Osmosis is the movement of water molecules from high concentration to low concentration through semipermeable membranes, caused by the difference in concentrations on the two sides of a membrane (Rbowen, L.). It occurs in both animals and plants cells. In human bodies, the process of osmosis is primarily found in the kidneys, in the glomerulus. In plants, osmosis is carried out everywhere within the cells of the plant (World Book, 1997). This can be shown by an experiment with potato and glucose/salt solution. The experiment requires putting a piece (or more) of potatoes into glucose or salt solution to see the result of osmosis (a hypertonic type of solution is mostly used as it would give the most prominent visual prove of osmosis, as was mentioned in an observation of an experiment). As the potatoes are left in the solution, water molecules from the potatoes would move out through the semipermeable membranes to the hypertonic solution surrounding it in an attempt to equalise the amount of glucose/salt within the solution to the same amount that the potatoes have. This would result in the potatoes’ cells shrinking-when the fluid left the vacuole, and the cytoplasm also being pulled away from the cell wall by the vacuole (dragging the cell wall in, too) in the process of plasmolysis-and the entire potatoes piece shrink, becoming soft and flaccid; as it was osmosis & the fluid in the vacuole that helped it keep its turgid shape and feel of density and stiffness in the first place (Bradley, O., 2006). The potatoes being quite flexible was also shown in another experiment. Osmosis is founded in three types of solutions: hypertonic, hypotonic and isotonic solutions. Hypertonic solution is when there is a higher concentration of solutes (glucose, salt) on the outside of the cell wall in the solution. Hypotonic solution is when there is a higher concentration of solutes within the cell wall. And Isotonic solution is when the concentrations of solutes on both sides of the cell wall is equal, (osmosis is aimed to reorganise the molecules into isotonic solution), (BioGal, 2009). The movement of water molecules in osmosis is called a concentration gradient, and this occurs in both Hypertonic and Hypotonic solutions, but not in an Isotonic solution, because the concentration gradient is already equal. QUESTION: What is the effect of solute concentration on osmosis in potato cells? Aim: To find out how osmosis in potato cells is affected by solute concentration. HYPOTHESIS: If the glucose ratio to water in the solution increases, then the mass of the potato cylinders will decrease. Why: The glucose solution would contain more glucose than the potato, so the water molecules in the potato would leave the potato to try and balance out the concentration of glucose in the solution, and when the water leave the potato, its cell would deflate and become flaccid instead of turgid and also decrease in mass because there is less stuff that would cause mass in it. EXPERIMENTAL DESIGN
Variables: independent – concentration of glucose in moles
dependent – percentage change of mass (%)
controlled – distilled water, total amount of liquid (100 ml), size of potato cylinders, size of beakers, time, temperature, types of potatoes Materials: potatoes -same kind/type of potato-for reliability cork borer
beakers (x6) - same size-for reliability
distilled water - water without nutrients/chemicals
electric scale - for more accurate measurement
paper towels - for blotting
marker - to label the beakers
measuring cylinders (100ml) - for accuracy
(for diagram, see Appendix 1)
(1. Research about osmosis in potato cells before conducting the experiment to know the rough procedure and results of the experiment, if you are not doing a preliminary trial.) 1. Gather your materials.
2. Label the beakers as 0, 0.2, 0.4, 0.6, 0.8 and 1.0 M. 3. Make the solution:...
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