Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
An orange crust grows on a granite wall at a hill station. It is a lichen. Name its two partners, and say what each gives the other. Why is the association called symbiotic?
A lichen is a symbiotic association of an alga (the phycobiont), which makes food, and a fungus (the mycobiont), which gives shelter and takes in water and minerals. Lichens do not grow in polluted air, so they are pollution indicators.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The alga. The phycobiont is autotrophic. It makes food for both.
Step 2. The fungus. The mycobiont is heterotrophic. It gives shelter, and it takes in water and mineral nutrients for the alga.
Step 3. Symbiotic. Both partners gain, and they live so closely that they cannot be separated in nature.
Answer: an alga (food) and a fungus (shelter, water, minerals); both gain, so it is symbiotic.
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