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The leaf is a part of the plant that is charge of making food for the plant. This food making process is called photosynthesis.
Parts of the leaf
The leaf consists of the following parts:
Petiole - a thin stalk that connects the blad of the leaf to the plant's stem. These veins are called
Blade - a thin, flat part of the leaf that extends off the end of the petiole. It is green as it contains cholorophyll which is necessary in making the plant's food..
The blade contains veins which help bring in the water necessary for photosynthesis and to transport food out to all parts of the plant. The xylem is responsible for water transportation and the phloem for food.
The blade also has several layers. The top layer is covered with a waterproof coat called the cuticle. Both the upper and lower layer contain paired cells called guard cells. These guard cells manage the stomata, little openings in the leaf that allow for the taking in of carbon dioxide and the emission of oxygen during photosynthesis. Water vapor is also emitted in a process called transpiration.
In between the top and bottom layers of the blade are cells that are full of chlorophyll that is essential for the plant to make its food during photosynthesis.
Leaves come in a variety of shapes, sizes, color, and textures. Leaves can be grouped as simple with one blade or compound with many leaflets. The edges of leaves can be smooth, have jagged edges referred to as toothed or scalloped edges referred to as lobed edges. Leaves can also be divided into how their veins are arranged. The leaves of plants referred to as monocots have leaves that run parallel to each other off one central vein. Those that are referred to as dicots have leaves with veins that branch out two different ways.Pinnate have one main vein called the midrib, and smaller branching veins. Palmates have several large veins branching from the leaf base into the blade.
Some leaves have special features such as spines and bud scales to protect them. Some are climbing (tendrils). Others catch insects. Some store water. These are called succulents or store food such as bulb scales.
Leaves contain other substances besides chlorophyll that give the leaf color. These substances are called pigments and cause leaves to turn colors in autumn. These leaves are on deciduous trees and fall off and die. New ones grow back in the spring. Conifers or trees that bear cones can keep their needles for years and grow new ones as soon as they lose them.
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