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.
Contents17
- A1 and 2 only
- B2 and 3 only
- C1 and 3 only
- D1, 2 and 3
Show answer
Answer: (D) 1, 2 and 3
Symbiosis means two different organisms living together in a mutually beneficial relationship.
Cnidarians (Option 1) — Corals have a symbiotic relationship with zooxanthellae (dinoflagellate algae).
The algae provide food through photosynthesis; the coral provides shelter.
Fungi (Option 2) — Form mycorrhiza (fungi + plant roots, helping absorb nutrients) and lichen (fungi + algae, enabling survival on bare surfaces).
Protozoa (Option 3) — Certain protozoa live in termite guts and help digest cellulose.
The termite gets nutrition; the protozoa get habitat and food.
All three have symbiotic species.
Answer: (d).
Symbiosis is fundamental to major ecosystems - coral reefs depend on cnidarian-algae partnerships, forests rely on fungal-root networks, and many insects survive through protozoan gut partnerships.
UPSC is testing whether students can move beyond memorizing definitions to recognizing symbiosis across diverse biological groups from marine life to microorganisms.
Symbiosis and Mutualism
Environment symbiotic relationship organisms
Symbiosis: Types, Examples & UPSC Applications
Symbiosis means two different species living together in close association
Mutualism is when both species benefit (corals + algae, fungi + plant roots)
Commensalism is when one benefits, other is unaffected
Parasitism is when one benefits at the expense of the other
What is Symbiosis
Symbiosis refers to any close, long-term biological interaction between two different species. The term comes from Greek meaning 'living together'. This relationship can benefit both organisms, harm one, or have no effect on one partner.
Types of Symbiotic Relationships
Type | Effect on Species A | Effect on Species B | Classic Example |
|---|---|---|---|
Mutualism | Benefits (+) | Benefits (+) | Coral + Zooxanthellae algae |
Commensalism | Benefits (+) | No effect (0) | Barnacles on whales |
Parasitism | Benefits (+) | Harmed (-) | Tapeworm in human gut |
Amensalism | No effect (0) | Harmed (-) | Penicillium kills bacteria |
Question Connection
This PYQ tests whether students know that all three groups — Cnidarians, Fungi, and Protozoa — have species capable of forming symbiotic relationships. The trap is assuming only 'higher' organisms form complex relationships.
Trap: Thinking symbiosis only occurs in 'advanced' animals — even simple organisms like protozoa form complex partnerships
Trap: Confusing symbiosis (any close relationship) with mutualism (only mutually beneficial relationships)
Trap: Missing that corals are cnidarians — they're not plants despite being sessile
Cnidarians and Coral Symbiosis
Environment Cnidarians
Cnidarians: Coral-Algae Partnership & Marine Ecosystems
Cnidarians include corals, jellyfish, sea anemones, and hydra
Zooxanthellae are dinoflagellate algae living inside coral tissues
Coral bleaching occurs when zooxanthellae leave due to stress
What are Cnidarians
Cnidarians are aquatic animals with stinging cells called cnidocytes. They include corals, jellyfish, sea anemones, and hydra. Despite appearing plant-like, corals are animals that build limestone skeletons.
How Coral-Algae Symbiosis Works
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Zooxanthellae algae live inside coral tissues**
Microscopic dinoflagellate algae take shelter in coral polyps`"]
s2["`**Algae perform photosynthesis using sunlight**
Convert CO₂ and water into glucose and oxygen`"]
s3["`**Coral receives up to 90% of its nutrition**
Gets glucose, amino acids, and oxygen from algae`"]
s4["`**Coral provides CO₂, nutrients, and protection**
Gives algae nitrogen, phosphorus, and safe habitat`"]
s1 --> s2
s2 --> s3
s3 --> s4Ecological Significance
Enables corals to thrive in nutrient-poor tropical waters
Coral bleaching happens when stressed corals expel zooxanthellae
This partnership built the Great Barrier Reef and other major reef systems
Rising sea temperatures threaten this delicate symbiosis globally
Trap: Thinking corals are plants because they're sessile — they're animals in phylum Cnidaria
Trap: Confusing zooxanthellae (algae in corals) with mycorrhizae (fungi with plant roots)
Fungi Symbiotic Relationships
Environment Fungi
Fungi Partnerships: Mycorrhizae, Lichens & Ecological Roles
Mycorrhizae = fungi + plant roots for enhanced nutrient absorption
Lichens = fungi + algae/cyanobacteria living as one organism
Over 80% of plant species form mycorrhizal associations
Fungi as Symbiotic Partners
Fungi form two major types of symbiotic relationships that are crucial for ecosystem functioning. These partnerships enable life in extreme environments and enhance nutrient cycling in forests.
Major Fungal Symbioses
Partnership | Components | Fungus Gets | Partner Gets | Where Found |
|---|---|---|---|---|
Mycorrhizae | Fungi + Plant roots | Carbohydrates from photosynthesis | Enhanced water & mineral absorption | 80% of plant species |
Lichens | Fungi + Algae/Cyanobacteria | Organic compounds from photosynthesis | Structure, protection, minerals | Rocks, tree bark, extreme environments |
Endophytic fungi | Fungi + Grass tissues | Nutrients from plant | Protection from herbivores | Many grasses and crops |
Ecological Importance
Mycorrhizae increase plant root surface area by up to 1000 times
Lichens are pioneer species that colonize bare rock and begin soil formation
Many forest trees cannot survive without mycorrhizal partners
Lichens serve as air pollution indicators due to their sensitivity
Mycorrhizal Network
Source: Frontiers — Frontiers | Mycorrhizal hyphae as ecological niche for highly ... · www.frontiersin.org
Trap: Confusing mycorrhizae (fungi-root partnership) with rhizobia (nitrogen-fixing bacteria in legume roots)
Trap: Thinking lichens are single organisms — they're actually fungi + algae partnerships
Trap: Missing that most plants depend on mycorrhizae — it's not rare but essential
Protozoa Symbiotic Relationships
Environment Protozoa
Protozoa Partnerships: Termite Digestion & Microbial Symbiosis
Termite gut protozoa digest cellulose that termites cannot break down
Without these protozoa, termites would starve despite eating wood
Trichonympha and other flagellated protozoa live in termite intestines
Protozoa as Digestive Partners
Protozoa are single-celled eukaryotic organisms that form crucial symbiotic relationships, especially in digestive systems. The most famous example occurs in termite guts, where protozoa enable wood digestion.
Termite-Protozoa Digestion Process
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Termite chews and swallows wood pieces**
Mechanical breakdown but no cellulose digestion yet`"]
s2["`**Wood reaches hindgut containing protozoa**
Specialized chamber houses millions of symbiotic protozoa`"]
s3["`**Protozoa enzymes break down cellulose**
Convert cellulose into simple sugars and organic acids`"]
s4["`**Both organisms absorb nutrients**
Termite gets energy, protozoa get habitat and food particles`"]
s1 --> s2
s2 --> s3
s3 --> s4Other Protozoan Symbioses
Ruminant animals have protozoa in their stomachs helping digest grass
Some protozoa live symbiotically in coral tissues alongside zooxanthellae
Paramecium bursaria contains green algae that provide food through photosynthesis
Many protozoa form partnerships with bacteria in complex microbial communities
Trap: Thinking only 'higher' organisms form symbioses — single-celled protozoa create complex partnerships
Trap: Confusing protozoa (eukaryotic) with bacteria (prokaryotic) in digestive symbioses
Trap: Missing that termites cannot digest cellulose alone — they depend entirely on protozoan partners