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      Lesson details

      Learning outcome

      I can describe physical, chemical and mechanical plant defences against pathogens and pests.

      Key learning points

      1. Plants can be infected by pathogens, such as viruses, bacteria and fungi, that cause diseases.
      2. Pests, including insects, can damage plants by feeding on them, and can spread pathogens that cause diseases.
      3. Plants have physical, chemical and mechanical defences against pathogens.
      4. Examples of physical, chemical and mechanical defences in plants.

      Keywords

      • Pathogen - A virus, bacterium or other microorganism that causes disease.

      • Pest - An insect or other animal that damages plants and can spread plant pathogens.

      • Waxy cuticle - Waterproof coating on the surface of a leaf.

      • Cell wall - Structure made of cellulose that surrounds plant cells.

      • Antimicrobial - A substance that kills microorganisms or stops their growth.

      Common misconception

      Plants have no defence against pests or pathogens.

      Plants have physical, chemical and mechanical defences against pathogens.

      Teacher tip

      The lesson includes a video clip of the "sensitive plant" (Mimosa pudica) curling up, as an example of a mechanical defence. Demonstrating this effect in a real plant such as this one or any others that respond to touch can help to increase engagement and really bring the idea to life.

      Equipment

      None required.

      Licence

      This content is © Oak National Academy Limited (2026), licensed on Open Government Licence version 3.0
      except where otherwise stated. See Oak's terms & conditions
      (Collection 2).

      Lesson video

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      Prior knowledge starter quiz

      6 Questions

      Q1.
      Which of the following can be pathogens?

      antibiotics
      Correct answer: bacteria
      Correct answer: fungi
      Correct answer: viruses
      plants

      Q2.
      Pathogens can causes disease in plants.

      Correct answer: True
      False

      Q3.
      The image below shows the cross section of a leaf. What is being shown by label A?

      An image in a quiz
      palisade mesophyll cells
      chlorophyll
      Correct answer: waxy cuticle
      epidermal cells
      spongy mesophyll cells

      Q4.
      Label this plant cell.

      An image in a quiz
      Correct Answer:A,cell wall

      cell wall

      Correct Answer:B,cell membrane

      cell membrane

      Correct Answer:C,chloroplast

      chloroplast

      Correct Answer:D,vacuole

      vacuole

      Q5.
      What are plant cell walls made from?

      Correct Answer: Cellulose, cellulose

      Q6.
      Which organism in this food chain is a herbivore?

      An image in a quiz
      oak leaf
      Correct answer: aphid
      ladybird
      blue tit
      wildcat

      6 Questions

      Q1.
      Match the disease to the pathogen that causes it.

      Correct Answer:TMV,virus

      virus

      Correct Answer:crown gall disease,bacteria

      bacteria

      Correct Answer:chalara ash dieback,fungus

      fungus

      Q2.
      Which of the following are physical defences?

      Correct answer: tree bark
      production of poisons
      Correct answer: waxy cuticle
      Correct answer: cell wall
      production of antimicrobial substances

      Q3.
      Insects can transfer pathogens.

      Correct answer: True
      False

      Q4.
      What substance in the phloem of a plant do some insects feed upon?

      An image in a quiz
      Correct Answer: sap, cell sap

      Q5.
      Which plants produce poisons that deter herbivores from eating them?

      Correct answer: foxglove
      clover
      mint
      Correct answer: stinging nettles

      Q6.
      Which plants demonstrate mechanical defences?

      Correct answer: mimosa pudica
      lettuce
      Correct answer: thistles
      grasses

      To help you plan your 11 biology lesson on: Plant defences against disease, download all teaching resources for free and adapt to suit your pupils' needs...