Plant Defence Responses (Edexcel GCSE Biology)

Chemical Barriers

• Plants have a range of defence mechanisms to infections and infestations

• These can be split into chemical and physical defences

Chemical defences

• Plants have chemical adaptations to prevent herbivores from eating them

  • Antiseptics or antimicrobial enzymes

  • Chemical poisons to deter pests that might eat them

  • Mechanisms to attract other insects as a biological control

• These same chemicals can sometimes be used to treat human diseases

  • Chemicals with antimicrobial properties can be extracted for human use such as in antibiotics

  • Herbal face creams can use plant extracts such as tea tree oil, mint and witch hazel to have an antibacterial effect

  • The pain relief drug, aspirin, originated from the bark of willow trees

Physical Barriers

Physical defences

• Plants also have several physical adaptations which provide protection

  • The cellulose cell wall not only provides support for the plant but also protection from microorganisms

  • The waxy cuticle of the leaf and stems acts as 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

  • Thorns or hairy stems also makes it more difficult for pests to access the plant tissue to feed

Plant Adaptions Table