Name the parts labelled A, B, and C.
- (ii)Write the functions of A and C.
- (iii)Reflex arcs have evolved in animals? Why?
Step-by-step solution →Show answer
A is the sensory neuron, B the relay neuron and C the muscle; reflex arcs evolved because the brain's thinking is not fast enough.
(i) A is the sensory neuron, B is the relay neuron (the interneuron lying in the grey matter of the spinal cord) and C is the muscle, which acts as the effector. (ii) A carries the impulse from the receptors in the skin of the hand to the spinal cord. C contracts when the impulse reaches it through the motor neuron, and in contracting it pulls the hand away from the hot object. (iii) Reflex arcs have evolved because the thinking process of the brain is not fast enough for such situations, and many animals have very little of the complex neuron network needed for thinking. A ready-made connection in the spinal cord produces the response at once and so protects the body from harm. - Q234 CBSE 2023Name the plant hormone that helps in the bending of the plant stem towards light. Explain its function. Also name this phenomenon.Step-by-step solution →
Show answer
Auxin, made at the shoot tip, moves to the shaded side and makes those cells elongate more, bending the shoot towards light: phototropism.
The hormone is auxin. It is made at the tip of the growing shoot and promotes the elongation of cells. When light falls on one side of the shoot, the auxin diffuses towards the shaded side, so the cells on the shaded side receive more auxin and elongate more than those on the lighted side. The shaded side therefore grows longer and the stem bends towards the light. The phenomenon is called phototropism (the shoot shows positive phototropism). - Q235 CBSE 2023Name the phenomenon occurring in plants which are under the control of gravity, water and chemicals with one example each that shows the movement involved.Step-by-step solution →
Show answer
These are tropisms: geotropism for gravity (roots grow down), hydrotropism for water (roots towards moist soil), chemotropism for chemicals (pollen tube towards ovule).
These are tropic movements (tropisms): growth movements of a plant part in a direction set by the stimulus. Gravity: geotropism. The root grows downwards, towards the pull of the earth (positive geotropism), and the shoot grows upwards, away from it (negative geotropism). Water: hydrotropism. Roots grow towards a source of water, such as moist soil. Chemicals: chemotropism. The pollen tube grows down the style towards the ovule. - Q236 CBSE 2023Name the hormone released and the gland which secretes it in human beings during scary situations. How does the body respond to enable it to deal with the situation ?Step-by-step solution →
Show answer
Adrenaline from the adrenal gland speeds up the heart and breathing and supplies the muscles with more oxygen and glucose.
The hormone is **adrenaline** and it is secreted by the **adrenal gland**, which sits on top of each kidney. Adrenaline is poured straight into the blood and is carried to all parts of the body. The body responds as follows: the heart beats faster and harder, so more oxygen reaches the tissues; the blood vessels of the skin and the digestive system contract while those of the skeletal muscles widen, so a larger share of the blood is sent to the muscles; the rate of breathing rises because the diaphragm and the rib muscles contract faster, so more oxygen is taken in; and the liver releases glucose into the blood. Together these changes supply the skeletal muscles with much more oxygen and glucose, so that energy can be released rapidly and the body is ready either to fight the danger or to run away from it. - Q237 CBSE 2023Explain the directional movement due to growth in response to touch in a pea plant.Step-by-step solution →
Show answer
Unequal growth makes a pea tendril bend towards and coil round a support it touches; this growth movement in response to touch is thigmotropism.
Pea plants climb by means of tendrils, which are sensitive to touch. When a tendril comes in contact with a support, the part of the tendril touching the support does not grow as rapidly as the part away from it. Because the far side grows more, the tendril bends towards the support, circles round it and clings to it. The movement is due to growth and its direction is decided by the stimulus, so it is a directional growth (tropic) movement in response to touch, known as thigmotropism; it lets the pea plant climb up a support. - Q238 CBSE 2023
- (i)List three points of difference between nervous and hormonal mechanisms for control and coordination in animals.
- (ii)How are auxins related with the bending of plant shoot towards unidirectional light ? Explain.
Step-by-step solution →Show answer
Nervous control is fast, electrical and short-lived; hormonal is slow, chemical and long-lasting; auxin on the shaded side bends the shoot towards light.
(i) Nervous mechanism: the message travels as an electrical impulse along neurons; it is very fast, taking milliseconds; and it reaches only the particular muscle or gland the nerve supplies, its effect ending as soon as the impulses stop. Hormonal mechanism: the message is a chemical (a hormone) secreted by an endocrine gland; it travels slowly in the blood, taking seconds to hours; and it is carried to every cell of the body, acting on the target organs that carry its receptors, with an effect that is long-lasting. (ii) Auxin is made at the tip of the growing shoot and makes cells elongate. When light falls from one side only, auxin moves away from the lighted side to the shaded side. The shaded side therefore gets more auxin, its cells elongate more and it grows longer than the lighted side, so the shoot curves towards the light. This directional growth response is called phototropism. - Q239 CBSE 2023
- (i)Name the disorder which a person is likely to suffer from due to the following : (I) Over-secretion of growth hormone (II) Deficiency of oestrogen in females (III) Less secretion of thyroxine Also name the gland that secretes each of the hormones mentioned above.
- (ii)How is the timing and amount of hormone released regulated ? Explain with the help of an example.
Step-by-step solution →Show answer
Gigantism (pituitary), failed female sexual development (ovary) and goitre (thyroid); feedback regulates hormone timing and amount, as insulin does for blood glucose.
(i) (I) Gigantism — the person grows abnormally tall; the hormone is growth hormone, secreted by the pituitary gland. (II) The female secondary sexual characters fail to develop, so puberty is delayed, the reproductive organs stay immature and the menstrual cycle is not established; the hormone is oestrogen, secreted by the ovary. (III) Goitre — the thyroid gland enlarges and the neck swells; the hormone is thyroxine, secreted by the thyroid gland. (ii) The timing and the amount of a hormone released are controlled by a feedback mechanism: the level of what the hormone controls is sensed and the secretion is adjusted accordingly. For example, when the level of glucose in the blood rises after a meal, the pancreas detects the rise and secretes more insulin; the insulin makes the liver and muscle cells store the glucose as glycogen and the level falls; as it falls the pancreas detects this and cuts down the secretion of insulin. Secretion therefore rises only when it is needed and falls back as the level returns to normal, and its amount matches the size of the rise. - Q240 CBSE 2023Hormones are chemical informational molecules that are required in minute amounts and are directly poured into the blood stream. The animal hormones are secreted in the desired amounts by the endocrine glands. Each hormone is responsible for carrying out specific actions in the body. The deficiency or excess of hormones has a harmful effect on our body. Hence, the timing and the amount of hormones secreted by glands are controlled by the feedback mechanism.
- (a)Name the hormones secreted by ovary and testes.[1]
- (b)Write the function of adrenaline.[1]
- (c)(i)Write the name and function of a hormone secreted by (i) Pituitary gland and (ii) Thyroid gland.[2]
- (c)(ii)OR : What is the meaning of feedback mechanism ?[2]
Step-by-step solution →Show answer
Oestrogen and testosterone; adrenaline prepares for fight or flight; growth hormone and thyroxine; in feedback, a hormone's effect regulates its own secretion.
(a) The ovary secretes oestrogen (and progesterone); the testes secrete testosterone. (b) Adrenaline is secreted by the adrenal glands into the blood when a person is frightened, angry or excited, and it prepares the body for fight or flight: the heart beats faster so that more oxygen is supplied to the muscles, the blood supply to the digestive system and the skin is reduced by the contraction of the small arteries around them and is diverted to the skeletal muscles, and the breathing rate increases through the contraction of the diaphragm and the rib muscles. (c)(i) Pituitary gland: growth hormone - it regulates the growth and development of the body; too little in childhood causes dwarfism and too much causes gigantism. Thyroid gland: thyroxine - it regulates the metabolism of carbohydrates, proteins and fats so as to provide the best balance for growth; iodine is essential for its production, and a deficiency of iodine causes goitre. OR (c)(ii) Feedback mechanism means that the timing and the amount of a hormone secreted are controlled by the body itself: the result of the hormone's action - the level of the substance it regulates, or of the hormone itself - acts back on the gland. For example, when the sugar level in the blood rises, the cells of the pancreas detect it and secrete more insulin; as the cells take up the sugar and the blood sugar level falls, the secretion of insulin is reduced. So the output of the gland regulates its own further secretion and the level is kept steady.