GCSE Biology revision

Communicable (infectious) 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 Viruses?, Measles and HIV: The Virus in the context of communicable (infectious) diseases.

MOST 🎯🎯

Explain the relationships between What Are Viruses?, Measles and HIV: The Virus and how they contribute to communicable (infectious) diseases.

SOME 🎯🎯🎯

Apply and analyse knowledge of What Are Viruses?, Measles and HIV: The Virus to interpret unfamiliar information about communicable (infectious) diseases.

Revision summary

Key knowledge

Read on screen, then print for Cornell-style active revision.

What Are Viruses?

Viruses are not cells and are not considered living organisms, yet they are still classified as organisms.
They are approximately 10,000 times smaller than animal cells and cannot reproduce independently.
Once inside a host cell, viruses hijack the cell's own machinery to produce many copies of themselves.
Viruses eventually burst the host cell, releasing new viruses to infect further cells — this cell damage is a key reason viruses make us feel ill.

1. What Are Viruses?AQA

Notes

Viruses are not cells and are not considered living organisms, yet they are still classified as organisms.
They are approximately 10,000 times smaller than animal cells and cannot reproduce independently.
Once inside a host cell, viruses hijack the cell's own machinery to produce many copies of themselves.
Viruses eventually burst the host cell, releasing new viruses to infect further cells — this cell damage is a key reason viruses make us feel ill.

Measles

Measles is a viral disease spread via droplets released when an infected person coughs or sneezes.
The main symptoms include a distinctive red rash across most of the body and a fever (high temperature).
Although measles can be serious and sometimes fatal, it is rare in the UK due to widespread vaccination in childhood.

HIV: The Virus

HIV stands for Human Immunodeficiency Virus, meaning it affects humans and causes a deficient (inadequate) immune system.
HIV is spread through unprotected sexual contact or by exchanging bodily fluids, such as sharing needles.
When first infected, a person may experience flu-like symptoms — fever, tiredness, and aches — for a few weeks before appearing to recover.
Despite feeling better, the virus continues to damage the immune system over time without treatment.

3. HIV: The VirusAQA

Notes

HIV stands for Human Immunodeficiency Virus, meaning it affects humans and causes a deficient (inadequate) immune system.
HIV is spread through unprotected sexual contact or by exchanging bodily fluids, such as sharing needles.
When first infected, a person may experience flu-like symptoms — fever, tiredness, and aches — for a few weeks before appearing to recover.
Despite feeling better, the virus continues to damage the immune system over time without treatment.

HIV and AIDS

AIDS (Acquired Immune Deficiency Syndrome) is the disease that develops when HIV has weakened the immune system so severely that the body can no longer fight off infections.
At the AIDS stage, a person becomes vulnerable to unusual infections and certain cancers that a healthy immune system would normally control.
Anti-retroviral drugs are medications that prevent HIV from replicating inside the body, allowing people to live normal lives if treated early.

4. HIV and AIDSAQA

Notes

AIDS (Acquired Immune Deficiency Syndrome) is the disease that develops when HIV has weakened the immune system so severely that the body can no longer fight off infections.
At the AIDS stage, a person becomes vulnerable to unusual infections and certain cancers that a healthy immune system would normally control.
Anti-retroviral drugs are medications that prevent HIV from replicating inside the body, allowing people to live normal lives if treated early.

Tobacco Mosaic Virus (TMV)

Tobacco Mosaic Virus (TMV) is a viral disease that affects plants, particularly tobacco and tomato plants.
TMV causes a distinctive mosaic pattern of discolouration on the leaves of infected plants.
The discoloured patches cannot carry out photosynthesis, reducing the plant's ability to produce sugars needed for growth.
As a result, infected plants suffer from stunted or poor growth due to insufficient sugar production.

5. Tobacco Mosaic Virus (TMV)AQA

Notes

Tobacco Mosaic Virus (TMV) is a viral disease that affects plants, particularly tobacco and tomato plants.
TMV causes a distinctive mosaic pattern of discolouration on the leaves of infected plants.
The discoloured patches cannot carry out photosynthesis, reducing the plant's ability to produce sugars needed for growth.
As a result, infected plants suffer from stunted or poor growth due to insufficient sugar production.