Chemistry Essays - Membrane Biology, Cell Biology,

Chemistry 1. a) Bulk movement is the overall movement of a fluid. The molecules all move in the same direction. Diffusion however is the random movement of molecules which usually results in a fairly even distribution. In other words the movement is not guaranteed to move in one direction but the probability that it will move in the lower gradient is greater. Osmosis is similar to diffusion but is differentiated by the membrane's behavior. The cell membrane does allow water to move from higher to lower concentrations but does not allow solutes do that. b) Water potential is the capacity of water to move to a from a region where there is high water potential to low water potential. This action happens without the affect of outside forces. When outside actions due occur and they give water a high potential energy than the water will move to the region where less potential energy is. Hydrostatic pressure is the pressure required to stop water the movement of water. This is a method of measurement. The osmotic potential is the measure of tendency of water to move through a membrane which contains a solution. This occurs when a cell does not allow a hypertonic solution to leave the cell membrane. The cell begins to increase with water but the cell membrane can not release the solution and thus the water potential within the cell increases. This causes the water to no longer enter the cell. c) Hypotonic is less solute to a certain amount of water. Hypertonic is more solute to a certain amount of water. Isotonic is the equal amount of solutes in two different solutions. d) Endocytosis is the inward bulge causes by incoming molecules. Exocytosis is the expelling of a material outside a cell. e) Phagocytosis is the process where the cell obtains solid matter. This is different from the pinocytosis where the cell obtains liquid matter. These both are endocytic processes. Receptor-mediated endocytosis is the process where there are interactions between a material and receptor sites on the cell. In this process the cell accepts the material if it matches with the receptor sites. f) Coated pits are areas which peripheral proteins indent the membrane. This is where the vesicles for certain materials are formed. The vesicle which is formed is called the coated vesicle. g) Plasmodesmata are the links which hold two adjacent cells together. Gap junctions are the channels which allow materials to flow between cells. 2. The concentration gradient is the difference in the density of a material from one region to another region. The concentration gradient affects diffusion by allowing the substance to flow from high concentration to low concentration. The concentration gradient affects osmosis by the same manner it does in diffusion. The cell does not allow the solution to exit the cell when water is entering. This keeps the solution in the cell making the concentration high and thus no further penetration of water. 4. Diffusion is more rapid in gases because they are less dense than liquids. They repel each other more resulting in faster diffusion. Diffusion is greater at higher temperatures because of the greater kinetic energy among the molecules. They push each other more making them less dense. 5. The concentration of the solute is 1%. This happens because a 1% sugar solution is isotonic with that of the 1% sugar solution in the tubes. The 2% sugar solution was increased because the substance was hypertonic. The membrane did not allow the hypertonic solution to exit because the pressure from the hypotonic solution was forcing water in. This later reached an equilibrium when the hypertonic solution was gaining water potential and the water stopped rising. The vice versa happened in the distilled water solution.