Mesophyll is the internal tissue of a leaf, located between the upper and lower epidermis (the outer layers of the leaf). It's the primary site of photosynthesis in plants. Think of it as the leaf's "food factory."
Structure and Function of Mesophyll
The mesophyll is primarily composed of two types of parenchyma cells:
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Palisade Parenchyma: This layer is typically found near the upper epidermis. It consists of elongated cells packed tightly together, maximizing light absorption for photosynthesis. These cells contain a large number of chloroplasts, the organelles responsible for photosynthesis.
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Spongy Parenchyma: Located beneath the palisade parenchyma, this layer has loosely arranged, spherical or ovoid cells with numerous air spaces between them. These air spaces facilitate the diffusion of carbon dioxide (CO2) and oxygen (O2) for photosynthesis and respiration.
The Role of Mesophyll in Photosynthesis
As mentioned earlier, the mesophyll plays a critical role in photosynthesis. The process begins when CO2 enters the leaf through tiny pores called stomata. From there, it diffuses through the air spaces of the spongy mesophyll and into the palisade mesophyll cells. Within the chloroplasts of these cells, CO2 is converted into sugars using energy from sunlight and water.
The efficiency of this process is partially determined by mesophyll conductance (gm), which represents the rate at which CO2 moves from the intercellular air spaces into the chloroplasts. This conductance is a significant factor in determining the overall rate of photosynthesis. Recent studies highlight the importance of understanding and improving mesophyll conductance for enhancing crop yields. For example, research has shown that mesophyll conductance has doubled in domesticated soybeans compared to their ancestors, leading to increased photosynthetic efficiency.
In summary: Mesophyll is the vital photosynthetic tissue within a leaf, acting as the crucial site where plants convert light energy into chemical energy. Its structure, including both palisade and spongy parenchyma, is optimized for efficient gas exchange and light capture necessary for photosynthesis.
References: The provided references all support the above description, emphasizing the location of mesophyll between the epidermal layers, its role in photosynthesis, and the existence of palisade and spongy mesophyll. Specific examples of research related to mesophyll conductance were also cited.
