It helps sustain tbe population because of the food chain. everything needs to eat, so the more diverse a population is, the more options things have to eat. The population is sustained because everything is able to eat to survive
If there was a sudden, significant event in the area (such as a volcanic eruption) then a population with higher biodiversity is more likely to contain at least 1 species which will be adapted enough to survive in the changed environment than an area with lower species diversity.
Intestinal gland secretes intestinal juice ,it contains enzymes and their role is to decompose food more and then conduct them into the large intestine or by intestinal absorption to the blood
