Describe How Materials of Different States Pass Into and Out of Cells

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Unit 13 P2 Describe how materials of different states pass into and out of cells. The cells plasma membrane is not only used for structural purposes. Its functions to allow certain substances in and out of the cell. It can allow other substances into the cell against the concentration gradient or allow other substances (for example waste) out of the cell. There are two ways that the cell can transport substances; passive transport processes and active transport processes. Passive transport processes are when the cell does not use any energy during the transport process. The other transport processes require energy from the cell’s reserves. These processes are called active transport processes’. Passive transport processes: Diffusion Diffusion is the movement of ions or molecules from regions of high to low concentration; down a concentration gradient. Diffusion and the plasma membrane The plasma membrane is semipermeable which means it will allow certain substances to go in and out but not others. Moecules that pass through the phospholipid bilayer easily: Hydrophobic molecules: 02 and N2 Non-polar: Benzene Small uncharged polar molecules: H20, Urea, glycerol and CO2 Molecules that don’t pass through the phospholipid bilayer easily: Large uncharged molecules: Glucose Polar molecules: Sucrose Ions (charged): H+, Na+, HCO3, K+Ca2+, Cl- and Mg2+ Therefore the three characteristics of a molecule that determine their permeability through the membrane are: 1. Polarity- Hydrophobic vs Hydrophilic 2. Charge- Charged vs Uncharged 3. Size- Large vs Small. Although some molecules are effected by the presence of the membrane proteins. These proteins are involved in both passive and active transport. Osmosis Osmosis is the movement of water from a region of high water concentration to a region of lower water
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