AQA GCSE Biology

Revision Notes

3.3.2 Plant Defence Responses

Physical & Chemical Defences

  • Plants have a range of defence mechanisms to infections and infestations
  • These can be split into physical and chemical defences
  • Plants have adaptations to prevent herbivores from eating them (see Adaptations)

Physical Defences

  • The cellulose cell wall not only provides support for the plant but also protection from microorganisms
  • The waxy cuticle of the leaf is a barrier to microbes from entering the plant. The only place that they can enter in the leaf is through the stomata
  • Bark provides a tough layer around the stem of the plant to prevent pathogens from entering
  • As deciduous trees lose leaves in the winter the infection can be taken with them

Chemical Defences

  • Many plants produce chemicals that have antimicrobial properties
  • Many herbal face creams can use plant extracts such as tea tree oil, mint and witch hazel to have an antibacterial effect
  • More plants are being studied for their potential source of antibiotics as more strains are becoming resistant to current antibiotics

Adaptations Against Herbivores

  • Herbivores eating a plant can seriously damage the plant structures and they will not flower and reproduce
  • Smaller insect infections can remove essential nutrients and energy from the plant and act as vectors for pathogens

Plant adaptions table

Plant Defence Responses table, downloadable IGCSE & GCSE Biology revision notes

Exam Tip

Being able to link concepts together such as adaptations and why this will help the plant is essential for answering 2+ mark questions. When you state an adaptation always say how this will help the plant.

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Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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