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Cell types
Stomate
A stomate is a group of cells in
the epidermis made up of guard
cells and subsidiary cells.
Stomata are designed to allow
gas exchange.
Stomata are most frequently
found on the bottom (abaxial)
side of leaves, but may occur on
the top (adaxial) of leaves, stems
and even fruit.
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Cell types
Stomate
A stomatal complex consists of:
Subsidiary
cells
Guard cells
and
Subsidiary cells.
Guard
cells
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Cell types
Stomate
Guard cells are a pair of kidney shaped cells that form the opening of
the stomate.
When the guard cells are turgid (full
of water), they are open and allow gas
to enter the stomate.
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However, this also exposes the leaf
to potential water loss.
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When the guard cells are flaccid (less
water), they are closed to prevent air
exchange and water loss.
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Cell types
Stomate
Subsidiary cells - These are cells
bordering guard cells of the stomate.
They do not directly participate in
the opening and closing of the
stomate, but may aid it in their
functioning.
These cells vary in their arrangement
and pattern depending on the plant
species.
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*
*
*
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Cell types
Stomate
When the plant is turgid (full of water)
the guard cells are swollen and the
stomate is open. This allows carbon
dioxide to enter the leaf for
photosynthesis, but it also allows water
to leave the opening. Water leaving the
leaf is called transpiration.
During times of water stress, the guard
cells lose water and shrink. This closes
the stomate. Most stomata are also
closed at night, since most plants do not
need to fix carbon dioxide in the dark
and the plant does not need to lose
water needlessly.
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Closed stomate
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Open stomate
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Cell types
Stomate
In side view, the stomatal cavity is evident.
The stomatal cavity helps with gas exchange across the leaf.
Epidermis (cuticle layer)
Palisade mesophyll
Spongy mesophyll
Stomatal cavity
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Stomates
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Cell types
Stomate
This is a stomatal cavity in
pine. This is an example of
a sunken stomatal cavity.
Guard cells are not directly
on the epidermal surface.
This arrangement is more
efficient at preventing
water loss.
Guard
cell
Epidermis
Stomatal cavity
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Cell types
Stomate
A photomicrograph and electron micrograph of the guard cells.
Guard cells
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Guard cells
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Cell types
Stomate
Inside leaf
(stomatal chamber)
Cell wall
An electron micrograph of
the guard cells reveals the
large nucleus, relatively
thick cell walls, numerous
vacuoles and chloroplasts.
Nucleus
Vacuole
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Ledge
Chloroplast
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Cell types
Stomate
Surface view of a typical stomate by scanning electron microscopy.
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Cell types
Stomate
Electron
micrograph
of
stomate in dogwood shows a
wonderful surface pattern
over subsidiary cells made by
strands of wax.
Wax on the epidermal cells
helps
to
reduce
water
evaporation from the surface.
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