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New techniques in cryogenics have resulted in 90 percent survival rates for thawed human eggs. This technique offers women an opportunity to store viable eggs prior to therapeutics that might damage her ability to produce healthy eggs. Years after freezing, the eggs can be thawed and fertilized. This new ability in extending egg viability presents an ethical dilemma. Should a woman who is in her 60s (average lifespan of 75) be permitted to parent a child who might well be motherless by the time the child is in his/her mid-teens?

by Michael DiSpezio

published online September 19, 2005

Freezing Life

Bakers yeast is a type of fungi that causes dough to rise. It is often sold freeze-dried in packets found in the refrigerated section of a food market. This process results in small pellets packed with yeast cells that remain in a state of suspended animation. When activated, the yeast "awake" and assume their regular metabolic activity. In this activity, you'll develop your own strategy for inquiry to explore yeast activation.




Yeast granules Warm water Sugar Test tubes Hand lens Assorted materials as required by individual experiments




1. Working with a partner, open a fresh packet of freeze-dried yeast. Divide the packet contents into five equal amounts. 2. Use a hand lens to examine yeast granules. Draw what you see. 3. Activate one of the five samples of yeast according to the instructions on the packet exterior. (Remember to use 1/5 of the ingredients identified in the instructions.) 4. Observe the yeast activation and note any changes in the yeast mixture appearance. 5. Make a list of all the factors that might affect yeast activation. 6. Select one of the factors you have identified. Design a controlled experiment that will test the effect of this factor on the activation of yeast. 7. Share your experimental design with your instructor. With his or her approval, proceed with your inquiry. 8. When your exploration is completed, present your findings to classmates. Use a poster board to display what you investigated and what you discovered about yeast activation.

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