Text 8.1 The Leaf

■ Essential targets:

By the end of this text you should be able to:

· describe the structure of a dicotyledonous leaf;

· distinguish between parenchyma, collenchyma, clerenchyma and sclerenchyma.

Pre-reading

■ Working in pairs, discuss the following questions with your partner:

1. What does leaf shape provide?

2. How are leafs arranged on many plants?

■ Read the given text and make your essential assignments:

The leaf is the main site of photosynthesis, the process by which green plants manufacture their own food. The lamina or blade of a leaf is flat and thin. Its shape provides a large surface area for absorption of light and carbon dioxide. The leaf is attached to a stem or branch by a leaf stalk or petiole. The stalk holds the leaf in a position such that its surface is exposed to the maximum amount of light. From the stalk, the main vein leads down the leaf with side veins branching out on either side. These veins connect the leaf to the rest of the plant, bringing the leaf some of the raw materials required for photosynthesis, and carrying products of photosynthesis away from it. This veins also provide mechanical support, maintaining the shape of the leaf. The stem and branches raise the leaves above the ground so they are exposed to the light. On many plants the leaves are arranged on branches in such a way that they do not shade one another.