Communicable Disease 2 - Viruses Lesson | GCSE Biology Edexcel Higher Triple

Communicable Disease 2 - Viruses

This lesson covers:

What viruses are
How viruses spread
Examples of viral diseases

Ebola - key information

Pathogen - Ebola virus
Transmission - direct contact with bodily fluids of an infected person or through contaminated surfaces
Symptoms - fever, bleeding, severe headache, muscle pain
Treatment - supportive care, including rehydration
Prevention - strict infection control measures, with isolation of patients and sterilisation of all contaminated surfaces, and public health education

The lifecycle of a virus

Viruses can only reproduce inside the cells of living organisms.

Viruses can reproduce via two different pathways, depending on the environmental conditions and the type of virus:

Lytic pathway
Lysogenic pathway

Lytic pathway

Illustration showing a virus attaching to a host cell, initiating the infection process.

1Virus attaches to a host cell.

Diagram showing the lifecycle of a virus including viral DNA and host DNA

2Virus injects genetic material into the host cell.

Illustration showing the lifecycle of a virus inside a host cell.

3The cell machinery of the host cell produces viral components.

Illustration showing the lifecycle of a virus with three viral particles inside a cell.

4New viruses are assembled from the replicated components.

Illustration showing the lifecycle of a virus attaching to a host cell.

5The host cell bursts, releasing new viruses - which go on to infect other cells and repeat the cycle.

Lysogenic pathway

Illustration showing a virus attaching to a host cell.

1Virus attaches to a host cell.

Illustration of a virus injecting its genetic material into a host cell.

2Virus injects genetic material into the host cell.

Diagram showing viral DNA incorporating into the host genome.

3Viral DNA incorporates into the host cell's genome. Virus remains dormant, and does not cause immediate harm.

Illustration showing the lifecycle of a virus with two stages.

4The host cell divides, replicating the viral DNA (contained within the host's genome) into each daughter cell.

Illustration showing how viral DNA exits the genome triggered by environmental factors to start the lytic pathway.

5Environmental triggers can cause a switch to the lytic cycle, and the viral DNA exits the host's genome

Illustration showing the lytic pathway in the virus lifecycle starting from step 3

6The lytic pathway starts - the host cell's machinery beings to produce viral components.

Illustration showing the structure of two viruses with geometric shapes and spikes.

Are viruses living organisms?

Yes

Are viruses made of cells?

Yes

Viruses are about 10,000 times __________ than animal or plant cells.

larger

smaller

How viruses spread and multiply

spread / food / infect / virus / cells

Viruses can pass between humans via the air, contaminated or water, or by direct contact.
As they can't reproduce themselves, viruses have to enter one of our , and then use it to create multiple copies of the virus itself.
Once there are lots of copies, the viruses cause the cell to burst, and then go on to neighbouring cells.

food

cells

infect

How can measles be spread between people?

Via direct contact

Via droplets in air when an infected person coughs or sneezes

Via contaminated food

What are the symptoms of measles?

(Select all that apply)

Fever (feeling hot and cold)

Red skin rash

Compromised immune system

In the UK, are most people are vaccinated against measles?

Yes

HIV stands for Human Immunodeficiency Virus.

This is because it affects humans, it weakens the immune system (immunodeficiency), and it is a virus.

Which two ways can HIV be spread between people?

Sexual contact

Exchange of bodily fluids

Coughing or sneezing

Infection with the HIV virus can lead to __________. This is where the immune system is so weak that the person can catch unusual infections.

SDIC

SIDS

AIDS

What is the treatment for HIV/AIDS?

Statins

Antiretroviral drugs

Kidney transplant

What type of organism does Tobacco Mosaic Virus (TMV) infect?

Bacteria

Plants

Fungi

Animals

What is the main symptom of Tobacco Mosaic Virus (TMV)?

Roots start to die

Leaves turn black

Patches of the leaves get discoloured

Tobacco Mosaic Virus (TMV) reduces the amount of photosynthesis that a plant can do.

What are the consequences of this?

(Select all that apply)

The plants leaves will turn purple

The plant won't be able to grow as well

The plant won't be able to produce as many sugars

What is the main mode of transmission for the Ebola virus?

Airborne droplets from sneezing

Direct contact with infected bodily fluids

Mosquito bites

Contaminated food