1. A balanced diet should have six parts to it – carbohydrates (including fibre), fats, proteins, vitamins, minerals and water.
2. Foods which have carbohydrates in them include sugars and starches like bread, potatoes and pasta. Roughage like fibre helps to prevent constipation. Carbohydrates provide us with energy.
3. Foods which have fats in them include crisps, animal and vegetable oils. Fats provide us with energy, protection of vital organs (like the heart) and insulation.
4. Protein foods include dairy products like milk and cheese. Nuts are also an excellent source of protein. We need proteins for growth and body-building, and for repairing tissues. We also need proteins to make enzymes.
5. Vitamins are very important for the body as each has a specific job to do, usually to help an enzyme. They are represented by letters: A, B, C, etc. Vitamin A is important for our eyes, Vitamin C keeps the delicate lining of the mouth cavity and other body surfaces in a healthy state and so it prevents scurvy (bleeding gums).
6. Mineral salts contain certain chemical elements. All these elements have particular jobs to do. For example, calcium (in milk and cheese) is used to keep bones healthy and iron is needed in our blood to form the substance haemoglobin (which helps to transport oxygen around the body).
7. Water is essential for life. A person can go without food for several weeks, but would die in a few days from lack of water. We take in water mainly from drinking. However, there is plenty of water in most solid foods. A lettuce or cabbage is 90 % water and even bread is about 40 % water.
8. Foods can be divided into common groupings, e.g. meats, fruits, vegetables, breads etc... . In order to have a healthy diet, a certain amount of each food group should be eaten every day. This can be represented by means of a food pyramid. An example of a food pyramid is given below.
9. Mandatory Experiment – The food tests
(a) Starch: You add a few drops of dilute iodine solution to a sample of the food, either liquid or solid. A blue-black colour indicates that starch is present.
(b) Reducing Sugar: Add Benedict’s solution and boil the mixture. If sugar is present, a brown precipitate (if a lot of sugar is present this precipitate is brick red).
(c) Protein: Add a small amount of sodium hydroxide solution and then add a few drops of copper sulfate solution (blue in colour) also know as Buiret Reagent and if a purple colour is observed then protein is present present in the food sample.
(d) Fats: A simple test for fats is to rub the food on a thin piece of brown paper. Fat will make a translucent (see-through) mark on the brown paper.
10. The energy values of foods can be found on food product labels. These labels also give the quantity of each type of food present.
11. Mandatory Experiment – The conversion of chemical energy in food to heat energy
A food calorimeter is a device which is used to measure how much energy there is in a sample of food. It is a quite complicated piece of machinery but a much simpler laboratory version is shown in the picture below.
You stick a sample of food – a peanut for example – on the end of a mounted needle. You then ignite the food and immediately put the flame under the bottom of the test tube and measure the rise in temperature of the water in the test tube.
12. Digestion is the body breaking down food so that it can enter the bloodstream.
13. When you take some food into your mouth, your mouth waters – it becomes full of saliva. Saliva contains an enzyme called amylase. This acts on starch, breaking it down into malt sugar (maltose). Saliva also contains an enzyme which kills bacteria.
14. Once swallowed the food passes down the oesophagus. The oesophagus has muscle tissue in its wall. A ring of muscular contraction moves slowly downwards, passing the food in front of it. This is called peristalsis.
15. The stomach produces hydrochloric acid which kills any bacteria on the food. It also contains enzymes to break the food down even further.