What is the use of these small pores on the leaf to a plant? What do they do and how do they help the plant to survive?
The stoma(plural)(stomata=singular) are small microscopic pores which are usually found on the underside of the leaf. In plants in which the leaf is floating on water the stoma are found on the upper surface of the leaf.
The are called microscopic because these pores can only be seen through a microscope and not by the naked eye. The pore is formed by two specialised cells called guard cells and these are responsible for the size of the stoma.
The electron micrograph of a stomata.
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The stoma are used for a certain purpose. As you know for the plant to successfully photosynthesise there are a number of requirements. Carbon dioxide and water are some of them.
Now we do know that water travels up the xylem and reaches the leaf. In the leaf the water forms a moisture layer around the spongy and palisade cells.
Diagram showing the cross section of a leaf.
After the water is used for photosynthesis it is released into the atmosphere through the stoma. Carbon dioxide which is another requirement also diffuses through the stoma to help in photosynthesis. Oxygen an end product also leaves the leaf for the atmosphere through this opening.
If the guard cells are turgid then the opening of the stoma are wide. When the guard cells lose turgidity then the stoma close.
The stoma are also sensitive to light and open wider in the presence of light. (More light = more photosynthesis). More water in the soil gives the plant more water making the guard cells more turgid. When the guard cells are turgid the stomata are widely open. So that means more water in the soil makes the stoma open wider. Light also make the stomatal opening open wider. So in the day time the stoma are usually open.
Cross section of a stomatal opening as seen through a light microscope.
Image via Wikipedia
If there are no stoma then the plant would not be able to photosynthesise. There would be no transpiration pull so no transpiration. Eventually the plant would die.
So the stoma help the plant to do a number of the many functions a plant carries out. To read more about pollination in plants click here.
Hopefully this article has helped you in some way. If you have suggestions or questions please comment below.