S-Cool Revision Summary

S-Cool Revision Summary

We eat all sorts of food. It all looks very different, but if we examine it closely we can spot different food types.

There are three main food types:

Carbohydrates: Used to give us energy and come from sugary or starchy foods

Proteins: Important for building up muscle and other cells.

Fats: Also used to give energy but have other uses too.

However, there are another four types of chemicals that are sometimes described as being 'food types'. These include:

Minerals: Simple ions (charged atoms) such as calcium, iron and fluoride.

Vitamins: More complex organic molecules.

Both Minerals and Vitamins are needed in only tiny amounts but have critical uses in the body and their absence causes disease.

Roughage: The indigestible bits of food that our body cannot cope with and so pass through unaffected.

Water: Also get this through drinks and in our food.

Without enough protein we cannot grow properly or be able to repair our cells. This problem is also seen in areas of the world suffering from famine - people can develop swollen abdomens from a disease called kwashiorkor.

We can test for protein using the Biuret test. This involves adding the piece of food to a copper sulphate solution with a little sodium hydroxide added. The light blue colour changes to purple if proteins are present.

Food contains fat if a white emulsion (tiny droplets of fat in water) is made after mixing the food with water and ethanol. This is called the alcohol emulsion test.

Carbohydrates come either as starch or sugars.

If you add a few drops of iodine to food it will go blue/black if starch is present.

For sugars we can use Benedict's test.

The whole point of the digestive system is to 'digest', or break down, your food from large molecules small molecules that your cells can use for things such as respiration.

The start of the process of digestion occurs in the mouth using the teeth and tongue.

There are four different types of human teeth:

  1. Incisors for cutting.
  2. Canines for piercing.
  3. Pre-molars for cutting and crushing.
  4. Molars for crushing and grinding.

All teeth have the similar features.

After the food has been mechanically broken up it is also mixed with saliva which moistens it and adds the enzyme salivary amylase which begins to digest starch.

The tongue helps to form the food into a small, moist ball called a bolus, which can be easily swallowed.

The bolus is squeezed down the oesophagus (gullet) by wavelike contractions of the surrounding muscle. This is called peristalsis.

Peristalsis occurs throughout the length of the digestive system.

In the stomach, the food is mixed up with hydrochloric acid, which acidifies the food, helping to soften it further and kill any nasty bugs. The acid conditions also allow a protease enzyme called pepsin to start to act on any proteins in the food.

The stomach continually churns up the food so that it is in a nice sloppy mess!

A ring of muscle called a sphincter is relaxed to allow the food out of the stomach. Next it passes into the small intestine, or if you want the fancy names, the duodenum and the ileum (both parts of the small intestine). In the duodenum the food is mixed with bile, which is made in the liver but stored in the gallbladder. This emulsifies any fats in the food, breaking them up into small globules and allows lipase enzymes to attack them.

The pancreas secretes alkali, protease, carbohydrase and lipase enzymes into the duodenum. These further digest all the food types into their smaller molecules.

Within the ileum, the main part of the small intestine, more enzymes act on any remaining large molecules.