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H2O2 and Yeast
Name: Pat G.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 2/19/2003
Question:
WoW! I am so impressed that this sight is available to
teachers,
I do an experiment with my student where they pour hydrogen peroxide over
yeast and it produces oxygen. I know yeast mixed with water yields carbon
dioxide. Please explain why or what is happening. No student has asked
as of yet because they are so excite about the resulting reaction when
they stick a glowing stick into the oxygen produced.
Replies:
Pat,
Glad you like the site. We are happy to assist.
As you probably already know, the source of oxygen is the decomposition of
the hydrogen peroxide into oxygen gas and water. The enzymes in the yeast
assist the decomposition. However, almost any finely divided solid will
accelerate peroxide's decomposition rate. Try the experiment using a small
amount of finely ground up salt or powdered sugar and compare the bubbling
rate with that produced when using yeast.. Be careful, do not start
experimenting, Some materials can decompose peroxide with explosive
violence.
Regards,
ProfHoff 571
The yeast contain an enzyme (that we have as well by the way) called
catalase. Metabolism in oxygen produces substances that are toxic to the
cells such as hydrogen peroxide and superoxide anion (free radicals).
Organisms must have a way of breaking this down or be poisoned. The enzyme
catalase turns hydrogen peroxide into water and oxygen, both harmless. So
when you pour hydrogen peroxide on the yeast, you are seeing the effect of
this enzyme and the chemical reaction it mediates. When yeast metabolize
sugar, they produce carbon dioxide as a by product of metabolism (which we
also do by the way-yet we exhale it). So the production of carbon dioxide
will not be immediate, but as they begin to use the sugar, bubbles will
appear. These bubbles will be carbon dioxide. They also produce ethanol
(alcohol) in the balanced chemical reaction. Bakers use yeast to rise
dough-the carbon dioxide escaping gets trapped as gas pockets in the dough
and it begins to expand. This also gives the bubbles in fermented beverages
such as beer (also alcohol). So yes, yeast do produce both gases but for
very different reasons and at different times and rates during their life
cycles.
Van Hoeck
I know that I speak for all of the contributors to Newton BBS that it is
our small way to contribute, to give back to our children and to their
teachers that spark of why?, how? and what if? that led each of us to
pursue his or her path in science. On this particularly sad day we reflect upon
those special scientists and engineers who have made their ultimate
contribution to each ones quests for knowledge. (2.Feb.2003)
Yeast mixed with water (and for even better results with a bit of sugar)
produce CO2, the reaction that causes bread to "rise". When you mix hydrogen
peroxide with yeast several things can occur that cause the evolution of
oxygen. It may oxidize any number of components present in a yeast culture,
or the microscopic particles of yeast can serve as sites for the spontaneous
decomposition of peroxide -- that is, it may just be a physical effect in
contrast to some chemical reaction.
Vince Calder
Hydrogen peroxide is a toxic by-product of respiration. Organisms that
obtain energy by oxidation of foods must develop mechanisms to limit the
damage it causes. This is primarily accomplished by a class of enzymes
called catalases, which catalyze the reaction
2 HOOH --> 2 H2O + O2
Yeasts can operate both in the presence and the absence of oxygen. In the
presence of oxygen, they break sugars down to water and carbon dioxide,
consuming oxygen and in the process making some unintended hydrogen
peroxide, which must be removed using catalase. So the yeast have catalase
ready to go. When hydrogen peroxide is added to them, it is broken down by
the catalase.
Humans, too, must de-toxify hydrogen peroxide produced in the process of our
metabolism. We, too, use catalase for this purpose. That is why hydrogen
peroxide foams when poured on a cut: the catalase in our tissues breaks
hydrogen peroxide down to may water and oxygen.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
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