Concept preview

What you will be able to do

1. 01Distinguish mechanical digestion from chemical digestion and give examples of each.
2. 02Name the key digestive enzymes (salivary amylase, pepsin, pancreatic amylase, trypsin, lipase) and state where each acts and what it breaks down.
3. 03Describe the roles of the accessory organs: the liver and bile, the pancreas, and the gallbladder.
4. 04Explain how carbohydrates, proteins, and fats are each broken down into absorbable units.

Digestion happens in two complementary ways that work side by side. Mechanical digestion is the physical breaking of food into smaller pieces without changing what the molecules are: the teeth chop and grind, the stomach churns, and bile breaks fat into tiny droplets. Chemical digestion is the chemical splitting of large molecules into small ones using enzymes — biological catalysts that speed up reactions. The two are partners rather than rivals. Mechanical digestion matters because it creates a huge surface area for chemistry to act on: a single lump of food offers enzymes only its outer skin, but the same food chopped and churned into a paste exposes an enormous surface. So the physical work of chewing and churning is not merely tidying up — it directly speeds and completes the chemical breakdown that follows.