Chapter 7: Control and coordination

Internal Question and Answer:

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

Answer: The difference between a reflex action and walking is :

Reflex action	Walking
It is an automatic, involuntary response to a stimulus.	It is a voluntary action done consciously.
It is controlled mainly by the spinal cord.	It is controlled by the brain (higher centres).
It occurs very quickly without thinking.	It requires coordination and practice of muscles.
Example: sudden withdrawal of hand from a hot object.	Example: moving from one place to another by legs.

2. What happens at the synapse between two neurons ?

Answer: At the synapse between two neurons, the electrical signal from the first neuron cannot directly pass to the next neuron. It triggers the release of chemical substances called neurotransmitters. These chemicals cross the synaptic gap and generate an electrical impulse in the next neuron, allowing the message to continue.

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

Answer: The part of the brain that maintains posture and equilibrium of the body is the cerebellum.

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

Answer: We detect the smell of an agarbatti when the volatile chemicals released from it reach the olfactory receptors in our nose, which then send electrical signals to the brain for interpretation.

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

Answer: In a reflex action, the brain does not take part in the immediate response. The reflex is controlled by the spinal cord to ensure a quick reaction. The brain is informed about the stimulus after the response has taken place.

Internal Question and Answer:

1. What are plant hormones?

Answer: Plant hormones are chemical compounds that help in controlling and coordinating various growth and developmental activities in plants, such as cell division, elongation, flowering, fruiting and responses to stimuli.

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

Answer: The movement of the leaves of the sensitive plant happens in response to touch (a stimulus), and it does not depend on the direction of the stimulus. The leaves fold up quickly. In contrast, the movement of a shoot towards light is a growth movement that depends on the direction of light, so the shoot bends and grows slowly towards the light.

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

Answer: An example of a plant hormone that promotes growth is auxin.

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

Answer: When a tendril touches a support, auxin moves to the side away from the contact. The cells on that side grow faster, while the touched side grows less. This unequal growth makes the tendril bend and wrap around the support.

5. Design an experiment to demonstrate hydrotropism.

Answer: Take two beakers A and B filled with soil. Place a porous pot containing water in beaker A, while beaker B has no water source. Plant equal seedlings in both beakers. Keep the setup undisturbed for a few days. In beaker A, the roots bend and grow towards the porous pot due to the presence of moisture, while in beaker B the roots grow normally. This shows that roots respond to water and grow towards it. This movement of roots towards water is called hydrotropism.

Internal Question and Answer:

1. How does chemical coordination take place in animals?

Answer :  Chemical coordination in animals takes place through hormones. Hormones are chemical messengers that are secreted by endocrine glands directly into the blood. The blood carries them to the target organs where they act on specific cells to control and regulate various body functions such as growth, development, reproduction and response to stress.

2. Why is the use of iodised salt advisable?

Answer: The use of iodised salt is advisable because iodine is needed by the thyroid gland to make the hormone thyroxine. A lack of iodine in the diet can cause a deficiency disease called goitre . Therefore, consuming iodised salt helps prevent goitre and ensures proper thyroid function.

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

Answer: Adrenaline is released into the blood and reaches different organs like the heart. It increases the heart rate and supplies more oxygen to muscles. Blood flow to digestive system and skin decreases, while more blood goes to muscles. Breathing rate also increases, making the body ready to respond quickly to the situation.

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

Answer: Some patients of diabetes are treated with insulin injections because their pancreas does not produce enough insulin. Insulin is a hormone that helps regulate blood sugar (glucose) levels. Without enough insulin, blood sugar rises too high and leading to diabetes. Injecting insulin helps lower and control the blood sugar level.

Exercises of Chapter 7: Control and coordination

1. Which of the following is a plant hormone?

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

Answer : (d) Cytokinin

[ Plant hormones are chemical substances that control growth and development in plants. Cytokinin is a plant hormone that promotes cell division, growth of lateral buds, and delays ageing in plants.]

2. The gap between two neurons is called a

(a) dendrite.   (b) synapse. (c) axon.   (d) impulse.

Answer: (b) Synapse

[ The synapse is the tiny gap between two neurons. It helps in the transmission of nerve impulses from one neuron to another through chemical signals. ]

3. The brain is responsible for

(a) thinking.    (b) regulating the heart beat.   (c) balancing the body.   (d) all of the above.

Answer: (d) All of the above

[ The brain controls different functions of the body:

Thinking → controlled by the forebrain

Regulating heartbeat → controlled by the hindbrain (medulla)

Balancing the body → controlled by the cerebellum

So, the brain is responsible for all these functions. ]

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?

Answer: The function of receptors in our body is to detect changes in the environment like light, sound, heat or touch and send messages to the brain. If receptors do not work properly, then we cannot sense danger or pain. For example, if skin receptors are damaged, we may not feel heat from a fire and may get burned. If eye receptors fail, we cannot see. If ear receptors fail, we cannot hear. This makes it difficult for the body to respond correctly to protect itself.

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

Answer: The structure of a neuron:
A neuron has a star-shaped cell body with a nucleus. It has many short branched parts called dendrites and one long part called an axon. The axon may be covered by a protective sheath and ends in tiny branches called nerve endings.

   

The function of a neuron:
A neuron carries messages in the form of electrical signals from one part of the body to another. Dendrites receive the signal, the cell body passes it to the axon, and the axon sends it to nerve endings. These endings then pass the signal to the next neuron or to muscles and glands so that the body can react to a stimulus.

6. How does phototropism occur in plants?

Answer: Phototropism in plants occurs due to the plant hormone auxin. When light falls on one side of the shoot and auxin moves to the shaded side. This makes cells on the shaded side grow longer and faster than cells on the lighted side. As a result, the shoot bends and grows towards the light.

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

Answer: In case of a spinal cord injury, the signals that get disrupted are the ones traveling between the brain and the lower parts of the body. This includes both the signals for voluntary actions  and the signals for reflex actions . The brain will not receive sensory messages from below the injury, and it will also not be able to send commands to those body parts.

8. How does chemical coordination occur in plants?

Answer: Chemical coordination in plants occurs with the help of plant hormones . These hormones are made in one part of the plant and transported to another part where they act. They control or regulate growth, development, flowering, fruit ripening, and responses to stimuli like light, gravity and touch. Examples of plant hormones are auxin, gibberellin, cytokinin, abscisic acid and ethylene.

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

Answer: The need for a system of control and coordination in an organism is to respond to changes in the environment (stimuli) and to work all body parts together in a proper way. This helps the organism find food, avoid danger, maintain body functions and survive. Without such a system, the body would not be able to react correctly or keep internal balance.

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

Answer: The difference between involuntary actions and reflex actions are:

Involuntary Actions	Reflex Actions
These are controlled by the brain (midbrain and hindbrain).	These are controlled by the spinal cord.
They are not under our will or control.	They are also not under our will.
Examples: beating of the heart, movement of food in the intestine.	Example: pulling away hand from a hot object.
They are slow and continuous.	They are quick and spontaneous.

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

Answer: The differences between nervous and hormonal mechanisms for control and coordination in animals are :

Nervous Mechanism	Hormonal Mechanism
(i) It uses nerve impulses (electrochemical) for communication.	(i) It uses hormones (chemicals) for communication.
(ii) The signal is transmitted through neurons.	(ii) The signal is transmitted through the bloodstream.
(iii) The response is very fast.	(iii) The response is usually slow .
(iv) The effect is short-lived.	(iv) The effect is often long-lasting.
(v) The action is highly localized.	(v)The action is widespread .
Example: Withdrawal of hand from a hot object.	Example: Growth hormone regulating body growth.

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

Answer: The difference between the manner in which movement takes place in a sensitive plant and movement in our legs is :

Movement in Sensitive Plant (Touch-me-not plant)	Movement in Our Legs
(i) It is a type of growth-independent movement .	(i) It is a type of voluntary movement controlled by the nervous system.
(ii) No specialized tissue like muscles or nerves is involved. Movement occurs due to change in water pressure in specific cells at the base of leaves.	(ii) Movement involves specialized contractile tissues called muscles, which are attached to bones.
(iii) The response is triggered by electrical changes in the plant cells, but no nervous or muscular system is used.	(iii) The response is triggered by electrical impulses sent through nerves from the brain/spinal cord to the leg muscles.
(iv) It does not serve the purpose of locomotion.	(iv) It helps in locomotion .
(v) The movement is slow compared to animal movement.	(v) The movement is rapid and immediate.
(vi) It is an involuntary response to touch or stimulus.	(vi) It is a voluntary action .