Plant Defences

Plants face constant threats from herbivores (animals that eat them), pathogens (disease-causing microorganisms) and environmental damage. Unlike animals, plants cannot run away, so they have evolved a range of defence mechanisms. This lesson covers the physical, chemical and mechanical defences of plants, as well as their wound responses, as required by Edexcel GCSE Biology (1BI0) Topic 6.

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Why Do Plants Need Defences?

Plants are under constant attack from:

• Herbivores — animals (including insects) that feed on plant tissue
• Pathogens — bacteria, viruses and fungi that cause disease
• Parasites — organisms that live on or in the plant and take nutrients from it

Without defences, plants would be consumed, infected and destroyed. Natural selection has led to the evolution of many defence mechanisms that help plants survive and reproduce.

Exam Tip: When discussing plant defences, always classify them as physical, chemical or mechanical. This shows the examiner you understand the different categories and can organise your knowledge clearly.

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Physical Defences

Physical defences are structural barriers that prevent pathogens from entering the plant and deter herbivores from feeding.

1. Cellulose Cell Walls