Chemical defences in plants

Health, disease and the development of medicines · Plant defences and plant disease · note 2 of 3

Spec 5.10B

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Chemical defences in plantsSpec 5.10B

In short

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.

Some plants produce chemicals that defend them against attack. Some of these chemicals kill or slow the growth of microorganisms. Others are poisons that make the plant harmful or unpleasant for pests to eat.

Some of these plant chemicals can be used by humans to treat disease or relieve symptoms. Common examples are:

willow bark contains a chemical that the painkiller aspirin was developed from
foxgloves contain digitalis, a chemical used to treat some heart conditions
the bark of the cinchona tree contains quinine, which was used to treat malaria

Exam tip:

The spec does not require named examples. One example, such as aspirin from willow, is enough to illustrate the point.

This is also why plant extracts are tested for antimicrobial properties, as in the core practical later in this topic.

Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026

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.