Practise Viral diseases. 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
The three viral diseases in the specification: measles and HIV in humans, and tobacco mosaic virus (TMV) in plants. Expect questions on their symptoms, how they are spread, how the spread is controlled and why TMV reduces plant growth.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Name viral diseases of humans and plantsMeasles and HIV in humans; tobacco mosaic virus (TMV) in plants.
4
Describe the symptoms and spread of measlesFever and a red skin rash; it is spread by breathing in droplets from coughs and sneezes.
4
Describe how HIV is spreadBy sexual contact or by exchange of body fluids such as blood, e.g. when drug users share needles.
5
Describe how measles and HIV are controlledMeasles: vaccinating young children; HIV: condoms, not sharing needles and antiretroviral drugs.
6
Explain why TMV reduces plant growthThe discoloured parts of the leaves have less chlorophyll, so there is less photosynthesis and less glucose for growth.
7
Explain how HIV leads to AIDSHIV attacks immune cells; when the immune system is badly damaged, the body cannot deal with other infections or cancers.
Notes
Measles
Symptoms: fever and a red skin rash.
Spread by breathing in (inhaling) droplets from an infected person's coughs and sneezes.
Measles is a serious illness that can be fatal if complications arise, so most young children are vaccinated against it.
HIV and AIDS
HIV first causes a flu-like illness.
Unless it is controlled with antiretroviral drugs, the virus attacks the body's immune cells (a type of white blood cell).
Late-stage HIV infection is called AIDS. It happens when the immune system is so badly damaged that the body can no longer deal with other infections or cancers.
HIV is spread by sexual contact or by exchange of body fluids such as blood, e.g. when drug users share needles.
To reduce spread: use condoms, do not share needles, and treat infected people with antiretroviral drugs. These drugs do not cure HIV, but they control it.
Tobacco mosaic virus (TMV)
A widespread plant pathogen that infects many species of plants, including tomatoes.
It causes a distinctive mosaic pattern of discolouration on the leaves: patches of the leaves turn pale yellow or white.
The discoloured patches have less chlorophyll, so less light is absorbed and there is less photosynthesis. The plant makes less glucose, so it grows less.
TMV spreads by contact, e.g. between the leaves of neighbouring plants or on hands and tools. Infected plants should be removed and destroyed.
Treating viral diseases
Antibiotics do not kill viruses.
Viruses live inside cells, so it is hard to make drugs that kill them without also damaging the body's tissues.
Cheatsheet
Measles: fever and red skin rash; spread by droplets from coughs and sneezes
Most young children are vaccinated against measles
HIV: flu-like illness at first, then attacks immune cells
AIDS = late-stage HIV: immune system too damaged to deal with other infections or cancers
HIV spread: sexual contact and body fluids, e.g. blood on shared needles
HIV is controlled (not cured) with antiretroviral drugs
TMV: mosaic discolouration of leaves → less photosynthesis → less growth
Antibiotics do not work on viruses
How to answer each type of question
Give symptoms and describe how a virus spreads
1 to 3 marks4
Learn the exact symptoms for each disease.
For spread, say how the virus gets from one person into the next person.
Example. Measles is caused by a virus. (a) Give two symptoms of measles. (b) Describe how the measles virus is spread.
Show the model answer
(a) Fever (1); red skin rash (1) (b) By breathing in droplets from an infected person's coughs or sneezes (1)
Suggest ways to reduce the spread of HIV
2 to 3 marks5
Think about each route: sexual contact and blood.
Give one method for each route, then add treatment with antiretroviral drugs.
Example. Suggest three ways to reduce the spread of HIV.
Show the model answer
Use condoms during sex (1). Drug users should not share needles / should use sterile needles (1). Treat infected people with antiretroviral drugs, so they are less likely to pass the virus on (1).
Explain why TMV reduces growth or yield
3 marks6
Start with the symptom: mosaic discolouration, so less chlorophyll.
Link to less light absorbed and less photosynthesis.
Finish with less glucose for growth (or for making fruit).
Example. Tomato plants infected with tobacco mosaic virus (TMV) produce fewer tomatoes than healthy plants. Explain why.
Show the model answer
TMV causes a mosaic pattern of discoloured patches on the leaves, where there is less chlorophyll (1). So less light is absorbed and the rate of photosynthesis is lower (1). So the plant makes less glucose, which it needs for growth and to make fruit (1).
Explain why people with AIDS get other infections
3 marks7
Say what HIV attacks: the body's immune cells (white blood cells).
Say that in AIDS the immune system is badly damaged.
Link to the body being unable to destroy other pathogens or cancer cells.
Example. A person with late-stage HIV infection (AIDS) became seriously ill with tuberculosis, a disease caused by a bacterium. Explain why people with AIDS are more likely to become seriously ill with infections like this.
Show the model answer
HIV attacks the body's immune cells / white blood cells (1). In AIDS the immune system is so badly damaged (1) that it can no longer destroy pathogens such as the tuberculosis bacteria, e.g. it cannot produce enough antibodies (1).
Shortcuts and memory tricks
Measles = rash and heat: red skin rash and fever. It travels through the air.
HIV is the virus; AIDS is the late stage, when the immune system has been badly damaged.
TMV: 'mosaic' = a patchwork of pale and green → less chlorophyll → less photosynthesis → less growth.
Virus = no antibiotics. If a question asks how to treat a viral disease, antibiotics are always wrong.
Where marks are lost
Saying HIV is spread by kissing, coughing or touching. It is spread by sexual contact and body fluids such as blood.
Saying antiretroviral drugs cure HIV, or calling them antibiotics. They control the virus but do not cure the infection.
Writing that TMV 'stops photosynthesis' or 'kills the leaves'. It reduces photosynthesis because the discoloured patches have less chlorophyll.
Saying people 'catch AIDS'. People are infected with HIV; AIDS is the late stage of the infection.
Saying people with AIDS die of the virus itself. They become ill with other infections or cancers that their immune system can no longer deal with.
Exam technique
For TMV, write the whole chain: less chlorophyll → less light absorbed → less photosynthesis → less glucose → less growth. Each link can earn a mark.
Use the key phrases examiners look for: 'inhaling droplets', 'sexual contact', 'body fluids', 'immune cells'.
If a question asks why young children are vaccinated against measles, say that measles is serious and can be fatal if complications arise.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Measles is a disease caused by a virus. Give two symptoms of measles.
Fever and a red skin rash.
What type of illness does a person usually have soon after being infected with HIV?
A flu-like illness.
Describe how a grower could recognise a tomato plant infected with TMV.
A mosaic pattern of discoloured (pale / yellow) patches on the leaves.
Viruses are much smaller than bacteria. They can only reproduce inside living cells. Measles is a viral disease. Give two symptoms of measles.
Fever and a red skin rash.
Unless it is controlled with drugs, HIV attacks the body's immune cells. What is the name of the late stage of HIV infection, when the immune system is so badly damaged that it can no longer deal with other infections?
AIDS
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Measles is a disease caused by a virus.
(a) Give two symptoms of measles.[2]
(b) How is the measles virus spread? Tick (✓) one box.[1]
By drinking water containing the virus
By inhaling droplets from coughs and sneezes
By the bite of an infected mosquito
By sexual contact
(c) Most young children in the UK are vaccinated against measles. Give one reason why.[1]
(d) A child with measles was not given antibiotics. Explain why.[1]
Show the answer and mark scheme
(a)Answer: Fever and a red skin rash.
fever / high temperature
red (skin) rash
(b)Answer: By inhaling droplets from coughs and sneezes
(c)Answer: Measles is a serious illness that can be fatal.
measles is a serious illness / measles can be fatal (if complications arise)
(d)Answer: Antibiotics do not kill viruses.
measles is caused by a virus and antibiotics do not kill viruses
Question 2Medium8 marks
HIV is a virus that attacks the body's immune cells.
(a) What type of illness does a person usually have soon after being infected with HIV?[1]
(b) Give two ways that HIV can be spread from one person to another.[2]
(c) Explain why a person with late-stage HIV infection (AIDS) can die from an infection that would not harm a healthy person.[3]
(d) The spread of HIV within the body can be controlled with antiretroviral drugs. Suggest how antiretroviral drugs can stop a person developing AIDS.[2]
Show the answer and mark scheme
(a)Answer: A flu-like illness.
a flu-like illness
(b)Answer: Sexual contact; sharing needles (exchange of blood).
sexual contact / unprotected sex
sharing needles (by drug users)
(other) exchange of body fluids such as blood
(c)
HIV attacks / destroys the immune cells / white blood cells
(so) the immune system is so badly damaged it can no longer deal with other infections
(so) other pathogens are not destroyed and can reproduce / cause serious illness
(d)
(the drugs) stop / slow down the virus reproducing / reduce the amount of virus
(so) fewer immune cells are destroyed / the immune system is not badly damaged
Question 3Hard6 marks
A rapid test for HIV uses monoclonal antibodies. The antibodies bind to a protein that is found only on the surface of HIV.
(a) Explain why the monoclonal antibodies in the test bind to HIV but not to other viruses or to bacteria.[2]
(b) A person who tests positive has not been treated for HIV. Tests show the person has a much lower number of white blood cells than normal. Explain why this person is at greater risk of becoming seriously ill from other infections.[2]
(c) Explain why it is important that people who are infected with HIV are identified as early as possible, even if they have no symptoms.[2]
Show the answer and mark scheme
(a)
monoclonal antibodies are specific to (the shape of) one antigen / one protein
other pathogens have different antigens / proteins on their surface, so the antibodies do not bind to them
(b)
HIV attacks / destroys the body's immune cells (white blood cells)
so the immune system cannot destroy other pathogens, e.g. by phagocytosis or by producing antibodies / cannot deal with other infections
(c)
they can start treatment with antiretroviral drugs early
which stops the virus damaging the immune system / stops AIDS developing
they can take steps to avoid passing HIV on, e.g. using condoms and not sharing needles