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Transcript
Name __________________________________ Date _________________ Block____ Biology •The cell membrane regulates what enters and leaves the cell and also provides the protection and support. The cell takes in food and water and eliminates wastes through the cell membrane. Structure of the Cell Membrane: The cell membrane is actually a double layered sheet called the lipid bilayer (remember lipid is another name for fat). This bilayer forms a strong flexible structure that acts as a barrier between the cell and its surroundings. Name __________________________________ Date _________________ Block____ Biology • There are two types of proteins associated with the membrane integral and peripheral. Integral membrane proteins are tightly bound to the membrane and usually extend all the way through the membrane (transmembrane proteins). These proteins act as channels that allow certain substance to move from the exterior to the interior of the cell. Peripheral proteins are not totally embedded in the membrane. These proteins can function as receptors. Diffusion: Diffusion is a simple process where molecules move from a high concentration to a low concentration. Name __________________________________ Date _________________ Block____ Biology If a substance is small enough to move through a cell membrane, then it will move from a high concentration to a low concentration until there are equal amounts on both sides, this is called equilibrium. Even after equilibrium is reached the molecules will continue to move across the membrane. Roughly the same number of molecule will move in each direction. Solutions: In chemistry and biology, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent. A Name __________________________________ Date _________________ Block____ Biology common example is a solid, such as salt or sugar, dissolved in water, a liquid. There are three different ways to classify a solution. Hypotonic: contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode. Isotonic Solutions: contain the same concentration of solute as an another solution (e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic. Hypertonic Solutions: contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel. Name __________________________________ Date _________________ Block____ Biology Osmosis: Most biological membranes are selectively permeable; this means that some substances can pass through it and others . Osmosis is the diffusion of water through a selectively permeable membrane, this means that water moves from a high concentration to a low concentration across a membrane. can not The inside of a cell is not just made of pure water it is a solution that has many different things dissolved in it, such as sugar. If there is a large amount of water on the outside of the cell in which direction does the water want to go? The water goes from an area of high concentration to an area of low concentration until equilibrium is reached. There is no energy required for diffusion to occur. Name __________________________________ Date _________________ Block____ Biology Facilitated Diffusion: As we have seen some molecules are able to pass directly through the cell membrane i.e. water. Other molecules that are too big or have a charge are unable to diffuse directly through the membrane, they need help. This is where the embedded proteins come into play. The membrane proteins act as channels that let molecules diffuse from high to low concentrations, this is facilitated diffusion. This process does not require energy. Active Transport: Active transport is a process that requires energy. This process requires energy because the protein membranes are moving things from low to high concentration. Because this action is pumping against the gradient it requires energy. Name __________________________________ Date _________________ Block____ Biology