Copy of Copy of AP Bio Lab Diffusion & Osmosis Remote Lab.pdf

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Name _Siddhi Bhirud______________________________Hour: ___5th_______ AP Biology Investigation: Diffusion and Osmosis Background Information:Molecules are in constant motion and tend to move from regions where they are in higher concentration to regions where they are less concentrated. Diffusionis the net movement of molecules down their concentration gradient. Diffusion can occur in gases, in liquids, or through solids. An example of diffusion in gases occurs when a bottle of perfume is opened at the front of a room. Within minutes people further and further from the source can smell the perfume.Osmosisis a specialized case of diffusion that involves the passive transport of water. In osmosis water moves through a selectively permeable membrane from a region of its higher concentration to a region of its lower concentration. The membrane selectively allows passage of certain types of molecules while restricting the movement of others. Biologists use water potentialto describe the tendency of water to leave one place in favor of another. Water always moves from an area of higher water potential to an area of lower water potential. Water potential is affected by two factors: pressure and the amount of solute. Water potentialis calculated using the following formula: Water Potential (Ψ) = Pressure Potential (Ψp) + Solute Potential (Ψs) Pressure Potential (Ψp): In a plant cell, pressure exerted by the rigid cell wall that limits further water uptake. Solute Potential (Ψs): The effect of solute concentration. Ψs = -iCRT [i=ionization constant; C = solute concentration; R = pressure constant R=0.0831 liter bar/mole°K; T=temperature in °K] Pure water at atmospheric pressure has a solute potential of zero. As solute is added, the value for solute potential becomes more negative. This causes water potential to decrease also. Bars is the unit of measure for water potential; 1 bar = approximately 1 atmosphere. In sum, as solute is added, the water potential of a solution drops (it becomes more negative), and water will tend to move into the solution.
Part A: Simulated Cell Membrane Using Dialysis Bags Problem: How do concentration gradients affect movement of molecules across membranes? Investigation: In Part A, we are simulating cell membranes by using dialysis tubing. Dialysis tubing is selectively permeable, like a cell membrane. Molecules larger than the pores cannot pass through the membrane but small molecules can do so freely. Dialysis tubing is used in dialysis, a process which involves the removal of very small molecular weight solutes from a solution. It consists of regenerated cellulose. The tubing is flat and clear, and provided in rolls. You will be investigating the relationship between solute concentration and water movement by filling six dialysis bags with 0.5 M sucrose and placing the bags into cups with increasing concentrations of sucrose. After the time for the experiment has elapsed, you will compare the initial weight of each bag with its final weight, calculate the percent change in mass, and graph your results.

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