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 & explanation
Answer: (d) 1, 2 and 3
All three groups contain species that live in close, often mutually beneficial, partnerships with other organisms. Reef-building corals (cnidarians) host photosynthetic zooxanthellae; fungi form lichens and mycorrhizae; and many protozoa live as symbionts, some carrying algae inside their own cells.
- ✓ 1. Corals, which are cnidarians, house zooxanthellae in their tissues; the algae supply sugars from photosynthesis and the coral gives them shelter and carbon dioxide.
- ✓ 2. Fungi team up with algae or cyanobacteria to form lichens, and with plant roots to form mycorrhizae that help plants absorb phosphorus.
- ✓ 3. Many protozoa live as symbionts; the ciliate Paramecium bursaria, for instance, carries symbiotic Chlorella algae in its cytoplasm. The two benefit each other: the ciliate gives the algae a protected habitat and the algae add to its nutrition through photosynthesis.
Remember · Mutualism examples: coral + zooxanthellae, fungus + alga (lichen), fungus + root (mycorrhiza), Paramecium bursaria + algae, legume + Rhizobium.
📘 Read it in NCERT: Class 9 Exploration, Ch 12 (practise this chapter) · Class 12 Biology, Ch 11 (practise this chapter) · Class 9 Exploration, Ch 12 (practise this chapter)
Sources
- NOAA National Ocean Service, Corals Tutorial: What is Zooxanthellae? ↗ “Most reef-building corals contain photosynthetic cells called zooxanthellae that live in their tissues. The corals and zooxanthellae have a mutualistic relationship.”
- NCERT Class 9 · Exploration, Chapter 12 “Cnidarians, such as Hydra (Fig. 12.14), jellyfish (Fig. 12.16b) and corals show a major change in body organisation.”
- NCERT Class 12 · Biology, Chapter 11 “Lichens represent an intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria. Similarly, the mycorrhizae are associations between fungi and the roots of higher plants.”
- NCERT Class 9 · Exploration, Chapter 12 “Some of the fungi establish a mutualistic (symbiotic) relationship with other organisms while others live as parasites, and cause diseases in plants and animals.”
- Kodama et al., 'Effects of the Symbiotic Chlorella variabilis on the Host Ciliate Paramecium bursaria Phenotypes' (PubMed Central) ↗ “The relationship between P. bursaria and symbiotic Chlorella spp. is characterized by mutualism, in which both organisms benefit from this association.”
Question and answer: UPSC's official GS Paper I (2021, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). ·