Control and Coordination-NCERT Solutions

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

Ans. Reflex action takes place without thought, i.e., it gives a reaction to stimuli. It is controlled by the spinal cord. It is an involuntary action. Walking takes place after thought, i.e., according to our wishes. It is controlled by a part of hind brain called cerebellum. It is a voluntary action.

2.  What happens at the synapse between two neurons?

Ans. Synapse is the gap between nerve ending of one neuron and dendrites of another. At synapse, the electrical impulse generated at dendrites of a neuron is passed on to dendrite of another neuron in the form of chemicals by on ending of the first neuron. Synapse ensures that nerve impulse travels only in one direction. A similar synapse allows the delivery of impulse from the neuron to the other cells, like muscle cells.

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

Ans. Cerebellum, which is a part of the hind brain.

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

Ans. Smell of an incense stick is detected by the olfactory receptors located in the fore-brain.

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

Ans. Spinal cord is made up of nerves which supply information to think about. Thinking involves more complex mechanisms and neural connections. These are concentrated in the brain, which reacts to the stimuli and is the main coordinating center of the body. The brain and spinal cord constitute the central nervous system. They receive information from all parts of the body and integrate it. Hence, brain plays an important role in reflex action.

6.  What are plant hormones?

Ans. Plant hormones are chemicals present in plants which help to coordinate growth, development and responses to stimuli and environment. For example, auxins, gibberellins, cytolcinins, abscisic acids are different plant hormones.

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

Ans. The movement of leaves of a sensitive plant is neither towards, nor away from the stimulus touch; it is a non-directional movement (nastic movement) while movement of shoot is towards the stimulus like light; it is a directional movement (tropic movement).

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

Ans. Auxin is the plant hormone that helps in cell growth and elongation. Gibberellins promote growth of stem.

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

Ans. When tendrils come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This is caused by the action of auxin hormone. Less auxin occurs on the side of contact as compared to the free side. As a result, auxin promotes growth on the free side and the tendrils coil around the support.

10.  Design an experiment to demonstrate hydrotropism.

Ans. •  Take a tray filled with soil.

           •  Plant a seedling in the tray at one end.

           •  To the other end add water to the soil with the help of a pipe as shown in the figure.

           Observation: The root (radicle) of the plant seedling moves towards the wet soil. This shows that roots are positively hydrotropic.

11.  How does chemical coordination take place in animals?

Ans. In animals, chemical coordination is maintained by hormones secreted by endocrine glands, which function as chemical messengers. They are released by endocrine glands directly into the blood without any involvement of special ducts from where they reach the target tissue or organ to act. These organs and tissues then respond and enables the body to deal with different situations.

12.  Why is the use of iodised salt advisable?

Ans. Iodine is necessary for the thyroid gland to make thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth. If iodine is deficient in our diet, there is a possibility that we might suffer from goitre. The thyroid gland enlarges causing swelling in the neck. Iodised common salt contains proper content of iodine. Thus, to avoid deficiency of iodine, iodised salt is recommended.

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

Ans. Adrenaline hormone is secreted in large amounts when a person is frightened, or mentally disturbed. When it reaches the heart, it beats faster to supply more oxygen to our muscles. The breathing rate also increases because of the contractions of diaphragm and the rib muscles. It also raises the blood pressure, and allows more glucose to enter into the blood. All these responses together enable our body to deal with the emergency situations.

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

Ans. Diabetes is caused due to less or no secretion of hormone insulin by pancreas. In such a person, blood sugar level is high. Insulin converts extra sugar present in blood into glycogen. Thus, patients suffering from diabetes are given insulin injection to control their blood sugar level.

1.  Which of the following is the plant hormone?

      (a)  Insulin

(b)  Thyroxine

(c)  Oestrogen

(d)  Cytokinin

Ans. (d) Cytokinin

2.  The gap between two neurons is called a

      (a)  dendrite.

(b)  synapse.

(c)  axon

(d)  impulse.

Ans. (b) synapse.

3.  The brain is responsible for

      (a)  thinking.

(b)  regulating the heart beat.

      (c)  balancing the body.

(d)  all of the above.

Ans. (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?

Ans. The receptors in our body collect information about changes in the environment around us in the form of stimuli. They are located in our sense organs such as the inner ear, nose, tongue, eye, etc.

      These then pass the information in the form of nerve impulses to central nervous system (spinal cord and brain) where message is interpreted and instructions are sent to effectors which reveal responses.

      When receptors do not work properly, the environmental stimuli are not able to create nerve impulses and body does not respond.

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

Ans. Functions: The information acquired at the end of the dendritic tip of a neuron sets off a chemical reaction which creates an electrical impulse. This impulse travels from the dendrite to the cell body, and then along the on to its end. At the end of on, the electrical impulse sets off the release of some chemicals, which cross the synapse and start a similar impulse in a dendrite of the next neuron.

      In this way nervous impulses travel in the body. Thus, nervous tissue is made up of an organized network of neurons which are specialized for conducting information via electrical impulse from one part of the body to another.

6.  How does phototropism occur in plants?

Ans. Movement of shoot towards light is called phototropism. This movement is caused due to more growth of cells towards the shaded side of the shoot as compared to the side of shoot towards light. More growth of cells is due to secretion of auxin towards the shaded side.

      •   Fill a conical flask with water.

      •   Cover the neck of the flask with a wire mesh.

      •   Keep two or three freshly germinated bean seeds on the wire mesh.

      •   Take a cardboard box which is open from one side.

      •   Keep the flask in the box in such a manner that the open side of the box faces the light coming from a window.

      •   After two or three days, you will notice that the shoots bend towards light and roots away from light.

      •   Now, turn the flask so that the shoots are away from light and the roots towards light. Leave it undisturbed in this condition for a few days.

      •   The old parts of the roots and shoots change directions.

      •   New growth in shoot is in direction of sunlight.

      Conclusion: Shoot shows phototropism.

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

Ans. (a) Reflex action

      (b) Impulses from various body parts will not be conducted to brain.

      (c) Message from brain will not be conducted to various organs of the body.

8.  How does chemical coordination occur in plants?

Ans. In plants, chemical coordination occurs with the help of plant hormones (phytohormones). Different plant hormones help to coordinate growth, development, and responses to the environment. They are synthesized at places away from where they act and diffuse to the area for action, for example, auxin promotes cell growth, gibberellins promote stem growth, cytokinins promote cell division and abscisic acid inhibits growth and its effects include wilting of leaves.

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

Ans. The body of a multicellular organism consists of a number of components and sub-components and each is specialized to perform a particular function. Therefore, it is necessary that various organs of the body of an organism work together in a proper manner for proper functioning to a stimulus. In human beings nervous system and endocrine system work together to control and coordination.

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

Ans. (a) Involuntary action involves autonomic nervous system.

      (i) They occur in response to internal stimuli.

      (ii) They are connected with functioning of internal body parts.

      (iii) It occurs without the will of the organism. E.g., heartbeat, breathing, etc.

      (iv) These are regulated by medulla oblongata (hind brain).

      (b) Reflex action involves all parts of voluntary nervous system though they are not voluntary.

      (i) They operate against harmful stimuli which are generally external.

      (ii) They are connected with emergency i.e, response to stimuli.

      (iii) Some reflexes involve the brain, rather than the spinal cord.

      (iv) Reflex action is generally controlled by spinal cord.

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

Ans. In human beings, the nervous system controls the various functions by small units called neurons. Neurons receive the information through sensory nerves and transfer them through motor nerves. Whereas, hormones coordinate the activities and growth of the body. Important functions like sugar level metabolism, growth and development etc. are controlled by hormones secreted by endocrine glands. Hence, in human beings, hormones show long lasting responses. The action of hormones is highly specific.

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

      (i) It occurs in response to an external stimulus like touch and shock.

      (ii) Plant cells change shape by changing the amount of water.

      (iii) No nerves are involved.

      (iv) There is no specialized tissue in plants for conduction of information.

      (v) Plant cells do not have specialized proteins.

      Movement in our legs

      (i) It occurs in response to our requirements and is a voluntary action.

      (ii) Movement in our legs is voluntary action which is controlled by cerebellum part of hind brain.

      (iiip) Nerves carry the message for movement of legs.

      (iv) There is specialized nervous tissue in animals for conduction of information and muscle cells to help in movement.

      (v) Animal cells have specialized protein which help muscles to contract or relax.