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Food molecules which are needed in very small quantities in the diet


Food molecules which are needed in large quantities in the diet

Nervous system

The system which coordinates the actions of the body in response to changes in the environment using electrical signals travelling through a system of nerves

Cell membrane

The membrane which forms the boundary between the cytoplasm of a cell and the medium surrounding it and controls the movement of substances into and out of the cell.


The protein that carries oxygen within red blood cells.

Amino acid

The basic building blocks of proteins. There are twenty amino acids used, in different combinations, to make every protein required by the human body.

Fatty acid

Large molecule consisting of a carboxylic acid (RCOOH) with the 'R' being a long unbranched hydrocarbon chain.


A complex carbohydrate which makes up plant cell walls


A chemical which is a building block of lipids.


A polymer made up of amino acids joined by peptide bonds. The amino acids present and the order in which they occur vary from one protein to another.


Chemical needed in very small amounts as part of a balanced diet to keep the body healthy.


Molecules which contain a lot of stored energy built up of fatty acids and glycerol. Lipids include oils and fats


A complex carbohydrate made as an energy store plants


Material which cannot be digested in the gut, needed to provide bulk which enables food to move through the digestive system.


A large organ in the upper abdomen which manufactures, stores and breaks down substances as required by the body

Diet and nutrition

Wherever you live and whatever you eat, the right balance of food is of enormous importance to your health and well-being. A balanced diet contains enough of the major food groups to supply the energy and nutrients you need to grow and maintain the cells, tissues and organs of your body.

Some types of food are needed in large amounts. These are the macronutrients which include carbohydrates, lipids and proteins. Other substances are just as important in our diets but are only needed in tiny amounts. They are the micronutrients and they include minerals and vitamins.

The main components of a balanced diet are:

Carbohydrates provide us with easy-to-use energy. They contain the chemical elements of carbon, hydrogen and oxygen. All carbohydrates are made up of units of sugar. Some carbohydrates contain only one sugar unit. The best known of these is glucose. Some carbohydrates are made of two sugar units joined together. Sucrose, the compound we call sugar in everyday life, is an example. Complex carbohydrates such as starch and cellulose are made up of long chains of sugar molecules joined together by condensation reactions.

Carbohydrate-rich foods

Carbohydrate-rich foods include sugar, bread, pasta, potatoes and rice

Lipids are fats (solids) and oils (liquids). The molecules contain a lot of energy and are a very important source of energy in your diet. They are also an important part of your cell membranes, as hormones and in your nervous system. Like carbohydrates they contain the chemical elements of carbon, hydrogen and oxygen. A lipid is made up of three fatty acid molecules joined to a molecule of glycerol. The glycerol is always the same. It is the different fatty acids that affect the lipid and determine if it is a fat or an oil.

Lipid-rich foods

Lipid-rich foods include butter, olive oil, cream, nuts and egg yolks

Proteins contain carbon, hydrogen and oxygen and also nitrogen. They are used for building the cells and tissues of your body, and enzymes are also made of protein. Protein molecules are made up of long chains of amino acids joined together. There are 20 amino acids and different arrangements of these various amino acids give us all the different proteins. The long protein molecules are often folded or coiled to give them unique three dimensional shapes.

Protein-rich foods

Protein-rich foods include meat, fish, cheese, egg whites and pulses

Minerals and vitamins are needed in your body in very tiny amounts but they are vital for your body to grow and function healthily. A lack of them in the diet can lead to many different deficiency diseases.

Minerals include:

  • Iron, needed for the haemoglobin which carries oxygen in the red blood cells. Found in red meat, leafy green vegetables, apricots and eggs
  • Calcium, needed for strong bones and teeth. Found in dairy products, fish, bread and vegetables

Vitamins include:

  • Vitamin A, needed for a healthy retina and good vision. Found in fish liver oils, butter, liver and carrots
  • Vitamin B1, needed for cell respiration. Found in yeast extract and cereals
  • Vitamin C, needed for cell layers to stick together. Found in citrus fruits and fresh vegetables
  • Vitamin D, needed for healthy bones and teeth. Found in fish liver oils and made in the skin in sunlight
Food rich in minerals and vitamins

Food rich in minerals and vitamins - milk (calcium), red meat (iron), citrus fruits (vitamin C) and cod liver oil capsules (vitamin D)

Fibre (also known as roughage) is material which you cannot digest - for example the cellulose in plant cell walls. It does not get broken down but it is very important for the healthy working of the digestive system. It provides bulk which allows the muscles to contract and move food through the digestive system steadily.


High fibre foods