Answer briefly :
(a) How do you perceive the colour of an object ?
(b) Which part of our body helps us in maintaining the body balance ?
(c) How does the eye regulate the amount of light that falls on the retina.

Which of the following helps in maintaining posture and balance of the human body? a. Cerebrum b. Cerebellum c. Medulla d. Pons

Answer briefly: (a) Why are villi present in the intestine and not in the stomach? (b) How does pepsinogen change into its active form? (c) What are the basic layers of the wall of alimentary canal? (d) How does bile help in the digestion of fats?

Find out from your grandparents or other elders ………… (a) how did they go to school? (b) how did they get water for their daily needs when they were young ? (c) what means of entertainment did they use ? Compare the above answers with how you do these takes now. Is there a difference? If yes, in which case more energy from external sources is consumed?

In an experiment to estimate the size of a molecule of oleic acid 1 mL of oleic acid is dissolved in 19 ml of alcohol. Then I mL of this solution is diluted to 20 mL by adding alcohol. Now 1 drop of this diluted solution is placed on water in a shallow through. The solution spreads over the surface of water forming one molecule thick layer. Now lycopodium powder is sprinkled evenly over the film and its diameter is measured. Knowing the volume of the drop and area of the film we can calculate the thickness of the film which will give us the size of oleic acid molecule. Read the passage carefully and answer the following questions. (a) Why do we dissolve oleic acid in alcohol ? (b) What is the role of lycopodium powder ? (c) What would be the volume of oleic acid in each ml of solution prepared ? (d) How will you calculate the volume of n drops of this solution of oleic acid ? (e) What will be the volume of oleic acid in one drop of this solution ?