Food and drink
The body is sometimes described as a very complicated chemistry set, but where do the chemicals come from? To answer this, we have to go back to the beginning of the universe. The universe is thought to have come into existence about thirteen billion years ago. It formed in a huge explosion called the Big bang. At this time just two chemicals were formed. They were hydrogen and helium. They swirled around into clouds and eventually formed hot bright globes of gas called stars.

The heat inside a star is not due to flames like those on a bonfire. It is due to the force of gravity. There is a force of gravity between everything in the universe and inside stars. This force is so great that it squashes hydrogen so hard that it turns into helium. As this happens, a large amount of energy is released which escapes from the star as light and heat. The heat inside stars also causes other chemicals to form, such as oxygen, nitrogen and carbon. A star does not last forever. Eventually it runs out of hydrogen to squash. When this happens, it may puff out the chemicals it has made into space or it may explode in a super nova. When a star explodes it produces even more heat and this leads to other chemicals being formed.

In time, the chemicals made by the stars formed dust and mixed with more hydrogen and helium in space. One cloud of dust and gas swirled around to form the Solar System. The hydrogen and helium formed the Sun. The other chemicals that were made in the stars, formed the planets and everything on them.

It is thought that the first living things formed from a mixture of chemicals. These chemicals came together in the rock pools of ancient seas. These living things needed more chemicals for their bodies so they took in more chemicals from the sea water. These chemicals in sea water were the first food.

There has been life on Earth for over three billion years and during this time millions of different kinds of life forms developed. Also during this time, the chemicals which form food became organised in certain ways. Today we divide food into five different groups according to the way the chemicals are arranged. The name of one food group called carbohydrate even gives a clue to some of the chemicals it contains. Carbohydrates are formed from carbon, hydrogen and oxygen. The other four groups also contain certain combinations of chemicals. For example, fats contain mostly carbon and hydrogen while proteins contain the same chemicals as carbohydrates but also contain nitrogen and sometimes sulphur. Vitamins contain a wide range of chemicals while each mineral, such as iron or calcium, contain only one.

Our bodies need food to provide us with materials for growth and the repair of damaged body parts. The main food group to provide these materials is protein but some minerals such as calcium and phosphorous are important too. Our bodies also need food to provide us with energy. This gives us the power to carry out all the processes of life. Energy is stored in carbohydrates and fat.

At every meal, food seems more important than drink but this is not the case. All drinks contain large amounts of water. Water is the substance in which all the chemicals in food dissolve so they can be used by the body. Without water, food is useless. While people may survive for a few weeks without food they may only survive a few days without water.

Next time you are having supper, look out of the window at the stars and think of the cosmic connection between those shining points of light and the food on your plate.

Is water made from chemicals in stars?
Yes, it is. It is made from hydrogen and oxygen.

How do plants make food?
They take water from the ground and carbon dioxide from the air. These two substances meet in the leaf. The leaf has a green substance called chlorophyll which traps some of the energy in sunlight. The plant uses this energy to rearrange the chemicals in water and make sugar and oxygen. The sugar is used as a food and the oxygen is released into the air.

Do plants only make sugar?
No. They convert some of the sugar to starch. Sugar and starch are carbohydrates. Plants also convert large amounts of sugar to a substance called cellulose. This makes up most of the plant's body. It is best seen in the fibres in a celery stalk. Cellulose is also known as fibre.

It helps our body digest our food. Plants convert some of their sugar into fats. Some plants such as the groundnut store fat inside their seeds. We call the groundnut seeds peanuts. Plants take nitrogen and sulphur from the ground and use them with sugar to make proteins. Vitamins are made by plants and a wide range of minerals are taken up by their roots and stored. So instead of just being a source of sugar, plants provide foods for the whole five food groups.

Do animals make foods?
No. Animals must get their food from plants or other animals. When they take in food they break it down into simple chemicals that dissolve in water then join the chemicals together in new ways to make the substances they need. For example, starch does not dissolve in water so animals break it down to sugar, which does dissolve. The dissolved sugar can then be digested. If the sugar is not used to provide energy straightaway it is changed into fat and stored in the body.

What are food additives?
Most food additives are chemicals that are added to foods to keep them edible. They are added to many manufactured foods such as biscuits and packet soups and mayonnaise. If you look on a food packet or a bottle you may see the words antioxidant, emulsifier, stabiliser, colouring, flavours. An antioxidant stops fats in the food from becoming rancid or going 'off'. An emulsifier stops solids and oils separating in foods such as mayonnaise. A stabiliser keeps the food looking fresh to eat. Colourings and flavourings may be from natural substances or from chemicals. They are used to replace the colour that has been lost when the food has been prepared. These food additives are not added to make the food more nourishing.

Some foods such as breakfast cereals have added minerals and vitamins to make them more nourishing.