Revision - GCSE Biology - disease and drugs

Disease in humans

Diseases are caused by bacteria or viruses.

Bacteria are living cells. They are much smaller than body cells, and they reproduce quickly. They make you feel ill by damaging your own cells, and by producing toxins. However, bacteria are useful in the correct place.

Viruses are smaller, and are just a strand of DNA surrounded by a protein. They make you ill by damaging your cells. They reproduce by entering into a body cell; they then use the DNA in the nucleus to copy themselves until the cell bursts. They can reproduce very quickly this way.

The skin is a physical barrier against micro-organisms, and if it is cut blood clots quickly. The eyes also produce enzymes which kill bacteria. If they should get into the stomach, the hydrochloric acid there should kill them. The respiratory tract is full of goblet cells which produce mucus. Any invading organisms will be touched by the mucus, and the cilia then waft them up.


The immune system

  • Phagocytes – Consume bacteria by engulfing and eating them
  • Lymph cells – Identify the bacteria, and then can create antibodies. While identifying can take a while (a couple of days), once it is done it will remember what the bacteria is. Antibodies are then produced very quickly which flow around the bacteria. They also make antitoxins which counter poisons made by the bacteria.

Vaccinations occur by injecting a patient with dead cells of a disease. The lymph cells detect what this is and produce antibodies to fight it. However, it is dead so it poses no real threat to the body. If you should come into contact with the disease the body has already identified the bacteria and can produce antibodies quickly killing the bacteria before they can harm you.


While at first they produce a nice sensation, after a while (illegal) drugs become addictive. There are tow types of addiction, psychological – where the person feels they need it, and chemical – where the body becomes used to having the drug in the system all the time, and so if the drug is taken away the person experience nasty withdrawal symptoms. Drugs often lead to a life of crime and ultimately an early death from contracting things like HIV, hepatitis, or choking on vomit.

Stimulants – Make you feel more alert and awake by increasing nervous activity (speeding up the chemicals at the synapse). An example of a stimulant is caffeine. However, after a while a strong addiction builds up as when you are not on the drug you feel depressed. Examples include Methedrine and amphetamine. Constant taking leads to hallucinations and changes in personality, and people also think they are performing better and more efficiently than they are.

Depressants - Do the opposite; they slow you down, make you depressed, and cause slow reaction, poor judgement. They slow activity of the nervous system. Barbiturates are similar, but make you sleepy (tranquilizers)

Pain killers – Are used in hospitals. However, they are often very addictive as they create a warm happy place people with no future can retreat to. Heroin and morphine are examples. Even aspirin has bad effects if you overdose.

Solvents – Damage your nervous system, causing hallucinations. They can damage your kidneys, lungs brain and liver, and causes serious personality changes. They can also cause instant death.

Alcohol is bad because it can wreck your life. It is a poison to your liver, reducing brain ability. It also impairs judgement, and costs a lot. While it does make you more relaxed when with friends, too much impairs everything. It is a depressant and is bad.

Smoking coats the inside of your lungs with tar, which means they become very unproductive. It also covers the cilia in tar which means the lungs can become infected very easily as the cilia cant work. It causes heart disease and lung and throat cancer. It causes emphysema and bronchitis, and carbon monoxide wastes the haemoglobin in the blood, turning it into carboxyhaemoglobin, and in mothers with unborn babies it starves the baby of oxygen.

Also See

Here are the other comprehensive GCSE Biology notes by Prometheus: