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Work through the notes, try the practice questions, then take the quiz. The report tells you exactly what to revise next. (2026)
Question
A gardener notices a rose plant with purple-black spots on the leaves and many leaves dropping early. Suggest the most likely disease, the type of pathogen, and TWO control methods. (4 marks)
Solution
Black/purple spots on roses + early leaf drop is a textbook description of rose black spot.
Rose black spot is caused by a FUNGUS — so anti-fungal measures apply.
Two control methods: spray with a fungicide; remove and burn affected leaves to stop spore spread.
Answer
Rose black spot (1). Caused by a fungus (1). Control: spray with a fungicide (1); remove and burn affected leaves to prevent spores spreading (1).
Examiner note
Always burn (not compost) fungal-infected leaves — composting spreads spores.
Question
A tomato plant has very yellow leaves but growth seems normal in height. Suggest the most likely cause and explain WHY the leaves are yellow. (3 marks)
Solution
Uniform yellowing with otherwise normal growth points to magnesium deficiency (not nitrate, which would stunt growth).
Magnesium is needed to make chlorophyll; without it leaves cannot make the green pigment.
Answer
Magnesium ion deficiency (1). Magnesium is needed to make chlorophyll (1). Without chlorophyll the leaves cannot stay green and appear yellow (chlorosis) (1).
Question
A nettle has stinging hairs that inject formic acid into anything that touches them. Identify TWO categories of plant defence shown by the nettle and explain how each works. (4 marks)
Solution
The hairs themselves are a mechanical defence — physical structures that deter animals.
The formic acid is a chemical defence — an irritant poison.
Answer
Mechanical defence (1): the stinging hairs are physical structures that physically deter and pierce skin of herbivores (1). Chemical defence (1): formic acid is an irritant injected when the hair breaks, causing pain that deters the animal from eating further (1).
Examiner note
Many real defences combine categories — top-band answers explain the mechanism for each.
Question
Name TWO medicines that originated from plant defence chemicals and give the plant they come from. (4 marks)
Solution
Aspirin originated from willow bark (salicylic acid as a defence chemical).
Digitalis (a heart drug) came from foxglove plants.
Answer
Aspirin (1) from willow bark (1); digitalis (1) from foxglove plants (1).
A microorganism (virus, bacterium, fungus or protist) that causes disease in a plant.
Yellowing of plant leaves due to reduced chlorophyll production; often caused by magnesium ion deficiency.
A widespread plant virus that produces a mosaic pattern of light and dark patches on leaves, reducing photosynthesis and stunting growth.
A barrier in or on a plant that prevents pathogens reaching cells — for example, cellulose cell walls, waxy cuticle, bark.
Substances produced by a plant that kill pathogens (antibacterial chemicals) or poison/deter herbivores.
Structural or behavioural feature (thorns, hairs, leaves that droop or curl, mimicry) that physically prevents an animal from eating or damaging the plant.
Mistake
Calling all yellow leaves 'chlorosis' regardless of pattern.
Why it happens
Yellow looks like yellow.
How to avoid it
Look at the pattern. Uniform yellowing = magnesium deficiency. Mosaic patches = TMV. With dark spots = rose black spot.
Mistake
Calling aphids a pathogen.
Why it happens
Aphids cause disease-like damage.
How to avoid it
Aphids are INSECT PESTS, not pathogens. They damage the plant by feeding on phloem, not by infecting cells.
Mistake
Suggesting TMV can be cured with antiviral spray.
Why it happens
Students assume there's always a treatment.
How to avoid it
There is no cure for TMV. Control = destroy infected plants and disinfect tools.
Mistake
Saying plants produce antibodies.
Why it happens
Confusion with the human immune response (4.3.1.4).
How to avoid it
Plants do NOT make antibodies. They make chemicals (antibacterial substances and poisons) plus physical/mechanical barriers.
Mistake
Calling thorns a 'physical' defence.
Why it happens
Thorns are physical objects.
How to avoid it
AQA classifies thorns and hairs as MECHANICAL defences. 'Physical' refers to the barriers that block pathogens (cell wall, cuticle, bark).
Mistake
Naming a category but no example.
Why it happens
Students remember the list of categories but not the AQA examples.
How to avoid it
Memorise one named example per category: cellulose wall (physical); mint / foxglove (chemical); thorns / Mimosa (mechanical).