# Explain how the structural features of the vacuole in a mature plant cell are related to its functions.

> IB DP Biology Higher Level (2023 syllabus) — B2.2 Organelles and compartmentalisation · Explain · 4 marks

## Mark scheme (4 marks)

1. The vacuole is enclosed by the tonoplast (a selectively permeable membrane), which controls the movement of ions and solutes into and out of the vacuole, allowing turgor pressure to be regulated.
2. The large, central vacuole occupies up to 90% of the cell's volume, providing a large hydrostatic (turgor) pressure against the cell wall, which maintains cell rigidity and support in non-woody tissues.
3. The vacuole stores solutes such as ions, sugars, amino acids, and secondary metabolites (e.g. anthocyanins, tannins), sequestering them away from the cytoplasm where they could interfere with metabolic reactions.
4. The vacuole has an acidic lumen (maintained by proton pumps in the tonoplast), which activates hydrolytic enzymes stored within it, enabling the vacuole to function in degradation of waste or damaged cell components (analogous to lysosomes in animal cells).

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