Fungal diseases — AQA GCSE Combined Science
Test yourself on Fungal diseases with AQA GCSE practice questions.
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Fungal diseases explained
Rose black spot is caused by a fungus that infects rose leaves.
Read the full explanation
Purple or black spots appear on the leaf surface; surrounding tissue often turns yellow, and infected leaves drop early. Because leaves carry out photosynthesis, losing leaf area reduces the plant's photosynthesis, so growth is reduced. The fungus spreads in the environment by water or wind, so spores land on healthy leaves and start new infections. Treatment combines fungicides, which kill or inhibit the fungus, with removing and destroying affected leaves to reduce the source of spores. Destroying, rather than composting, the leaves matters because surviving spores could reinfect the plant.
Your focus
- Describe the symptoms of rose black spot and identify the pathogen as a fungus.
- Explain how leaf loss caused by rose black spot reduces photosynthesis and plant growth.
- State that rose black spot spreads by water or wind and describe how fungicides and removal of affected leaves control it.
Fungal diseases exam tips
Marking Points
- Rose black spot is a fungal disease of rose plants, so the pathogen is a fungus rather than a bacterium or virus.
- Purple or black spots develop on leaves, and the surrounding leaf tissue often turns yellow.
- Infected leaves often drop early, reducing the total leaf area available for photosynthesis.
- Reduced photosynthesis lowers the plant's growth because less glucose is made for respiration and new tissue.
- The disease spreads in the environment by water or wind, which carry fungal spores to healthy leaves.
- Treatment can use fungicides and/or removal and destruction of affected leaves to reduce reinfection.
Examiner Tips
- 💡Link each visible symptom to its effect: spots and yellowing reduce photosynthesis, and leaf drop reduces leaf area further.
- 💡When asked how it spreads, name both water and wind as environmental agents carrying spores.
- 💡For control, give both parts of the treatment: fungicides and removing and destroying affected leaves.
Common Mistakes
- Calling rose black spot a viral or bacterial disease: correct this by naming the pathogen as a fungus and linking the spots to fungal growth.
- Saying the plant dies immediately from the spots: correct this by explaining that leaf loss reduces photosynthesis, which reduces growth.
- Treating only with fungicide while leaving fallen infected leaves on the ground: correct this by also removing and destroying affected leaves to reduce spores.