Chapter 7 Control and Coordination | Class 10 Science |

 

                Chapter 7  Control and Coordination

 

                  Textual Question and Answers

 

Page 119

 

1. The differences are

a)  A reflex action is fast and spontaneous while walking is a slower action.

b) A reflex action does not require thinking while walking requires thinking.

c)  A reflex action is generally controlled by the spinal cord while walking is controlled by the brain.

2.  The gap between the axon of a neuron and the dendrite of the next neuron is called as the synapse. It allows the transmission of an impulse in one direction only. Any impulse brought by the axon terminates at the synapse but releases chemical neuro-transmitters that cross the synapse and generate a similar impulse at the dendrite of the next neuron.

3.  Cerebellum, which is a part of the hind brain, maintains posture and equilibrium of the body.

4.  The smell of incense (agarbatti) is first detected by the olfactory receptors present in the nose. This stimulus is then converted into nerve impulse and transmitted to the brain by the sensory neurons. The brain interprets the information and then indentifies the smell.

5.  The brain has no direct role to play in a reflex action. This is because most of the reflex actions are under the control of the spinal cord. However the brain is aware of the response only after the action has been completed.

 

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1.  Plant hormones are naturally synthesised chemical compounds that help in different growth and development activities of the plants. They are produced in different parts of the plant and are translocated to the regions where they are required.

2.  The differences are

a)  The movement of leaves of sensitive plants is a type of nastic movement while the movement of shoot toward light is a type of tropic movement.

b) The movement in the leaves of sensitive plants is due to change in the shape of some specialized cells while the movement of shoot is due to unequal growth in the shoot region.

3.  Auxin and gibberellins are plant hormones that promote growth.

4.  The growth of a tendril around a support is a thigmotropic movement in response to contact. It is regulated by the hormone auxin. When a tendril comes in contact with a support, the diffusion of auxin to that region in contact decreases. On the other hand the diffusion of auxin to the region away from contact increases. This causes the region away from contact to grow more rapidly than the region which is in contact to the support. As a result of this unequal growth the tendril starts coiling around the support.

5.  A few soaked gram seeds are allowed to germinate in a perforated tray filled with dry sawdust. A few days later roots will be seen growing through the holes of the tray toward the ground. The tray is then raised to a height of about 15 to 20 cm above the ground using a support and the sawdust is regularly watered. Another few days later the roots will be seen growing upward towards the watered sawdust. This activity demonstrates the positive hydrotropism of roots.

 

Page 125

 

1.  In animals chemical coordination occurs with the help of the chemical messengers called hormones. These hormones are secreted by the ductless glands called endocrine glands. The endocrine glands along with their hormones regulate the developmental activities of the animal’s body.

2.  Iodine is an important mineral necessary for the secretion of thyroxine hormone by the thyroid gland. In the absence of iodine the thyroid gland cannot secrete sufficient amount of thyroxine hormone, and the gland enlarges leading to a condition called goitre. So the use of iodised salt is advisable to supplement the requirement of iodine in one’s body.

 

3.  Adrenaline is secreted by the adrenal gland and is transported by the blood to different target organs like heart, diaphragm, skin, intestine, etc. It increases the rate of heart beat and the rate breathing. It also helps to withdraw blood from the skin and intestine, and direct this blood towards the muscles so that more oxygen and nutrients are transported to the muscles. This way adrenaline hormone prepares the muscles for any action during situations of emergency.

4.  Diabetes is a condition of abnormal increase in the level of glucose in the blood. This is caused due to insufficient production of insulin hormone by the pancreas (Islets of Langerhan). So diabetic patients with very low insulin production are treated with insulin injection to regulate the level of glucose in blood.

 

                                   Exercise

1.  Option (d)

2.  Option (b)

3.  Option (d)

4.  The function of the receptors in our body is to sense any stimulus and transport the information to the brain.

If the receptors do not function properly we would not be able to detect any changes in the surrounding around us and thus would not be able to carry out desired responses.

5.                         Diagram

The main function of a neuron is the transmission of information in the form of electric signals called nerve impulse. For this the dendrites receive the impulse from another neuron while the axon sends the impulse to the next neuron.

6.  Phototropism is the movement of a part of plant in response to light. It is very evidently observed in the shoots which show positive phototropism. This movement is regulated by the hormone auxin. Auxin helps in cell elongation and is synthesised at the tip of the shoot. More auxin diffuses towards the shady regions of the shoot than toward the brighter region. This causes the shady region to elongate more rapidly than the brighter region. Thus the shoot starts bending towards the source of light.

7.  In case of a spinal cord injury the signals transmitted to and from the brain specially limbs and internal organs will be disrupted.  It will also disrupt many of our reflex actions.

8.  In plant chemical coordination occurs with the help of chemical messengers called plant hormones or phytohormones. They are naturally synthesised chemical compounds that help in different growth and development activities of the plants. They are produced in different parts of the plant and are translocated to the regions where they are required.

9.  Most responses to environmental stimuli involve actions. The accomplishment of any action requires the coordinated movement of different organ. Along with responses various development activities also require communication among the different part of the body. Thus in order to establish this communication between the various part of the body as well as between the outside and inside of the body a system of control and coordination is needed in an organism.

10.      The differences are

a)  Involuntary actions are comparatively slower actions while reflex actions are fast and rapid.

b) Involuntary actions involve involuntary muscles while reflex actions involve voluntary muscles.

c)  Involuntary actions are under the control of the brain while most reflex actions are under the control of the spinal cord.

11.    The comparisons and contrasts are

a)    In the nervous mechanism information is transmitted in the form of electric signals while in the hormonal mechanism information is transmitted in the form of chemicals.

b)   In the nervous mechanism neuron are the agents of transport while in the hormonal mechanism blood is the agent of transport.

c)    Transmission of information is rapid through the nervous mechanism while it is slower in the hormonal mechanism.

d)   Both the mechanisms involve communicating different parts of the body.

12.      The differences are

a)  Movement in sensitive plants is due to external stimulus while movement in our leg is due to internal stimulus.

b) Movement in sensitive plants is caused by osmosis but contraction (or relaxation) of muscle cells cause movement in our leg.

c)  Movement in sensitive plants is stimulated by electro-chemical signals while movement in our leg is stimulated by electric signals.