Explain how the molecular structure of cellulose makes it suitable for its role as a structural component of plant cell walls.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Cellulose is a polymer of β‑glucose linked by β‑1,4‑glycosidic bonds.
The β‑1,4 linkage forces each glucose unit to be rotated 180° relative to its neighbour, giving a straight, unbranched chain.
Many parallel chains align and the –OH groups on adjacent chains form extensive hydrogen bonds, bundling the chains into microfibrils.
These microfibrils have high tensile strength, allowing the cell wall to resist turgor pressure and maintain cell shape.
The β‑1,4 linkage forces each glucose unit to be rotated 180° relative to its neighbour, giving a straight, unbranched chain.
Many parallel chains align and the –OH groups on adjacent chains form extensive hydrogen bonds, bundling the chains into microfibrils.
These microfibrils have high tensile strength, allowing the cell wall to resist turgor pressure and maintain cell shape.
Examiner tips
- Mention the β‑1,4 linkage and the 180° flip to show chain straightness. Explain how hydrogen bonding between chains bundles them into microfibrils. Link the microfibril strength to resisting turgor pressure and maintaining shape.
Common mistakes
- Confusing α‑glucose with β‑glucose. Forgetting to state the 180° flip or the straight chain. Failing to connect microfibril formation to tensile strength and cell shape.
Mark scheme (4 marks)
- Cellulose is composed of β-glucose monomers linked by β-1,4-glycosidic bonds.
- Alternating glucose monomers are flipped 180° relative to each other, producing straight, unbranched chains.
- Parallel chains form hydrogen bonds between hydroxyl (–OH) groups on adjacent chains, bundling them into microfibrils.
- The resulting microfibrils provide high tensile strength, resisting the turgor pressure of the plant cell and maintaining cell shape.
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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