AP Bio Lab Report Essay

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Celeste Bond October 12, 2014
Ms. Bulahan AP Biology

Osmosis & Diffusion Lab Report

Introduction: Cells are made up of atoms, which has kinetic energy. Hence, cells are in constant motion. With all this motion, these cells bump into each other and change direction, which results in diffusion. Diffusion is the movement of molecules from an area of high to low concentration. Diffusion is vital to many life functions of the cell. It allows nutrient transport without expenditure of excess energy. Osmosis is a special kind of diffusion where water moves through a selectively permeable membrane. Diffusion or osmosis occurs until dynamic equilibrium has been reached. This is the point where the concentrations in both areas are equal and no net movement will occur from one area to another. Once the concentrations’ of both solutes are the same, is at equilibrium, the solution is called isotonic. If the solutions differ in concentration, then the solution can be either hypotonic or hypertonic. The hypertonic solution has a lower concentration of solute. Water will move out of a hypertonic solution, while solute will move in. The hypotonic solution has a higher concentration of solute, and therefore has less water. This solution will gain water, while losing solute. This movement between the hypotonic and hypertonic solutions will continue until the point of dynamic equilibrium is reached. Water moves from an area of high water potential to an area of low water potential. Water potential is the measure of free energy of water in a solution and is represented by the symbol psi. Water potential is affected by two physical factors: the addition of a solute and pressure potential. The addition of solutes to a concentration will lower the water potential of that solute, causing water to move into the area. Water movement is directly proportional to the pressure potential.

Procedure: PART 1-You begin the experiment by obtaining 6 strips of dialysis tubing and tie a knot in one at each end. Then you pour approximately 10 mL of distilled water, 0.2 M sucrose, 0.4 M sucrose, 0.6 sucrose, 0.8 sucrose, and 1.0 M sucrose solutions in its own strip. After placing the solutions into each baggie, rinse the baggie carefully to remove any sucrose that may have spilled. Next, you will record the mass of each baggie. Fill 6 250 mL beakers with distilled water and place a bag in each of them. After the bag has sat in the water for 20-30 minutes, remove the baggies from the water. Then measure the mass of each baggie and record the initial mass, final mass, mass difference, percentage change in mass and the class average. PART 2- Pour 100 mL into a beaker and slice a potato into 6 equal cylinders. Determine the mass of the 6 potato cylinders together and record. Then place the cylinders into the beakers with your assigned solution and cover it with plastic, and leave it overnight. The next day, remove the cylinders from the beakers and carefully blot any excess solution. Next, determine the mass of the 6 potato cylinder together, record and calculate the percentage change. \

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