8A Food and Digestion

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Why do we need food?

We need to consume a balanced diet which contains a variety of food in the proportions shown in the diagram.

The body needs:

• Carbohydrates which provide energy.

• Proteins for repair and growth.

• Vitamins and minerals to keep the body healthy.


Food Groups Pop Quiz


What is a balanced diet?


What do carbohydrates provide?

Starchy foods contain carbohydrates, which aremade of long chains of identical small sugar molecules.

Carbohydrate

1 Sugar molecule


The body has to break these large food molecules up into smaller pieces.

The small sugar molecules are very useful. The body can use them to make…

This energy is used to make the body work.

ENERGY

What do carbohydrates provide?


What do proteins provide?

As with carbohydrates, proteins are made of chains of chemicals. However, instead of the chain containing identical molecules, in protein these molecules are different.

Protein is made up of chains of amino acids. There are over 20 different kinds of amino acid.

Protein is used to allow the body to grow and to repair the body.


What happens to food in the digestive system?


Food is firstly broken down (mechanical breakdown) into smaller parts by the teeth in the mouth. It is then mixed with saliva and swallowed.

Mechanical digestion


Food enters the stomach, which is basically a muscular bag, filled with hydrochloric acid (HCl). Two things happen here:• Chemical breakdown of the food.• Microbes are destroyed.

food enters from the gullet

cross section of stomach

digested food leaves

muscle tissue

The stomach


The small intestine

Food enters the small intestine from the stomach. It passes along the small intestine where the soluble food is taken into the blood through the walls.


The large intestine

The remains of the food are then passed on to large intestine (colon).

All that is left is waste material and water. The body will want to leave the waste material within the digestive system but the water is valuable and so it is re-absorbed here.

The waste material is passed to the rectum where it is stored until it leaves the body through the anus.


Why breakdown large molecules into smaller ones?

The body must go through mechanical and chemical digestion to convert large insoluble molecules into smaller soluble ones.

Carbohydrate molecule

Protein molecule (folded up)

Fat molecule

This is because smaller molecules can pass through the walls of the small intestine and then dissolve into the blood stream. Larger molecules cannot do this.

Sugar


Digestion quiz


Enzymes

Enzymes are chemicals which break the larger molecules down into smaller molecules. There are three types of enzymes that you need to know about.


Enzymes

• Carbohydrase chops carbohydrates into smaller sugar molecules.

The three types of enzymes are:

• Protease cuts proteins into the soluble amino acids.

• Lipase breaks fats down into the smaller fatty acids and glycerol.


Proteins are digested in the stomach by an enzyme called Protease. This enzyme needs to work in an acidic environment. Protease breaks proteins (chains of different molecules) down into up to 20 different amino acids (four of which are shown).

Proteins digestion

Protease

Folded up protein chain

Amino acids


Carbohydrates are chains of identical sugar molecules. The enzyme called Carbohydrase breaks the chemical bonds between the individual sugar molecules (called glucose) as part of digestion.

Starch/ carbohydrates

Carbohydrase

Long carbohydrate Small sugar


FatsFats are digested in two stages:

• Firstly bile (released by the gall bladder) allows the fat to “mix” with water by breaking the fat up into smaller droplets. This is called emulsification.

• Secondly, an enzyme called Lipase breaks the fats down into the smaller fatty acid molecules and glycerol.

Bile

Lipase +

Fat

Fatty

acidGlycerol

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8A Food and Digestion