Why does changing the ph of a solution affect the ability of an enzyme to catalyze a chemical reaction

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

Elephants in the savanna regions of africa dig holes in dried up river beds to reach water lying just below the surface. these holes provide drinking water for other animals as well. so, without the elephants, many animals might otherwise die from lack of water during the dry season. the location in which the elephants live is an example of a/n and the role they play in creating water holes is an example of a a) ecosystem; habitat b) community; niche c) habitat; niche d) niche; habitat

Number and variety of living organisms includes genetic, species, and ecological types