Leaf cells resemble other cells in their basic components: a sturdy cell wall, a cell membrane immediately inside the cell wall, cytoplasm with various organelles, and a nucleus with nucleic acids that direct the life of the cell. But the structure of each leaf cells varies with its function in the leaf.
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A single layer of epidermal cells form a protective lining on the upper and lower surface of a leaf. The special structural feature of epidermal cells is a waxy cuticle on the cells' outer surface. Epidermal cells sometimes have little hairs called trichomes.
Two guard cells surround little pores that penetrate the epidermis of the leaf. Their unique structural feature is their ability to swell and shrink to regulate the size of the pores.
Mesophyll cells occur in the middle of the leaf. They have thinner cell walls containing mostly cellulose instead of tougher substance such as lignin. Two types exist: cylindrical palisade cells that lie in layers immediately beneath the epidermis and irregularly shaped cells that lie below the palisade cells in a more loosely packed tissue called spongy parenchyma. All these cells have organelles called chloroplasts where the cell makes food for the plant.
Xylem and Phloem
Xylem cells form a conduit for the transportation of water. Phloem cells form a conduit for the transportation of food-containing sap. Structurally, they have lost such cellular components as the nucleus. They have thicker cell walls. Xylem cells are dead at maturity.
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