Viral, Fungal and Protist Diseases

Question 1

Explain three viral diseases.

Answer 1

1. Measles - spread by droplets from an infected person’s sneeze or cough. People with measles develop a red skin rash, and they’ll show signs of a fever. Measles can be very serious, or even fatal if there are complications. E.g, measles can sometimes lead to pneumonia (lung infection) or a brain infection called encephalitis.
2. HIV - a virus spread by sexual contact, or by exchanging bodily fluids such as blood. This can happen when people share needles when taking drugs. HIV initially causes flu-like symptoms for a few weeks. Usually, the person doesn’t then experience any symptoms several years. During this time, HIV can be controlled with antiretroviral drugs. These stop the virus replicating in the body. The virus attacks the immune cells. If the body’s immune system is badly damaged, it can’t cope with other infections or cancers. At this stage, the virus is known as late-stage HIV infection or AIDS.
3. Tobacco mosaic virus (TMV) - a virus that affects many species of plants, e.g. tomatoes. It causes a mosaic pattern on the leaves of the plants - parts of the leaves become discoloured. The discolouration means the plant can’t carry out photosynthesis as well, so the virus affects growth.

Question 2

Explain an example of a fungal disease.

Answer 2

Rose black spot - a fungus that causes purple or black spots to develop on the leaves of rose plants. The leaves can then turn yellow and drop off. This means that less photosynthesis can happen, so the plant doesn’t grow very well. It spreads through the environment in water or by the wind. Gardeners can treat the disease using fungicides and by stripping the plant of its affected leaves. These leaves then need to be destroyed so that the fungus can’t be spread to other rose plants.

Question 3

Explain one disease caused by a protist.

Answer 3

Malaria - part of a malarial protist’s life cycle takes place inside the mosquito. The mosquitoes are vectors - they pick up the malarial protist when they feed on an infected animal. Every time the mosquito feeds on another animal, it infects it by inserting the protist into the animal’s blood vessels. Malaria causes repeating episodes of fever. It can be fatal. The spread of malaria can be reduced by stopping the mosquitoes from breeding. People can be protected from mosquitoes using insecticides and mosquito nets.