What is a leaf?

Leaves are usually flat, green structures that grow from plant stems. Although they come in many shapes and sizes, almost all of them capture sunlight and produce food for the plant. Leaves get their green color from a pigment called chlorophyll that uses sunlight to produce food from the plant in a process called photosynthesis.

Stomata ❯ Tiny pores on the underside of the leaf, called stomata, open during the day to take in carbon dioxide but close at night to avoid losing too much water.

Petiole ❯ This is the stiff stalk connecting the leaf to the plant stem. In some plants, these stalks can help leaves move and follow the sun in order to absorb more light.

Small netted veins ❯ Networks of tiny veins connect the green tissues of the leaf to the main vein inside the midrib and the stem beyond.

Blade ❯ The flat part of the leaf is called the leaf blade. It is the green tissue that absorbs sunlight to make the sugar the plant needs to grow.

Midrib ❯ Running along the center of the leaf, this thickened area contains the central vein. It also provides support to the leaf to prevent it from bending and breaking.

Vein ❯ Plant veins have two types of tubes running through them. One type, called xylem, carries water from the roots to the shoots. The other type, known as phloem, transports sugars around the plant. Photosynthesis

Plants make their own food in a process called photosynthesis. Their leaves contain a lightharvesting pigment called chlorophyll. This green chemical uses the sun’s energy to convert carbon dioxide from the air and water from the soil into food (in the form of sugars) and oxygen.

Carbon dioxide enters the leaf.

Sugar is produced in green leaf tissues.

Water and minerals are absorbed through the roots and transported up the stem. Sunlight provides the energy needed for photosynthesis.

Oxygen is released as a by-product.

Fall leaves

As fall approaches, the green pigment chlorophyll is replaced at a slower rate than it is used up. The reduced chlorophyll levels mean other leaf pigments, including orange-yellow ones, become more obvious. At the same time, plants start producing red-purple pigments. These changes result in the beautiful fall displays of leaf colors.