Explain how the structure of the cell wall in prokaryotic cells is related to its functions.

IB DP Biology Standard Level (2023 syllabus) — A2.2 Cell structure · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

The cell wall is made of peptidoglycan, a mesh‑like polymer of sugars and amino acids.

Its rigid, cross‑linked structure gives mechanical strength, so the cell keeps its shape.

The strength prevents lysis when the cell is in a hypotonic environment by withstanding turgor pressure.

Because the wall is porous, water, ions and small molecules can pass through freely, allowing nutrient uptake without restriction.

Examiner tips

  • Use the word ‘peptidoglycan’ and describe it as a mesh of sugars and amino acids. Mention the rigid, cross‑linked nature and link it to shape and resistance to lysis. State that the wall is porous, enabling free passage of small molecules.
  • common_mistakes
  • :
  • Confusing peptidoglycan with other cell wall components (e.g. cellulose). Forgetting to link the porous nature to nutrient uptake. Using vague terms like ‘strong’ without explaining how it prevents lysis.

Mark scheme (4 marks)

  1. The cell wall is composed of peptidoglycan (murein), a mesh-like polymer of sugars and amino acids
  2. The rigid, cross-linked structure of peptidoglycan provides mechanical strength, maintaining the shape of the cell
  3. The cell wall prevents the cell from bursting (lysis) by withstanding the internal turgor pressure / osmotic pressure when the cell is in a hypotonic environment
  4. The porous nature of the cell wall allows water, ions, and small molecules to pass through freely, so the wall does not restrict nutrient uptake

Key terms in this question

cell wall

Related

More Cell structure questions

▶ Try answering this question with AI marking (free) →