How does the waxy cuticle on a leaf defend the plant against disease?

It is a waterproof layer over the surface that pathogens cannot pass through, and water carrying spores runs off it instead of settling.

How does the cell wall of a plant cell act as a defence against pathogens?

It is a tough layer of cellulose outside the cell membrane, so a pathogen must break it down before it can reach the living contents of the cell.

Explain why a fungus must release enzymes in order to infect a leaf.

It has to digest a way through the waxy cuticle and the cellulose cell walls before it can reach and feed on the cell contents.

How does bark protect a tree from infection?

It is a thick layer of dead cells that pathogens cannot grow through, and it is shed from the trunk, carrying any pathogens on it away.

How do hairs on the surface of a leaf help to defend it?

They hold water droplets and small insects away from the leaf surface, so spores are less likely to land on it or be carried into the tissue.

OCR GCSE Biology A J247

Cell Level Systems

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Physical and chemical plant defences

3 things to know
Paper 4

Overview

How the waxy cuticle, cell walls, bark and leaf hairs defend a plant, why fungi release enzymes and why damage makes infection likely, how a wound is sealed, antimicrobial chemicals from plants such as mint and witch hazel, how chemical and physical defences differ, poisons such as digitalis and atropine, why chemical defences still work inside the plant, their use in medicines, and their cost to the plant.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Give two physical plant defences other than the cuticle and the cell wall.

Key term

Explain why damage to a leaf makes infection much more likely.

Key term

How does a plant limit the spread of infection after it has been wounded?

Questions from this subtopic

Each one with the model answer underneath.

1
How does the waxy cuticle on a leaf defend the plant against disease?
Model answer
It is a waterproof layer over the surface that pathogens cannot pass through, and water carrying spores runs off it instead of settling.
2
How does the cell wall of a plant cell act as a defence against pathogens?
Model answer
It is a tough layer of cellulose outside the cell membrane, so a pathogen must break it down before it can reach the living contents of the cell.
3
Explain why a fungus must release enzymes in order to infect a leaf.
Model answer
It has to digest a way through the waxy cuticle and the cellulose cell walls before it can reach and feed on the cell contents.
4
How does bark protect a tree from infection?
Model answer
It is a thick layer of dead cells that pathogens cannot grow through, and it is shed from the trunk, carrying any pathogens on it away.
5
Give two physical plant defences other than the cuticle and the cell wall.
Model answer
Layers of dead cells such as bark that are shed, and hairs or thorns on the surface that keep animals and insects away.
6
How do hairs on the surface of a leaf help to defend it?
Model answer
They hold water droplets and small insects away from the leaf surface, so spores are less likely to land on it or be carried into the tissue.

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