Welcome back to my channel, in today’s video we are going to take a look at the stomata
found on the surface of plant leaves under the microscope.
The first type of leaf we are looking at, is that of the pea plant, as an example of
what stomata look like in dicotyledon plants.
Stomata are mostly found on the bottom surface of the leaf, so this sample we are looking
at is a peel of the outer layer of epidermal cells from the bottom surface of the leaf.
Here on the lowest magnification you can see a whole bunch of small oval shaped structures
on the surface of the leaf, these are where the stomata are, as you can see there are
a lot of them.
Now if we go to a higher magnification you can see them more clearly.
What we are seeing mostly are the two guard cells that surround the stoma, the stoma is
the pore found between these two guard cells.
These two guard cells are what we call kidney shaped.
We can also see that the stoma, or pore between these two guard cells is open.
In addition to the specialised guard cells and the stoma, we can see the layer of irregular
epidermal cells the cover the surface of the leaf.
These guard cells function in controlling whether the stomatal pores are open or closed.
When the guard cells are flaccid, the stomatal pore is closed and CO2 can not enter into
the leaf.
When the guard cells are turgid, the stomatal pore is open and allows CO2 to enter and diffuse
into the cells to be used in the process of photosynthesis.
How does this process work?
Guard cells sense and respond to a variety of external factors to the plant, including
temperature and relative humidity.
But the main external factor these guard cells react to is light, both the intensity and
quality of light.
In response to external factors that are in favour of stomatal opening, such as good light
levels during daytime, a series of reactions occur within the cell that cause potassium
molecules to be taken into the guard cell.
This increases the potassium solute concentration in relation to the water concentration inside
the guard cells, decreasing the osmotic potential, and as a result water also moves into the
guard cells.
As this water moves into the guard cells, the turgor pressure within the cell increases
as well as the cell volume, which causes the cells to swell and the stomatal pore to open.
When the conditions are not favourable for the stoma to be open, such as low light intensity
during the night or low water levels in the soil, another series of reactions occur that
stop more potassium entering the cell and the amount of potassium drops, as does the
water potential and the cells become flaccid, which causes the stomatal pole to be closed.
In dicotyledon’s such as this pea plant, we have seen that the guard cells are kidney
shaped.
But what about the guard cells in monocotyledon plants?
If we take a look at this non-grass monocotyledon, again we can see a whole bunch of oval shaped
structures, which are again the guard cells that surround the stomatal opening.
Unlike in the dicotyledon leaf surface, the epidermal cells in monocots are more regular
and rectangular in shape.
If we go up to a higher magnification, we can see, that although they are slightly different
to those seen in the peas plant, the guard cells still have a kidney shape.
These kidney shaped guard cells surrounding the stomatal pores are the typical shape found
in dicotyledon plants and many monocots, but some monocots, especially in the grasses have
a different shape.
If we now look at the surface of a blade of grass, we can see here the guard cells surrounding
the pore are more elongated, with bulbous ends, giving a dumbbell like appearance.
The stomatal pore itself is more like a long slit between these elongated guard cells.
In these plants, the guard cells have the help of subsidiary cells to help control the
opening of the stomatal pores, these subsidiary cells flank the guard cells and are actually
differentiated epidermal cells.
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