5.8 Diseases Caused by Fungi and Protists

A free GCSE Biology lesson for AQA (8461) from OBA School: rose black spot and other fungal diseases, malaria and how its mosquito vector is controlled. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe the symptoms of rose black spot and explain how it affects plant growth
• Describe how rose black spot spreads and how it is treated
• Describe the life cycle of the malaria protist, including the mosquito vector
• Evaluate ways of controlling the spread of malaria using data

Key words

• Fungus: An organism made of thread-like hyphae (or single cells such as yeast). Some fungi are pathogens. Plural: fungi.
• Spores: Tiny reproductive cells released by fungi. They spread the fungus to new hosts.
• Fungicide: A chemical that kills fungi.
• Protist: A single-celled eukaryotic organism. Some protists are pathogens, e.g. the one that causes malaria.
• Malaria: A disease caused by a protist and spread by mosquitoes. It causes recurrent fevers and can be fatal.

Fungal diseases

Fungi grow as networks of thread-like hyphae that spread through tissues. They release spores that can be carried to new hosts. In humans, athlete's foot is a fungus that makes the skin between the toes cracked, itchy and scaly. It is treated with antifungal cream.

Rose black spot is a fungal disease of roses:

• Symptoms; Rose black spot Purple or black spots develop on leaves. The leaves often turn yellow and drop early.
• Effect on plant; Rose black spot Growth is affected because there is less leaf area for photosynthesis, so less glucose is made.
• How it spreads; Rose black spot Spores are spread by water (rain splash) or by wind.
• Treatment; Rose black spot Spraying with fungicides, and/or removing and destroying affected leaves (burning, not composting).

Malaria: a disease caused by a protist

Malaria is caused by a protist. Its life cycle includes mosquitoes, which act as the vector. Malaria causes recurrent episodes of fever (the fevers keep coming back) and can be fatal.

Controlling malaria

The spread of malaria is reduced by stopping the vectors breeding and by stopping people being bitten.

• Drain or treat standing water; spray insecticide; How it helps Mosquitoes lay their eggs in still water. Fewer mosquitoes means fewer bites.
• Sleep under mosquito nets (often treated with insecticide); How it helps Mosquitoes that carry malaria often bite at night. Nets stop them reaching people, and insecticide kills them.
• Antimalarial drugs; How it helps Treat infected people, and protect travellers, so fewer people carry the protist.

Worked example: comparing rates

In one season, a village where people used nets had 36 malaria cases among 1500 people. A nearby village without nets had 99 cases among 1100 people.
With nets: 36 ÷ 1500 × 100 = 2.4%. Without nets: 99 ÷ 1100 × 100 = 9.0%.
Reduction = (9.0 − 2.4) ÷ 9.0 × 100 = 73% (to 2 s.f.).

Answer: The rate was about 73% lower in the village with nets

Exam tip: Other factors could also differ between villages, such as how close each is to standing water. A fair comparison controls these.

Common mistakes

• Calling malaria a bacterial or viral disease. It is caused by a protist.
• Saying the mosquito causes malaria. The mosquito is the vector; the protist is the pathogen.
• Saying rose black spot is spread by insects. It is spread by water and wind.
• Putting infected rose leaves on the compost heap. They should be destroyed, or the spores spread again.

Revision questions

Try these, then check your answers below each one.

Question 1. What type of pathogen causes malaria? (Choose from: Virus, Bacterium, Fungus, Protist.)

Answer: Protist

Working: Malaria is caused by a protist. Its life cycle includes mosquitoes.

Question 2. How is rose black spot spread? (Choose from: By insects, By water and wind, By soil only, By birds.)

Answer: By water and wind

Working: The spores of the rose black spot fungus are spread by water (rain splash) and by wind.

Question 3. True or false? The mosquito is the vector for malaria.

Answer: True

Working: True. The mosquito carries the malaria protist from one person to another. It is not made ill itself.

Related lessons

• Previous lesson: 5.7 Bacterial Diseases
• Next lesson: 5.9 Human Defence Responses
• In this chapter: 5.1 Health and Disease
• In this chapter: 5.2 Pathogens and Disease
• In this chapter: 5.3 Growing Bacteria in the Lab

Continue in the full course

This lesson is section 5.8 (AGCBH0508) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.