about the definition of living

Living may refer to:

*****Life, a condition that distinguishes organisms from inorganic objects and dead organisms
*****Personal life, the course of an individual human's life
*****Living wage, refers to the minimum hourly wage necessary for a person to achieve some specific standard of living


The cell membrane (also called the plasma membrane, plasmalemma or "phospholipid bilayer") is a semipermeable lipid bilayer found in all cells.[1] It contains a wide variety of biological molecules, primarily proteins and lipids, which are involved in a vast array of cellular processes, and also serves as the attachment point for both the intracellular cytoskeleton and, if present, the cell wall.

The cell membrane surrounds the cytoplasm of a cell and, in animal cells, physically separates the intracellular components from the extracellular environment, thereby serving a function similar to that of skin. In fungi, bacteria, and plants an additional cell wall forms the outermost boundary, however, the cell wall plays mostly a mechanical support role rather than a role as a selective boundary. The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, and in attaching to the extracellular matrix to help group cells together in the formation of tissues.

The barrier is selectively permeable and able to regulate what enters and exits the cell, thus facilitating the transport of materials needed for survival. The movement of substances across the membrane can be either passive, occurring without the input of cellular energy, or active, requiring the cell to expend energy in moving it. The membrane also maintains the cell potential.

Specific proteins embedded in the cell membrane can act as molecular signals which allow cells to communicate with each other. Protein receptors are found ubiquitously and function to receive signals from both the environment and other cells. These signals are transduced into a form which the cell can use to directly effect a response. Other proteins on the surface of the cell membrane serve as "markers" which identify a cell to other cells. The interaction of these markers with their respective receptors forms the basis of cell-cell interaction in the immune system.


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