AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Cellulose cell walls. • Tough waxy cuticle on leaves. • Layers of dead…
Full specification wording
Plant defence responses: Cellulose cell walls. • Tough waxy cuticle on leaves. • Layers of dead cells around stems (bark on trees) which fall off.
These three structures are the named physical defences of plants.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 3 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
These three structures are the named physical defences of plants. Cellulose cell walls surround every plant cell; cellulose is strong and rigid, so walls resist penetration by microorganisms and help the plant withstand mechanical damage. A tough waxy cuticle covers the leaf epidermis; it is waterproof and forms a smooth barrier that repels water, so fungal spores and bacteria cannot easily settle and enter. Around stems, layers of dead cells form bark on trees; this outer layer protects deeper living tissues and eventually falls off, carrying pathogens away with it. A useful method is to sketch a cross-section of a leaf and stem, label each barrier, and annotate how it blocks microorganism invasion.
What earns the marks
- Cellulose cell walls are strong and rigid and resist penetration by microorganisms.
- A tough waxy cuticle covers leaves and acts as a waterproof physical barrier to pathogen entry.
- Layers of dead cells around stems form bark on trees and protect the living tissues beneath.
- Bark falls off, so pathogens on its surface are removed from the plant.
- Each named structure should be linked to how it prevents microorganisms entering or spreading.
Common mistakes and how to put them right
Writing that the cuticle is made of cellulose.
Put it right by stating that the cuticle is waxy and covers the leaf surface, while cellulose forms cell walls.
Saying bark is living and grows outward.
Put it right by stating that bark is made of layers of dead cells that fall off.
Describing cell walls as flexible membranes.
Put it right by stating that cellulose cell walls are strong and rigid.
Exam tips
- Learn the three structures as a set: cellulose cell walls, waxy cuticle and dead bark layers.
- Add one function to each structure so your answer explains defence, not just names parts.
- Use a labelled diagram if asked to show where each barrier is located in a leaf or stem.
Try the lesson
The start of the Plant defence responses: Cellulose cell walls. • Tough waxy cuticle on leaves. • Layers of dead cells around stems (bark on trees) which fall off. lesson, made from checked teaching notes for this specification point.
Have a go first
Which substance makes up the cell wall of a plant cell, providing a physical barrier against microorganisms?
Listen
These three structures are the named physical defences of plants. Cellulose cell walls surround every plant cell; cellulose is strong and rigid, so walls resist penetration by microorganisms and help the plant withstand mechanical damage. A tough waxy cuticle covers the leaf epidermis; it is waterproof and forms a smooth barrier that repels water, so fungal spores and bacteria cannot easily settle and enter. Around stems, layers of dead cells form bark on trees; this outer layer protects deeper living tissues and eventually falls off, carrying pathogens away with it. A useful method is to sketch a cross-section of a leaf and stem, label each barrier, and annotate how it blocks microorganism invasion. A strong answer earns marks for these points. Cellulose cell walls are strong and rigid and resist penetration by microorganisms. A tough waxy cuticle covers leaves and acts as a waterproof physical barrier to pathogen entry. Layers of dead cells around stems form bark on trees and protect the living tissues beneath. Bark falls off, so pathogens on its surface are removed from the plant. A common slip: Writing that the cuticle is made of cellulose. Instead, stating that the cuticle is waxy and covers the leaf surface, while cellulose forms cell walls. Exam tip: Learn the three structures as a set: cellulose cell walls, waxy cuticle and dead bark layers.
See it
Key words
Say what each word means before you turn the card.
Cellulose cell walls
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Waxy cuticle
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Bark and dead cell layers
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Barriers against microorganism invasion
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See every definition
- Cellulose cell walls
- Strong and rigid walls that surround every plant cell and resist penetration by microorganisms.
- Waxy cuticle
- A tough, waterproof covering on leaves that forms a smooth barrier so fungal spores and bacteria cannot easily settle and enter.
- Bark and dead cell layers
- Layers of dead cells around stems that protect deeper living tissues and eventually fall off, carrying pathogens away.
- Barriers against microorganism invasion
- The named physical defences of plants, each linked to how it prevents microorganisms entering or spreading.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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