UPSC Prelims 2014 · Question 2 of 100

UPSC Prelims 2014 question on Lichens Ecological Succession

Lichens, which are capable of initiating ecological succession even on a bare rock, are actually a symbiotic association of

  1. algae and bacteria
  2. algae and fungi
  3. bacteria and fungi
  4. fungi and mosses
Show answer

Answer: B. algae and fungi

Verdict

The answer is algae and fungi. A lichen is a mutualistic partnership between a fungus and a photosynthetic partner, either an alga or a cyanobacterium.

Analysis

The fungal partner supplies the physical structure, anchors the body to bare rock and absorbs moisture and mineral ions. The photosynthetic partner supplies carbohydrate. That combination is exactly why lichens can colonise bare rock and act as pioneer species in xerarch succession. Algae and bacteria is wrong because the structural partner in a lichen is always a fungus, never a bacterium. Bacteria and fungi is a near miss: cyanobacteria are bacteria and can be the photosynthetic partner, but the option omits algae and does not describe the standard textbook definition. Fungi and mosses is wrong because mosses are bryophytes and are not lichen partners at all.

Source

NCERT Class XII Biology, Unit 10, Chapter 13.

How to crack it

This is a fundamental question sitting in the ecological succession pages of Class XII Biology. The same two pages generate a cluster of favourites: lichens as pioneers on bare rock, mosses as the next stage, hydrarch versus xerarch succession, and the fact that both series converge on a mesic climax. Revise that page as a block rather than as a single fact and you cover four or five possible questions at once.

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