Leaf pores. Coloured scanning electron micrograph SEM of stomata holes on the surface of a leaf. These structures perform a similar function to the pores in human skin, allowing water to pass out of the leaf. They also act like lungs, allowing carbon dioxide and oxygen found in air to pass into and out of the leaf. The stomata can be opened and closed depending on the conditions and the need to retain water. Water and carbon dioxide are combined in photosynthesis to produce sugars transported around the plant in veins, one seen, brown and oxygen released via the stoma. This is a coriander plant leaf Coriandrum sativum.