Pre-Lab: Detecting Diffusion
Problem How can you determine whether solutes are diffusing across a membrane?
Materials dialysis tubing, scissors, metric ruler, 250 mL beakers, twist ties, 10-mL graduated cylinders, 1% starch solution, iodine solution, forceps, 15% glucose solution, glucose test strip
Lab Manual Chapter 7 Lab
Skills Focus Use Models, Infer, Compare and Contrast
Connect to the The cell membrane forms a thin flexible barrier between a cell and its surroundings. The cell membrane controls what enters the cell and what leaves the cell. Diffusion is the process responsible for much of the movement across a cell membrane. During diffusion, solutes move from an area of high concentration to an area of lower concentration. When water is the molecule that is diffusing, the process is called osmosis. Proteins embedded in the membrane can facilitate the diffusion of many particles, including water. In this lab, you will use dialysis tubing to model the diffusion of small molecules.
Review What does it mean to say that a membrane is selectively permeable?
Explain Does the movement of molecules stop when the concentration of a solute is equal on both sides of a membrane? Explain.
Compare and Contrast What is the main difference between passive transport and active transport?
Preview the procedure in the lab manual.
Draw Conclusions How will you know whether starch has diffused across the membrane in Part A? How will you know whether iodine has diffused across the membrane?
Draw Conclusions How will you be able to tell whether glucose has diffused across the membrane in Part B?
Use Analogies How is a window screen similar to a cell membrane?
Visit Chapter 7 online to test yourself on chapter content and to find activities to help you learn.
Untamed Science Video Travel to the ocean's depths with the Untamed Science crew to explore how fish maintain water homeostasis.
Art in Motion View a short animation that explains the different types of active transport.
Art Review Review your understanding of plant and animal cell structures with this activity.
InterActive Art Build your understanding of osmosis and diffusion with these animations.
Visual Analogy Compare the structures of the cell to the parts of a factory.
Data Analysis Analyze data that explains why some cell types have more mitochondria than others.
Tutor Tube Hear suggestions from the tutor for help in remembering cell structures.