Enzyme activity is affected by ph because .

 change the shape of the active site of an enzyme

Explanation:

Enzymes are also sensitive to pH . Changing the pH of its surroundings will also change the shape of the active site of an enzyme. ... This contributes to the folding of the enzyme molecule, its shape, and the shape of the active site. Changing the pH will affect the charges on the amino acid molecules.

as in mitosis, dna replication occurs during interphase.   in meiosis, it occurs specifically in s phase of interphase 1.

meiosis is the first to occur after the nuclei of opposite of opposite mating types fuse