5.9B Describe how some plants defend themselves against attack from pests…

The idea

Plants cannot move away from pests or pathogens, so they rely on physical barriers to stop invaders entering. The leaf cuticle is a waxy layer covering the upper surface of leaves; it is waterproof and resists water loss while blocking many pathogens and small pests from penetrating the leaf surface. The cell wall is a tough layer outside the cell membrane made largely of cellulose; it gives structural support and acts as a barrier that pathogens must breach before reaching the cell contents. Together these barriers reduce entry points, so fewer pathogens or pests reach the living tissue and cause disease or damage.

What earns the marks

• The leaf cuticle is a waxy, waterproof layer on the leaf surface.
• The cuticle blocks pathogens and reduces water loss, limiting entry points.
• The cell wall is a tough layer outside the cell membrane, made largely of cellulose.
• The cell wall provides a physical barrier that pathogens must breach to reach cell contents.
• Physical barriers reduce the number of pathogens or pests that can enter plant tissue.

Common mistakes and how to put them right

• Confusing the cuticle with the cell wall.

  Put it right by noting the cuticle is a waxy surface layer and the cell wall is a tough structural layer around each cell.

• Saying the cell wall is inside the cell membrane.

  Put it right: Correct it to outside the cell membrane.

• Claiming the cuticle lets water through freely.

  Put it right: Correct it to a waterproof waxy layer that resists water loss.

Exam tips

• Name each barrier and state what it physically blocks or resists.
• Use the words waxy for the cuticle and cellulose for the cell wall to show precise knowledge.
• Keep the answer to physical barriers, not chemical defences, to match the statement.