CBSE Class 10 Science Control and Coordination Assignment Set 07

This is Set 07 of mixed practice assignment questions for CBSE Class 10 Science Chapter 6, Control and Coordination, with marks, step-by-step answers and a Teacher's Note for every question. It covers tropic and nastic movements, plant hormones, the hydrotropism experiment, and the hormones of animals such as thyroxine, insulin and adrenaline.

Very Short Answer Questions (1 Mark)

Question 1. Name one movement in plants which is fast.
Answer:
The folding up and drooping of the leaves of the touch-me-not (sensitive) plant on touching is a very quick movement. It is a nastic (seismonastic) movement.
In simple words: The leaves of Mimosa pudica fold within seconds when touched.

Teacher's Note:
1. Tropic movements are slow because they depend on growth.
2. Nastic movements are fast because they depend on changes in water content.

Question 2. What is the general name of chemical substances which bring about control and coordination in plants?
Answer:
Phytohormones (plant hormones or plant growth regulators) bring about control and coordination in plants.
In simple words: Plants use hormones for coordination.

Teacher's Note:
1. Plants do not have a nervous system.
2. Name five phytohormones for revision.

Question 3. Give an example of a plant hormone that promotes growth.
Answer:
Auxin is a plant hormone that promotes growth (gibberellin and cytokinin also promote growth).
In simple words: Auxin helps cells grow longer.

Teacher's Note:
1. Abscisic acid is the growth inhibitor.
2. Give the name and one effect.

Question 4. State the main function of abscisic acid in plants.
Answer:
Abscisic acid is a growth inhibitor. It promotes the dormancy of seeds and buds, so it inhibits growth and seed germination. It also closes the stomata and causes wilting of leaves.
In simple words: Abscisic acid applies the brakes to plant growth.

Teacher's Note:
1. It is called the stress hormone.
2. Auxin, gibberellin and cytokinin promote growth.

Question 5. Name the diseases by which a person is likely to suffer due to deficiency of:
(i) Iodine,
(ii) Insulin.
Answer:
(i) Deficiency of iodine causes goitre, because the thyroid cannot make enough thyroxine.
(ii) Deficiency of insulin causes diabetes (mellitus).
In simple words: Too little iodine gives goitre and too little insulin gives diabetes.

Teacher's Note:
1. Link each deficiency with the hormone and the gland.
2. Goitre shows as a swelling in the neck.

Question 6. Name a gland associated with the brain. Which problem is caused due to the deficiency of the hormone released by this gland?
Answer:
The pituitary gland is attached to the base of the brain. It releases the growth hormone. Its deficiency in childhood causes stunted growth (dwarfism).
In simple words: The pituitary under the brain gives growth hormone; less of it gives a short stature.

Teacher's Note:
1. The hypothalamus is also associated with the brain.
2. Give the problem in one word: dwarfism.

Question 7. Give examples of chemotropism.
Answer:
The growth of the pollen tube towards the ovule during fertilisation is an example of chemotropism. Chemicals secreted by the ovule guide the growth of the tube.
In simple words: A pollen tube grows towards the chemicals given out by the ovule.

Teacher's Note:
1. Chemotropism is growth in response to a chemical.
2. Phototropism responds to light.

Question 8. Name the hormone in humans which regulates carbohydrate, protein and fat metabolism in the body. Mention the site where it is synthesised.
Answer:
The hormone is thyroxine. It is synthesised in the thyroid gland, which is situated in the neck. Iodine is needed for its formation.
In simple words: Thyroxine from the thyroid controls the body's metabolism.

Teacher's Note:
1. Do not confuse with insulin, which controls the sugar level.
2. Iodine is necessary for thyroxine.

Short Answer Questions (2 and 3 Marks)

Question 9. Why do Mimosa pudica leaves drop down when touched?
Answer:
Step 1: The leaves of Mimosa pudica are sensitive to touch.
Step 2: On touching, water moves out of the cells at the base of the leaflets and petioles, so the cells lose their turgor.
Final answer: Because of the change in turgor pressure the leaves fold and drop down. This is a nastic movement and not a growth movement.
In simple words: The leaf droops because its cells lose water when touched.

Teacher's Note:
1. The plant uses electrical-chemical signals from cell to cell.
2. The movement is quick and reversible.

Question 10. Why do stem and root show unilateral growth towards light and earth's gravity respectively?
Answer:
Step 1: The stem is positively phototropic and the root is positively geotropic. The hormone auxin is made at the shoot tip and root tip.
Step 2: Stem: When light falls from one side, auxin collects on the shaded side. This makes the cells there grow longer, so the shoot bends towards light.
Step 3: Root: Under gravity, auxin collects on the lower side of the root. In the root, this amount of auxin slows the growth of the lower cells, so the upper side grows faster and the root bends downwards, towards the earth.
Final answer: Unequal distribution of auxin gives unequal growth on the two sides, so the stem bends to light and the root bends to the earth.
In simple words: Auxin collects on one side and the unequal growth bends the stem and the root.

Teacher's Note:
1. Write the effect of auxin on the stem and on the root separately.
2. Stem is negatively geotropic and root is negatively phototropic.

Question 11. Why is abscisic acid known as stress hormone?
Answer:
Abscisic acid brings about various responses in plants under stress conditions. For example, it closes the stomata when there is a shortage of water, promotes the dormancy of seeds and buds, and inhibits growth under unfavourable conditions. So it is known as the stress hormone.
In simple words: Abscisic acid helps the plant to survive hard times.

Teacher's Note:
1. Give two examples of stress responses.
2. It also causes wilting of leaves and fall of leaves and fruits.

Question 12. Define tropism. What are different types of tropism?
Answer:
Tropism is the directional movement of a part of a plant in response to an external stimulus. It is a growth movement. Its types are:
1. Phototropism: response to light. Shoots bend towards light and roots bend away from it.
2. Geotropism: response to gravity. Roots grow downwards, shoots grow upwards.
3. Chemotropism: response to chemicals. The pollen tube grows towards the ovule.
4. Hydrotropism: response to water. Roots bend towards water.
(Thigmotropism, the response to touch, is seen in tendrils.)
In simple words: Tropism means growing towards or away from a stimulus.

Teacher's Note:
1. Give one example with each type.
2. Positive means towards the stimulus and negative means away from it.

Question 13. How do auxins promote the growth of a tendril around a support?
Answer:
Step 1: Tendrils are sensitive to touch. The hormone auxin is made at the tip.
Step 2: When a tendril touches a support, auxin moves to the side away from the support.
Step 3: The side with more auxin grows faster than the side in contact with the support.
Final answer: The outer side grows longer than the inner side, so the tendril curls and coils around the support.
In simple words: More auxin on the far side makes it grow faster, so the tendril coils.

Teacher's Note:
1. Name the type of movement: thigmotropism.
2. Tendrils help weak climbers like the pea plant.

Question 14. How does chemical coordination occur in plants?
Answer:
Chemical coordination in plants occurs with the help of plant hormones (phytohormones). They are produced in very small amounts in one part of the plant and diffuse to the other part where they show their effect.
The main hormones are auxins, gibberellins, cytokinins, ethylene and abscisic acid. They control cell elongation, cell division, growth of stems, ripening of fruits, dormancy of seeds and closing of stomata.
In simple words: Plants coordinate their activities through hormones that spread through the body.

Teacher's Note:
1. Plants have no nervous system.
2. Name at least three hormones with their effects.

Question 15. What will happen if the intake of iodine in our diet is low?
Answer:
Step 1: Iodine is necessary for the thyroid gland to make the hormone thyroxine.
Step 2: If the intake of iodine is low, less thyroxine is made. The thyroid gland enlarges to make up for it.
Final answer: The person suffers from goitre (swelling in the neck), the metabolism becomes slow, and in children growth and mental development are affected.
In simple words: Low iodine means low thyroxine and a swollen neck called goitre.

Teacher's Note:
1. Use of iodised salt prevents the problem.
2. Name the gland, the hormone and the disease.

Question 16. How does our body respond when adrenaline is secreted into the blood?
Answer:
Step 1: Adrenaline is secreted by the adrenal glands during emergencies such as fear, anger or danger.
Step 2: The heartbeat increases, so that more oxygen is supplied to the muscles. The breathing rate also increases.
Step 3: The blood supply to the digestive system and skin falls and more blood is sent to the skeletal muscles.
Final answer: These responses prepare the body to face the emergency.
In simple words: Adrenaline gets the body ready to fight or run.

Teacher's Note:
1. Mention heartbeat, breathing and blood supply.
2. Adrenaline is called the emergency hormone.

Question 17. What is the feedback mechanism of hormone regulation? Take the example of insulin to explain this phenomenon.
Answer:
Step 1: The timing and the amount of a hormone released are controlled by a feedback mechanism, in which the product controls its own production.
Step 2: When the blood sugar level rises, the cells of the pancreas detect it and secrete more insulin into the blood, which lowers the sugar level.
Step 3: As the blood sugar level falls, the secretion of insulin is reduced.
Final answer: The pancreas keeps the sugar level steady through feedback.
In simple words: Like a thermostat, the body switches insulin on and off as the sugar changes.

Teacher's Note:
1. Write the example in the order rise, secretion, fall, reduction.
2. Feedback mechanisms prevent the hormone from becoming too much or too little.

Teacher's Note:
1. Both are nastic movements.
2. Name the stimulus and one example for each.

Teacher's Note:
1. Compare the type, growth, speed and cause.
2. Write the answer as a table.

Question 20. (A) The stimulus in blooming of flowers and a sunflower aligning itself in direction of sunlight is light. Then how are these movements different from each other?
(B) What type of movement do roots exhibit?
Answer:
(A) The blooming of flowers is a photonastic movement. It is non-directional, because it does not depend on the direction of light, and it does not involve growth. The sunflower aligning itself in the direction of sunlight is a directional response to the light, so it is a phototropic (tropic) movement and it involves growth.
(B) Roots exhibit tropic movements, such as positive geotropism (towards gravity), positive hydrotropism (towards water) and negative phototropism (away from light).
In simple words: Flowers open to light in a non-directional way, but a sunflower turns towards it.

Teacher's Note:
1. Ask whether the movement has a direction and uses growth.
2. Roots always grow towards water and gravity.

Teacher's Note:
1. Write three clear points in a table.
2. Plants do not need quick movements like animals do.

Long Answer Questions (5 Marks)

Question 22. What is hydrotropism? Design an experiment to demonstrate this phenomenon.
Answer:
Step 1: The movement of the root of a plant towards water is called hydrotropism.
Step 2: Set up: Take two glass troughs A and B and fill each two-thirds with soil. In trough A plant a tiny seedling. In trough B plant a similar seedling and also place a small clay pot inside the soil.
Step 3: Water the soil in trough A daily and uniformly. Do not water the soil in trough B, but put some water in the clay pot buried in the soil. Leave both troughs for a few days.
Step 4: Observation: Dig out the seedlings carefully. The root of the seedling in trough A is straight, because water reaches it from all sides. The root of the seedling in trough B is bent towards the clay pot, from which water oozes out.
Conclusion: The root of a plant grows towards water, so the root is positively hydrotropic.
In simple words: A root bends towards the wet clay pot, which shows that roots grow towards water.

Teacher's Note:
1. Include the control set up (trough A) in your answer.
2. Draw two troughs with the clay pot if a diagram is asked.

Teacher's Note:
1. Learn the table by writing a single keyword for each hormone.
2. Ethylene is the only gaseous hormone.

Question 24. Mention one function for each of these hormones:
(i) Thyroxine
(ii) Insulin
(iii) Adrenaline
(iv) Growth hormone
(v) Testosterone
Answer:
(i) Thyroxine regulates the metabolism of carbohydrates, fats and proteins, and influences the growth of the body.
(ii) Insulin lowers the blood glucose level, as it helps to convert the excess glucose into glycogen in the liver.
(iii) Adrenaline is the emergency hormone. It prepares the body for fight or flight by increasing the heartbeat and the breathing rate.
(iv) Growth hormone is essential for the normal growth and development of the body.
(v) Testosterone stimulates the development of the male secondary sexual characters at puberty.
In simple words: Each hormone has its own job: metabolism, sugar control, emergency, growth and male features.

Teacher's Note:
1. Make a table of gland, hormone and function.
2. Testosterone is secreted by the testes.