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Q50 (IAS/2021) Environment & Ecology › Ecology & Ecosystem Basics › Species interactions Official Key

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:

Result
Your answer: —  Âˇ  Correct: D
Explanation

The correct answer is Option 4 (1, 2 and 3) because all three groups contain species capable of forming symbiotic relationships.

  • Cnidarians: Many cnidarians, most notably corals, host photosynthetic algae called zooxanthellae. This mutualistic relationship is vital for reef-building, where the algae provide nutrients and the coral provides protection.
  • Fungi: Fungi are renowned for symbiosis. They form lichens in partnership with algae or cyanobacteria and mycorrhizae with plant roots, assisting in nutrient uptake in exchange for carbohydrates.
  • Protozoa: These single-celled organisms frequently engage in symbiosis. For example, protozoa living in the guts of termites help digest cellulose, while others live within ruminants. Some protozoa also host endosymbiotic algae.

Since biological evidence confirms that species from all three categories exhibit various forms of symbiosis (mutualism, commensalism, or parasitism), the most comprehensive and accurate choice is 1, 2, and 3.

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Q. Which of the following have species that can establish symbiotic relationship with other organisms? 1. Cnidarians 2. Fungi 3. Protozoa Se…
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Origin: Mixed / unclear origin Fairness: Moderate fairness Books / CA: 6.7/10 ¡ 0/10
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This is a classic 'Science-Ecology Overlap' question. While Cnidarians (Corals) and Fungi (Lichens) are standard textbook examples found in Shankar/PMF, Protozoa requires biological intuition or the 'Possibility Heuristic'. The question tests the breadth of your understanding of 'Symbiosis'—it's not just mutual benefit, but any close long-term interaction.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Do any species of Cnidaria (cnidarians) establish symbiotic relationships with other organisms?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > 4.9. CORAL REEFS > p. 50
Presence: 5/5
“50 • Coral is actually a living animal. Coral has a symbiotic relationship (each gives something to the other and gets something back in return) with 'zooxanthellae' microscopic algae which live on coral [i.e. instead of living on the sea floor, the algae lives up on the coral which is closer to the ocean surface and so that the algae gets adequate light]. • Zooxanthellae assist the coral in nutrient production through its photosynthetic activities. These activities provide the coral with fixed carbon compounds for energy, enhance calcification , and mediate elemental nutrient flux. • The tissues of corals themselves are actually not the beautiful colors of the coral reef, but are instead clear (white)”
Why this source?
  • Explicitly states that coral (a living animal) has a symbiotic relationship with zooxanthellae algae.
  • Explains the mutual benefits: algae provide photosynthetic nutrients and enhance coral calcification.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Coral Reefs > p. 219
Presence: 4/5
“• Coral reefs are formed by the accumulation of calcareous skeletons of dead coral polyps. Polyps are related to anemones and jellyfish (phylum cnidaria).• They are shallow warm water organisms which have a soft body covered by a calcareous skeleton. The polyps extract calcium salts from seawater to form these hard skeletons. They occur in different forms and colours, depending upon the nature of the salts they are made of.• The polyps live in colonies fastened to the rocky seafloor. The tubular skeletons grow as a cemented calcareous rocky mass, collectively called corals. When the coral polyps die, they shed their skeleton (coral) on which new polyps grow.”
Why this source?
  • Identifies coral polyps as members related to anemones and jellyfish in phylum Cnidaria.
  • Links the organism (coral polyps) described in the symbiosis example to the cnidarian group.
Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > 12.8 How Do Interactions Maintain Balance in Ecosystems? > p. 203
Presence: 3/5
“Chapter 12 — How Nature Works in Harmony 203 • z Mutualism: Both organisms benefit. For example: Honeybees and flowers.• z Commensalism: One organism benefits while the other is not affected. For example: Orchids on trees.• z Parasitism: One organism benefits while the other is harmed. For example: Ticks on the body of dogs. These interactions are all part of the complex web of life in an ecosystem. Fig. 12.16: Different types of interactions between organisms”
Why this source?
  • Defines mutualism as an interaction where both organisms benefit, framing symbiosis type relevant to coral–algae relationships.
  • Places mutualism among standard interaction types, helping classify coral–zooxanthellae association.
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