Make sure that the entire picture is colored and that the color matches the If the guard cells are full of water, they swell up and bend away from each other which opens the stoma. Changes within water pressure cause the stoma (singular of stomata) to open or close. Specialized cells, called guard cells (C) surround the stomata and are shaped like two cupped hands. The leaf also has tiny holes within the epidermis called stomata. Mesophyll cells (both palisade and spongy) are packed with chloroplasts, and this is where photosynthesis actually occurs.Įpidermis also lines the lower area of the leaf (as does the cuticle). The air spaces between the spongy cells allow for gas exchange. Palisade cells are more column-like, and lie just under the epidermis, the spongy cells are more loosely packed and lie between the palisade layer and the lower epidermis. Mesophyll can then be divided into two layers, the palisade layer (D) and the spongy layer (F). The word mesophyll is greek and means 'middle' (meso) 'leaf' (phyllon). Within the leaf, there is a layer of cells called the mesophyll. Recall that xylem transports water and phloem transports sugar (food). In the picture, xylem is the upper layer of cells (G) and is shaded a little lighter than the lower layer of cells - phloem (H). The outer layer of the vein is made of cells called bundle sheath cells (E), and they create a circle around the xylem and the phloem. Veins are actually extensions that run from to tips of the roots all the way up to the edges of the leaves. The vascular tissue, xylem and phloem are found within the veins of the leaf. Directly underneath the cuticle is a layer of cells called the epidermis (B). (Plants that leave entirely within water do not have a cuticle). The outer surface of the leaf has a thin waxy covering called the cuticle (A), this layer's primary function is to prevent water loss within the leaf. Leaves with a single undivided blade are called simple, those with two or more leaflets are called compound leaves.

Sometimes leaves are divided into two or more sections called leaflets.

It consists of a flattened portion, called the blade, that is attached to the plant by a structure called the petiole. The leaf is the primary photosynthetic organ of the plant.

Plant structure and function answers