5.1.3 Common Infections · 5. Health, Disease and the Development of Medicines | Edexcel GCSE Combined Science 1SC0: Biology

Section 1 of 9Viral diseases of humans

Measles is caused by a virus spread by droplets from coughs and sneezes. Symptoms are a fever and a red skin rash. Serious complications such as pneumonia, brain damage or death can follow, especially in young children. It is controlled by vaccination (the MMR vaccine) and isolating infected people.

HIV (human immunodeficiency virus) is spread by sexual contact, by exchange of body fluids such as through infected needles, and from mother to baby.

At first the infected person has flu-like symptoms; the virus then attacks the white blood cells of the immune system.

AIDS

Without treatment the disease advances to AIDS, in which the immune system is so weak that other infections and some cancers occur.

Antiretroviral drugs stop the virus from reproducing, so most people treated can live a near-normal lifespan.

Condoms and not sharing needles reduce spread.

Section 2 of 9Bacterial diseases

Salmonella food poisoning comes from bacteria in food, especially raw eggs and poultry, or from food prepared with dirty hands or utensils. Symptoms: fever, abdominal cramps, vomiting and diarrhoea, caused by toxins. It is controlled by cooking food thoroughly, good hygiene in kitchens, and vaccinating poultry.

Gonorrhoea is a sexually transmitted infection caused by bacteria. Symptoms are pain on urinating and a thick yellow or green discharge from the vagina or penis. It was once treated with penicillin but many strains are now resistant to antibiotics. Spread is reduced by using condoms and by tracing and treating partners.

Section 3 of 9Protist disease: malaria

Malaria is caused by a protist, Plasmodium, carried by Anopheles mosquitoes. The protist enters the blood when the mosquito bites, infects red blood cells and the liver, and causes recurring fevers, shivering and sometimes death. It is controlled by killing mosquitoes with insecticides, removing standing water where they breed, using bed nets, and taking drugs to prevent or cure infection.

Section 4 of 9Plant diseases

1Rose black spot

Rose black spot is a fungal disease.

Purple or black spots appear on the leaves, which turn yellow and drop early.
Photosynthesis is reduced, so growth is weakened.
The fungus spreads by spores carried by wind and water.
It is controlled by removing and destroying infected leaves and by spraying with fungicide.

2Tobacco mosaic virus (TMV)

Tobacco mosaic virus (TMV) infects many plants, including tomatoes.

It produces a mosaic pattern of discoloured (yellow and green) patches on the leaves.
Chloroplasts are damaged, less photosynthesis happens and growth is stunted.
It is spread by contact and by insects.
Control is by good hygiene, destroying infected plants and growing resistant crop varieties.

Section 5 of 9Comparing the diseases

Disease	Pathogen type	Transmission	Main control
Measles	Virus	Droplets	Vaccination
HIV	Virus	Body fluids	Condoms, antiretrovirals
Salmonella	Bacterium	Contaminated food	Hygiene and cooking
Gonorrhoea	Bacterium	Sexual contact	Condoms, antibiotics
Malaria	Protist	Mosquito vector	Vector control
Rose black spot	Fungus	Spores	Fungicide, removing leaves
TMV	Virus	Contact, insects	Hygiene, resistant plants

Learn at least one example from each pathogen type, together with its method of spread and control.

Section 6 of 9Applying the facts in exam answers

Questions usually give a disease you have met and ask you to link its pathogen to symptoms and control, or give an unfamiliar disease with a description and ask you to deduce how it spreads.

1

Use the stem for clues.

2

A disease that appears after a swimming trip suggests water; a disease affecting people who ate at the same event suggests food; one that spreads among sexual partners suggests contact; one that follows insect bites suggests a vector.

3

For measles, vaccination provides herd immunity: when most of the population is immune, the pathogen finds it hard to move between susceptible people,

so even unvaccinated people are protected.

4

For HIV, mention that the virus can lie hidden in cells for years,

so people can pass it on without knowing,
which is why testing and counselling matter.

5

For plant diseases, link every symptom to reduced photosynthesis: less chlorophyll or less leaf area means less glucose, less growth and lower crop yield,

which matters to farmers and to food supply.

6

Plants respond to attack with physical barriers such as the cell wall and waxy cuticle, and with chemicals that kill microbes,

which links to the next lesson on plant diseases and defence.

7

Always quote the symptom, the pathogen type and the route of spread together.

Section 7 of 9Exam-style questions

Describe how Salmonella food poisoning can be prevented. [3]3 marks
Explain why the symptoms of rose black spot reduce the growth of the plant. [3]3 marks
Explain why HIV can lead to death from other infections. [3]3 marks

Section 8 of 9Key terms

Term	Meaning
Measles	A viral disease with fever and a red rash, spread by droplets.
HIV	A virus that attacks white blood cells.
AIDS	The late stage of HIV infection in which the immune system fails.
Salmonella	Bacteria that cause food poisoning.
Gonorrhoea	A bacterial sexually transmitted infection.
Malaria	A disease caused by Plasmodium and spread by mosquitoes.
Rose black spot	A fungal disease of roses that reduces photosynthesis.
Tobacco mosaic virus	A virus causing discoloured leaves in plants.

Section 9 of 9Exam technique

1

Saying HIV and AIDS are the same. HIV is the virus; AIDS is the condition that develops later.

2

Describing TMV symptoms as spots. TMV causes a mosaic of discoloured patches; spots are rose black spot.

3

Believing antibiotics treat gonorrhoea reliably today. Resistance is common.

4

Stating that malaria spreads directly between people. The mosquito vector is needed.