Question

Where does chemical digestion start and end?

Answer 1

The saliva contains amylase which starts to break down starch in the food when eaten. Then, pepsin is secreted in the stomach to break down proteins. Next is the small intestine more proteases, sucrase and lipase etc are released to break down food into its constituent elements that can be absorbed.
The large intestine just absorbs water from the remnant of the digested food and does not chemically digest any food.