Question

Coral polyps often contain algae living within their tissues, which contribute to their spectacular colours. The algae generally do not survive outside the polyp and the coral grows more slowly if the algae are not present. This association could be best described as:
(a) competition
(b) commensalism
(c) allelopathy
(d) mutualism.

Answer 1

It is mutualism. Both organisms benefit from the interaction: corals grow faster, while algae survive in it.