what is tha function of leaves?
Answers
Answer:
The main function of a leaf is to produce food for the plant by photosynthesis. Chlorophyll, the substance that gives plants their characteristic green colour, absorbs light energy.
Explanation:
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Answer: A leaf is an above-ground plant organ and it is green. Its main functions are photosynthesis and gas exchange. A leaf is often flat, so it absorbs the most light, and thin, so that the sunlight can get to the chloroplasts in the cells. Most leaves have stomata, which open and close. They regulate carbon dioxide, oxygen, and water vapour exchange with the atmosphere.
Plants with leaves all year round are evergreens, and those that shed their leaves are deciduous. Deciduous trees and shrubs generally lose their leaves in autumn. Before this happens, the leaves change colour. The leaves will grow back in spring. Leaves are normally green in color, which comes from chlorophyll found in the chloroplasts. Plants that lack chlorophyll cannot photosynthesize.
Leaves come in many shapes and sizes. The biggest undivided leaf is that of a giant edible arum. This lives in marshy parts of the tropical rain forest of Borneo. One of its leaves can be ten feet across and have a surface area of over 30 square feet (~2.8 sq. metres).[1]
However, leaves are always thin so carbon dioxide can diffuse quickly to all cells.
Explanation:Anatomy
A leaf is a plant organ and is made up of a collection of tissues in a regular organisation. The major tissue systems present are:
The epidermis that covers the upper and lower surfaces
The mesophyll (also called chlorenchyma) inside the leaf that is rich in chloroplasts
The arrangement of veins (the vascular tissue)
Epidermis
The epidermis is the outer layer of cells covering the leaf. It forms the boundary separating the plant's inner cells from the external environment.
The epidermis is covered with pores called stomata. Each pore is surrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lack chloroplasts. Opening and closing of the stoma complex regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. This allows photosynthesis, without letting the leaf dry out.
Mesophyll
Most of the interior of the leaf between the upper and lower layers of epidermis is a tissue called the mesophyll (Greek for "middle leaf"). This assimilation tissue is the main place photosynthesis takes place in the plant. The products of photosynthesis are sugars, which can be turned into other products in plant cells.
In ferns and most flowering plants, the mesophyll is divided into two layers:
An upper palisade layer of tightly packed, vertical cells, one to two cells thick. Its cells contain many chloroplasts. The chloroplasts move by a process called "cyclosis". The slight separation of the cells provides maximum absorption of carbon dioxide. Sun leaves have a multi-layered palisade layer, while shade leaves closer to the soil are single-layered.
Beneath the palisade layer is the spongy layer. The cells of the spongy layer are more rounded and not so tightly packed. There are large air spaces between the cells. These cells contain fewer chloroplasts than those of the palisade layer. The pores or stomata of the epidermis open into chambers, which are connected to the air spaces between the spongy layer cells.
Plants with leaves all year round are evergreens, and those that shed their leaves are deciduous. Deciduous trees and shrubs generally lose their leaves in autumn. Before this happens, the leaves change colour. The leaves will grow back in spring.
Veins
Branching veins on underside of taro leaf
The 'veins' are a dense network of xylem, which supply water for photosynthesis, and phloem, which remove the sugars produced by photosynthesis. The pattern of the veins is called 'venation'.
In angiosperms the pattern of venation differs in the two main groups. Venation is usually is parallel in monocotyledons, but is an interconnecting network in broad-leaved plants (dicotyledons).
Waxy Cuticle
The waxy cuticle is the waterproof, transparent outer surface of the leaf. It is waterproof to reduce water loss (transpiration) and transparent to allow light to enter the palisade cell.
Shape
What leaves look like on the plant varies greatly. Closely related plants have the same kind of leaves because they have all descended from a common ancestor. The terms for describing leaf shape and pattern is shown, in illustrated form, at Wikibooks.
Basic types
Leaves of the White Spruce (Picea glauca) are needle-shaped and their arrangement is spiral
Lycophytes have microphyll leaves.[2]
Ferns have fronds
Conifer leaves are typically needle-, awl-, or scale-shaped
Angiosperm (flowering plant) leaves: the standard form includes stipules, a petiole, and a lamina
Sheath leaves (type found in most grasses)
Other specialized leaves (such as those of Nepenthes)
Arrangement on the stem
Different terms are usually used to describe leaf placement (phyllotaxis):
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