data collected from my lab indicates that the ranking of leaves from greatest
to lowest stomatal density is: baby red romaine (82.6 stomata/mm squares),
spinach (53.3 stomata/ mm squared), and then red leaf lettuce (45.3 stomata/ mm
Stomata are tiny holes within the epidermis that are either open
or closed due to specialized cells that surround them called guard cells. When
the stomata are open, the guard cells are full of water, which causes them to
swell and bend away from each other. When the stomata are open, they allow for
carbon dioxide to enter to be used in photosynthesis and releases oxygen and
water. When the guard cells lose water, it causes for the stomata to close.
The stomatal density also controls the rate of gas exchange within
a plant. A greater stomatal density allows for a greater carbon dioxide intake
and a greater release of oxygen and water by the plant.
The majority of the water that is lost in a plant is through the
stomata (approximately 95%). This process is called transpiration.
Transpiration is the loss of water from leaves mainly through the
stomata. The stomatal density has an effect on the amount of water lost. All of
the leaves that my group observed are found in the South Western region of the
United States, which is generally, hot and dry. This is why the stomatal
density of all the leaves is relatively low when compared to leaves that grow
in areas that have access to a large amount of water. The more stomata a leaf
has, the more carbon dioxide it is able to absorb which allows for
photosynthesis to occur at a faster rate. This faster rate of photosynthesis
results in a greater loss of water, which is an issue for plants that grow in
areas with a lack of water as the leaves will be unable to survive. Therefore,
leaves that grow in dry areas will have less stomata to reduce the amount of
water loss and slow down the rate of transpiration.
Plants that have access to a lot of water will be able to perform
photosynthesis much quicker. This means that the leaf must absorb more carbon
dioxide to keep up with the fast process of photosynthesis. Since the leaf
needs more carbon dioxide, it will need more stomata in order to absorb more
carbon dioxide. Water will cause the guard cells to swell and bend away from
each other therefore opening the stomata. When a stoma is open it allows for
water to escape from the plant. Since there are more stomata, the leaf is able to
absorb more carbon dioxide, release more water through the stomata and the rate
of transpiration will increase. However this loss of water for these plants are
not an issue as they have access to a large amount of water.