LEAVES are an important components of plants. The other components are Stems, Roots, Flowers, Fruits and related organs. Most of the leaves are green in color and other colors occurrence are depends on plants variety or climate. As I was told by the university lecturer during my undergraduate, leaves provide trees with all their food because they turn sunlight into food energy. Chlorophyll makes this energy transformation possible. Leaves also make the oxygen in the air that we breathe everi seconds. This process are defined as Photosinthesis activity for million of years. Actually the Chlorophyll is a pigment found in the cells of leaves which is formed only in the presence of light and is the substance that colors plants green. Chorophyll is contained in chloroplasts and has the property of capturing light energy.
The process of Photosynthesis (the process by which plants make sugar from sunlight, water, and carbon dioxide):
Sunlight shines through the top of the leaf and reaches the next layer of cells. The light energy is trapped by the chlorophyll in the chloroplasts. In the chloroplasts, a process that uses water changes the light energy into a kind of chemical energy. This chemical energy is stored in the chloroplasts. The chloroplasts use the chemical energy to make food. Air enters the leaf through the stomata and moves into tiny spaces around the food-making cells in the leaf. Carbon dioxide from the air passes through the cell walls and membranes of the cells. Carbon dioxide enters the chloroplasts where the previously stored chemical energy converts the carbon dioxide into sugar. Tubes in the plant carry sugar from the leaf cells to other parts of the plant, such as roots, stems, and fruits. Cells in these parts of the tree store some of the sugar.
There are three main parts to a leaf:
a. The base which is the point at which the leaf is joined to the stem.
b. The stalk or petiole is the thin section joining the base to the lamina - it is generally cylindrical or semicircular in form.
c. The lamina or leaf blade is the wide part of the leaf .
Leaves can be of many different shapes:
Primarily, leaves are divided into simple - a single leaf blade with a bud at the base of the leafstem; or compound - a leaf with more than one blade. All blades are attached to a single leafstem. Where the leafstem attaches to the twig there is a bud.
Leaves may be arranged on the stem either in an alternate arrangement - leaves that are staggered or not placed directly across from each other on the twig; or in an oppositearrangement - 2 or 3 leaves that are directly across from each other on the same twig. The margin (the edge of a leaf) may be entire, singly-toothed, doubly-toothed, or lobed. Compound leaves may be palmate - having the leaflets arranged round a single point like fingers on the palm of a hand; or pinnate - when the leaves are joined on the two sides of the stalk, like the vanes of a feather.
The form of leaves is related with all their functions and their environment. In addition to photosynthesis, the leaf also carries out all the other exchanges with the atmosphere. It is through the leaf that the plant "breathes" (absorbs oxygen and gives off carbon dioxide plus energy) and transpires. Epidermic tissues in the leaf contain stomata - microscopic openings like valves which regulate opening or closing, permitting or preventing transpiration, through which the plant loses the major part of the water it absorbs so as to allow further absorption by the roots. In most plants the stomata are located on the underside of the leaves. Their function is regulated so that plants living in dry climates have a substantially smaller number of them than those in humid climates, where they are numerous and prominent. Where humidity is low the stomata may actually be recessed or partly protected by soft hairs which can prevent excessive transpiration.
(11 Febuary 2013)