In order to survive, all organisms need to move molecules in and out of their cells. Molecules such as gases (e.g., O2, CO2), water, food, and wastes pass across the cell membrane. There are two ways that the molecules move through the membrane: passive transport and active transport. While active transport requires that the cell uses chemical energy to move substances through the cell membrane, passive transport does not require such energy expenditures. Passive transport occurs spontaneously, using heat energy from the cell’s environment.
Diffusion is the movement of molecules by passive transport from a region in which they are highly concentrated to a region in which they are less concentrated. Diffusion continues until the molecules are randomly distributed throughout the system. Osmosis, the movement of water across a membrane, is a special case of diffusion. Water molecules are small and can easily pass through the membrane. Other molecules, such as proteins, DNA, RNA, and sugars are too large to diffuse through the cell membrane. The membrane is said to be semipermeable, since it allows some molecules to diffuse through but not others.
In this experiment, you will use a Gas Pressure Sensor to measure the rate of pressure change as water moves in to or out of the cell (dialysis tubes filled with various concentrations of sucrose solution). The pressure generated is called osmotic pressure and is in response to the overall movement of molecules, both water and sucrose, inside the dialysis cell.
In this experiment, you will
- Investigate the relationship between various non-polar molecular solutions and distilled water separated by a semi-permeable membrane using a Gas Pressure Sensor.
- Determine the water potential of potato cells.
Sensors and Equipment
This experiment requires each of the following Vernier sensors and equipment (unless otherwise noted):
You may also need an interface and software for data collection.What do I need for data collection?
Download Experiment Preview
The student-version preview includes:
- Step-by-step instructions for computer-based data collection
- List of materials and equipment
Note: The experiment preview of the computer edition does not include essential teacher information, safety tips, or sample data. Instructions for Logger Pro and other software (such as LabQuest App or TI handheld software, where available) are on the CD that accompanies the book. We strongly recommend that you purchase the book before performing experiments.