UPSC Prelims 2014 Q22: Science & Technology – Biology
Lichens, which are capable of initiating ecological succession even on a bare rock, are
actually a symbiotic association of
- (a) algae and bacteria
- (b) algae and fungi
- (c) bacteria and fungi
- (d) fungi and mosses
Answer: (b) algae and fungi
Explanation
Lichens
A lichen is a symbiotic association of an alga and a fungus.
| Partner | Name | Role |
|---|---|---|
| Alga (or cyanobacterium) | Phycobiont | Makes food by photosynthesis |
| Fungus | Mycobiont | Gives shelter, and absorbs water and minerals |
Why lichens matter:
| Role | Detail |
|---|---|
| Pioneer species | First to grow on bare rock; their acids break rock into soil |
| Pollution indicators | They die where air has much sulphur dioxide |
| Uses | Litmus dye; food for reindeer |
The options checked:
| Option | Verdict |
|---|---|
| (a) Algae and bacteria | Incorrect |
| (b) Algae and fungi | Correct |
| (c) Bacteria and fungi | Incorrect |
| (d) Fungi and mosses | Incorrect |
Answer: (b) algae and fungi.
Why each option is right or wrong
- (a) Incorrect. A lichen needs a fungus; algae and bacteria alone do not form one.
- (b) CORRECT. Lichens are a symbiotic association of algae and fungi.
- (c) Incorrect. Bacteria and fungi do not make a lichen; a photosynthetic partner is needed.
- (d) Incorrect. Mosses are separate plants and not part of a lichen.
Key point
Lichen = alga (phycobiont, makes food) + fungus (mycobiont, gives shelter and water); pioneer on bare rock; indicator of sulphur dioxide pollution.
Remember
Lichen = algae + fungi, living together.
Common mistakes
- Confusing lichens with mosses, which are true plants.
- Forgetting that lichens are sensitive to air pollution.
- Mixing up lichen (alga + fungus) with mycorrhiza (fungus + root).
Exam tip
Lichen: the alga cooks, the fungus gives the house. Both gain, so it is symbiosis.
Sources
- NCERT Class XI — Biology, Ch 2 (Biological Classification: Viruses, Viroids and Lichens)
- NCERT Class XII — Biology (Ecosystem: ecological succession)