Correct Option (B)
Lichens represent a classic example of a symbiotic relationship between two different organisms: an alga (or a cyanobacterium) and a fungus. The algal or cyanobacterial component, known as the photobiont, performs photosynthesis, producing carbohydrates that serve as food for both partners. The fungal component, called the mycobiont, provides a protective structure, absorbs water and minerals from the environment, and anchors the lichen to its substrate. This mutualistic association enables lichens to thrive in harsh environments, including bare rocks, where they act as pioneer species. By secreting acids and trapping dust, they contribute to the weathering of rocks and the initial stages of soil formation, thereby initiating ecological succession.
Incorrect Options:
Option 1 (algae and bacteria): While bacteria can form various symbiotic relationships, they are not the typical fungal partner in the composite organism known as a lichen. Lichens specifically involve a fungus and a photosynthetic partner (alga or cyanobacterium).
Option 3 (bacteria and fungi): This combination lacks a photosynthetic component. Lichens require a photobiont (alga or cyanobacterium) to produce organic food through photosynthesis, which is essential for their survival and the definition of the symbiotic association.
Option 4 (fungi and mosses): Mosses are bryophytes, which are independent photosynthetic plants. They do not form the specific symbiotic association with fungi that defines lichens. While fungi can associate with plant roots (mycorrhizae), this is distinct from the lichen symbiosis.