What are the stomata of leaves and how big are they?

There are many tiny pores on the epidermis of leaves, which are called stomata. Stomata are surrounded by two half-moon guard cells, and the cell walls of the guard cells regulate the opening and closing of stomata.

Generally expressed in microns (one micron is equal to one thousandth of a millimeter), a pore is measured to be about 3 ~ 12 microns wide and about 10 ~ 40 microns long.