The majority of plants are capable of making their own food, an ability which animals and humans do not have; leaves are vital to this process. Food is produced in a plant by a simple process called photosynthesis, the act of collecting energy from light and converting it to chemical energy. This energy is then stored in the bonds of sugar; sugar helps the plant to live and grow.
How a Leaf Produces the Plant's Food
The leaf captures the energy from light with the help of chlorophyll, a green pigment in the plant; chlorophyll looks green to the human eye because it absorbs the red and blue light wavelengths and reflects the green. As the green light is not absorbed by the plant and the red and blue light is, it is actually the red and blue light which is used in photosynthesis, even though the leaf appears green.
The process of photosynthesis involves the addition of water and carbon dioxide but it is the captured light which is important in converting the energy to chemical energy. The chemical energy is stored within the leaf in the sugars; the bonding of the chemicals to the sugars results in a similar molecule to the building blocks of human DNA. Photosynthesis takes place in the chloroplasts of the leaf.
How a Leaf Breathes
A plant is a living thing and as such needs to breathe; a leaf has minute slits like a mouth which are called stomata (single stoma), a name derived from the Greek word for mouths. The stomata can be found on the underside of a leaf and allow water vapor and gases to pass in and out of the leaf.
The rate at which a plant loses water is controlled by the stomata, a process called transpiration. Air enters the plant through the stomata, thus allowing it to breathe; the air contains carbon dioxide which is used in the photosynthesis process. Oxygen, as a by-product of photosynthesis, is dispersed from the leaf through the stomata.
How Desert Plants Differ
Certain species of plants, in particular desert plants, open their stomata at night, not during the day. These plants belong to a group known as the CAM plants (Crassulacean acid metabolism, after the plant family Crassulaceae); water evaporates more slowly in the cooler desert night than throughout a hot, dry desert day when a plant needs to conserve its water. The following day, carbon dioxide is released when the stomata are once again closed. Plants which do this include cacti and pineapple.
The Variety of Leaf Types
Leaves come in numerous types which are listed in an introduction to plant anatomy. Some leaves possess special features; cacti leaves for example need to conserve water from a hot, dry climate and have narrow spines to do this. Plants in strong sunlight and situated in high mountains have furry leaves to protect them.
Water plants have thick, waxy leaves, which water easily runs off, and prevents the plant from being overcome by water, such as those in rain forests; and finally, deciduous trees lose their leaves in Fall whereas evergreens do not. A leaf is without doubt an important part of a plant.
References:
Taylor, Barbara 1997 Inside Guides: Incredible Plants UK: Dorling Kindersley Ltd
For Further Reading:An Introduction to Flowers
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