Lab Report: Diffusion and Osmosis

Abstract

The purpose of this laboratory experiment conducted on June 4, 2013, was to gain a visual understanding of diffusion and osmosis. Diffusion is the spontaneous movement of substances from an area of high concentration to an area of low concentration, requiring no energy input. Osmosis, on the other hand, is the movement of molecules across a cell membrane, necessitating energy input. Through a series of experiments involving carmine powder, dialysis tubing, and potato cylinders, this lab aimed to illustrate how chemicals move across cell membranes.

Introduction

Diffusion is a fundamental process in biology, where molecules naturally move to equalize their concentration. Osmosis, a specialized form of diffusion, involves the movement of water and solutes across a selectively permeable membrane, such as a cell membrane. This lab report presents the methods, results, and conclusions of experiments designed to explore these processes.

Materials and Methods

The following materials were used in the experiments:

• Dropper bottle of water
• Substance microscope
• Dissecting needle
• Carmine powder
• Slide and coverslip
• 3 test tubes
• Transfer pipets
• 2 400 ml beakers
• 30 cm damp dialysis tubing
• 500ml beaker
• Hot plate
• Benedicts reagent
• I2KI solution (starch solution)
• Wax pencil
• 30% glucose solution
• String or rubber band
• Test tube rack
• Slides and cover plates

Experiment 1: Carmine Powder Observation

1. Prepare a slide of dry carmine and water and cover slip.

2. Place the slide under the microscope and observe at different magnifications, recording your findings for later analysis.

Experiment 2: Dialysis Tubing

1. Use dialysis tubing that has been soaked in water, fold it "accordion style," and use string to seal the ends, creating a bag-like structure.

2. Roll the opposite end of the bag until it opens and add 4 pipettes of 30% glucose and 4 pipettes of starch solution into it.

3. Mix the contents with the bag closed, then rinse with tap water.

4. Add 300 mL of water to a 400-500 ml beaker and add a few drops of I2KI solution until it turns an amber-yellow color.

5. Leave the bag in the beaker for thirty minutes and then remove it.

6. Record observations.

Experiment 3: Potato Cylinder Experiment

1. Obtain 7 equal-sized bore hole cylinders from the potato, ensuring they are roughly the same size. Record the length and weight of each.

2. Prepare 7 cups, each filled with 100 ml of glucose solutions of varying concentrations (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, and pure water).

3. Record the time and submerge the potato cylinders in the solutions, allowing them to sit for an hour and a half before removal, weighing, and recording the final weight.

Results

Experiment 1: Carmine Powder Observation

Observations: The carmine powder exhibited random movement, resembling continuous vibrations when observed under a microscope.

Experiment 2: Dialysis Tubing

After allowing the bag to sit in the bath for 30 minutes, the solution inside the bag changed from clear to a slight yellow color. The results of the Benedicts test indicate the movement of carbohydrates from inside the bag to the surrounding solution.

Experiment 3: Potato Cylinder Experiment

Observations: The size of the potato cylinders decreased as the concentration of glucose in the surrounding solutions increased. In contrast, the potato immersed in pure water remained the same size.

Discussion

The results of Experiment 1 demonstrated the principle of diffusion, as carmine powder particles exhibited movement under a microscope without requiring energy input. Diffusion is the process of molecules moving from areas of high concentration to areas of low concentration without the need for energy.

Experiment 2 involved dialysis tubing and provided insights into osmosis. The change in color observed in the solution inside the bag after the Benedicts test suggests that carbohydrates moved from inside the bag to the surrounding solution. This indicates the movement of solutes across a cell membrane, illustrating osmosis, which requires energy input for the process to occur.

Experiment 3 further supported the concept of osmosis. The decrease in size and weight of the potato cylinders as the concentration of glucose in the surrounding solutions increased indicated the movement of water out of the potato cells, in an attempt to equalize the solute concentration inside and outside the cells. Conversely, the potato immersed in pure water swelled, indicating that the concentration inside the potato was lower than the concentration outside.

Conclusion

This laboratory experiment provided valuable insights into the processes of diffusion and osmosis. The carmine powder experiment confirmed the principle of diffusion, demonstrating the movement of particles without requiring energy input. On the other hand, the experiments involving dialysis tubing and the potato cylinders illustrated the movement of solutes and water across a cell membrane, illustrating osmosis. The color change observed after the Benedicts test in the dialysis tubing experiment highlighted the presence of sugars in the surrounding solution.

Recommendations

Further experiments and investigations could explore the specific factors that influence the rate of diffusion and osmosis, such as temperature, concentration gradients, and membrane permeability. Understanding these factors in greater detail would contribute to a more comprehensive understanding of these fundamental biological processes.