Animal and plant cells: a permanent vacuole filled with cell sap.

The idea

The permanent vacuole is a large, fluid-filled organelle found in plant cells. It is filled with cell sap, a solution of sugars, salts and other substances. The vacuole helps maintain turgor pressure, keeping the cell firm and supporting the plant. It also stores nutrients and waste products. When a plant cell is placed in pure water, water enters by osmosis, the vacuole expands, and the cell becomes turgid. In a concentrated sugar solution, water leaves the vacuole, and the cell becomes plasmolysed. Animal cells do not have a permanent vacuole; they may have small temporary vacuoles. The presence of a permanent vacuole is a key feature that distinguishes plant cells from animal cells.

For example: In a wilted plant, the vacuoles have lost water, so the cells are no longer turgid and the plant droops.

What earns the marks

• The permanent vacuole is a large organelle found in plant cells.
• When water enters by osmosis, the vacuole expands and the cell becomes turgid.

Common mistakes and how to put them right

• Thinking animal cells have a permanent vacuole.

  Put it right: Animal cells may have small temporary vacuoles, but not a large permanent one.

• Confusing cell sap with cytoplasm.

  Put it right: Cell sap is the fluid inside the vacuole; cytoplasm is the jelly-like substance outside the vacuole.

• Stating that the vacuole provides energy.

  Put it right: The vacuole stores substances and maintains turgor; mitochondria release energy.

Exam tips

• When labelling a plant cell, write 'permanent vacuole' and indicate that it is filled with cell sap.
• In questions about osmosis, link the vacuole to changes in cell shape (turgid or plasmolysed).
• Use the term 'cell sap' accurately; do not call it 'water' alone, as it contains dissolved substances.