What are small openings on the of leaves?
They are from animals(like flies and caterpillars) who eat leaves as a food.
"Stoma" comes from Greek, meaning: mouth. It usually indicates openings, sometimes other than mouths. A stoma is a surgically created opening on the abdomen which allows stool or urine to exit the body. Stoma is also the name for small openings on the underside of leaves that facilitate transpiration.
The stomata are openings in plant leaves through which gasses pass in and out. During the day carbon dioxide passes from the air through the stomata to the leaves and oxygen, produced by the leaf, passes back out through them. At night plants yield up small amounts of carbon dioxide through the stomata.