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

Answer: (b) Algae and fungi

Lichen is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.
Lichens are important actors in nutrient cycling and act as producers which many higher trophic feeders feed on, such as reindeer, gastropods, nematodes, mites, and springtails.
Lichens do not have roots that absorb water and nutrients as plants do, but like plants, they produce their own nutrition by photosynthesis. When they grow on plants, they do not live as parasites, but instead use the plant’s surface as a substrate.
Lichens occur from sea level to high alpine elevations, in many environmental conditions, and can grow on almost any surface. They are abundant growing on bark, leaves, mosses, or other lichens and hanging from branches “living on thin air” (epiphytes) in rainforests and in temperate woodland. They grow on rock, walls, gravestones, roofs, exposed soil surfaces, rubber, bones, and in the soil as part of biological soil crusts. Various lichens have adapted to survive in some of the most extreme environments on Earth: arctic tundra, hot dry deserts, rocky coasts, and toxic slag heaps. They can even live inside solid rock, growing between the grains (endolithic).
It is estimated that 6–8% of Earth’s land surface is covered by lichens.
Lichens are a keystone species in many ecosystems and benefit trees and birds.

Algae are in another kingdom (Protista) separate from plants and fungi. Algae are chlorophyll-bearing, simple, thalloid, aurotrophic and largely aquatic plants.
They occur in moist stones, soils, and wood or in association with fungi and animals.
There are several types of algae: green, brown, red, gold. They can survive in salt water and in freshwater on their own, and in any environment when part of a lichen relationship.
Although cyanobacteria are called blue-green algae, they are actually bacteria, and are part of the bacteria kingdom, Monera. The “blue” in the common name refers to the fact that they need to live in water, and “green algae” refers to their photosynthetic abilities, like green algae.

Fungi are a diverse group of organisms that are in their own kingdom (Fungi), separate from plants.
Fungi is a Eukaryotic organism that includes micro-organism such as yeast, moulds and mashrooms.
Fungi do not contain chlorophyll or any other means of producing their own food so they rely on other organisms for nutrition.
Fungi are widely known for their role in the decomposition of organic matter. They are also necessary for the survival of the ecosystem around them, such as partnering with plants and trees for nutrients and survival.
Lichens are another such partnership for fungi to gain nutrients from another organism. The algal partner photosynthesizes and provides food for the fungus, so it can grow and spread.

Bacteria are microscopic, single-celled organisms that exist in their millions, in every environment.
They constitute a large domain of prokaryotic microorganisms.
Bacteria were among the first life forms to appear on Earth.