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Cell biology
Vacuole
The vacuole can occupy between
20 and 90% of a cell’s volume.
Vacuole
It contains mostly water with
dissolved inorganic and organic
substances.
The vacuole is surrounded by a
semipermeable membrane called
the tonoplast.
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Cell biology
Vacuole
In meristematic cells or
specialized cells like the
guard cells in a stomate,
there are numerous small
vacuoles (red stars) in
the cell.
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Vacuole
In a mature parenchyma cell, the vacuole
occupies most of the cell and pushes the
cytoplasm and organelles to the periphery
of the cell. A major function of the vacuole
is maintaining cellular turgor by regulating
water movement within the cell.
Vacuole
Chloroplasts
Electron micrograph of a
parenchyma cell.
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Cell biology
Vacuole
The vacuole regulates the turgor
pressure in a cell by actively
moving ions (especially potassium)
across the tonoplast membrane.
Turgor is created by moving water
by osmosis into the vacuole
exerting more pressure against
the cell wall.
Guard cells
In the guard cells of a stomate,
the stomatal aperture is open
when the cell has reduced turgor
pressure and is closed when cells
are fully turgid.
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Cell biology
Vacuole
The vacuole may store reserve materials such as proteins, sugars and organic
acids or they can accumulate various compounds like tannins and anthocyanins.
The vacuole can also be involved with cellular waste management, enzymatically
digesting or storing unwanted substances.
Anthocyanin
Tannins
Vinca (Catharanthus) petal
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Pine (Pinus) leaf
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Vacuole
In specialize storage cells like those
in some seeds, protein is stored in
membrane-bound protein bodies
that form from the vacuole.
Protein bodies in legume cotyledon cells.
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Vacuole
Various types of crystals can
also form within the vacuole.
Crystals
Raphide crystals
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