Plant Biology Watch
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What is the main job o a leaf palisade cell and how does its structure help carry out its job?
Palisade cells themselves are a type of chlorenchyma cell [cells containing chloroplasts] and they are packed full of a particularly high number of chloroplasts. These chloroplasts are distributed around the perimiter of the cell's vacuole, meaning they are very close to the cell membrane granting them access to the greatest light intensity possible. They are cylindrical/rectangular in shape and arranged in vertical columns of 1-5ish cells (like bricks stacked ontop of eachother end to end rather than flat). They usually form closest to the epidermis closest to or facing the strongest light source, this is often the upper epidermis but in some cases it can form closest to the lower dermis. In most monocot leaves there is rarely much differentiation into spongy and palisade layers or between the upper and lower dermis, forming a more uniform mesophyll surrounding the vascular tissue.
Here is a microscopy image of leaf structure, the blueish rectangular cells near the surface are palisade cells.
Palisade cells form "Palisade parenchyma tissue". Parenchyma just means functional mass, i.e part of the organ that does something.
The palisade parenchyma is part of the mesophyll layer. "Mesophyll" is the bulk of the functional tissue between the dermis layers.
From outside to in layers go:
Cuticle(skin like) - -> Epidermis (layer just under cuticle. There are upper and lower dermis layers) - - > mesophyll (the tissues forming the interior of the leaf) layers of the leaf.
Their primary function is the conversion of light energy into chemical energy, facilitated by their large number of chloroplasts and their large vacuole which forces distribution of those chloroplasts to be as close as possible to the membrane of the cell .The cellular distribution within the mesophyll layer puts them closest to the cuticle, granting access to the greatest light intensity. Their cylindrical shape and vertical stacking puts them at 90 degrees to the cuticle minimising the number of cell walls light must penetrate to reach choloroplasts, thereby maximising the amount of light energy available as the walls absorb/reflect less. Cell walls are also particularly thin to further reduce wasted energy. Their structure also allows for extracellular space and increased surface area to volume ratio which aids gaseous exchange within the mesophyll
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