An enzyme is a catalysts in living things.
A catalysts speeds up the process of breaking down molecules.
An example would be Lactose. It can be broken down by the enzyme Lactase.
Species is the most narrow category
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I would say individuals can adapt to change as this agrees with the theory of natural selection that in any species there are varieties and these can consist of individuals that are better adapted to the environmental conditions so they will thrive and propogate themselves and can result in a new species.