Which of the following have species that can establish symbiotic relationship with other organisms? ​ 1. Cnidarians ​ 2. Fungi ​ 3. Protozoa ​ Select the correct answer using the code given below. ​

All three groups have species that live in symbiosis with other organisms, so the answer is D. Symbiosis covers mutualism, commensalism and parasitism, so a group qualifies if any member species forms such a relationship.

• 1. Cnidarians: Reef-building corals host dinoflagellate algae called zooxanthellae in their tissues. The algae supply photosynthetic sugars and the coral provides shelter and nutrients. Hydra viridis also carries green algae inside its cells.
• 2. Fungi: Mycorrhizal fungi form mutualistic partnerships with plant roots, exchanging phosphorus and water for sugars. Lichens are a stable partnership between a fungus and an alga or cyanobacterium.
• 3. Protozoa: Wood-feeding termites depend on flagellates such as Trichonympha in their gut to digest cellulose. The protozoa get a habitat and food, and the termite gets usable energy.

The core concept is mutualism. For Mains, link coral bleaching under warming seas to the fragility of such partnerships, and mycorrhizal inoculants to sustainable agriculture.

Trap: Aspirants fixate on protozoa as disease-causing parasites like Plasmodium and reject option D. Parasitism is only one kind of symbiosis, and mutualistic protozoa are equally valid.