Leaf Structure and Function

How is the structure of a leaf adapted to make photosynthesis more efficient?

Recall from Chapter 8 that photosynthesis uses carbon dioxide and water to produce sugars and oxygen. Leaves, therefore, must have a way of obtaining carbon dioxide and water as well as distributing end products. The structure of a leaf is optimized to absorb light and carry out photosynthesis.

Anatomy of a Leaf To collect sunlight, most leaves have a thin, flattened part called a blade. The flat shape of a leaf blade maximizes the amount of light it can absorb. The blade is attached to the stem by a thin stalk called a petiole (PET ee ohl). Like roots and stems, leaves have an outer covering of dermal tissue and inner regions of ground and vascular tissues, as shown in Figure 23–15.

▸ Dermal Tissue Leaves are covered on their top and bottom surfaces by epidermis. Leaf epidermis is made of a layer of tough, irregularly shaped cells with thick outer walls that resist tearing. The epidermis of nearly all leaves is also covered by a waxy cuticle. The cuticle is a waterproof barrier that protects tissues and limits the loss of water through evaporation.

▸ Vascular Tissue The vascular tissues of leaves are connected directly to the vascular tissues of stems, making them part of the plant's fluid transport system. Xylem and phloem tissues are bundled in leaf veins that run from the stem throughout the leaf.

▸ Ground Tissue The area between leaf veins is filled with a specialized ground tissue known as mesophyll (MES uh fil), where photosynthesis occurs. The sugars produced in mesophyll move to leaf veins, where they enter phloem sieve tubes for transport to the rest of the plant.