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Plasma Membrane or Cell Membrane
• Cell membrane is also called the plasmamembrane.
• It can be observed only through an electron microscope.
• Plasma membrane is the outermost covering of the cell that separates the contents of the cell from its external environment.
• The plasma membrane is flexible and is made up of organic molecules called lipids and proteins.
• The flexibility of the cell membrane also enables the cell to engulf in food and other material from its external environment. Such processes are known as endocytosis (endo → internal; cyto → of a cell). Amoeba acquires its food through such processes.
• Plasma membrane is a selectively permeable membrane [The plasma membrane is porous and allows the movement of substances or materials both inward andoutward].
• Some substances like carbon dioxide or oxygen can move across the cell membrane by a process called diffusion [spontaneous movement of a substance from a region of high concentration (hypertonic solution) to a region where its concentration is low (hypotonic solution)].
• Thus, diffusion plays an important role in gaseous exchange between the cells as well as the cell and its external environment.