Aloe leaf. Coloured scanning electron micrograph (SEM) of a section through an aloe leaf (Aloe sp.) showing stomata (holes) and cells inside the leaf. Aloe is a type of succulent cactus. Stomata are openings in a leaf's surface which help regulate gas exchange between the leaf's interior and the atmosphere. In the day they open to allow gas exchange during photosynthesis and at night they close to prevent water loss. They are opened and closed by two bordering guard cells (not seen). Below the leaf's outer layer are cells with chloroplasts (green). These contain the pigment chlorophyll which makes photosynthesis possible. Magnification: x450 at 6x7cm size.