Lesson: Chapter 6 — Human body processes

6.1. Digestion and the digestive system 1 of 2

What digestion is

The body needs energy for every life process, and that energy comes from food. But proteins, carbohydrates and lipids are large, complex molecules that do not dissolve in water, and they cannot be absorbed as they are.

Digestion

Digestion is the process that turns the complex organic compounds in food into simple organic compounds that can be absorbed.

Mechanical digestion

The physical form of the food changes.

Example: teeth cutting food into small pieces in the mouth.

Chemical digestion

Enzymes act on complex compounds and turn them into simple ones.

Example: salivary amylase turning starch into maltose in the mouth.

Some things need no digesting

Mineral salts, some vitamins, glucose, fructose and galactose are already small enough, and are absorbed directly.