Diet and exercise
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 are carbohydrates, fats and proteins.
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. Note that you do not need to know how the nutrients work or the effects of any particular deficiency in the diet for your exam.
Defending against infection
Pathogens are microorganisms - such as bacteria and viruses - that cause disease. Bacteria release toxins, and viruses damage our cells. White blood cells can ingest and destroy pathogens by producing antibodies that destroy the infectious microorganisms, and antitoxins to neutralise toxins created as a by-product.
Bacteria and viruses are the main types of pathogen. Bacteria are microscopic organisms. They come in many shapes and sizes, but even the largest are only 10 micrometres long - that's 10 millionths of a metre.
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
- whooping cough.
Viruses are many times smaller than bacteria. They are among the smallest organisms known and consist of a fragment of genetic material inside a protective protein coat.
Viruses can only reproduce inside host cells and they damage the cell when they do this. A virus can get inside a cell and, once there, take over and make hundreds of thousands of copies of itself. Eventually the virus copies fill the whole host cell and burst it open. The viruses are then passed out in the bloodstream, the airways, or by other routes.
Diseases caused by viruses include:
- influenza (flu)
- chicken pox
White blood cells
White blood cells can:
- ingest pathogens and destroy them
- produce antibodies to destroy particular pathogens
- produce antitoxins that counteract the toxins released by pathogens.
In a written examination, it is easy to get carried away with metaphors about invaders and battles: stick to the point. Note that:
- the pathogens are not the disease - theycausethe disease
- white blood cells do not eat the pathogens…