Effect of concentration on penetration and diffusion in dialysis tubing

By examining the movement of solutes such as potassium iodide and glucose, and tracking weight changes at different sucrose concentrations, the experiment was designed to demonstrate the principles of passive transport and how concentration gradients affect the movement of molecules across membranes.

This experiment studies how different concentrations of solutes affect the permeability and diffusion processes of a semipermeable membrane (dialysis tube), examining the movement of water and solutes as well as the changes in the properties and weight of the resulting solution over time.

introduce

Osmosis and diffusion are fundamental processes of cellular transport and play an important role in maintaining homeostasis and achieving basic biochemical functions (Alberts et al., 2014). Both are forms of passive transport that allow molecules to move across biological membranes without the use of energy. Osmosis is defined as the movement of water molecules through a semipermeable membrane from an area of ​​lower solute concentration to an area of ​​higher solute concentration until equilibrium is reached. In contrast, diffusion involves the movement of solute particles from an area of ​​higher concentration to an area of ​​lower concentration (Binod, 2024).

Understanding the dynamics of these processes is necessary to explore how cells interact with their environment, absorb nutrients, and eliminate waste products. There are three main types of osmosis: high osmosis, where there is more solute outside the cell than inside the cell, causing water to flow out of the cell; hypotonicity, where there is less solute outside the cell, causing water to enter the cell; isotonic, where the solute inside and outside the cell is The concentration is the same, resulting in no net movement of water (Binod, 2024).

In this experiment, dialysis bags were used in the experiment because they are semi-permeable and represent artificial cells to study penetration and diffusion. The hypothesis for this experiment is that the starch/glucose solution within the dialysis tubing will exhibit a color change due to the diffusion of potassium iodide. The weight of the dialysis bag changes due to osmosis, depending on the sucrose concentration.

Materials and methods

Steps in studying diffusion and osmosis using dialysis tubing

Diffusion experiment:

1. Prepare the diffusion solution:
   • Fill a small beaker with water.
   • Add 10 drops of potassium iodide solution to the beaker to obtain a medium brown color.
2. Observe the spread:
   • Record the initial color and appearance of the potassium iodide solution in the beaker.
   • Wait for the solution to spread and observe the color change until the solution completely turns yellow, indicating complete diffusion.
3. Prepare dialysis tubing:
   • Cut a piece of dialysis tubing about 10 cm long.
   • Clamp one end of the pipe securely and leave the other end open.
4. Fill the dialysis tubing:
   • Fill the open end of the dialysis tubing approximately two-thirds with the starch/glucose solution.
   • Clamp the open end of the pipe securely.
5. Record preliminary observations:
   • Record the colors of the potassium iodide solution in the beaker and the starch/glucose solution in the dialysis tube, as shown in Table 1.
   • Dip the glucose test paper into the beaker solution and record the results in Table 2.
6. Place the dialysis tube into the beaker:
   • Immerse the prepared dialysis tube into a beaker containing potassium iodide solution.
7. Wait and watch:
   • After 30 minutes, record the color changes of the potassium iodide solution in the beaker and the starch/glucose solution in the dialysis tube, as shown in Table 1.
   • Dip the glucose test paper into the beaker solution again and record the results as shown in Table 2.

Penetration experiment:

After 60 minutes, record the final weight of all dialysis cells in Table 3.

Prepare the osmotic solution:

• Fill a small beaker about two-thirds full with the 25% sucrose solution.
• Pour about two-thirds of the 1% sucrose solution into a large beaker.

Prepare dialysis tubing for artificial cells:

• Obtain four soaked dialysis tubes.
• Clamp one end of each dialysis tubing. Label the clips A, B, C, and D.

Fill the dialysis tubing:

• Open “Unit A” and fill it approximately two-thirds with 1% sucrose solution, then clamp it firmly.
• Fill “Unit B” with a 1% sucrose solution, “Unit C” with a 10% sucrose solution, and “Unit D” with a 25% sucrose solution, and clamp each unit securely.

Record initial weight:

• Weigh each of the four dialysis cells and record their initial weight in Table 3.

Immersed dialysis cells:

• Place “Cell A” into a small beaker containing 25% sucrose solution.
• Place “Cells B, C and D” into a large beaker containing 1% sucrose solution.

Wait and weigh:

• After 15 minutes, cells were removed from their respective beakers, dried slightly, and weighed.
• Record the new weight in Table 3.
• Place the cells back into their respective beakers.

Repeat the weighing process:

• Repeat the process of taking out, drying, weighing and recording the weight after 30 minutes, 45 minutes, and 60 minutes.

Final weight:

• After 60 minutes, record the final weight of all dialysis cells in Table 3.

result

The experimental results demonstrate the diffusion of potassium iodide and the behavior of glucose within the dialysis tubing, as shown in the table below.

Table 1. Diffusion of potassium iodide solution from beaker to starch/glucose solution in dialysis tubing

Table 2. Diffusion glucose test strip test

The results of the osmotic experiment are demonstrated by changes in the movement and weight of the solute through the dialysis tubing, indicating the hyperosmotic, hypotonic, or isotonic nature of the environment.

Table 3. Changes in dialyzed cell weight over time

discuss

Experiments show that potassium iodide diffuses into the starch/glucose solution inside the dialysis tube, causing a color change and confirming successful diffusion. Furthermore, the weight of the dialysis bag changes depending on the sucrose concentration around it, showing the effect of osmosis: cells in hypertonic solutions lose weight, while cells in isotonic solutions remain stable.

Preliminary observations show that the potassium iodide solution begins to appear yellowish-brown, while the starch/glucose solution appears white. After 30 minutes, the potassium iodide solution

Become clear and the starch/glucose solution turns purple/turbid, indicating successful diffusion of iodine into the tube.

The glucose test strip initially displays a cyan color, indicating that glucose is not present. At the end of the experiment, the test strip turns brown/green, confirming the presence of trace amounts of glucose in the beaker solution.

Changes in weights over time indicate different responses to surrounding solutions. After 10 minutes, the weight of Cell A increased slightly, but then fluctuated, indicating a hyperosmotic environment in the beaker. Cell B remained relatively stable, showing an isotonic environment. In contrast, Cell C’s body weight gradually decreased, while Cell D’s body weight decreased significantly, reflecting water loss caused by its hyperosmotic environment. Solutes move from higher to lower concentrations to maintain homeostasis (Alberts et al., 2014).

This experiment has flaws, such as differences in how well the dialysis tubes allow substances to pass through, which can lead to uneven results. Additionally, not controlling temperature and relying on color changes for measurements may make the results less reliable.

Overall, the results support the hypothesis that diffusion occurs across the dialysis membrane and highlight the influence of osmotic pressure on dialysis bag weight.

Further experiments

Future experiments could study how temperature affects penetration and diffusion, with higher temperatures expected to make these processes occur faster. We can also try different substances, such as salt or sugar, to see how they change the way molecules move.

refer to

Albert, B., Johnson, A., Lewis, J., Love, M., Roberts, K., & Walter, P. (2014). cell molecular biology (6th ed.). Garland Science.

GC, Binod. “Infiltration and Diffusion: Differences and Factors Affecting Them.” science notesApril 14, 2023. October 2, 2024.

Mika, TA, Klein, RJ, Brejan, AE, Connaugh, RL, Swimmer, LM, White, RE,

Gosses, MW, Carter, TE, Andrews, AM, Maier, JL, & Sidiq, F. (Eds.). (2024). Anatomy and Physiology BIO 211 Laboratory Manual (3rd ed.). Owens Community College.

GC, Binod. “Cellular Transport: Passive and Active Mechanisms.” science notesSeptember 3, 2024. October 2, 2024.