Fungi are the largest micro-organisms. Some make threads that invade cells for nutrients- eg. mould, others such as yeast are single-celled. Fungi can live on living and decaying tissues. Dieseases caused include athletes foot, ringworm and thrush.

Protozoa are single-celled organisms like amoeba. They are larger than viruses and bacteria. They absorb nutrients from around them. Malaria and amoebic dysentry are caused by protozoa.

There are two types of respiration: aerobic- needs oxygen and happens in cells when glucose reacts with oxygen. It takes place in animal and plant cells as well as some microbes.
Glucose + Oxygen→Carbon dioxide + Water + energy released

and anaerobic- does not need oxygen. It happens when there is not enough oxygen for aerobic respiration. It happens in animal cells, some bacteria, plant cells and some microbes such as yeast.
Glucose → Lactic Acid + some energy released

The three conditions that microbes need to grow are: nutrients, water and ideal temperature.

There are three types of white blood cells: ones that engulf and break up bacteria, produce antitoxins to neutralise the toxins produced by the bacteria and produce antibodies which stick to bacteria together so that other types of white blood cells can engulf and destroy them.

There is a delay between being infected and feeling ill because the bacteria needs time to reproduce to actually cause illness. They cause illness because they multiply and make toxins.

Viruses make you feel ill because they burst the cells open and multiply, releasing more viruses. The difference between bacteria and viruses is that bacteria make copy of themselves and viruses infect other cells and take them to produce more copies.

1. When you are infected by a microbe, it takes time for your body to start fighting the infection, it does this by making antibodies.

2. You recover when enough antibodies have been produced. Some of the white blood cells that produce the correct antibodies remain in your blood.

3. When you get infected a second time by the same microbe, your body makes the correct antibodies much faster.

4. The microbe does not get a chance to make you ill and this is known as being immune to the microbe and the infection it causes.

1. Every cell has unique proteins on their surfaces called antigens.

2. The antigens on pathogens are very different is the antigens that cover our human cells.

3. Our immune system recognises that the antigens are different.

4. Our immune system launches an attack against the pathogen by producing antibodies or antitoxins or engulfs them.

5. White blood cells produce antibodies that are specific to the shape of the antigens, latch onto the pathogen and destroy it.

6. White blood cells then remember how to produce these antibodies. The infected person will have been ill, but their white blood cells will now be able to produce antibodies quickly if they are infected again and are now immune.

Edward Jenner was the pioneer of smallpox vaccination and the father of immunology. In 1796, he carried out an experiment on eight-year-old James Phipps. Jenner inserted pus taken from a cowpox pustule and inserted it into an incision on the boy's arm. He was testing his theory, drawn from the folklore of the countryside, that milkmaids who suffered cowpox never contracted smallpox, one of the greatest killers of the period.

Types of white blood cells include:

Monocytes. They have a longer lifespan than many white blood cells and help to break down bacteria.

Lymphocytes. They create antibodies to defend against bacteria, viruses, and other potentially harmful invaders.

Neutrophils. They kill and digest bacteria and fungi. They are the most numerous type of white blood cell and your first line of defense when infection strikes.

Basophils. These small cells appear to sound an alarm when infectious agents invade your blood. They secrete chemicals such as histamine, a marker of allergic disease, that help control the body's immune response.

Eosinophils. They attack and kill parasites, destroy cancer cells, and help with allergic responses.

Antibodies are disease-specific. For example, measles antibody will protect a person who is exposed to measles disease, but will have no effect if he or she is exposed to mumps.

Bacteria- Bacteria are single-celled microorganisms. They need food, heat and water to grow and can live in or outside other organisms. They can make copies of themselves and cause disease such as cholera, pneumonia and TB.