Structure of a flowering plant leaf

Probably the most distinctive feature of plants is that they produce their own food. Leaves are the “food factories” of plants. Within leaves, energy from the sun combines carbon dioxide and water, turning them into glucose, which is the plants’ source of food. This production process is called photosynthesis. Different parts of the leaf are specialised for different tasks.

Each part is adapted to make sure that photosynthesis takes place successfully and efficiently. Let’s have a closer look! The surface of the leaf is covered in waxy, protective coating, which repels water. This coating is the cuticle, and its role is to reduce the amount of water lost from the plant’s surface. The cuticle is produced by the outermost tissue layer of the leaf.

This outermost tissue is transparent and consists of a layer of tightly packed cells. This is called the epidermis. The majority of cells in the epidermis can’t carry out photosynthesis because they don’t contain the cell parts necessary for it - the chloroplasts. The only cells in the epidermis that do contain chloroplasts, are the so-called guard cells. Guard cells surround small holes in the leaf surface and control when these holes are opened and closed.

In this way, guard cells control the movement of carbon dioxide, oxygen and water vapour in and out of the leaf through the openings. Between the epidermis on the upper side and lower side of the leaf, is the tissue that makes up most of the leaf. This tissue is the mesophyll. It is split into two layers. The top layer is the palisade mesophyll.

Here the cells are large, shaped like cylinders and packed closely together. The cells are full of chloroplasts and placed so that they get the maximum amount of sunlight. Because of this, the palisade mesophyll layer carries out most of the photosynthesis. The bottom layer of mesophyll is the spongy mesophyll. Here the cells are smaller, more rounded and have fewer chloroplasts.

The cells are loosely packed and there are many larger, air spaces between them. These air spaces lie close to the small openings in the leaf surface, and help to move gases in and out of the leaf. Most leaves of flowering plants have this basic structure on the inside. And even though the leaves of different plants might look very different, they have some things in common on the outside too! Leaves are typically attached to the stem by a short and thin stalk, called the petiole.

The largest and widest part of every leaf is the lamina. This surface is permeated by a network of transport vessels, called veins. Veins support the leaf and make sure that every cell is supplied with water, air and minerals. Leaves come in all shapes and sizes. From duckweed, a tiny plant with leaves so small they could fit through a needle hole; to the enormous leaves of the giant rhubarb plant which spread around three metres high and wide.

But leaves are much more similar to each other than they seem at first glance. And they are all specialists in food production!