When a person eats sugary food, then organisms A present in his mouth act on sugar to produce a substance B. The substance B first dissolves the calcium salts from the top part C of the tooth and then from its middle part D forming holes E. These holes ultimately reach the part F in the lower part of tooth which contains nerves and blood vessels. The substance B irritates the nerve endings inside the tooth causing toothache.

1. What are (i) organisms A, and (ii) substance B?
2. What are (i) part C, and (ii) part D, of tooth known as?
3. By what name are the holes E in the tooth known?
4. Name the part F of the tooth.
5. What will happen if organisms A reach part F of the tooth known?

Explain the mechanism of photosynthesis.

Distinguish between aquatic and terrestrial respiration.

If a person holds his breath after expiration for about 25sec, would there be occurrence of any exchange of respiratory gases in the lungs during this period? Explain.

Describe the alimentary canal of man.

X is a wild animal which eats only the flesh of other animals whereas Y is a domestic animal which feeds mainly on green grass.

1. What are animals like X known as?
2. What are animals Y known as?
3. Which animal, X or Y, has a longer small intestine? Why?
4. Name one animal which is like X.
5. Name one animal which is like Y.

In the artificial kidneys, the tubes are all with semi-permeable lining. Why?

Describe the process of nutrition in Draw labelled diagrams to show the various steps in the nutrition in Amoeba.

Describe the structure and functioning of nephrons.

Water and dissolved minerals get into the root hair of a plant by a process called A and enter the conducting tissue B. The process C helps the water and dissolved minerals to move up through the tissue B in roots and stem, and reach the leaves of a plant. In the leaves food is made by a process D. This food is then transported to all the parts of a plant through tissue E. The process of distributing food made in the leaves to all the parts of the plants is called F.

1. What are (i) A, (ii) B, (iii) C, (iv) D, (v) E, and (vi) F?
2. Which tissue is made up of living cells: B or E?
3. Which tissue, B or E, contains sieve tubes?
4. Which tissue, B or E, contains tracheids?