Cell membrane: The cell membrane has the function of regulating which materials enter and leave the cell. It also holds all the contents of the cell together, so there can be a cell and a living organism. The cell membrane contains lipids and a lipid bilayer, carbohydrate chains, and membrane proteins. The lipid bilayer gives the cell membrane a flexible structure and provides a strong barrier that keeps water out and holds it together. The membrane proteins form channels and pumps that help move larger materials across the cell membrane. The carbohydrate chains act as chemical identification cards that the cells use to send signals to between one another. |
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Cellular Transport: There are six types of cellular transport, or how materials move across the cell. One is diffusion, where solute particles (sugar) move from areas of high to low concentration or from hypertonic (high sugar, low water) to hypotonic (high water, low sugar). There is also facilitated diffusion where molecules cannot directly pass across the membrane, but instead they pass through special protein channels. Osmosis is another form much like diffusion, except osmosis involves solvent particles (water) moving from areas of high to low concentration, or hypotonic to hypertonic. These three forms are all passive transport because it doesn't require the cell to use energy. Protein pumps are also a form of cellular transport. They allow small molecules to be carried across the membrane by protein pumps. Another form is endocytosis, where the cell membrane takes materials into the cell by pockets in the cell membrane. A final form of cellular transport is exocytosis or the releasing of large amounts of material out of the cell by the vacuole. These three types of transport are known as active transport because they require the cell to use energy.
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