Viral Diseases- Measles, HIV and TMV
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of how pathogens cause disease.
What is a pathogen?
A pathogen is a microorganism that causes disease.
How do viruses make us ill?
They invade our cells to reproduce, destroying them.
How are infectious diseases commonly spread between individuals?
Through air (droplets), direct contact, or contaminated surfaces / objects.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains viral diseases- measles, HIV and TMV, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Viral Diseases – Measles, HIV and TMV
What Are Viral Diseases?
- Caused by viruses – non-living infectious agents.
- They invade host cells to replicate, often damaging or destroying the cells.
- There are 3 examples of viral diseases you need to know about...
|
Viral Disease |
Symptoms |
Transmission |
Effects / Risks |
Prevention / Control |
|
Measles |
Fever and red skin rash. |
Inhalation of droplets from sneezes or coughs. |
Can lead to serious complications such as brain damage or death. |
Vaccine given to young children. Isolation of infected individuals. |
|
HIV (Human Immunodeficiency Virus) |
Flu-like illness shortly after infection. |
Sexual contact or exchange of body fluids (e.g. blood, sharing needles). |
Destroys white blood cells → leads to AIDS if untreated (immune system badly damaged). Increases susceptibility to other infections. |
Spread reduced using barrier methods of contraception (e.g. condoms). Controlled with antiretroviral drugs to prevent development of AIDS. |
|
TMV (Tobacco Mosaic Virus) |
Yellow mosaic pattern of discolouration on leaves. |
Contact between infected and healthy plants (e.g. contaminated tools or hands) |
Reduced chlorophyll → less photosynthesis → less glucose produced → less respiration and less protein synthesis → poor plant growth |
Affected plants removed / burnt. Equipment sterilised. |
Key Terms & Definitions
|
Term |
Definition |
|
Pathogen |
A microorganism that causes disease. |
|
Antiretroviral drugs |
Drugs used to prevent viruses from replicating. |
No answer provided.
Exam Tips
- For HIV, don’t just write "it causes AIDS"- explain that it destroys white blood cells leading to increased vulnerability to infections..
- For TMV, always link mosaic patterns to reduced photosynthesis and then poor growth.
No answer provided.
Practice Question
Explain why Tobacco Mosaic Virus (TMV) infection leads to the stunted growth of a plant. (3 marks)
Model Answer:
- TMV destroys the chloroplasts and reduces the amount of chlorophyll in the leaf.
- As a result, the rate of photosynthesis decreases as less light is absorbed.
- The plant makes less glucose for respiration and growth.
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!