Osmosis and Diffusion Lab Report

Abstract:

The purpose of this lab was to investigate the processes of osmosis and diffusion using a model of a membrane system.

We examined the effect of solute concentration on water potential in living plant tissue. The experiments involved dialysis tubing and potato cores in various sucrose concentrations. The data supported our hypothesis, showing that as the sucrose concentration increased, both the mass and the percent change in mass also increased.

Introduction:

Objective:

1. Investigate the process of osmosis and diffusion in a model of a membrane system.
2. Investigate the effect of solute concentration on water potential as it relates to living plant tissue.

Background Information:

Molecules are in constant motion, tending to move from areas of high concentration to areas of low concentration. This principle can be categorized into two types: diffusion and osmosis. Diffusion involves the random movement of molecules from high to low concentration and is a passive form of transportation. Osmosis, a special type of diffusion, occurs when water moves through a selectively permeable membrane from an area of higher water potential to an area of lower water potential.

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Water potential depends on osmotic potential and pressure potential, with the overall equation being Ψw = Ψp + Ψπ.

The objective of this lab is to observe the physical effects of osmosis and diffusion and determine if they occur. Our hypothesis is that molecules will diffuse down a concentration gradient, causing the mass of dialysis tubes to increase. Additionally, we believe that as the sucrose molarity increases, the percent change in mass will also increase.

Materials:

Exercise 1:

1. 6 strips of dialysis tubing
2. Distilled water (15-20ml)
3. 0.4 M sucrose (15-20ml)
4. 0.8 M sucrose (15-20ml)
5. 0.2 M sucrose (15-20ml)
6. 0.6 M sucrose (15-20ml)
7. 1.0 M sucrose (15-20ml)
8. 6 beakers

Exercise 2:

1. 100ml of distilled water
2. 100ml of 0.4 M sucrose
3. 100ml of 0.8 M sucrose
4. 100ml of 0.2 M sucrose
5. 100ml of 0.6 M sucrose
6. 100ml of 1.0 M sucrose
7. 6 beakers
8. Potato slices (4 for each solution)
9. Scale
10. Plastic wrap
11. Thermometer

Methods:

Exercise 1:

1. Obtain 6 strips of dialysis tubing and tie a knot in one end of each.
2. Pour approximately 15-20ml of each solution into separate bags.
3. Remove most of the air from the bag and tie the baggie.
4. Rinse the baggie carefully in distilled water to remove any spilled sucrose and blot dry.
5. Record the mass of each baggie.
6. Fill six 250ml beakers 2/3 full with distilled water and place a bag in each, noting which baggie is which.
7. Let the bags sit for 20-30 minutes.
8. After 20-30 minutes, remove the baggies from the water and blot them dry.
9. Measure the mass of each baggie and record.

Exercise 2:

1. Pour 100ml of your assigned solution into a beaker.
2. Slice a potato into 4 equal lengths resembling French fries or tubes.
3. Determine the mass of the 4 potato cylinders together and record.
4. Place the cylinders into the beaker with your assigned solutions and cover with plastic wrap. Leave overnight.
5. Remove the cylinders from the beakers, carefully dry them, and record the room temperature in Celsius.
6. Determine the mass of the 4 potato cylinders together and record.

Results:

The data collected from both exercises showed that as the concentration of sucrose increased, the mass of the dialysis tubes and potato cylinders also increased. This indicates that diffusion and osmosis occurred until dynamic equilibrium was reached. The tables below present the specific data:

Exercise 1 Data:

Exercise 2 Data:

Discussion:

The change in mass of the dialysis tubes and potato cylinders was dependent on the concentration of sucrose. When the sucrose concentration inside the dialysis tubing was greater than outside, water moved into the bag, increasing the mass. Conversely, when the sucrose concentration inside the bag was lower than outside, water moved out, decreasing the mass. These changes were directly proportional. As the mass increased, so did the molarity. Conversely, as the sucrose molarity inside the bag became more concentrated, it became more dilute outside. Equilibrium was reached between the two concentrations.

The data supported our hypothesis that as the sucrose concentration increased, the mass increased as well. However, there were potential sources of error. The tightness of the string tying the dialysis tubing could lead to leaks or breaks, affecting the data. Additionally, inadequate drying of the potato samples might leave drops on the electronic balance, leading to incorrect measurements. Simple mathematical errors could also occur, introducing inaccuracies into the results.

Conclusion:

This lab successfully demonstrated the physical mechanisms of osmosis and diffusion and how molar concentration affects diffusion. The data supported our hypothesis, showing that as the sucrose concentration increased, both the mass and the percent change in mass increased. Exercise 1 revealed that water moved more readily across the selectively permeable membrane of dialysis tubing than sucrose sugar. Exercise 2 demonstrated that potatoes absorbed water when placed in a distilled water solution, indicating that potatoes contain sucrose molecules. Potatoes had a lower water potential and higher solute potential than the distilled water solution.

This experiment not only reinforces the principles of osmosis and diffusion but also provides valuable insights into how water and particles move in and out of cells. Understanding these biological processes is crucial for various fields, including physiology, medicine, and agriculture.

Recommendations:

Based on the results of this lab, it is recommended to further explore the effects of osmosis and diffusion on various types of plant tissues and under different conditions. Additionally, investigating the impact of temperature on osmosis and diffusion could yield valuable insights. Further research in this area can contribute to our understanding of how these processes function in living organisms and can have practical applications in agriculture and medicine.