NCERT Solutions for Class 10 Science Chapter 7 Control and Coordination

NCERT Intext Questions

Page Number 119

1. What is the difference between a reflex action and walking?

Ans.

Reflex action Walking
1. It is an involuntary action. It is a voluntary action.
2. It is under control of peripheral nervous system i.e., spinal cord. It is under control of central nervous system i.e., brain.
3. It is the action that takes place in response to certain stimuli like touching a hot object and does not involve a thinking process. It does not require any stimulus to process and involves a thinking process.

2. What happens at the synapse between two neurons?

Ans. The small empty space between two nerve cells is called synapse. At synapse, the electric signal are converted into a chemical signal at the end of axon of one nerve cell that reaches to the other nerve cell through the dendrite where it is again converted into electrical signal. Thus, information is transmitted from one nerve cell to other nerve cell by synapse.

3. Which part of the brain maintains posture and equilibrium of the body? 

Ans. Cerebellum, a part of hind brain, is responsible for maintaing posture and equilibrium of the body.

4. How do we detect the smell of an agarbatti (incense stick)?

Ans. The smell of agarbatti (incense stick) diffuses in the air. It is detected by olfactory receptors present in the nose. This information is sent to olfactory lobe by sensory nerves located in the forebrain, where it is analyzed and reacted upon.

5. What is the role of the brain in reflex action?

Ans. Brain has no direct involvement in reflex action. It is mainly controlled by spinal cord as these actions do not require thinking and are very quick actions.

Page Number 122

1. What are plant hormones?

Ans. Plant hormones are the chemical substances which regulate growth, flowering, height, development of plants and their response to the environment. Plant hormones are also called phytohormones.

Different types of phytohormones are – auxins, gibberllins, cytokinins, abscisic acid and ethylene.

2. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light? 

Ans.

Movement of leaves of sensitive plant Movement of a shoot towards light
1. It is a nastic movement which does not depend on the direction of stimulus applied. It is a tropic movement which depends on the direction of stimulus applied.
2. Touch is the stimulate. Light is the stimulate.
3. It is caused by the sudden loss of water from the swellings at the base of leaves. It is caused by the unequal growth on the two sides of the shoot.
4. It is not a growth movement. It is a growth movement.
5. Occurs very fast. Occurs slowly.

3. Give an example of a plant hormone that promotes growth.

Ans. Auxin is a plant hormone that promotes growth. Auxin promotes all elongation, helps in the growth of stems etc.

4. How do auxins promote the growth of a tendril around a support ?

Ans. When a tendril comes in contact with a support, auxin stimulates faster growth of the cells on opposite site so the tendril forms a coil around the support.

5. Design an experiment to demonstrate hydrotropism.

Ans. Take two glass troughs A and B and fill each one of them with two-thirds of soil. In trough A plant a tiny seedling. In trough B plant a similar seedling and place a clay pot inside the soil. 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. Leave both the troughs for a few days. 

wet soil

Now, dig up the seedlings carefully from both the troughs without damaging their roots. We will find that the root of seedling in trough A is straight. On the other hand, the root of seedling in trough B is found to be bent to the right side i.e., towards the clay pot containing water. In trough A, the root of the seedling gets water from both sides. But in trough B, the roots get
water oozing out from the clay pot which is kept on the right side. Therefore, the root of seedling in trough B grows and bends towards the source of waterto the right side. This experiment shows that the root of a plant grows towards water. In
other words, the root of a plant is hydrotropism.

Page Number 125

1. How does chemical coordination take place in animals ?

Ans. Chemical coordination in animals takes place through the special chemical substances called hormones secreted by the endocrine glands. Coordination in animals takes place through hormone system as well as nervous system which is called endocrine system. Endocrine glands secrete animal hormones directly into the blood that reach to the specific cells. Special type of molecules are present on the surface of cells to detect these hormones. These cells act according to the information that a particular hormone carries.

2. Why is the use of iodised salt advisable?

Ans. Iodine is essential for thyroid gland to produce thyroxine hormone. This hormone regulate metabolism of proteins, fats and carbohydrates in our body. If the quantity of iodine is less than required, will produce less thyroxine hormone, which leads to enlargement of throid gland. The disease is called goitre. Therefore the iodine salt is advised.

3. How does our body respond when adrenaline is secreted into the blood?

Ans. Adernaline is a hormone released by adrenal glands into the blood when the body is in a stressful situation.

Our body response when adrenaline is released in blood stream:

  1. Heartbeat becomes faster which results in more supply of oxygen to muscles.
  2. Blood to digestive system and skin is reduced.
  3. This diverts blood to our skeleton muscles.
  4. The breathing rate increases, because of the contraction of the diaphragm and the ribs muscles.

All of these leads to fight or flight response.

4. Why are some patients of diabetes treated by giving injections of insulin?

Ans. Insulin is a peptidal hormone secreted by pancreas that regulates the sugar level in blood. When there is less or no secretion of insulin, it leads to increased sugar levels in blood, causes disease called diabetes mellitus. Thus, patients suffering from diabetes are given insulin injection to control their blood sugar levels.

NCERT Exercise Questions

1. Which of the following is a plant hormone?

  • (a) Insulin
  • (b) Thyroxin
  • (c) Oestrogen
  • (d) Cytokinin
  • Ans. (d) Cytokinin

Explanation: Insulin, thyroxin and oestrogen are the animal hormones which are produced by pancreas, thyroid gland and ovary respectively. Cytokinin is a plant hormone that promotes cell division in plants.

2. The gap between two neurons is called a:

  • (a) Dendrite
  • (b) Synapse
  • (c) Axon
  • (d) Impulse
  • Ans. (b) Synapse

Explanation: The gap between two neurons is called synapse. It is a junction where the axon of one neuron forms a connection with another neuron for the transmission of signal.

3. The brain is responsible for:

  • (a) Thinking
  • (b) Regulating the heart beat
  • (c) Balancing the body
  • (d) All of the above
  • Ans. (b) All of the above

Explanation: The brain is responsible for thinking (fore-brain), regulating the heart beat (mid-brain) and balancing the body (hind-brain).

4. What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?

Ans. Receptors are specialised cells located in our sense organs like ear, nose, skin, tongue and eyes. The function of receptors is to detect information from the environment. For example, olfactory receptors detect smell. If receptors do not work properly, the information obtained from the environment will be delayed to reach the spinal cord or brain. In this situation, the response to the environmental stimulus will be delayed causing harm to the body. For example, if skin receptors are damaged, and an individual accidentally touches a hot object, then his/her hands might get burnt as the damaged receptor cannot perceive the external stimuli of heat and pain.

5. Draw the structure of a neuron and explain its function.

Ans. Nerve cell or neuron is the functional unit of nervous system. A nerve cell has three parts:

  • 1. cell body
  • 2. dendrite
  • 3. axon
nerve cell

Function: The function of nerve cells is to carry information in the form of electrical signals which are called nerve impulses. Cells receive stimulus to send it to spinal cord and brain and carry the message from brain to the target organ.

6. How does phototropism occur in plants ?

Ans. Phototropism is a directional response of a plant that allows the plant to grow towards or in some cases away from the light. Leaf and stem stip have a hormone called auxin, that allows the plant to grow towards light called positive phototropism. The roots of plant grow away from light and it is called negative phototropism.

7. Which signals will get disrupted in case of a spinal cord injury ?

Ans. In case of spinal cord injury the following signals get affected:

  1. All the involuntary actions will get disturbed.
  2. Reflex actions will be disturbed because reflexes are located in the spinal cord. Therefore, the quick responses required to safeguard the body will not take place.

8. How does chemical coordination occur in plants ?

Ans. Chemical coordination in plants occurs with the help of fluid secreted in plant, called phytohormones or plant hormones. The hormones regulate the growth of plant. For e.g., auxin is responsible for the growth of plant and cytokinin is responsible for the cell division in plants.

9. What is the need of a system of control and coordination in an organism?

Ans. An organism needs control and coordination system for the following functions:

  1. To save the body of the organisms from the harmful changes in the environment.
  2. To control the speed of voluntary and involuntary actions.
  3. To have the capability to think and learn for responding to any stimuli.

10. How are involuntary actions and reflex actions different from each other?

Ans. 

Involuntary actions Reflex actions
1.It does not require conciousness or thinking. It is an immidiate response to a stimulus.
2. Involuntary actions are controlled by mid and hind brain. Reflex actions are controlled by spinal cord.
3. It is relatively slow process. Example: Breathing, beating of heart, etc. It is relatively fast process. Example: Sneezing, coughing, etc.

11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.

Ans. 

Nervous mechanism Hormonal mechanism
1. Nerve cells are involved. Endocrine glands are involved.
2. It is a fast process. It is a slow process.
3. Neural responses are quick and short-lived. Hormonal effects are slow but are long term.
4. Arteries and glands are affected. It affects the target organ.
5. It transmits in electrochemical form. It transmits in chemical form.
6. It does not control metabolism. It controls metabolism.
7. Growth is not affected. Growth is affected.

12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs ?

Ans. 

Movement in a sensitive (mimosa) plant Movement in legs of a human
1. The leaves of a sensitive plant like mimosa are sensitive to touch and it is involuntary action. Movement of Leg is in control of nerve muscles and it is a voluntary response.
2. It is not controlled by any part of the plant. It is controlled by brain and spinal cord.
3. In this, cells change their shape on changing the amount of water in them. Amount of water has no effect on the movement of muscles.
4. Movement in a sensitive plant does not involve any specific protein. Contraction and relaxation in leg muscles is to bring about leg movement and it is assisted by specific proteins like actin and myosin.