Biology B1 (Keeping healthy)

Regular exercise and a balanced diet are needed to keep the body healthy. Too little food leads to a person being underweight and prone to certain types of illness, while too much food and not enough exercise leads to a person being overweight and other types of ill health.

A mixture of different types of food in the correct amounts is needed to maintain health.

The main food groups

Food groupFound inNeeded by our bodies for: Carbohydrates

potatoes, pasta, bread, bananas, sugar and rice a source of energy for life processes Fats

cheese, butter, margarine and oils a source of energy for life processes: fats are also needed to make cell membranes and to insulate our bodies Proteins

meat, fish, eggs and cheese growth and repair - building cells

Mineral ions and vitamins are also important in a healthy diet. They are needed in small amounts for healthy functioning of the body.

An imbalanced diet causes a person to become malnourished. For example:

• too little food may lead to a person being underweight
• too much food may lead to a person being overweight.

A poor diet may also lead to deficiency diseases. For example, too little vitamin D in the diet can lead to rickets, which affects the proper growth of the skeleton. Type 2 diabetes is also a problem related to poor diet.

Exercise

If someone’s diet consists of food with a lower energy content than the amount of energy their body uses, the person will lose body mass.

Respiration is a chemical reaction that allows cells to release energy from food.

Metabolic rate is the speed at which such chemical reactions take place in the body and varies because of several factors, including age, gender and inherited factors.

Metabolic rate is also affected by the:

• proportion of muscle to fat in the body
• amount of exercise and other physical activity.

The metabolic rate increases as we exercise and stays high for a while afterwards. People who exercise regularly are usually healthier than people who don't.

Other factors affect health too, including inherited factors. For example, the cholesterol level in the blood can affect health. Cholesterol is made in the liver and is needed for healthy cell membranes. However, too much cholesterol in the blood increases the risk of heart disease and diseased arteries.

Pathogens are microorganisms - such as bacteria and viruses - that cause disease. Bacteria release toxins which are foreign to our body, and viruses damage our cells. These chemicals (toxins) are called antigents.

Pathogens : Bacteria

Bacteria and viruses are the main types of pathogen. Bacteria are microscopic organism. Bacteria are living cells and, in favourable conditions, can multiply rapidly. Once inside the body, they release poisons or toxins that make us feel ill. Diseases caused by bacteria include:

• food poisoning
• cholera
• typhoid
• whooping cough.

Pathogens : Viruses

Viruses are alot smaller than bacteria. They consist of a fragment of genetic material inside a protective protein coat. Viruses can only reproduce inside host cells and…