Explain how the molecular structure of cellulose makes it well suited to its function as a structural component of plant cell walls.

IB DP Biology Standard Level (2023 syllabus) — B1.1 Carbohydrates and lipids · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Cellulose is a polymer of glucose monomers linked by β‑1,4‑glycosidic bonds. The β‑linkage forces each glucose unit to be flipped relative to the previous one, giving a straight, unbranched chain. Parallel chains can then form extensive hydrogen bonds, bundling into microfibrils. These microfibrils are highly tensile, providing mechanical strength that prevents the cell wall from bursting under osmotic pressure and gives the plant cell its structural support.

Examiner tips

  • Mention β‑1,4‑glycosidic bonds and the straight chain
  • Explain hydrogen bonding between chains
  • Link microfibrils to tensile strength and cell wall stability

Common mistakes

  • Confusing α‑glucose with β‑glucose
  • Failing to state that chains are unbranched
  • Not linking microfibrils to mechanical support

Mark scheme (4 marks)

  1. Cellulose is composed of glucose monomers/subunits linked by glycosidic bonds
  2. The β-1,4-glycosidic linkages cause alternating glucose units to be flipped/inverted, allowing the chain to remain straight/unbranched
  3. Hydrogen bonds form between parallel cellulose chains, bundling them into microfibrils
  4. The resulting microfibrils provide high tensile strength, preventing the cell wall from bursting under osmotic pressure / providing mechanical support to the cell

Key terms in this question

cellulose · cell wall

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