This week in AP Bio we learned about the gatekeeper of the cell. This guardian of the cell is called the plasma membrane. The plasma membrane is made of a phospho-lipid bi-layer and proteins. The phospho head of the bi-layer is hydrophillic, while the lipid tail is hydrophobic this characteristic of is called amphipathic. The along with proteins embedded in membrane allows the cell to be selectively permeable. The function of the plasma membrane is to maintain homeostasis by controlling what goes in and out of the cell.
There is two different ways the plasma membrane diffuses what goes in and out of the cell. One is passive transport that requires no energy; there is two types of passive transport diffusion and facilitated diffusion. Diffusion is when molecules move from a high concentration gradient to a low concentration gradient. Osmosis is also diffusion, but it is when water diffuses across the plasma membrane. Facilitated Diffusion is when molecules move from an are of high concentration to an area of low transportation using a transport protein. The other type of transport that the plasma membrane uses is active transport, and it does require energy. The molecules are moving from an area of low concentration to high concentration, and the cell uses energy from the mitochondria called ATP.
When cells require to move large particles into or out of the cells they use endocytosis ans exocytosis. Endocytosis is when when the membrane is taking the particles into the cell by vesicles created by the membrane. Once the particles are taken to their destination the membrane is reabsorbed by the cell. There are three types of endocytosis. Phagocytosis although it is also called cell eating; it is when the vacuole or vesicle the material is contained in is sent to the lysosomes to be digestive. In pinocytosis, when the plasma membrane engulfs the materials is also takes in the extracellular fluid this is very important in red blood cells. The third type of endocytosis is receptor-mediator endocytosis it is when the cell binds itself to specific particles. Exocytosis is used when the cell is moving molecules out of the cell. The large particle exiting the cell is enveloped by a vesicle that is fused with the membrane once it's materials exit.
Each of our cells have a surrounding plasma membrane, even prokaryote cells have one. Is is very crucial to all organisms in maintaining homeostasis.
You need to proof-read your blog before posting. I know we didn't talk about receptor mediated endocytosis specifically in class, but it was in the text. It means that a certain molecule has to bind to the glycolipids or glycoproteins found on the outer surface of the cell for the cell to allow a vesicle to form to engulf the particles. Similar to the lock and key mechanism that a virus uses to gain entry into the cell.
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