For ten points, name these cells which control the opening and closing of a plant's stomata.
Their inner walls are thicker than their outer walls. When they are filled with water they become turgid, their outer wall balloons outward, drawing the inner wall with it. Their main function is to control excessive water loss, closing on hot, dry or windy days and opening when conditions are more favorable for gas exchange. For ten points, name these cells which control the opening and closing of a plant's stomata.
Their inner walls are thicker than their outer walls. When they are filled with water they become turgid, their outer wall balloons outward, drawing the inner wall with it.
{guard} cells