Health and disease, Year 10: pathogens, viruses and bacteria

protists; fungi

提示One group includes the organism behind malaria; the other includes moulds and mushrooms.

为什么A pathogen is a microorganism that causes infectious disease, and GCSE names four kinds. Each of the four has its own named example in the course: measles (virus), salmonella (bacterium), malaria (protist) and rose black spot (fungus).

toxins

提示The word shares its root with 'toxic'.

为什么Once inside the body, bacteria can reproduce rapidly. Many of them release poisonous chemicals as they grow, and it is these, as much as the bacteria themselves, that damage tissue and cause the symptoms of the illness.

Inside the body's cells

提示A virus cannot copy itself alone; it needs to borrow machinery from its host.

为什么A virus gets into a cell and uses it to make many copies of itself. This damages the cell, and the new viruses go on to infect more cells. That cell damage is what makes a viral infection harmful.

By water and by air

提示Think of drinking, and of a sneeze.

为什么Some pathogens pass on by touch or sexual contact, some are carried in contaminated water or food, and some travel in droplets coughed or sneezed out. Knowing the route tells you how to block it: hygiene, clean water, or keeping infected individuals apart.

The virus can no longer pass from it to healthy plants

提示Ask what the pathogen needs in order to reach its next host.

为什么Preventing disease is about breaking the route by which the pathogen travels. Removing the source of infection, isolating infected individuals, good hygiene and vaccination all work by stopping the pathogen reaching a new host.

measles

提示Most young children in the UK are vaccinated against it, in a combined jab.

为什么Measles is caused by a virus and passes from person to person in droplets in the air. It can be fatal if complications arise, which is why most young children are vaccinated against it.

The body's immune cells

提示It damages the very system that should be fighting it.

为什么HIV first causes a flu-like illness. Unless it is kept under control with antiretroviral drugs, the virus then attacks the cells of the immune system, so the body gradually loses its ability to defend itself.

Exchange of body fluids such as blood

提示Ask what is left inside a used needle.

为什么The virus is carried in body fluids. It can pass on during sex, or when blood from an infected person enters someone else's body, as happens when needles are shared.

AIDS

提示It is a four-letter abbreviation, and the 'I' stands for 'immune'.

为什么HIV is the virus; this is the name for the condition it can lead to if it is not successfully controlled. At that stage the person is harmed by other infections and cancers that a healthy immune system would deal with.

The discoloured patches cannot photosynthesise properly

提示Think about what a green leaf is for, and what the pale areas have lost.

为什么Tobacco mosaic virus (TMV) infects many species of plants. The discoloured patches carry out little photosynthesis, so the plant makes less glucose and has less material and energy for growth.

salmonella

提示It is a kind of food poisoning, and its name sounds as though it comes from a fish.

为什么Salmonella bacteria are taken in with food, or with food prepared in unhygienic conditions. The symptoms are caused by the bacteria and by the toxins they secrete.

Poultry are vaccinated against it

提示The measure protects the birds, so that their meat and eggs are safer for us.

为什么Chickens and other farmed birds can carry salmonella bacteria. Vaccinating the birds reduces the bacteria in meat and eggs, so fewer people are infected. Good kitchen hygiene and cooking food thoroughly deal with what remains.

Gonorrhoea

提示It was once easily cured with penicillin.

为什么Gonorrhoea is caused by a bacterium and is spread by sexual contact. The discharge comes from the vagina or the penis. Because it is bacterial, it is treated with antibiotics.

Many strains of the bacterium have become resistant

提示The drug has not changed. Ask what has changed in the pathogen.

为什么Over time, strains of the gonorrhoea bacterium appeared that penicillin no longer kills. Doctors now have to use other antibiotics, and resistance to those is a growing concern too.

antibiotics; condom

提示One cures people who are already infected; the other blocks the route during sex.

为什么Treating infected people removes the source of the bacteria, and a barrier such as a condom stops the bacteria passing from one person to another during sexual contact.