Plant defences and plant disease — Edexcel GCSE Biology
Triple only: how plants defend themselves with physical barriers and chemicals, and how plant diseases are detected and identified.
Revision notes
3 short notes, in the order of the specification. Each one in short:
Plants defend themselves against pests and pathogens with physical barriers. The leaf cuticle is a waxy layer on the surface of leaves that pathogens and pests find hard to get through. The cellulose cell wall around every plant cell is a strong barrier that pathogens must get past before they can enter the cell.
Some plants produce chemicals to defend themselves. Some kill or slow the growth of microorganisms, and others are poisons that make the plant harmful or unpleasant for pests to eat. Humans use some of these chemicals as medicines: aspirin was developed from a chemical in willow bark, and digitalis from foxgloves treats some heart conditions.
Detecting and identifying plant diseases
Higher tierPlant diseases are detected and identified in four ways. Environmental causes, such as a mineral deficiency, are eliminated. Distribution analysis maps affected plants to see whether a pathogen is spreading. Visible symptoms, such as spots or wilting, are compared with known diseases. Diagnostic testing, for example using antibodies or DNA tests, identifies the pathogen.
Exam questions
3 exam-style questions (8 marks), each with its mark scheme.
Answer the questionsFlashcards
7 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of health, disease and the development of medicines on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
Quick check questions
Name two physical barriers that protect plants from pathogens.
Show answer
The leaf cuticle and the cell wall.
Give one way plant chemicals can be useful to humans.
Show answer
Some can be used as medicines to treat disease or relieve symptoms, for example aspirin from willow.
Why do scientists eliminate environmental causes when investigating a plant disease?
Show answer
To check that the symptoms are not caused by something such as a mineral deficiency, rather than a pathogen.
What is distribution analysis?
Show answer
Recording where the affected plants are to look for a pattern that suggests the cause.
Frequently asked questions
How do plants defend themselves against pathogens?
Plants defend themselves with physical barriers and chemical defences. The waxy leaf cuticle and the cellulose cell walls are barriers that pathogens find hard to get through. Some plants also produce chemicals that kill or slow the growth of microorganisms, or poisons that make the plant harmful or unpleasant for pests to eat.
Which medicines come from plants?
Several medicines come from chemicals that plants make to defend themselves. The painkiller aspirin was developed from a chemical in willow bark. Digitalis, from foxgloves, is used to treat some heart conditions. Quinine, from the bark of the cinchona tree, was used to treat malaria. Plant extracts are still tested for antimicrobial properties.
How are plant diseases identified?
Higher tier Plant diseases are identified by first eliminating environmental causes such as a mineral deficiency or drought. Distribution analysis shows whether affected plants cluster around a source, suggesting a spreading pathogen. Visible symptoms such as spots or wilting are compared with known diseases, and diagnostic tests using antibodies or DNA confirm which pathogen is present.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026