Physical barriers in plantsSpec 5.9B
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.
Plants can be attacked by pests (such as insects) and by pathogens. Some plants defend themselves with physical barriers that stop these entering.
- The leaf cuticle is a waxy layer on the surface of leaves. It forms a barrier that pathogens and pests find hard to get through.
- The cell wall is made of cellulose around every plant cell. It is a strong barrier that pathogens must get past before they can enter the cell.
Exam tip:Name the barrier and say what it does. 'The waxy cuticle stops pathogens entering the leaf' earns the mark; just 'the cuticle' does not.
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.
