CBSE Class 10 Science Control and Coordination Important Questions Set 01

Answer: Insulin regulates blood sugar level. It is secreted by the pancreas.

Teacher's Note:
1. Insulin lowers the blood glucose level by helping cells take up and store glucose.
2. Its low secretion leads to diabetes, which is a common follow-up question.

Answer: Abscisic acid is a growth inhibitor. It promotes dormancy in seeds and buds, closes stomata and causes wilting and falling of leaves.

Teacher's Note:
1. Remember that it works opposite to auxins, gibberellins and cytokinins.
2. It is often called the stress hormone of plants.

Answer: Growth hormone (GH), follicle stimulating hormone (FSH) and luteinising hormone (LH). Thyroid stimulating hormone and prolactin are also secreted by it.

Teacher's Note:
1. The pituitary is called the master gland because it controls the secretion of many other glands.
2. Learn growth hormone first as it is the one most often asked.

Answer: Growth of the pollen tube towards the ovule is an example of chemotropism.

Teacher's Note:
1. Chemotropism is the directional growth of a plant part in response to a chemical.
2. Pollen tubes grow towards chemicals released by the ovule.

Answer: (a) Synapse. A synapse is the gap between the axon end of one neuron and the dendrite of the next, across which the impulse is passed chemically.

Teacher's Note:
1. Synapse is the correct term for the neuron-to-neuron junction.
2. Synapsis is a different term used in cell division.

Answer: (d) Cytokinin. Insulin, thyroxin and oestrogen are animal hormones.

Teacher's Note:
1. Cytokinins promote cell division in plants.
2. The other three options are secreted by animal glands.

Answer: (c) dendrite → cell body → axon → axon end. Dendrites receive the information, which then moves through the cell body and along the axon.

Teacher's Note:
1. The direction of an impulse in a neuron is always fixed.
2. Draw the neuron and mark this path to remember it.

Answer: (a) Pituitary. It secretes hormones that control the working of other endocrine glands.

Teacher's Note:
1. The pituitary itself is controlled by the hypothalamus.
2. Do not confuse it with the thyroid, which controls metabolism.

Answer: (d) rapid cell division in the tendril cells that are away from the support. The side away from the support grows faster, so the tendril curls around the support.

Teacher's Note:
1. This is a case of differential growth, as in other tropic movements.
2. The side touching the support grows more slowly.

Answer: (a). Both statements are true, and the reduced insulin is why sugar stays high and causes diabetes, so R explains A.

Teacher's Note:
1. Both statements are true and linked.
2. Insulin deficiency leaves too much sugar in the blood.

Answer: (a). A reflex response is generated in the spinal cord, which saves time, so R correctly explains A.

Teacher's Note:
1. The brain is informed later, but the response has already happened.
2. This is why we pull our hand away from a hot object before we feel the pain.

Answer: (a) Iodine. (b) Insulin.

Teacher's Note:
1. Thyroxin contains iodine, so the gland needs it from the diet.
2. Insulin is made by the pancreas.

Answer: The parts are the dendrites, the cell body (which contains the nucleus) and the axon. Dendrites receive information from the receptors or from other neurons and carry it to the cell body as an electrical impulse.

Teacher's Note:
1. A neuron is the structural and functional unit of the nervous system.
2. The axon then carries the impulse away from the cell body.

Answer: When the blood sugar level rises after a meal, the beta cells of the pancreas secrete more insulin. Insulin makes the cells and the liver take up glucose and store it, so the sugar level falls. When the level falls, insulin secretion decreases.

Teacher's Note:
1. This is an example of feedback control of hormones.
2. If the pancreas secretes too little insulin, the person suffers from diabetes.

Answer: (a) Iodine is needed by the thyroid gland to make thyroxin, which regulates the metabolism of carbohydrates, proteins and fats.
(b) Goitre.
(c) The neck swells because the thyroid gland enlarges. Other symptoms are weight gain, high blood pressure and tiredness.

Teacher's Note:
1. Thyroxin controls growth and the balance of body metabolism.
2. Iodised salt prevents goitre in areas where soil and water lack iodine.

Answer: A reflex action is a sudden, automatic and involuntary response to a stimulus that protects the body from harm.
Steps in the reflex arc:
1. Receptor in the skin detects the stimulus.
2. A sensory neuron carries the impulse to the spinal cord.
3. A relay neuron in the spinal cord passes it on.
4. A motor neuron carries the response to the effector (muscle).
5. The muscle contracts and the body part moves away, for example the hand pulled from a hot object.

Teacher's Note:
1. The path of the impulse in a reflex is called the reflex arc.
2. The signal reaches the brain only after the response has already taken place.

Answer: (a) Phototropism. (b) Chemotropism. (c) Hydrotropism.

Teacher's Note:
1. These are all tropic movements, where the direction of growth depends on the direction of the stimulus.
2. Growth towards the stimulus is positive and away from it is negative.

Answer: Auxin is synthesised at the shoot tip.
When light falls on a shoot from one side, auxin diffuses to the shaded side of the shoot. The higher concentration of auxin on the shaded side makes those cells elongate faster than the cells on the lighted side. Because of this unequal growth the shoot bends towards the light, which is positive phototropism.

Teacher's Note:
1. Auxin promotes cell elongation, so the side with more auxin grows longer.
2. This question is best answered with the words shaded side and unequal growth.

Answer: The human brain has three main parts: the fore-brain, the mid-brain and the hind-brain.
Cerebellum (hind-brain): controls and coordinates voluntary muscle movements, maintains the posture and balance of the body.
Pons (hind-brain): acts as a relay between different regions of the brain and takes part in regulating involuntary actions such as breathing.
The medulla, the third part of the hind-brain, controls involuntary actions such as blood pressure, salivation and vomiting.

Teacher's Note:
1. The fore-brain is the main thinking part of the brain and contains the cerebrum.
2. Walking in a straight line and riding a bicycle depend on the cerebellum.

Answer: 1. Auxin: promotes cell elongation and helps the shoot grow towards light.
2. Gibberellins: help in the growth of the stem, break dormancy in seeds and promote fruit growth.
3. Cytokinins: promote cell division, are abundant in fruits and seeds, and delay ageing of leaves.
4. Abscisic acid: inhibits growth, causes wilting and promotes dormancy and closing of stomata.

Teacher's Note:
1. The first three promote growth, while abscisic acid works as a growth inhibitor.
2. Tabulate hormone, site and function for quick revision.