Organisms and Populations — BIOLOGY STD 12 Science — Question

Mutualistic: Both the interacting organisms are benefitted from each other e.g. Lichens- Algae and fungi mutually help each other or any other appropriate example.
Competition: When two organisms belonging to closely related species/unrelated groups compete for the same resources that are limiting both are losers, e.g. superior barnacle dominates and excludes the small barnacles/in some South American lakes visiting flamingoes and resident fishes compete for their common food (zooplankton) in the lake.
Parasitic: One of the two organisms is dependent on the other( host) for nutrition and support/the host is harmed and the parasite is benefitted. e.g. Malarial parasite and human/Cuscuta on host plant.