Question

Explain why:
(i) Raisins swell up in water.
(ii) We gargle with saline solution in case of throat infection.
(iii) Bacteria and fungi do not grow in pickles, jams, jellies, and squashes.
(iv) The leaves of wilted lettuce, if kept in cold water, become crisp.

Answer 1

(i) Raisins swell up in water because of their uptake of water by endosmosis. The concentration of solutes in raisins is higher than that in the solution outside, and thus water moves into the raisins, causing them to swell up.

(ii) We gargle with saline solution in case of throat infection so that all the bacteria are plasmolysed by exosmosis because of the hypertonic nature of the saline solution.

(iii) Bacteria and fungi do not grow in pickles, jams, jellies and squashes because the water content of these food items is reduced by adding salts or sugars. Thus, bacteria and fungi are deprived of moisture that is essential for their growth. The salts and sugars also help carry out plasmolysis of infecting cells.

(iv) The leaves of wilted lettuce, if kept in cold water, become crisp because of endosmosis of water.