Modeling Cell Transport With Dialysis Tubing

Summary

In this experiment, students investigate the processes of diffusion and osmosis using dialysis tubing filled with glucose and starch solutions. The lab involves preparing two cell models, measuring initial masses, and submerging them in distilled water. The presence of glucose is tested using glucose test strips, while iodine is used to detect starch diffusion. After 30 minutes, the mass changes are recorded, and conclusions are drawn based on observations, revealing how different molecules move across semi-permeable membranes through diffusion and osmosis.

Takeaways

• 😀 Ensure dialysis tubing is soaked in water before use; if dry, soak in distilled water for a couple of minutes.
• 😀 Secure the ends of dialysis tubing with waxed dental floss to prevent liquid from leaking out.
• 😀 Fill each dialysis tubing with different solutions: glucose solution for one, starch solution for the other.
• 😀 Tie off the open end of the dialysis tubing tightly to create a secure 'cell model' for the experiment.
• 😀 Before starting the experiment, rinse and blot the dialysis tubing to remove excess moisture.
• 😀 Measure the initial mass of the cell models (glucose and starch solutions) to detect changes later.
• 😀 Prepare two beakers of distilled water: one with iodine solution for the starch cell and the other plain.
• 😀 Iodine solution turns blue or purple in the presence of starch, allowing you to track starch diffusion.
• 😀 Use glucose test strips to check for glucose diffusion out of the glucose-filled dialysis tubing into the distilled water.
• 😀 After waiting, examine the external environment to check for changes in color, indicating diffusion or osmosis.
• 😀 Record the final mass of each cell model to compare against initial measurements and evaluate the effects of diffusion and osmosis.

Q & A

What is the first step in preparing the dialysis tubing for the experiment?

The first step is to tie one end of the dialysis tubing shut so that liquids can be added to the other end without spilling. This is done by resting the tubing on the edge of a beaker and using waxed dental floss to tie a double knot.

Why is it important to use waxed dental floss instead of regular floss?

Waxed dental floss is preferred because it does not absorb water, which would add weight to the cell and affect the experiment's results.

What two solutions are used to fill the dialysis tubing, and what are their roles?

The dialysis tubing is filled with a glucose solution (orange) and a starch solution (cloudy white). Glucose is a building block of starch, so the glucose molecules are smaller than the starch molecules.

Why is it important to avoid trapping air inside the dialysis tubing?

Trapping air inside the tubing could interfere with the experiment by altering the mass or the diffusion process, as it may prevent the correct measurement of the liquid inside the tubing.

What is the purpose of the iodine or Lugol's solution added to the beaker containing the starch cell?

The iodine solution is added to detect starch diffusion. It turns blue or purple in the presence of starch, allowing us to track whether the starch escapes the dialysis tubing into the surrounding water.

What method is used to check for glucose diffusion from the glucose cell?

Glucose test strips are used to check for glucose diffusion. After some time, the strips are dipped into the water surrounding the glucose cell to see if a color change occurs, indicating the presence of glucose.

How do you measure the initial mass of the dialysis cells?

The initial mass of the dialysis cells is measured by placing the filled tubing on a balance and recording the weight, ensuring that the balance is zeroed to ignore the weight of the weighing boat.

What happens when the starch cell is placed in the iodine solution, and what does it indicate?

When the starch cell is placed in the iodine solution, the iodine will not turn blue or purple unless starch has diffused out of the cell. If the solution around the cell doesn't change color, it indicates that no starch has left the dialysis tubing.

Why is it important to rinse and dry the dialysis cells before measuring their final mass?

Rinsing and drying the dialysis cells ensures that any external water or liquid is removed, so the final mass accurately reflects the content of the dialysis tubing alone, not the water absorbed from the environment.

What conclusions can be drawn from the presence of a color change in the glucose test strips?

A color change in the glucose test strips indicates that glucose has diffused out of the glucose cell and into the surrounding water. The specific color change corresponds to the amount of glucose in the water.