- Carbohydrate molecules contain the elements carbon, hydrogen and oxygen.
- Starch and glycogen are large, complex carbohydrates, which are made up of many smaller units (e.g. glucose or maltose molecules) joined together in a long chain.
- Proteins are made up of long chains of amino acids.
- They all contain carbon, nitrogen, hydrogen and oxygen atoms.
- Lipids (fats and oils) are built from fatty acids and glycerol.
- Lipids contain carbon, hydrogen and oxygen atoms.
A Balanced Diet
Carbohydrates Pasta, rice,sugar Provide energy.
Lipids Butter, oily fish Provide energy, act as an energy store and provide insulation.
Proteins Meat, fish Needed for growth and repair of tissue, and to provide energy in emergencies. Vitamin A Liver Improves vision and keeps skin and hair healthy.
Vitamin C Oranges Prevent scurvy.
Vitamin D Eggs Needed for calcium absorption.
Calcium Milk, cheese Needed to make bones and teeth.
Iron Red meat Needed to make haemoglobin for healthy blood.
Water Food and drink Replaces water lost through urinating, breathing and sweating.
Dietary fibre Wholemeal bread Aids the movement of food through the gut.
Enzymes and Digestion
Digestive enzymes break down big molecules into smaller ones
Amylase converts starch into maltose.
Maltase converts maltose into glucose.
Proteases convert proteins into amino acids.
Lipases convert lipids into glycerol and fatty acids.
Bile neutralises the stomach acid and emulsifies fats
The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile is alkaline - it neutralises the acid and makes conditions alkaline. The enzymes in the small intestine work best in these alkaline conditions.
Bile also emulsifies fats. In other words it breaks the fat into tiny droplets. This gives a much bigger surface area of fat for the enzyme lipase to work on - which makes its digestion faster.
The Alimentary Canal
Mouth - 1) Salivary glands in the mouth produce amylase enzyme in the saliva.
2) Teeth break down food mechanically.
Oesophagus - The muscular tube that connects the mouth and stomach.
Large intestine - Where excess water is absorbed from the food.
Stomach - 1) It pummels the food with its muscular walls.
2) It produces the protease enzyme, pepsin.
3) It produces hydrochloric acid for two reasons: a) To kill bacteria and b) To give the right pH for the protease enzyme to work (pH2 - acidic).
Pancreas - Produces protease, amylase and lipase enzymes. it releases these into the small intestine.
Small intestine - 1) Produces protease, amylase and lipase enzymes to complete digestion.
2) This is also where the nutrients are absorbed out of the alimentary canal into the body.
The Digestive Process
1) Ingestion - Putting food (or drink) into your mouth.
2) Digestion - The break-down of large, insoluble molecules into small, soluble molecules. It can be mechanically digested (teeth and stomach muscles) or chemically digested (enzymes and bile).
3) Absorption - The process of moving molecules through the walls of the intestines into the blood. Digested food molecules are absorbed in the small intestine - water is mainly absorbed in the large intestine.
4) Assimilation - Digested molecules are moved into body cells. The digested molecules then become part of the cells (assimilation).
5) Egestion - The undigested stuff forms faeces, which are of no use to your body - you get rid of them via the anus (egestion).