Does Photosynthesis Mainly Take Place in Mesophyll?
Although all green parts of a plant photosynthesize, most photosynthesis occurs in leaves. In particular, the mesophyll cells in leaves carry out most of a plant's photosynthesis.
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Mesophyll
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The word "mesophyll" comes from Greek, and means "middle of the leaf." The mesophyll region consists of all the cells in a plant's leaf between the upper and lower epidermis.
Epidermis
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The outside surface of a leaf is known as the epidermis. Many plants have a waxy covering over the epidermis, called a cuticle, which keeps in moisture. The epidermal cells are transparent, allowing sunlight to pass through to the mesophyll.
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Palisade Layer
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The mesophyll cells directly below the upper epidermis line up to form a tightly-packed row known as the palisade layer. The position of the palisade cells, directly under the transparent upper epidermis, gives them a lot of sunlight. Their main job is to use the light for photosynthesis.
Spongy Mesophyll
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Below the palisade cells lie other mesophyll cells that are less tightly packed. This region, known as the spongy mesophyll, has prominent gaps between cells and stretches from the palisade layer at the top to the bottom epidermis.
Gas Exchange
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The bottom layer of spongy mesophyll cells come up against the bottom epidermis, where most plants have stomata. Stomata are tiny holes the plant can open and close. The main job of the spongy mesophyll take in carbon dioxide through the stomata and hold it in the gaps between cells until the palisade cells need it for photosynthesis.
Adaptations
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Although palisade mesophyll cells are especially adapted for photosynthesis, all green parts of a plant perform some photosynthesis. However, there are special cases where green stems perform most of the photosynthesis. This occurs, for example, in drought-adapted plants that have little or no leaf surface, such as palo verde trees and cacti.
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References
- Photo Credit leaf image by Aidairi from Fotolia.com
