Stomata

What are Stomata?

Stomata are tiny pores on the surfaces of leaves that permit the exchange of gases between the atmosphere and the inside of the leaf. Each stoma is formed by two specialized epidermal cells, called guard cells. These cells change shape to open and close the pore on a time scale of minutes. In most plants, stomata are between 30 and 60 micrometers long and occur at densities between 50 and 200 per square mm.

Click on the following link to see MOVIES OF GUARD CELLS.

What do Stomata do?

Stomata must open to admit CO2 into the leaf for photosynthesis, but when they open, they allow water vapor to diffuse out of the leaf. Thus, stomata must open enough to support photosynthesis, but they must at the same time prevent excessive water loss. This dilemma has been formalized as a constrained optimization problem.

How do Stomata do it?

Guard cells have complex sensory and signal transduction machinery that allows them to respond to a variety of factor such as light, CO2, and water stress. Guard cells change size and shape by altering their solute concentration so that water flows in or out by osmosis.

* Here is a stomatal model created by Dr. Tom Buckley that describes this system.