1A- Diffusion
Purpose
The purpose of this lab was to understand the mechanisms of diffusion and to notice the effects of a selectively permeable membrane on diffusion between two solutions separated by the membrane.
Introduction
Diffusion is defined as the random movement of molecules from an area of high concentration of solute to an area of low concentration of solute. For example, if someone were to spray Axe Body Spray in the corner of a classroom, eventually everyone in the classroom would also be able to smell it because the particles would disperse evenly throughout the room. A semipermeable membrane, or selectively permeable membrane, is a membrane that only allows certain solutes and water to pass through it. The movement of a solute through a semipermeable membrane is called dialysis. In dialysis, smaller molecules will pass through the membrane easily, while larger ones will take a longer period of time, or won't pass through at all.
Methods
.
 |
| First we cut a piece of dialysis tubing. |
 |
| Then we soaked the dialysis tubing in water so that it would soften and we would be able to open it. After opening it, we tied off one end with a rubber band. |
 |
| Next we added 15 mL of a 15% glucose/1% starch solution into the bag. |
 |
| Before tying off the bag, we tested the solution for the presence of glucose. The solution tested positive because it was 15% glucose/1% starch. |
 |
| Then we put a solution of iodine and water into a beaker and tested it for the presence of glucose. It tested negative because it consisted of water and iodine. |
 |
| The solution in the bag was initially clear (15% glucose/1% starch) and the beaker was a red orange color (iodine and water). |
 |
| Then we placed the bag in the iodine solution and let it sit for 30 minutes. |
 |
| After 30 minutes, both the solution in the bag and in the beaker changed colors. |
 |
| Presence of glucose test in the cup before and after the experiment. |
 |
| Presence of glucose test in the bag before and after the experiment. Data |
Discussion
This experiment clearly displayed diffusion of substances through a selectively permeable membrane. In our initial experiment (before we put the bag of 15% glucose/1% starch into the iodine water solution) the bag tested positive for glucose and the beaker tested negative. However after the hydrolysis bag soaked in the solution for 30 minutes, both the bag and the beaker tested positive for the presence of glucose. This means that through the process of diffusion, the 15% glucose/1% starch solute moved out of the bag while water and iodine moved into the bag. The inside of the bag contained a high concentration of solute (15% glucose/1% starch) while outside the bag contained a low concentration. On the other hand, the outside of the bag contained a high concentration of iodine while the inside of the bag contained a low concentration of iodine. Looking at our results, the bag drastically changed colors from clear to a dark purple whereas the beaker changed from a red orange to a lighter shade of red orange. From this we can conclude that the membrane contained pores that better fit the iodine molecules than those of the 15% glucose/1% starch solution. It was easier for the iodine molecules to pass through the membrane which caused the inside of the bag to become so dark. Although the 15% glucose/1% starch molecules still must have passed through the membrane but at a much slower rate. The iodine molecules had to have been smaller than the pores of the membrane which must have been smaller than the glucose molecules. Because of this diffusion was able to occur through the membrane but at different rates for different substances.
Because membranes are semipermeable, different substances diffuse at different rates or not at all. Diffusion occurs when solutes move from an area of high concentration to an area of low. Because the dialysis bag membrane was more permeable to the iodine molecules, the bag turned a darker color than the original beaker. Although through the much slower diffusion of 15% glucose/1% starch molecules, both the cup and the bag tested positive for the presence of glucose.
Experiment 1B:
Purpose:
The purpose of this experiment was to investigate the relationship between solute and concentration and the movement of water through a selectively permeable membrane by the process of osmosis.
Introduction:
A selectively permeable cell membrane is one that allows certain molecules or ions to pass through it by means of active or passive transport. Selectively permeable membranes can be found around a variety of cells and places. All cell membranes are selectively permeable. This means that water can cross these membranes by osmosis. Osmosis do the diffusion of water. This will happen when the total concentration of solutes on one side of the membrane is different from that on the other side. When two solutions have the same concentration of salutes they are said to be isotonic to each other. If the two solutions are separated by a selectively permeable membrane, water will move between the two solutions, but there will be no net change in the amount of water in either solution.
Methods:
There were six bags filled with approximately 15ml of different solutions. One bag wag filled with distilled water, one with 0.2M sucrose, one with 0.4M sucrose, one with 0.6M sucrose, one with 0.8M sucrose, and one with 1.0M sucrose. After taking the mass of each bag, the bags were placed in different cups filled two thirds of the way full of distilled water. After thirty minutes, the bags were taken out, dried, and massed separately.
Data:
Graphs and Charts:
Discussion:
Solutions that are hyper tonic have more solute and therefore less water. All of these solutions are hypertonic because they gained mass because water rushed in, in order to reach equilibrium. The one solution that was isotonic was the 0.4M sucrose solution. The change in mass and the molarity of sucrose within the dialysis bags are directly proportional. As the mass increases, so does the molarity. If all the bags were placed in a 0.4M sucrose solution instead of distilled water they would be inversely proportional because whenever the sucrose molarity inside the bag is more concentrated, it will become more dilute and vise versa. The solutions will reach equilibrium somewhere between the two concentrations.
Conclusion:
This lab proved that water moves across the selectively permeable membrane much easier than sucrose does. The water moved to reach equilibrium between the solutions. Sucrose must be too large a molecule to pass through the membrane quickly.
Experiment 1C: Water Potential
Purpose-
The purpose of this experiment was to determine the water potential of potato cells.
Introduction-
The term water potential is used to determine the movement of water when entering or exiting a plant cell. The process has two main parts, the effect of the solute (solute potential) and the physical pressure (pressure potential). Water moves from places with higher water potential to areas with lower water potential. This is because areas with higher water potential have more molecules in it while lower water potential areas have less molecules in it. It is almost like when people gravitate to areas that are less crowded during an event. Movement is also determined by the solute potential on both sides of the cell membrane. When water moves into the cell, the cell expands, when it moves out, the cell shrinks. This is why plants that are experiencing droughts are wilting, while plants in the grocery store that are always being watered are sturdy and green.
Methods-
There were 5 cups filled with their assigned morality of sucrose, .2 M, .4 M, .6 M, .8 M, and 1.0 M, and one cup with distiller water. There were 4 potato cylinders for each beaker. The masses were recorded for each group of 4 potato cylinders. After, the four potato cylinders were placed into their chosen solutions. After a day, the potato cylinders were removed from the solutions and patted dry on paper towels. Then, each group of four potato cylinders was massed once again.
Data-
Discussion-
Water potential values allows to predict the flow of water into or out of a plant cell. As any plant dehydrates, so lutes become more concentrated, so the solute potential becomes more negative, that means that the water potential would decrease as well, becoming more negative. The less water in a plant means the less water potential. When a plant cell has lower water potential, which means less water and more salutes, it is hypertonic to its surroundings. This means the plant cell gains water when in a hypertonic state, because water moves from higher water concentration to lower.
Conclusion-
The lab showed that the potato cores had more water in them the day after the experiment than their original state. The water did so because the potato had less water concentration than the surrounding solution.
