Science 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

2. The gap between two neurons is called a

(a) dendrite.

(b) synapse.

(c) axon.

(d) impulse.

Answer: (b) synapse.

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

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: Functions of receptors:

(i) They sense the external stimuli such as heat or pain.

(ii) They also trigger an impulse in the sensory neuron which sends message to the spinal cord.

When the receptors are damaged, the external stimuli transferring signals to the brain are not felt. For example, in the case of damaged receptors, if we accidentally touch any hot object, then our hands might get burnt as damaged receptors cannot perceive the external stimuli of heat and pain.

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

Answer:

Neurons are the functional units of the nervous system. The three main parts of a neuron are axon, dendrite, and cell body.

6. How does phototropism occur in plants?

Answer: The growth movement in plants in response to light stimulus is known as phototropism.The shoots show positive phototropism and the roots show negative phototropism. This means that the shoots bend towards the source of light whereas the roots bend away from the light source.

Some examples of phototropism are as follows:

(a) The flower head of sunflower is positively phototropic and hence it moves from east to west along with the sun.

(b) The ovary stalk of groundnut is positively phototropic before fertilization and becomes negatively phototropic after fertilization, so that the fruit is formed underground.

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

Answer: In case of any injury to the spinal cord, the signals coming from the nerves as well as the signals coming to the receptors will be disrupted.

8. How does chemical coordination occur in plants?

Answer: Coordination occurs in plant by a special class of chemical substances known as hormones. These hormones are produced in one part of the plant body and are trans-located to other needy parts. For example, a hormone produced in roots is trans-located to other parts when required. The five major types of hormone are auxins, gibberellins, cytokinins, abscisic acid, and ethylene. These hormones are either growth promoters or growth inhibitors such as abscisic acid.

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

Answer: In the absence of Control and coordination, our body will not be able to function properly and we may harm our body seriously. For example, when we accidentally touch a hot utensil, we immediately withdraw our hand. In the absence of nerve transmission, we will not withdraw our hand and may get burnt.

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

Answer: Involuntary actions cannot be consciously controlled. For example, we cannot consciously control the movement of food in the alimentary canal. These actions are however directly under the control of the brain. On the other hand, the reflex actions such as closing of eyes immediately when bright light is focused show sudden response and do not involve any thinking. This means that unlike involuntary actions, the reflex actions are not under the control of brain.

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

Answer:

Nervous system mechanism	Hormonal system mechanism
The information is conveyed in the form of electric impulse.	The information is conveyed in the form of chemical messengers.
The axons and dendrites transmit the information through a coordinated effort	The information is transmitted or transported through blood.
The flow of information is rapid and the response is quick.	The information travels slowly and the response is slow.
Its effects are short lived.	It has prolonged effects.

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

Answer:

Movement in sensitive plants	Movement in our legs
The movement that takes place in a sensitive plant such as Mimosa pudica occurs in response to touch (stimulus).	Movement in our legs is an example of voluntary actions.
For this movement, the information is transmitted from cell to cell by electro-chemical signals as plants do not have any specialized tissue for conduction of impulses.	The signal or messages for these actions are passed to the brain and hence are consciously controlled.
For this movement to occur, the plant cells change shape by changing the amount of water in them.	In animal muscle cells, some proteins are found which allow the movement to occur.