Given below are some examples of commensalism.
A. Orchid and mango tree
B. Sea anemone and clownfish
C. Cattle egret and grazing cattle
D. Barnacles and whale

Select the option which includes only the organisms benefited from this interaction.

The correct option is C Orchid, clownfish, cattle egret, barnacles
Commensalism is a type of interaction between two different species, in which, one is benefited and the other is neither benefited or harmed. The organism that gets benefitted is called commensal and the organism that does not derive any benefit neither gets harmed is called as host.

Given below are few examples of commensalism:

• Some orchids grow as epiphytes on the branches of a mango tree. Epiphytes are plants that grow upon other plants only for support. In this case orchids are commensal organisms as they are benefited from the mango tree as it provides support. The mango tree is the host and it is neither benefited or harmed from this interaction.
• Sea anemone has stinging tentacles with specialised cells called cnidocytes that help in catching the prey and providing self-defence. The clown fishes live near the sea anemone. These fishes get protection from their predators because of the stinging tentacles of the sea anemone. The clownfish is a commensal organism in this interaction as it is getting benefited and sea anemone is the host which neither gets benefited or harmed.
• The cattle egrets and the grazing cattle also exhibit commensalism. Egrets are birds that are usually found near the grazing cattle. While grazing, the cattle stir up and flush out insects from the vegetation which the bird feeds on. The cattle egret is commensal in this interaction as it is getting benefited and the grazing cattle is neither benefited or harmed.
• Barnacles belong to the phylum Arthropoda. Certain barnacles are found attached on the back of the whales. The barnacles benefit from this interaction as they find a stable place to live, a free ride and access to plenty of food. Whales are unaffected by this interaction.

Hence, option c is correct.