Digestion

Many of the molecules in our food are polymers. These are large, complex molecules composed of long chains of monomers, small basic molecular units. 
Proteins and some carbohydrates are polymers.

In carbohydrates, the monomers are called monosaccharides. They contain the elements carbon, hydrogen and oxygen.
In proteins, the monomers are called amino acids. They contain carbon, hydrogen, oxygen and nitrogen.

The two types of digestion:
Physical digestion - food is broken down into smaller pieces by teeth in the mouth. It then moves to the stomach where it's broken down by the churning movement of the stomach muscles. Breaking food down into smaller pieces gives it a larger surface area, which makes chemical digestion faster.

Chemical digestion - the polymers in our food are insoluble (they can't be directly absorbed into our bloodstream). The polymers have to be hydrolysed into smaller, more soluble molecules by adding water. This process happens during chemical digestion. Hydrolysis is catalysed by digestive enzymes.

Parts of the digestive system:
Mouth - the mouth starts the digestive process. Teeth are used to break down food and the tongue is used to push food down into the oesophagus. Saliva is secreted to make the food easier to swallow and it contains enzymes which start the chemical digestion process.

Oesophagus - this is the tube that takes food down from the mouth to the stomach using waves of muscle contractions called peristalsis. Mucus is secreted from tissues in the walls, to lubricate…