Explain how the structure of the vacuole in plant cells is related to its functions.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The vacuole is surrounded by a single membrane, the tonoplast, which regulates the transport of ions and molecules into and out of the vacuole.
The large central vacuole occupies most of the cell volume and stores water together with dissolved solutes such as sugars, ions, pigments and waste products.
Because the cell sap inside the vacuole has a high solute concentration, water is drawn into the vacuole by osmosis, creating osmotic pressure that generates turgor pressure. This turgor pressure supports the cell wall and keeps the plant cell rigid.
The tonoplast also provides compartmentalisation, isolating stored substances (e.g. toxins, pigments or acids) from the cytoplasm. This protects metabolic reactions and can deter herbivores.
The large central vacuole occupies most of the cell volume and stores water together with dissolved solutes such as sugars, ions, pigments and waste products.
Because the cell sap inside the vacuole has a high solute concentration, water is drawn into the vacuole by osmosis, creating osmotic pressure that generates turgor pressure. This turgor pressure supports the cell wall and keeps the plant cell rigid.
The tonoplast also provides compartmentalisation, isolating stored substances (e.g. toxins, pigments or acids) from the cytoplasm. This protects metabolic reactions and can deter herbivores.
Examiner tips
- Use the word ‘tonoplast’ to show knowledge of the membrane. Show the link between high solute concentration, osmotic pressure and turgor. Mention the protective role of compartmentalisation. Keep each point concise to fit the 4‑mark format.
Common mistakes
- Forgetting to name the tonoplast. Mixing up the role of the vacuole with that of the cell wall. Not linking solute concentration to osmotic pressure and turgor.
Mark scheme (4 marks)
- The vacuole is enclosed by a single membrane called the tonoplast, which controls the movement of substances into and out of the vacuole.
- The large central vacuole occupies most of the cell volume, storing water and dissolved solutes (sugars, ions, pigments, or waste products).
- The vacuole contains cell sap at high solute concentration, generating osmotic pressure that draws water in by osmosis, creating turgor pressure that supports the cell.
- The compartmentalisation provided by the tonoplast isolates stored substances (e.g. toxins, pigments, or acids) from the cytoplasm, protecting metabolic reactions and/or deterring herbivores.
Key terms in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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