One slide is a leaf in isotonic solution: you should be able to identify the chloroplasts and an empty space in the middle of the cells which is the vacuole. The next leaf has been soaked in a salt water solution; compare the cells to the first slide. What will happen to animal cells placed in hypotonic solution?
Why should this be different from plant cells? Observe the movement of water across a semipermeable membrane. Obtain 4 strips of dialysis tubing and tie a knot in one end of each using the dental floss. Place a bag in each beaker be sure to keep track of which bag is in which beaker! Fill the beakers with enough of the appropriate solution to cover your bags refer to the above table.
Did your results match your predictions? Propose an explanation for why your results either overall or an individual bag may have differed from what you were expecting. Exercise 1: Diffusion Through a Gel One factor that can affect the rate of diffusion is the size of the molecule.
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- Osmosis and Diffusion Lab!
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Repeat with Janus green. Allow the plates to sit undisturbed for 30 minutes. Which dye do you think will have a faster diffusion rate?
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Radius mm. Diffusion Rate.
Questions: 1. Did your outcome match your expectation? Provide an explanation for your results.
Diffusion and Osmosis
What are other factors that can affect the rate of diffusion? Exercise 2: Observation of Osmosis in a Plant Cell Plants have cell walls that can prevent lysis if too much water flows into the cell. Procedure: Observe the two Elodea leaves under the microscope. What is the difference between a hypertonic solution and a hypotonic solution? What will happen to plant cells that are placed in a hypertonic solution? Why are dehydrated patients given saline intravenously instead of water?
The movement of water across the cell membrane depends on the concentration of solutes on both sides of the cell membrane. When water moves out of the cell, the cell will shrink, and when water moves into the cell, the cell will swell and possibly burst. Cell walls are present in plant cells which prevent the cell from bursting once it swells. When water enters the plant cell, the membrane is pressed up against the cell wall and creates turgor pressure. Water potential is used to sum up the differences in solute concentration and pressure to predict the direction water will diffuse in living plant tissues.
Water potential is measured in bars, metric units of pressure equal to 10 newtons per cm 2 or 1 atmosphere. Pure water has a water potential of 1 atmosphere. Dissolving substances in water will result the water potential dropping below zero. When solute concentration increases, water potential decreases. Pressure potential may be positive, negative, or zero. Even though water is diffused in all directions, water will always diffuse from an area of high water potential to and area of low water potential. The process of the cell wall pulling away from the cell membrane in a plant cell is called plasmolysis.
Activity A: Diffusion. Hypothesis: If we add glucose-starch solution to a dialysis tubing bag and submerged it in a cup of distilled water and IKI solution, then glucose will leave the dialysis tubing bag through pores into the IKI solution through diffusion. Dropping Pipet. First, we poured mL of distilled water into a cup and added about 4 mL of IKI solution to the water and mixed well. We recorded the initial color of the solution in Table 1.
After we were finished, we discarded the used glucose test strip. We recorded the initial glucose test result in Table 1. Then we discarded the used glucose test strip. After soaking a piece of dialysis tubing in water, a group member rolled the tubing between their thumb and index finger to open it.
We tied one end of the dialysis tubing to create a bag. Then we tied off the top of the bag to close it while leaving enough room in the bag for expansion. We then placed the dialysis bag into the solution in the cup. In doing so, we made sure the entire bag was covered by the solution in the cup. We then waited 30 minutes and worked on an activity relating to Figure 2. Figure 2 Activity:.
We were to indicate initial locations of molecules and predict in which direction they would move in diffusion into the bag, out of the bag, both into and out of the bag, or none. After completing the activity with figure 2, we were able to compare our predictions about the outcome to the actual results of the experiment. Distilled water was initially in the cup and is predicted to stay in the cup. IKI was initially in the cup and is predicted to stay in the cup and also move into the dialysis bag. Glucose was initially in the dialysis bag and is predicted to flow in and out of the dialysis bag and exist in both the cup and dialysis bag.
Sucrose was initially in the dialysis bag and is predicted to stay in the dialysis bag. After 30 minutes, we removed the dialysis bag from the cup and dried it with a paper towel. We then cut a hole into the bag large enough for a glucose test strip to enter. We then collected the final amounts of glucose and completed Table 1. Table 1. Solution Color. Glucose Test Results. Dialysis Bag.
Brownish Red. When comparing our results to our predictions, we had predicted correctly. We had no conflicts that would have made us revise our predictions. The results show the locations each molecule had gone and were the molecules ended up and proved our predictions were correct.
This activity proved the net movement of glucose from the dialysis bag to the cup and both the cup and dialysis tested positive for glucose at the end of the experiment. The data in this experiment tells us the sizes of molecules would have to be small enough to fit through the dialysis tubing because if it is not small enough, then the tubing will rebound the molecules and not let them pass through. Activity B: Osmosis. Hypothesis: If we add higher concentrations of sucrose to the dialysis bag, then the net movement of water into the dialysis bag will increase.
Paper Towels. Electronic Balance. For each sucrose solution, we poured mL of distilled water into a cup. We then labeled the cup with the concentration of sucrose that we tested. A group member then took a piece of dialysis tubing and opened it by rolling it between their thumb and index finger after being soaked in water. Then we tied off one end of the dialysis tubing to create a bag. Using a funnel, we poured 25 mL of sucrose solution into the dialysis bag.
Leaving enough room in the bag for expansion, we tied off the bag and dried it will paper towels. We weighed the bag and recorded its initial mass in Table 2. After measuring initial mass, we placed the bag in the cup of water, making sure the bag was completely submerged in the water.
Lab 6: Diffusion and Osmosis - Biology LibreTexts
We waited for 30 minutes before continuing. After 30 minutes, we removed the bag from the water and dried it with paper towels.
We then weighed the bag and recorded the final mass in Table 2. Table 2. Contents in the Dialysis Bag. Initial Mass. Final Mass. Change in Mass. Percent Change in Mass. To calculate the percent change in mass, we used the formula:. The change in mass in this activity indicates whether or not a solution entered or left the dialysis bags during the experiment.
In the case of Activity B, the change in mass increased and shows water entered the bags during the experiment. In this experiment, the variable being tested is water. Osmosis is the diffusion of water from a high concentration to a low concentration and water was the variable being tested in this activity because it is what made the mass increase for every sucrose solution. The amount of sucrose solution, dialysis bag, and time could all influence the outcome of this experiment.
The higher the amount of sucrose causes for more water to move into the dialysis bag. The dialysis bag is an influence because of pore size in relation to the size of the water molecules. Time could influence the movement of water because maybe, with more time, more water will move into the dialysis bag than shorter time periods. The graph we made is an accurate representation of our data and how the mass changed due to the sucrose solutions because water was adding to the weight of the dialysis bag. In osmosis, water molecules moved into the dialysis bags with higher sucrose molarities.
The solutions in the bag and outside of the bag were not isotonic to each other during this experiment because of the change in mass. If the experiment asked for the water to be inside the dialysis bag and the sucrose solution to be inside the cup, then we would have seen the mass of the dialysis bag decrease the higher the molarity of the sucrose. Drinking seawater can dehydrate the body because the water is hypertonic to the cells lining the small intestine, so this will pull the water out of the cells dehydrating the body.