Diffusion and Osmosis Lab Report

Jay Shah

Biology Lab: Thursday 3-4:50pm

Diffusion and Osmosis Lab Report

Introduction        

Diffusion is the movement of molecules from high concentrations to low concentrations, down a concentration gradient. A concentration gradient is a measurement of how the concentration of something changes from one place to another. Molecules can move because they have their own kinetic energy. They move the most freely in a gas form, less freely in a liquid form and they sit in place when they are in solid form. Molecules move on their own without help, which is known as a passive process. Osmosis is a different kind of diffusion, where water molecules move down their concentration gradient. Water diffuses through the membrane from the side of the lowest concentration of solutes to the side of the highest concentration of the solute, which will result in the two sides having equal concentrations of solutes, however with a different distribution of water volume on either side of the permeable membrane. The difference in concentration of water occurs if there is an unequal distribution of at least one dissolved substance on either side of a membrane and the membrane is impermeable to that substance which is called the osmotically active substance (Morgan and Carter, 2005). A hypertonic solution is where a higher concentration of solutes is compared to another solution. A plant cell will plasmolyze in a hypertonic solution, meaning water will diffuse out of the cell and the cell will shrivel. A hypotonic solution is where a lower concentration of solutes is compared to another solution. A plant cell will be turgid or firm in a hypotonic solution, meaning water will diffuse into the cell and the cell will swell and possibly burst. An isotonic solution is where an equal concentration of solutes is compared with another solution. A plant cell will be flaccid or limp in an isotonic solution.

My hypothesis for experiment 1B is since the rate of osmosis depends on molecular weight, glucose, which has less weight than starch, will move out faster during the dialysis tubing.

My hypothesis for experiment 3A is that with an increase in molarity the percent of weight change will inversely decrease. However I think that all of the potatoes slices will gain and not lose any weight after being immersed in the sucrose solution, which will make them all hypotonic.

Methods

In experiment 1B we first started off by taking the dialysis tubing and soaking it in water for a few minutes. We did this because the tubing could then be moist and easier to separate. We then took the tubing and opened one side and closed the end of the other side with a red stopper so that it would form a bag and so that the end of the bag would be secure and no solution would seep through. After we opened the bag we added 5mL of 30% glucose in the bag, and then 5mL of 1% starch solution to the glucose in the bag. We held the bag closed with its contents and recorded the color on our table. We rinsed the outside of the bag so that the extra solution that dripped out would go away. We then added 200mL of water to a beaker and added fifteen drops of I2KI to the water until it was visibly yellow and recorded that into our table. Afterwards, we placed the bag in the beaker so that the untied end of the bag hung over the edge of the beaker. We then left the bag in the beaker for about 30 minutes and checked on the bag periodically to see changes. After the 30 minutes we carefully removed the bag and put it in a dry beaker. We recorded the final color of the solution in the bag and the final color of the solution in the beaker. We then performed the Benedicts test for the presence of sugar in the solutions. We labeled three test tubes noted as control, bag, and beaker. We put 5mL of DI water into the control tube, 5mL of the bag solution in the bag tube, and 5mL of the beaker solution in the beaker tube. We then added ten drops of Benedict’s reagent to each tube. We then heated the tubes in boiling water which was on top of a hot plate for about three minutes until we started to see the color change.

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