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Plasma Membrance Structure and Functions
Figure 1. Structural Components of a Plasma Membrane
A phospholipid molecule as seen in Figure 1. Composed of a hydrophilic (water loving) head and a hydrophilic (repelling water) tail.
Passive transport of one molecule down a concrentration gradient until equilibrum is met.
Examples of Passive Transport
-Passive transport is diffusion through a biological membrane that does not require work
Facilitated diffusion is how water, amino acids and many sugars cross a membrane. A pore or tunnel as seen in the picture to the left is specific for the substance it moves.
The opposite of passive transport is active transport. The movement of a substance across a biological membrane against the concentration gradient with the aid of energy. This helps keeps stable levels of ions such as K+ and Na+.
Cells in an isotonic solution (same solute concentration) are much better off than a cell that's in a hypotonic or hypertonic solution. The control of how much water is in a cell is called osmoregulation.
Large molecules such as proteins enter and exit the cell through processes called endo and exocytosis. The above figure shows three types of endocytosis: phagocytosis, pinocytosis, and receptor-mediated endocytosis.
