Q.11 The association in which population of one organism is benefited and population of the other is unaffected is known as
(1) Symbiosis
(2) Commensalism
(3) Mutualism
(4) Parasitism
Understanding Symbiotic Relationships: Which One Benefits One Without Harming the Other?
In ecology and biology, organisms often interact in ways that shape ecosystems. Symbiotic relationships describe close associations between species, but not all are equal. A common multiple-choice question tests this: “The association in which population of one organism is benefited and population of the other is unaffected is known as” with options (1) Symbiosis, (2) Commensalism, (3) Mutualism, (4) Parasitism.
Correct Answer: (2) Commensalism
This defines commensalism definition biology perfectly—one species gains a benefit (like food or shelter) while the other experiences no positive or negative effect. Let’s break down all options with clear explanations and examples to solidify your understanding.
What is Commensalism? Key Features and Examples
Commensalism occurs when one organism (the commensal) benefits from another (the host) without affecting the host’s survival, growth, or reproduction.
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Benefits to one, neutral for the other: The host neither helps nor harms.
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Real-world example: Barnacles attach to whales’ skin. Barnacles get a free ride and access to food-rich waters; the whale swims on unaffected.
Other examples include:
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Clownfish living among sea anemone tentacles (anemone unharmed).
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Epiphytic plants (like orchids) growing on tree branches for sunlight, without drawing tree nutrients.
This “types of symbiosis” relationship highlights nature’s one-sided perks.
Symbiosis: The Broad Umbrella Term
Option (1) Symbiosis refers to any long-term, close interaction between two different species living together. It doesn’t specify benefit or harm—it’s neutral.
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Key trait: Proximity and interdependence, but outcomes vary.
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Example: Lichens (fungi + algae living together).
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Why not correct? Symbiosis is too general; it includes mutualism, commensalism, and parasitism.
Think of symbiosis as the parent category for specific “types of symbiosis.”
Mutualism: Win-Win for Both Species
Option (3) Mutualism is when both organisms benefit. It’s a cooperative symbiosis boosting survival for each.
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Key trait: Reciprocal gains, often essential.
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Example: Bees pollinate flowers while collecting nectar—flowers reproduce, bees get food.
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Comparison to commensalism: Here, both populations thrive, unlike commensalism’s one-sided benefit.
Mutualism powers ecosystems, like mycorrhizal fungi aiding plant roots for sugars in return.
Parasitism: One Benefits, the Other Suffers
Option (4) Parasitism harms the host while benefiting the parasite. The host survives but pays a cost.
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Key trait: Parasite exploits host resources, often weakening it.
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Example: Ticks feed on dog blood—tick gets nutrition, dog gets irritated and risks disease.
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Mutualism vs commensalism vs parasitism: Parasitism is negative for one (host damaged), contrasting commensalism’s neutrality.
Quick Comparison Table: Types of Symbiosis
| Relationship | Effect on Species 1 | Effect on Species 2 | Example |
|---|---|---|---|
| Commensalism | + (benefits) | 0 (unaffected) | Barnacles on whales |
| Symbiosis | Varies | Varies | Lichens (fungi + algae) |
| Mutualism | + (benefits) | + (benefits) | Bees and flowers |
| Parasitism | + (benefits) | – (harmed) | Ticks on mammals |
(+ = benefit, 0 = neutral, – = harm)
Why Commensalism Matters in Biology and Exams
Mastering commensalism definition biology helps in exams, research, and appreciating biodiversity. It shows evolution favors neutral coexistence when full mutualism isn’t possible.
Next time you see that MCQ, pick (2) confidently—it’s the precise fit.
