LAB3 - James Johnson Bio 101 Lab # 3 9/22/07 Mrs. Fealy...

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James Johnson Bio 101 Lab # 3 9/22/07 Mrs. Fealy Diffusion and Osmosis Lab 1. Introduction: Diffusion is the process by which molecules interact as a result of their random motion due to potential energy. The rate of diffusion depends upon the temperature, pressure, and concentration of the solutes of each side of the membrane. It occurs in animal and plant cells through a semi- permeable membrane, a membrane that selects what moves in and out based on size and solubility of the solute. Salts, proteins, sugars and many other particles are transported across the membrane and maintain a stable environment in the body that keeps us alive. This often occurs from an area of high concentration to an area of low concentration- that results in equilibrium. Random, or spontaneous, diffusion is known as passive diffusion or transport. In passive transport the cell does not have enough energy to make diffusion happen so it happens randomly. The concentration gradient is the potential energy and this makes the diffusion happen. Active transport is diffusion that requires energy. The substance moves against the concentration gradient, or from low to high concentration, with an energy input and help from special proteins. Osmosis is the net movement of water across a selectively permeable membrane from an area of high potential to an area of low potential of water. There is no input of energy in osmosis- this process releases energy and does work. Turgor pressure is the pressure of the cell contents against the cell wall. This pressure is determined by the water content in the cell, which is made from osmosis. There are three effects of osmosis on a cell.
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If a medium is isotonic there is no net movement of water across the cell membrane because the cell is in a solution with the same water concentration. A medium is hypotonic if a cell gains water through osmosis, which means the solution is dilute- having a higher water concentration than the cell. A medium is hypertonic when the cell loses water, which means the solution is concentrated- having a lower water concentration than the cell. In this lab we will find out how both diffusion and osmosis work, how concentration of solutes ad solvents affect the rate of diffusion, how a semi- permeable membrane selects certain materials and lets them through the membrane based on their size and solubility, and how cells become hypertonic, hypotonic, and isotonic depending on the properties around them. These objectives will be achieved through a series of three experiments. 2.
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LAB3 - James Johnson Bio 101 Lab # 3 9/22/07 Mrs. Fealy...

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