Digestion of Larger Insoluble Molecules

Digestion involves both physical and chemical processes.
The process begins in the mouth, where food is mixed with saliva. The action of the teeth and salivary enzymes break down large insoluble food particles into smaller soluble ones.
Saliva contains amylase, an enzyme that starts the breakdown of starch into glucose.
After chewing and lubricating, food is swallowed and travels down the oesophagus to the stomach.
In the stomach, hydrochloric acid and protease enzymes help to break down proteins into smaller peptides.
The partially digested food then moves into the small intestine. Here, three types of enzymes act on it: Amylase breaks down any remaining starch to glucose; Protease completes the digestion of proteins to amino acids; and Lipase converts fats into glycerol and fatty acids.
These enzymes are produced by the pancreas and secreted into the small intestine.
The small intestine wall produces enzymes too. Sucrase breaks down sucrose into glucose and fructose; Lactase digests lactose into glucose plus galactose; and Maltase, which converts maltose into glucose.
Once digested into small soluble molecules, nutrients are absorbed into the bloodstream through the intestinal walls by diffusion or active transport.
The remaining undigested food passes into the large intestine (colon) where the water and electrolytes are reabsorbed.
The remaining faecal matter is stored in the rectum and expelled from the body through the anus.
In summary, digestion of large insoluble molecules involves the breaking down of complex carbohydrates, proteins, and fats into smaller, soluble molecules that can be absorbed by the body for energy and for building and repairing cells.

Do not forget to revise the specific enzymes involved and where they are produced, as these are often a focus in test questions.