Download Diffusion and Cell Membranes

Diffusion and Cell Membranes
Skills • modeling a cell with a cell membrane
• observing the process of diffusion through a cell membrane
• predicting the direction of diffusion
• measuring the mass of an egg
Objectives : • Explain changes that occur in a cell as a result of diffusion.
• Distinguish between hypertonic and hypotonic solutions.
Purpose: In this lab, you will use eggs with a dissolved shell as a model for a living
cell. You will then predict the results of an experiment that involves the movement of
water through a membrane.
Background: Some chemicals can pass through the cell membrane, but others
cannot. Not all chemicals can pass through a cell membrane with equal ease. The cell
membrane determines which chemicals can diffuse into or out of a cell.
As chemicals pass into and out of a cell, they move from areas of high concentration
to areas of low concentration. Cells in hypertonic solutions have solute concentrations
lower than the solution that bathes them. This concentration difference causes
water to move out of the cell into the solution. Cells in hypotonic solutions have
solute concentrations greater than the solution that bathes them. This concentration
difference causes water to move from the solution into the cell. The movement of
water into and out of a cell through the cell membrane is called osmosis.
Predictions: Predict how the mass of each egg will change after 24 hours in each
liquid. (HINT: An egg is surrounded by a membrane. Inside the membrane, the egg
white consists mainly of water and dissolved protein. The yolk consists mainly
of fat and water. Syrup is sugar dissolved in water. The protein, fat, and sugar
are solutes.) Record your predictions in the data table 1. After 24 hours, observe your
eggs and record your observations and measurements.
What will have occurred if your egg gains or loses mass?
Table 1: Egg Observations
Egg
Liquid environment
1
2
3
Predicted Change after
24 hr
Observations after
24 hr
Table 2: Mass Differences of Eggs in Different Solute concentrations.
Mass
Percent Change in Mass*
Egg
Initial Mass Final Mass
Difference
(show work)
1
2
3
*To calculate Percent Change in Mass: Final Mass – Initial Mass x 100
Initial Mass
Analysis and Conclusions:
1. What effect did the vinegar have on the eggs?
2. What caused the change in appearance in Egg 1 after it soaked in water?
3. Why did the mass of the egg increase after soaking in the vinegar solution?
4. What material seems to have moved through the membrane of Egg 2 after it was
soaked in the syrup? In what direction did it move?
5. Which egg was in a hypertonic solution? Explain.
6. Which egg was in a hypotonic solution? Explain.