Microbes and disease

Done by Alyazia Ahmad

FungiMushrooms and toadstools are fungi, but these are made of lots of cells, so they are not microbes. Yeasts are single-celled fungi, so they are microbes. Fungi are usually the biggest type of microbe. If there is just one of them, we call it a fungus.

BacteriaBacteria are usually smaller than fungi. If there is just one of them, we call it a bacterium. Bacteria have many different shapes. Some have 'tails' (called flagella) that let them swim.

virusesViruses are the smallest type of microbe. As a virus can only reproduce inside a cell, some people are not convinced that viruses are really living things.

Differences between fungi, bacteria and viruses

The table shows some of the similarities and differences between the three types of microbe .

Feature Fungi Bacteria Viruses

Cell membrane

Cell wall (hard) (soft)( protein

coat )

Nucleus (circle) (strand)

Microbes - useful or not?• Useful microbes• Yeast cells are useful to bakers and

brewers. Yeast cells can change sugar into carbon dioxide, gas and alcohol. This is useful to bakers because the gas helps the bread rise, and it is useful to brewers because it adds the alcohol needed for their drinks. Bacteria are also useful to us. For example, certain bacteria cause the changes needed in milk to make yogurt and cheese out of it.

Microbes - useful or not?• Harmful microbes• Many microbes can cause diseases. For example,

fungi can cause athlete's foot and thrush. Here are some diseases caused by bacteria: • tuberculosis, TB (affects the lungs)• salmonella (causes food poisoning)• whooping cough (affects the lungs)Here are some diseases caused by viruses: • chicken pox (affects skin and nerves)• common cold• influenza, flu• measles (affects skin and lungs)Microbes cause disease when they are able to

reproduce in the body. They produce harmful substances, and damage tissues and organs. We say that someone who has harmful disease-causing microbes in them is infected.

Spreading microbes

Many harmful microbes can pass from one person to another. Diseases caused by such microbes are said to be infectious diseases. Here are some ways that harmful microbes can be spread:

• in air• through contact with animals• through contaminated food• through touch• in water

AirDroplets containing microbes fly into the air when people sneeze or cough. The microbes they contain get into other people if breathed in. Chicken pox, colds, flu, measles and tuberculosis are spread like this.

AnimalsAnimals may carry harmful microbes. The microbes can get into a person who is scratched or bitten by such an animal. Malaria is a tropical disease spread by a tiny fly called a mosquito.

FoodFood can have harmful microbes in and on it. The microbes get into the body when the food is eaten, causing food poisoning. Thorough cooking kills most microbes, but they can survive under-cooking and careless handling of food.

TouchMicrobes can be passed from one person to another when people touch each other, or when they touch something an infected person has handled. Athlete's food is spread like this. Bacteria on the skin can be killed by antiseptics, and bacteria on surfaces can be killed by disinfectants. Washing your hands reduces the chance of spreading microbes.

WaterWater can have harmful microbes in it. The microbes get into the body when the water is swallowed. Cholera is a disease caused by a bacterium that spreads like this. Thorough boiling or adding chlorine to the water can reduce

the chance of spreading microbes in this way .

Defence against microbes• Natural barriers• The body has natural barriers to stop

harmful microbes getting inside the body. Here are some of them:

• acid in the stomach kills many microbes• sticky mucus in the lungs traps microbes,

and then cilia sweep it out of the lungs• scabs form on the skin if you get a cut,

stopping microbes from getting into your body

• the skin stops microbes from getting into the body

• tears contain substances that kill bacteria

• The immune system• The body has an immune system that kills

microbes if they get past the natural barriers. The white blood cells are very important in the immune system. There are different sorts of these cells, but they can do two main jobs. Some white blood cells can engulf microbes and kill them.

• Some white blood cells can make substances called antibodies that stick to microbes.

• Microbes have substances called antigens. Different microbes have different antigens, so only white blood cells with the right antibodies can stick to them. But when this happens, the microbes can be killed, or clumped together to make it easier for other white blood cells to kill them.

Antibiotics and immunisation• Antibiotics• Antibiotics are substances used by doctors when harmful

microbes have made you ill. They are substances that harm bacteria. Some antibiotics stop the bacteria reproducing and others kill the bacteria.

Antibiotics are helpful to treat diseases caused by bacteria, such as tuberculosis and food poisoning. They do not harm viruses, so antibiotics cannot treat diseases such as colds and flu, which are caused by viruses. Immunisation

• When you are infected by a microbe, it takes time for your body to start fighting the infection by making enough white blood cells with the correct antibody. During this time, you continue to feel unwell. You begin to recover when enough antibodies have been produced. After the microbes have been killed, the amount of antibodies goes down again. Some of the white blood cells that produce the correct antibody remain in your blood. Check your understanding of this by studying the animation.