IGCSE Biology - Digestion and Enzymes HE

Ingestion

Taking food into the body through the mouth.

Digestion

The chemical and mechanical breakdown of food. It converts large insoluble molecules into small soluble molecules, which can be absorbed into the blood.

Peristalsis

Waves of muscle contraction that pass along the gut. Behind the food, circular muscles contract, longitudinal muscles relax, and the gut narrows pushing the food along.

Absorption

The movement of a substance across a cell membrane by means of diffusion or osmosis.

Assimilation

When soluble food molecules are absorbed from the blood into cells, and are used to build new parts of cells.

Egestion

The removal of undigested food as faeces.

Amylase

Digests starch into maltose. Produced by the salivary glands and pancreas.

Maltase

Digests maltose to glucose. Produced by the wall of the small intestine.

Lipase

Digests lipids to glycerol and fatty acids. Produced by the pancreas.

Proteases

An example would be Pepsin, which digests proteins to peptides. Pepsin is produced in the stomach.

Mouth

Where food is broken down mechanically into smaller pieces that have a large surface area.

Saliva

Moistens food and contains the enzyme amylase which begins the breakdown of starch in the mouth.

Oesophagus

Tube connecting the mouth and the stomach.

Stomach

Holds food for several hours. It's wall secretes hydrochloric acid and digestive enzymes.

Sphincter

Ring of muscles which holds food in the stomach until it is ready to enter the small intestine.

Hydrochloric acid

Secreted by the stomach wall to kill bacteria which can enter the body via food we have eaten.

Small intestine

Divided into the duodenum and the ileum, it's function is to breakdown food and absorb nutrients into the bloodstream.

Duodenum

First section of the small intestine which is responsible for the breakdown of food using enzymes.

Ileum

Final section of the small intestine which is adapted to absorb the products of digestion into the bloodstream.

Villi

Tiny projections from the lining of the ileum. Villi increase the surface area of the ileum to aid absorption.

Microvilli

Tiny projections from the surface of each villus, that help to increase the surface area of the villus.

Describe 4 adaptations of the small intestine that allow it to absorb digested food efficiently

1. Villi and microvilli increase surface area 2. Long length increases surface area 3. Rich blood supply helps carry absorbed molecules away 4. Thin wall means short diffusion distance

Large intestine

Absorbs the remaining water from semi-digested food to leave a semi-solid waste material called faeces.

Rectum

Stores faeces which are expelled via the anus.

Pancreas

Responsible for making several digestive enzymes that work in the small intestine.

Bile

A green alkaline liquid produced by the liver. It has two functions 1. To emulsify lipids 2. To neutralise stomach acid

Gall bladder

Stores bile.