Microbes and Disease

Microbes are very small living things and are sometimes called micro-organisms. Microbes are so tiny that they cannot be seen with the naked eye. They can only be seen using a microscope. What are microbes? How many different microbes can you name?

There are three types of microbes: Different types of microbes bacteriavirusesfungi microbes

Bacteria fact file Size: 1/1000 mm Shape: Bacteria can be spherical, rod-shaped or comma-shaped. Structure: Bacteria are single- celled organisms, which do not completely have a nucleus. Some cause disease, but many are useful. Reproduction: Bacteria reproduce very quickly. Two can very quickly become four, then eight and so on. Bacteria e.g. Salmonella and Streptococcus

Bacterium structure

Viruses fact file Size: 1/1,000,000 mm Shape: Viruses have regular and geometric shapes. Structure: A virus is a simple organism which does not display ALL the characteristics of living things. They are made up of a protein coating and some genetic material. Reproduction: Viruses can only grow and reproduce within other living things. Viruses e.g. flu virus and HIV (the AIDS virus)

Virus structure

Fungi fact file Size: Some fungi can actually be seen with the naked eye, others are slightly bigger than bacterial cells. Shape: Fungi come in many different shapes. Structure: Fungi have the most complex structures of all the microbes. They feed off other living things. Fungi e.g. Penicillium and yeast

Fungi (yeast) structure

Defence against microbes If microbes enter through the mouth (usually on food) they will be swallowed and enter the stomach. Within the stomach is hydrochloric acid which is highly concentrated and will kill them. Mouth

Defence against microbes These cells also produce mucous, a sticky liquid in which microbes can become stuck. The cilia then waft the mucus (including the trapped microbes) towards the mouth and nose where they are either swallowed or coughed up. Nose Cells lining the respiratory tract have hair-like folds in their cell membrane. These are known as cilia and the cells are termed ciliated.

Skin blood capillary thick layer of skin Microbes have to penetrate the layer of skin that covers the entire surface of our body. Once through this, they can then reach the blood system. Defence against microbes

Cuts When you cut the skin, the body will bleed because the blood vessels are ruptured. This leaves the blood exposed to the air. Microbes could then get into the blood. To limit this problem, the body can quickly heal wounds by firstly clotting the blood and secondly forming a scab over the wound to shield the blood from the air. Defence against microbes

The spreading of microbes and disease is known as transmission. How are microbes spread? A cough or a sneeze can release millions of microbes into the air which can then infect somebody else. Transmission by air Dirty water can transmit many diseases e.g. cholera which can be transmitted by drinking. Transmission by water

How are microbes spread? An animal can carry a microbe from one place to another, e.g. a mosquito which spreads the malaria parasite. Transmission by animals Many microbes can be exchanged from one person to another by direct or indirect contact: Transmission by contact direct contact by hand; direct contact by hand; indirect contact, e.g. by walking on a indirect contact, e.g. by walking on a wet floor already contaminated by wet floor already contaminated by someone else who has athlete’s foot; someone else who has athlete’s foot; sexual contact. sexual contact.

Transmission via breastfeeding If a child is being breastfed, he or she can also pick up microbes from the mother via the mother’s milk. If the mother develops the HIV/Aids infection, it can be passed on to the unborn child through the placenta. Transmission through the placenta Transmission through the placenta How are microbes spread? There are other forms of indirect contact, e.g. the transmission of microbes from mother to unborn child. Transmission by contact

What do white blood cells do? The human body has a number of natural defences against microbes. Noses are hairy inside to trap microbes! Some white blood cells can destroy microbes by engulfing them. Some white blood cells are able to produce chemicals called antibodies. These pairing with matching antigens on the surfaces of microbes and so help the white blood cells to engulf microbes. white blood cell antibody antigen The body also produces white blood cells to help defend it from microbes.

White blood cell engulfs microbe – animation

White blood cell and antibodies – animation