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

protists; fungi

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

The whyA 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

HintThe word shares its root with 'toxic'.

The whyOnce 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

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

The whyA 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

HintThink of drinking, and of a sneeze.

The whySome 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

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

The whyPreventing 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

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

The whyMeasles 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

HintIt damages the very system that should be fighting it.

The whyHIV 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

HintAsk what is left inside a used needle.

The whyThe 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

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

The whyHIV 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

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

The whyTobacco 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

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

The whySalmonella 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

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

The whyChickens 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

HintIt was once easily cured with penicillin.

The whyGonorrhoea 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

HintThe drug has not changed. Ask what has changed in the pathogen.

The whyOver 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

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

The whyTreating 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.