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Download Cell Walls and Boundaries Cells protect themselves by their cell
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Transcript
Cell Walls and Boundaries Cells protect themselves by their cell membrane (and cell wall in the case of plant cells). However, they will need nutrients so somehow the cells must have a way of allowing some things in while leaving some out. Think about your house, you want some people to stay out while your friends and family are allowed in. Two ways of doing this: passive transport and active transport Passive Transport = the movement of materials across the cell membrane without using cellular energy Every living cell exists in a liquid environment. One of the most important functions of the cell membrane is to keep the cell’s internal conditions relatively constant. o Regulate the movement of molecules from one side of the membrane to the other side. Types of passive transport: diffusion, facilitated diffusion, osmosis and filtration. Diffusion = process by which particles move from an area of high concentration to an area of lower concentration Is the driving force behind the movement of many substances across the cell membrane. The cytoplasm of a cell is a solution of many different substances dissolved in water. o In any solution, solute particles tend to move away from high concentration areas to lower concentrated areas. Much like moving west from the east coast to seek new land. Suppose a substance is present in unequal concentrations on either side of a cell membrane what will happen? o Cell membranes consist of a phospholipid bilayer with hydrophilic heads and hydrophobic tails. If the substance can cross the cell membrane, its particles will tend to move toward the area of less concentration until it is even or at a state of equilibrium o At equilibrium, the particles will continue to move across the membrane in both directions = no net change Facilitated Diffusion = molecules that cannot directly diffuse across the membrane pass through special protein channels (diffusion with help) Proteins act as carriers, or channels, making it easy for certain molecules to cross the cell membrane Facilitated diffusion does NOT require additional use of cell’s energy. Used by bigger molecules or charged molecules because the phospholipid bilayer only allows small uncharged particles through without help.