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.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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explanation: