Disease and response · GCSE Biology
Plant disease
GCSE Biology revision on plant diseases: TMV and rose black spot as named examples, symptoms, transmission, effects on photosynthesis and yield, and control by hygiene, fungicides and resistant varieties.
TMV = virus, mottled leaves, tools and seeds. Rose black spot = fungus, black spots, wind spores, remove leaves. Both cut photosynthesis → less glucose → weak plant. Antibiotics do not treat viruses or fungi on plants the same way as human bacterial disease.
The important bits
What you need to know
- 1
Plants can be infected by pathogens including viruses, fungi and bacteria. Damage often shows as discoloured or spotted leaves, stunted growth, or reduced yield — because less photosynthesis means less glucose for growth and storage.
- 2
Tobacco mosaic virus (TMV) is a viral plant disease. Symptoms include a distinctive “mosaic” mottled pattern of discolouration on leaves. TMV spreads through contact (contaminated tools, hands, seeds) and can persist in soil.
- 3
Rose black spot is a fungal disease. Dark purple-black spots appear on leaves, often with yellowing around them. Leaves may fall early. The fungus reduces photosynthetic area and weakens the plant.
- 4
Fungal spores of rose black spot spread by wind and water splash. They can overwinter on fallen leaves, so garden hygiene (removing infected material) is a key control measure.
- 5
Plant disease identification uses symptoms, distribution of damage, and sometimes test kits (Triple may mention monoclonal antibodies for detecting viral or bacterial pathogens).
- 6
Control methods: destroy infected plants or remove infected leaves; use resistant plant varieties; apply fungicides for fungal diseases; disinfect tools between plants; crop rotation and spacing to reduce spread; destroy aphid vectors for some viruses.
- 7
Antibiotics are not used routinely on plants in the same way as for human bacterial infections; prevention and fungicides / resistant strains are the GCSE story. Viral plant diseases have no chemical cure in the field — control is prevention.
- 8
Link to organisation: less chlorophyll or leaf area → less photosynthesis → less starch, cellulose, fruit and growth. Farmers and gardeners lose crop yield and quality.
Quotations worth analysing
Short evidence. Real method.
“TMV causes a mottled discolouration on leaves and is spread by contact and contaminated equipment.”
Name virus, symptom, and transmission. Do not call TMV a bacterium or treat it with antibiotics.
“Rose black spot is caused by a fungus; spores spread in wind and water.”
Fungus, not virus. Spores, not droplets from human coughs. Remove fallen leaves to break the life cycle.
“Plant diseases reduce photosynthesis and therefore growth and crop yield.”
Always link symptom to photosynthesis and glucose, not just “the plant looks ill”.
Go deeper
How do plant-disease answers differ from human ones?
Damage is often about photosynthesis: less chlorophyll, spotted leaves, stunted growth, less yield. Identification uses symptoms, distribution of spots, or testing kits (Triple may mention monoclonal antibodies). Control: destroy infected plants, resistant strains, pesticides, crop rotation. There is no antibody vaccination of a wheat field in the human sense. TMV survives in soil and on tools, so disinfection matters. Rose black spot spores overwinter on fallen leaves, so garden hygiene is biology, not fussiness. Link back to uses of glucose: less photosynthesis means less starch, cellulose and fruit. That sentence lifts a plant-pathogen answer from a description of spots to a whole-plant consequence.
Go deeper
TMV versus rose black spot — side-by-side for six marks
TMV: virus, mottled pattern, contact/tools/seeds, no cure — prevent by clean tools and resistant varieties. Rose black spot: fungus, black spots on leaves, wind/water spores, fungicide and remove leaves. Both reduce photosynthesis. Neither is treated with human antibiotics in the GCSE model. If the question asks for transmission, TMV is contact; rose black spot is spores. If it asks for control, hygiene versus fungicide. Mixing them up is a common zero.
Go deeper
Why farmers care beyond the garden bench
Wheat rust, potato blight and viral crop diseases reduce food supply. Resistant varieties bred by selective breeding or GM (if your spec mentions it) are long-term control. Fungicide spray is short-term cost and environmental trade-off. Aphids vector plant viruses — controlling insects controls virus spread. In evaluate questions, compare cost of fungicide, yield loss, and environmental impact of chemicals. Name a mechanism, not “farmers should be careful”.
See the idea in action
Describe rose black spot and how to reduce its spread (4 marks). Rose black spot is caused by a fungus. It produces purple-black spots on leaves, reducing photosynthesis as leaves yellow and fall. Spores spread in wind and rain splash. To reduce spread: remove and destroy infected leaves, especially fallen leaves where spores overwinter; use fungicide if needed; plant resistant rose varieties; space plants for airflow. TMV would be wrong here — that is viral with mottling, not black spots.
Exam technique
Turn knowledge into marks
Learn TMV and rose black spot as paired examples: virus vs fungus, symptom, spread, control. Always mention reduced photosynthesis. Do not prescribe antibiotics for viral plant disease.
Common mistakes
Do not give these marks away
- 01
Calling TMV a bacterium or fungus, or treating plant viruses with antibiotics.
- 02
Describing rose black spot without naming fungus or spore transmission.
- 03
Listing human disease controls (vaccination, condoms) for plant diseases.
Which pathogen causes rose black spot?
AA virus
BA fungus
CA bacterium only
DA protist
Show the answer
A fungus. Rose black spot is fungal, spread by spores. TMV is the viral example with mottled leaves.
Quick questions
If this is the bit you searched
What is TMV GCSE Biology?
Tobacco mosaic virus, a viral plant disease causing mottled leaf discolouration, spread by contact and contaminated tools or seeds.
How does rose black spot spread?
Fungal spores spread in wind and water splash. Spores can survive on fallen leaves over winter.
Why do plant diseases reduce crop yield?
They damage leaves and reduce photosynthesis, so the plant makes less glucose for growth, storage and reproduction.
How can rose black spot be controlled?
Remove infected leaves, use fungicides, plant resistant varieties, and improve hygiene by clearing fallen leaves.