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.

Answer: D. All three groups — CNIDARIANS, FUNGI, PROTOZOA — include species with SYMBIOTIC RELATIONSHIPS. SYMBIOSIS is a long-term interaction between two different species, including mutualism (both benefit), commensalism (one benefits, other unaffected), or parasitism (one benefits, other harmed). (1) CNIDARIANS — CORRECT. Many cnidarians form symbioses: - HARD CORALS host ZOOXANTHELLAE (Symbiodinium dinoflagellates) inside their tissues. The algae photosynthesise and supply the coral with sugars; the coral gives shelter and CO2. This mutualism enables coral reefs to thrive in nutrient-poor tropical waters. CORAL BLEACHING is the breakdown of this symbiosis. - ANEMONES host clownfish in a famous mutualism. - Some hydroids host green algae internally. (2) FUNGI — CORRECT. Fungi are the symbiosis champions: - MYCORRHIZAE — fungi associated with plant roots in mutualism (over 80% of plant species rely on this). - LICHENS — fungal-algal symbioses (Ascomycete fungus + green alga or cyanobacterium). - ENDOPHYTES — fungi inside plant tissues. - Many parasitic and pathogenic fungi too. (3) PROTOZOA — CORRECT. Several protozoa form symbioses: - Cellulose-digesting protozoans in TERMITE GUTS (mutualism — termites can't digest cellulose alone; protozoa cannot survive outside). - Trichonympha in wood-eating roaches. - The malaria parasite Plasmodium is a protozoan PARASITE of humans (parasitism is a form of symbiosis). - Many marine protozoans (foraminifera, radiolarians) host symbiotic algae. Source: NCERT Class 12 Biology — Organisms and Populations / Microbiology references.