1. The document discusses cellular respiration and fermentation in yeast cells. It provides background on how cells harvest energy from food sources and defines aerobic respiration, which uses oxygen to break down glucose, and anaerobic respiration, called fermentation, which occurs without oxygen. 2. The main steps of aerobic respiration and fermentation are described. Aerobic respiration breaks down glucose and oxygen to produce carbon dioxide, water, and ATP. Fermentation produces ethanol or lactic acid instead of using oxygen. 3. Yeast undergoes alcoholic fermentation, converting pyruvic acid to carbon dioxide and ethanol with some ATP also produced. The rate of carbon dioxide production during fermentation would be affected by the availability of

1. December
20, 2015
PRACTICAL CELL BIOLOGY LAB 9
Cellular Respiration and Fermentation in Yeast
BACKGROUND
Living systems require free energy and matter to maintain order, to grow,
and to reproduce. Energy deficiencies are not only detrimental to individual
organisms, but they cause disruptions at the population and ecosystem levels as
well. Organisms employ various strategies that have been conserved through
evolution to capture, use, and store free energy. Autotrophic organisms capture
free energy from the environment through photosynthesis and chemosynthesis,
whereas heterotrophic organisms harvest free energy from carbon compounds
produced by other organisms. In cellular respiration, free energy becomes available
to drive metabolic pathways vital to cellular processes primarily by the conversion
of ADP → ATP.
Cellular respiration is the process that cells use to transfer energy
from the organic molecules in food to ATP. The following equation
summarizes the chemical changes that occur in cellular respiration of the
monosaccharide glucose when oxygen is available.
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (as ATP)
The word equation for this is:
Glucose (sugar) + Oxygen → Carbon dioxide + Water + Energy (as ATP)
All living cells, including the cells in your body and unicellular such
as yeast, need energy for cellular processes such as pumping molecules
into or out of the cell, synthesizing needed molecules, their metabolism,

2. December
20, 2015
PRACTICAL CELL BIOLOGY LAB 9
their activity. ATP is a special molecule which provides energy in a form
that cells can use for cellular processes.
There is another important feature of cellular respiration which is
not shown in above equation. Cellular respiration involves many small
steps; these multiple steps allow the cell to use the energy from each
glucose molecule efficiently in order to make as many ATP molecules as
possible. The multiple steps of cellular respiration are described in your
textbook. Our description will focus on some major steps and how these
steps differ, depending on whether oxygen is available or not.
The first major step in cellular respiration is glycolysis
1 glucose converts to2 pyruvate + 2 ATP
What happens next depends on whether or not oxygen is available to the
cells. When oxygen is available, cells can use the Krebs cycle and the
electron transport chain to make up to 36 ATPs (see the right side of the
figure).
2 pyruvate + 6 O2 convert to6 CO2 + 36 ATP
Cellular respiration that uses O2 is called aerobic respiration. Most
of the time, the cells in our bodies use aerobic respiration. When oxygen is
not available, cells use anaerobic processes to produce ATP.

3. December
20, 2015
PRACTICAL CELL BIOLOGY LAB 9
Aerobic respiration
Is the process that takes place in the presence of oxygen and involves
break down of fuel molecule to obtain energy. The process of obtaining
energy in aerobic respiration can be represented in the following equation:
Glucose + Oxygen -------------->Energy + Water + Carbon dioxide
Anaerobic respiration
Is the process of oxidation of molecules in the absence of oxygen to
produce energy in the form ATP. Anaerobic respiration is synonymous with
fermentation. There are two types of fermentation
1. Lactate fermentation (Glucose -------------->energy + Lactic Acid +
Carbon dioxide).
2. Alcoholic fermentation (Glucose -------------->energy + Ethanol +
Carbon dioxide)

4. December
20, 2015
PRACTICAL CELL BIOLOGY LAB 9
Fermentation has two disadvantages compared to aerobic respiration.
 Low ATP production.
 Produces a toxic byproduct (lactic acid or alcohol).
Yeasts are tiny single-celled (unicellular) fungi. The organisms in
the Kingdom Fungi are not capable of making their own food. Fungi, like
any other organism, need food for energy. They rely on sugar found in
their environment to provide them with this energy so that they can grow
and reproduce.
Yeast will undergo alcoholic fermentation, which converts pyruvic acid into
CO2.as well as alcohol, Overall, the final equation for glycolysis plus fermentation
would be:
C6H12O6  2CO2 + 2C2H5OH, with 2 ATP also produced.
For the yeast cell, this chemical reaction is necessary to produce the energy
for life. The alcohol and the carbon dioxide are waste products produced by the
yeast. Fermentation can be watched and measured by the amount of carbon dioxide
gas that is produced from the breakdown of glucose.
Do you think that the rate of carbon dioxide production during fermentation
would be affectedby the availability of simple sugars?
PROCEDURE1:
1. Get two plastic cups and label them A and B.
2. Put water, sugar and yeast in cup A
3. Put water and yeast in cup B
4. Close the opening both cups with balloon
5. Wait for 1hr
6. Note the result.