Questions: Symbiosis

Question 1

Clownfish live among the stinging tentacles of sea anemones. The anemone's stings protect the clownfish from predators, and the clownfish drives away fish that would eat the anemone. What type of symbiosis is this?

• A. Parasitism
• B. Commensalism
• C. Mutualism
• D. Competition

Answer: (C)

This is mutualism because both species benefit. The clownfish gets protection from predators (the anemone's tentacles don't harm it due to a special mucus coating), and the anemone gets protection from its own predators plus nutrients from the clownfish's waste. Both organisms are better off together than apart.

Question 2

Symbiosis means the same thing as mutualism.

• T. True
• F. False

Answer: False

Symbiosis is the broader term — it refers to any close, long-term relationship between two different species. Mutualism is one type of symbiosis (both benefit), but parasitism (one benefits, one is harmed) and commensalism (one benefits, one is unaffected) are also forms of symbiosis.

Question 3

Why do most parasites NOT kill their host?

Model answer: A parasite depends on its host for food, shelter, or other resources. If the parasite kills the host, it loses its own source of survival and must find a new host — which may not be possible. Parasites that keep their host alive can feed for a longer time, so natural selection tends to favor parasites that harm but do not kill.

This is an example of evolutionary logic. A parasite that kills quickly would be less successful than one that keeps its host alive, because the slow-killing parasite gets more total resources. Over many generations, this dynamic selects for moderate virulence — a concept important in disease ecology.