One of the things that makes biology fascinating to so many people is its complexity. Consider what we've already learned about cells: the many different kind of cells, the specialized structures within cells, and the many molecules that have evolved to carry out those functions.

Studying the relationship between the structure and function of even a single molecule can be a monumental task. Sometimes biologists first have to isolate an organism in its environment. A particular cell may need to be isolated from tissues or organs. Much of the work comes in isolating the molecule of interest from the many other kinds of molecules in the cell.

We'll get a feel for how biologists do that in this Virtual Lab. Our goal is to isolate hemoglobin molecules from blood. As we conduct the experiment, we'll learn some important techniques that apply what we've already learned about cells and cell membranes.


  • Define the term "water potential."
  • Explain how to measure the water potential of a solution.
  • Describe how a laboratory centrifuge works.
  • Define the terms "hypotonic," "isotonic," and "hypertonic."
  • Explain what happens at the molecular level when a cell is placed in hypotonic or hypertonic solutions.
  • Describe the biological consequences of water gain or loss in a cell.
  • Define the term "plasmolysis."
  • Explain why plant cells thrive in hypotonic solutions, while animal cells may rupture.
  • Calculate the percent viability of a cell sample.
  • Use cell viability data to determine the best solution for hypotonic lysis.
  • Explain the molecular basis for selective precipitation.
  • Explain how selective precipitation can be used to separate a mixture of proteins.
  • Illustrate the processes of diffusion and osmosis during a dialysis experiment.
Last modified: Sunday, October 3, 2010, 10:17 PM