Describe how plants defend themselves against attack by pathogens and insects.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
1. The waxy cuticle covering the leaf surface acts as a physical barrier, preventing pathogen entry.
2. Cell walls, composed mainly of cellulose, provide a physical barrier that resists penetration by pathogens.
3. Plants synthesize antibacterial chemicals and antimicrobial substances that kill or inhibit invading pathogens.
4. Plants produce poisons or toxins that deter insects (and other herbivores) from feeding on them.
2. Cell walls, composed mainly of cellulose, provide a physical barrier that resists penetration by pathogens.
3. Plants synthesize antibacterial chemicals and antimicrobial substances that kill or inhibit invading pathogens.
4. Plants produce poisons or toxins that deter insects (and other herbivores) from feeding on them.
Examiner tips
- Use the exact terms: "waxy cuticle", "cellulose cell walls", "antibacterial chemicals", "poisons/toxins".
- Show each point as a separate sentence or numbered point.
- Keep the answer concise – 4 points for 4 marks.
Common mistakes
- Mixing up plant and animal defence terms; e.g., saying "immune system". Using vague words like "natural defence" instead of the specific mechanisms. Omitting the distinction between physical and chemical barriers.
Mark scheme (4 marks)
- Waxy cuticle on leaves acts as a physical barrier (prevents pathogen entry)
- Cell walls (made of cellulose) act as a physical barrier
- Plants produce antibacterial chemicals / antimicrobial substances that kill or inhibit pathogens
- Plants produce poisons / toxins that deter insects (or other herbivores) from eating them
Related
- Revision notes: Plant disease (Bio only) →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →