Food is needed for energy, growth, repair and protection against disease in the body. Food is made up of chemicals called nutrients A food’s energy value is how much energy that can be obtained from the food. A balanced diet consists of the correct amounts of each type of food.
The main nutrients
Carbohydrates (sugars) are found in sugar rich foods, e.g. honey, sweets, and jam. They provide energy and fibre (needed for muscles of the bowel to work properly [roughage]), They contain carbon, hydrogen and oxygen and are made of single sugar units which can be joined together in long chains. Starch is a long chain sugar and glucose is simple single sugar. e.g. starch in bread. To test a food for starch, add brown iodine solution. If it turns a blue/black colour then starch is present.with water and roughage.
Proteins e.g. fish contain carbon, nitrogen, oxygen, hydrogen and sometimes sulphur. They are found in fish and meat. They contain chains of amino acids joined together. They are used for building new cells. e.g.muscle and bone.
Vitamins e.g. vitamin D in milk are chemicals needed in small amounts to protects us against disease. For example vitamin A is needed for healthy eyes and skin and is got from carrots and cod-liver oil.
Roughage is also required to keep the digestive system in tone got from green vegetables (fibre).
Food is needed for:
- growth and repair
- protection against disease
Exp. Testing a food for starch
- Add 2cm of starch solution or food to a test tube.
- Add 2-3 drops of iodine (red/brown).
- If a blue/black colour is obtained. then starch is present
Exp. Testing for proteins
- Add milk or dissolve the food to be tested to a test tube (2cm level)
- Add an equal amount of sodium hydroxide
- Add a few drops of copper sulphate solution.
- If a violet colour is obtained then the food contains protein.
Exp. Testing for glucose
- Add 2cm³ of glucose or the food to a test tube.
- Add 2cm³ of benedict’s reagent (blue) to the test tube.
- Set up as shown in the diagram and heat.
- If a red/orange colour is obtained then the food contains glucose.
Exp. Testing for fats
- Rub margarine or the food on brown paper.
- Allow to dry and compare.
- Put a drop of water on another piece of brown paper.
- A translucent spot indicates that fats are present.
The Human Digestive System
The human digestive system has the following parts and functions:
- Mouth: Physical (chewing) and chemical digestion.
- Oesphagus: Mouth connected to the stomach
- Stomach: Churning and chemical digestion
- Pancreas: Makes digestive enzymes
- Liver: Makes bile for digestion of fats
- Small intestine: Enymes digest food and use nutrients absorbed into the blood
- Large intestine: Excess water absorbed and gets rid of undigested food.
- Ingestion: taking of food into to the mouth
- Digestion: break down of food into small soluble pieces
- Absorption: taking in of useful food into the bloodstream
- Assimilation: use of food for growth, repair and energy
- Egestion: removal of unused food from the body.
Stages of digestion
- Mouth Chewing and saliva
- Stomach: Churning, gastric juices, acid to kill germs
- Small intestines: digestive juices from pancreas
Results of digestion
- Carbohydrates → glucose
- Proteins → amino acids
- Fats → fatty acids and glycerol
An enzyme is a biological catalyst, it speeds up chemical reactions without being used up.
Exp. To show the action of an enzyme
- In test tube A add starch solution, iodine, and tap water, this blue/black solution is the control
- In test tube B add starch solution, iodine and saliva.
- Leave both for several minutes at 37oC.
- The mixture in tube B goes colourless.
- The mixture in tube A does not change.
- The enzyme in saliva breaks down starch.
Note: Saliva contains the enzyme amylase.
Exp: To show food contains energy (chemical energy)
- Set up as shown in the diagram.
- Record the temperature of the water at the start.
- Light the cracker with a match and hold it under the test tube with a tongs.
- After a few minutes record the temperature of the water.
- A rise in temperature in the water confirms chemical energy in the food was converted into heat energy.
- Enamel is a very hard substance which protects the tooth.
- Dentine is a bone-like substance, though softer than enamel.
- Pulp cavity contains living cells, blood vessels which supply the tooth with food and oxygen, and nerves.
- Cement protects the root from damage.
There are four types of tooth.
- Incisors – these teeth are used for cutting and biting food.
- Canines – these teeth are used for tearing food.
- Premolars – these teeth are used to grind food.
- Molars – these teeth are used to grind food.
Plaque and sugars cause tooth decay