Biology Lab on Osmosis

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Michelle Kim
2012.1.20
Biology

Iso-osmolar Concentration of Carrot Cells Lab
INTRODUCTION
For a more thorough understanding of this lab introduction, the concepts of, iso osmolar, membrane, equilibrium, and concentration gradient evaluated. Iso osmolar can be known as the point in which the substance of experimentation faces no change despite the amount of solute inside the solvent( because the solvent and solute concentration is equal. This is where the line on a graph would cross on the x-axis). Selectively permeable membrane can be defined as a microscopic double layer of lipids and proteins that bounds cells and organelles and forms structures within cells and it controls what comes in and out of the cell. Equilibrium is the state of a chemical reaction in which its forward and reverse reactions occur at equal rates so that the concentration of the reactants and products does not change with time. Before this experiment, we were educated on how osmosis functions. Osmosis is a process which molecules and water take to usually get through a selectively permeable membrane in order to reach equilibrium. It is a passive transport which requires no ATF and water moves from high to low water concentration. When osmosis is completed, there should be an equal concentration o water on both sides of the experiment. We have also learned about the iso osmolar point which is when the concentration of molecules are identical inside and outside. Also, we predicted that if the carrot sticks were placed into higher concentrations of sucrose solutions, then the sticks would loose more water.

The concentration of particles inside the carrot cells will be found by having them placed into various different solutions with different sucrose concentrations. This will cause the carrot cells to either lose or gain water as the control tries to reach equilibrium with the solution. By measuring the carrot mass before the experiment and after they sat in the mixture for two days, we are able to observe the change in mass of the carrots. The amount of water the carrot lost or gained would show the percentage of mass change, which then we can use to conclude the concentration of particles inside the carrot. By finding the iso osmolar point, we are able to find the concentration of particles inside the carrot, because the iso osmolar point exhibits the solution that has the same concentration both in the carrot and out.

The carrot sticks inside the 0.0, 0.2, 0.4, 0.6, 0.9, and 1.0M sucrose mixtures, will have water enter/leave them. In this experiment, the independent variable was the molarity/sucrose concentration of the solutions the carrot sticks were placed into. The dependent variable was the percentage change of mass for the carrot sticks. For about half of the experiments(4/6), water left the carrot cells causing them to loose mass because there was a uneven concentration of water inside the carrot and outside. In the sucrose solutions in which the carrots lost mass, there was more water inside the cell compared to the outside, causing the water molecules in the carrot sticks to move out into the solution as a result of osmosis. Generally, substances try to spread out and reach the state of equilibrium instead of being concentrated in one area. This is why water enters and leaves the carrots; a result of osmosis. Also, there is a solution of sucrose that is perfect for the carrots sticks, which would result in zero percentage mass change of the carrot. The solution, if it is found, is called the iso osmolar point, which there is no change because there is no concentration gradient. CONCLUSION

The results of the lab were fairly accurate because there was no team in the class that had a hugely differing result in their experiment. The 0.0 M sucrose had a +16.71% change in mass as a class average and we had a +21.05% percentage change in mass. The initial mass was 1.9g and the final mass was 2.3g. This happened because the...
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