CBSE Class 7 Answered

(i) The living together of two different species of plants as if they are parts of the same plant and help each other in obtaining food is called symbiosis.

(ii) Symbiosis occurs in the plants called ‘lichens’.

(iii) In lichens, the green coloured plant called ‘alga’ (autotroph) and non- green plant 'fungus' (saprophyte) live together. The fungus holds the alga cells in its mat of web-like hyphae (thin filaments). The fungus plant absorbs the water and mineral salts from the surroundings and supplies them to alga. The alga plant being green prepares the food by photosynthesis and shares it with fungus. Thus, both alga and fungus gain mutually from one another by living together. This is an example of symbiosis.