PLASMA MEMBRANE
Every animal cell is bounded by living, extremely, thin delicate membrane called as cell membrane. And in plant cells, this membrane occurs just below the cell wall. The cell membrane is the outer most layer of the cell that separates cytoplasm from the external environment. This is also known as "Plasma membrane" or "plasmalemma".
The term plasma membrane was first coined by "Nageli". This plasma membrane defines the shape and size of the cell, encloses the cytoplasm and protects it from the other external environment. This membrane serves as a boundary for the cytoplasm i.e, a fluid like content present in it. It is a biological membrane ranging from 6 to 8 nm and constitutes a layer of lipids and proteins. It acts as a protective barrier.
This membrane is a selectively permeable membrane as it controls the exit and entry of materials. This allows the transport of small molecules such as water, ions,oxygen, carbon dioxide, ethanol, glucose etc. It also maintains a constant internal environment called as homeostasis. Various processes occur here such as osmosis, diffusion, and the active transport which is carried out by special proteins called as "transport proteins". For bulk transport of large particles, it performs endocytosis and exocytosis. The permeability depends mainly on the electric charge and polarity of the molecule.
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