GCSE Biology revision

Viral diseases

Communicable diseases

AQA 4.1.1.1

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AQA student objectives

Learning pathway

All · Most · Some

ALL 🎯

Identify and describe What Are Viral Diseases?, Measles: Cause and Spread and Measles: Symptoms and Complications in the context of viral diseases.

MOST 🎯🎯

Explain the relationships between What Are Viral Diseases?, Measles: Cause and Spread and Measles: Symptoms and Complications and how they contribute to viral diseases.

SOME 🎯🎯🎯

Apply and analyse knowledge of What Are Viral Diseases?, Measles: Cause and Spread and Measles: Symptoms and Complications to interpret unfamiliar information about viral diseases.

Revision summary

Key knowledge

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What Are Viral Diseases?

Viral diseases are infections caused by viruses that invade the body's cells and disrupt normal biological processes.
Viruses can infect both animals and plants, making them a wide-ranging threat to living organisms.
Typically, the three key viral diseases to know about are measles, HIV, and tobacco mosaic virus (TMV).

1. What Are Viral Diseases?AQA

Notes

Viral diseases are infections caused by viruses that invade the body's cells and disrupt normal biological processes.
Viruses can infect both animals and plants, making them a wide-ranging threat to living organisms.
Typically, the three key viral diseases to know about are measles, HIV, and tobacco mosaic virus (TMV).

Measles: Cause and Spread

Measles is a viral infection caused by the measles virus.
It is spread through droplet infection, meaning the virus travels in tiny droplets of saliva released when an infected person sneezes or coughs.
Because it spreads through the air, measles is highly contagious in environments where people are in close contact.

2. Measles: Cause and SpreadAQA

Notes

Measles is a viral infection caused by the measles virus.
It is spread through droplet infection, meaning the virus travels in tiny droplets of saliva released when an infected person sneezes or coughs.
Because it spreads through the air, measles is highly contagious in environments where people are in close contact.

Measles: Symptoms and Complications

The main symptoms of measles include a red skin rash, a high fever, and small white spots inside the mouth.
A serious complication of measles is encephalitis, which is inflammation of the brain and can be fatal.
Deaths from measles have decreased significantly due to the widespread use of the MMR vaccine, which protects against mumps, measles, and rubella.

3. Measles: Symptoms and ComplicationsAQA

Notes

The main symptoms of measles include a red skin rash, a high fever, and small white spots inside the mouth.
A serious complication of measles is encephalitis, which is inflammation of the brain and can be fatal.
Deaths from measles have decreased significantly due to the widespread use of the MMR vaccine, which protects against mumps, measles, and rubella.

HIV: What It Is and How It Spreads

HIV stands for Human Immunodeficiency Virus, and as the name suggests, it causes a deficiency in the body's immune system.
HIV is spread through the exchange of bodily fluids, including unprotected sexual intercourse, sharing needles, and contact between open wounds and infected blood.
Preventative measures include using condoms, practising hygienic needle use, and covering open wounds — particularly important for healthcare workers.

4. HIV: What It Is and How It SpreadsAQA

Notes

HIV stands for Human Immunodeficiency Virus, and as the name suggests, it causes a deficiency in the body's immune system.
HIV is spread through the exchange of bodily fluids, including unprotected sexual intercourse, sharing needles, and contact between open wounds and infected blood.
Preventative measures include using condoms, practising hygienic needle use, and covering open wounds — particularly important for healthcare workers.

HIV: How It Affects the Body

HIV attacks and destroys CD4 T cells, which are a type of white blood cell essential for a functioning immune system.
Over time, the number of virus particles increases while the number of CD4 T cells decreases, progressively weakening the immune system.
When the immune system becomes severely weakened, the condition progresses to AIDS (Acquired Immune Deficiency Syndrome), leaving the patient extremely vulnerable to other infections.
Even a common cold can become life-threatening for a person with AIDS due to their severely compromised immunity.

5. HIV: How It Affects the BodyAQA

Notes

HIV attacks and destroys CD4 T cells, which are a type of white blood cell essential for a functioning immune system.
Over time, the number of virus particles increases while the number of CD4 T cells decreases, progressively weakening the immune system.
When the immune system becomes severely weakened, the condition progresses to AIDS (Acquired Immune Deficiency Syndrome), leaving the patient extremely vulnerable to other infections.
Even a common cold can become life-threatening for a person with AIDS due to their severely compromised immunity.

HIV: Treatment and Management

There is currently no vaccine or cure for HIV.
Antiretroviral drugs are used to control HIV by slowing the replication of the virus, significantly extending the life expectancy of those infected.
HIV patients must take extra precautions to avoid other infections, as their weakened immune system struggles to fight off pathogens.

6. HIV: Treatment and ManagementAQA

Notes

There is currently no vaccine or cure for HIV.
Antiretroviral drugs are used to control HIV by slowing the replication of the virus, significantly extending the life expectancy of those infected.
HIV patients must take extra precautions to avoid other infections, as their weakened immune system struggles to fight off pathogens.

Tobacco Mosaic Virus (TMV): Cause and Spread

Tobacco mosaic virus (TMV) is a viral disease that infects tobacco plants and other related species such as tomatoes and peppers.
TMV can spread when infected and healthy plants touch one another, or when a farmer handles an infected plant and then touches a healthy one.
To prevent the spread of TMV, farmers should keep plants separated, remove infected plants, and wash their hands between handling different plants.

7. Tobacco Mosaic Virus (TMV): Cause and SpreadAQA

Notes

Tobacco mosaic virus (TMV) is a viral disease that infects tobacco plants and other related species such as tomatoes and peppers.
TMV can spread when infected and healthy plants touch one another, or when a farmer handles an infected plant and then touches a healthy one.
To prevent the spread of TMV, farmers should keep plants separated, remove infected plants, and wash their hands between handling different plants.

Tobacco Mosaic Virus (TMV): Symptoms and Impact

TMV infects the chloroplasts of plant cells, damaging the chlorophyll and causing a characteristic mosaic-like pattern of yellow discolouration on leaves.
Because chlorophyll gives plants their green colour and is essential for photosynthesis, its destruction reduces the plant's ability to photosynthesise.
Infected leaves may also curl up, reducing the surface area available for light absorption and further limiting photosynthesis.
The overall reduction in photosynthesis stunts plant growth and significantly reduces crop yields, making TMV a major concern in agriculture.

8. Tobacco Mosaic Virus (TMV): Symptoms and ImpactAQA

Notes

TMV infects the chloroplasts of plant cells, damaging the chlorophyll and causing a characteristic mosaic-like pattern of yellow discolouration on leaves.
Because chlorophyll gives plants their green colour and is essential for photosynthesis, its destruction reduces the plant's ability to photosynthesise.
Infected leaves may also curl up, reducing the surface area available for light absorption and further limiting photosynthesis.
The overall reduction in photosynthesis stunts plant growth and significantly reduces crop yields, making TMV a major concern in agriculture.

Comparing the Three Viral Diseases

Measles and HIV are both human viral diseases, but they differ in how they spread — measles via droplets and HIV via bodily fluids.
TMV is a plant viral disease, distinguishing it from measles and HIV which affect animals.
All three diseases have no complete cure, highlighting the importance of prevention through vaccination (measles), safe practices (HIV), and good hygiene and crop management (TMV).

9. Comparing the Three Viral DiseasesAQA

Notes

Measles and HIV are both human viral diseases, but they differ in how they spread — measles via droplets and HIV via bodily fluids.
TMV is a plant viral disease, distinguishing it from measles and HIV which affect animals.
All three diseases have no complete cure, highlighting the importance of prevention through vaccination (measles), safe practices (HIV), and good hygiene and crop management (TMV).

Exam Tips for Viral Diseases

Examiners may show a photograph of mosaic-like yellowing on a plant leaf and ask you to identify the disease — recognising this pattern means it is tobacco mosaic virus.
Remember that HIV stands for Human Immunodeficiency Virus; breaking down the name in an exam can help you recall that it weakens the immune system.
The three key symptoms of measles — red rash, high fever, and white spots in the mouth — are a common short-answer exam question and should be memorised.
Knowing the difference between HIV (the virus) and AIDS (the advanced stage of the disease) is important for picking up marks in longer answer questions.

10. Exam Tips for Viral DiseasesAQA

Notes

Examiners may show a photograph of mosaic-like yellowing on a plant leaf and ask you to identify the disease — recognising this pattern means it is tobacco mosaic virus.
Remember that HIV stands for Human Immunodeficiency Virus; breaking down the name in an exam can help you recall that it weakens the immune system.
The three key symptoms of measles — red rash, high fever, and white spots in the mouth — are a common short-answer exam question and should be memorised.
Knowing the difference between HIV (the virus) and AIDS (the advanced stage of the disease) is important for picking up marks in longer answer questions.