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Topicwise Answers

Page No. 119

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


Reflex action:

  • Reflex action is a spontaneous immediate response to a stimulus.

  • It is controlled by the spinal cord.

  • It is an involuntary action.


  • Walking is a conscious response.

  • Controlled by hindbrain (cerebellum).

  • It is a voluntary action.


2. What happens at the synapse between two neurons?

Ans: Synapse is a successive gap present between the two neurons. Electrical impulses converted into chemical impulses (neurotransmitters) and pass across the synapse, reach to dendrites of the next neuron.


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

Ans: The Cerebellum (a part of the hindbrain) is responsible for the precision of voluntary actions and maintaining the posture and balance of the body


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

Ans: The scent of the incense stick initially reaches our nose, where it is detected by the olfactory receptors. The receptors then send electrical signals to the forebrain with this information. The forebrain then interprets this information as the smell of an incense stick, which it already has stored in its memory.


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

Ans: Reflex action is controlled by a reflex arc which is formed in the spinal cord and the information reaches the brain and brain stores the experience and response to it


Page No. 122

1. What are plant hormones?
Ans: Plant hormones or phytohormones are organic compounds that are produced in plant parts and regulate plant growth and development.


2. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
Ans: When a growing part of a plant detects light, a hormone called auxin, synthesized at the shoot tip diffuses towards the shady side of the plant. That is, on the opposite side of the direction of light. So, the concentration of the auxin increases towards shady side of the shoot and stimulates the cells to grow longer than the cells of the growing part of the shoot towards the light. So, more growth of cells on shady growing potion causes bending of this portion towards the light. This movement of the shoot is known as phototropism.

3. Give an example of a plant hormone that promotes growth.
Ans: Auxin promotes the growth of cells, gibberellins help in the growth of the stem, cytokinin promotes cell division.

4. How do auxins promote the growth of a tendril around a support?
Ans: Tendrils are sensitive to touch. When they come in contact with any support, the growth hormone auxin diffuses from the site. This causes growth in the part of the tendril away from the support. This causes the tendril to circle around the support. Tendrils help to climb the support.

5. Design an experiment to demonstrate hydrotropism.
Ans: Growth movements in response to the stimulus of water are termed as 
hydrotropic movements (hydrotropism).
Experiment: To demonstrate hydrotropism, take some germinating seeds which have a very high growth rate. Place water-soaked seed in a plastic container filled with soil and put water in a small pit away from the seed.
After sprout formation, roots will develop in two to three days. Here we will observe that roots of the newly germinated plants are towards the source of water.

Conclusion: Roots of the plant detect the presence of water and grow in the direction of higher humidity.


Page No. 125

1. How does chemical coordination take place in animals?

Ans: In animals, endocrine glands secrete their hormones into the blood directly. Hormones reach the target organ/tissue/cell through the bloodstream. The target cells have special molecules on their surface to detect these comical compounds and recognise the information a particular hormone carrying. Then the cells act accordingly.

2. Why is the use of iodized salt advisable?

Ans: Iodine is necessary for the proper functioning of the thyroid gland to make the thyroxine hormone. Thyroxine regulates carbohydrates, proteins, and fat metabolism in the body so as to provide the best balance of growth. Hence, iodized salt is advisable.


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

Ans: Adrenaline hormone secreted by adrenal gland directly into the blood and carries to different parts of the body.

  • The target organs are the specific tissues on which it acts include the heart. As a result, the heart beats faster, resulting in supply of more oxygen to our muscles.

  • The blood to the digestive system and skin is reduced due to the contraction of muscles around small arteries in the organs. This diverts the blood to our skeletal muscles.

  • The breathing rate also increases because of the contractions of the diaphragm and the rib muscles. All these responses together enable the animal body to be ready to deal with the situation.


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

Ans: Insulin hormone regulates blood sugar level. It converts excess of glucose into glycogen. If Islets of Langerhans fails to produce enough amount of insulin, causes an increase in the level of blood sugar. This condition is called Diabetes mellitus. To treat this insulin injection is given

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