2.
What effect do enzymes have on chemical reactions?

Enzymes are needed to speed up chemical reactions in organisms. They work by lowering the activation energy of reactions.

Enzymes position substrates into active sites.

Various conditions affect enzyme function. Pepsin and trypsin are two digestive enzymes that work in contrasting environments.

Explanation:

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genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).