1) The experiment studied cellular respiration in yeast under different conditions by placing yeast suspensions in test tubes with various reagents and measuring CO2 production. 2) It found that the tube with glucose and yeast produced CO2 most prominently, while tubes without one of the essential factors (yeast or glucose) did not produce CO2. 3) The results indicate that for cellular respiration to occur in yeast, both yeast and a simple sugar like glucose must be present.

1. Cellular Respiration
in Yeast
DOMINGO,GALOS,GENUINO,HILVANO,LAPIRA,LOZANO

2. Abstract
Cellular Respiration, a process by which an organism
produces energy from energy molecules such as glucose or
fatty acids, occurs differently under certain conditions. This
report makes use of these differences by exposing yeast
suspension under different conditions.

3. 5 Smith Fermentation tubes were
prepared and placed with glucose with
yeast, glucose, boiled yeast with
glucose, starch solution with glucose
and yeast respectively. The rates of
CO2 formed by the yeast in each tube
were compared for 40 minutes.

4. Abstract
It can be concluded that under the condition by which
yeast and a simple sugar such as glucose is present, the
production of CO2 will form more prominently than the
others.

5. I. Introduction
All organisms need energy to survive. Cells use a
process called Cellular Respiration to acquire the energy
needed. In Cellular Respiration an organism’s cells transforms
energy molecules like starch or glucose into an energy
currency called Adenosine Triphosphate or ATP.

6. I. Introduction
Cellular Respiration can be classified as Aerobic or
Anaerobic Respiration. In Aerobic Respiration, cells will
breakdown glucose in the presence of oxygen through certain
processes to produce CO2 and H2O. Aerobic Respiration
usually occurs within the cells of animals such as humans.

7. I. Introduction
On the other hand, Anaerobic Respiration which can be
divided further more into Alcoholic Fermentation or Lactic
Acid Fermentation occurs without any oxygen. The only
difference between the two processes is that Alcoholic
Fermentation produces ethanol, ATP and CO2 while Lactic
Acid Fermentation produces Lactic Acid and ATP.

8. I. Introduction
In terms of completeness in breakdown and production
of energy and CO2, Aerobic Respiration is complete and
produces 6 moles of CO2 and 36/38 ATP while Fermentation
produces 2 ATP and 2 moles of Lactic Acid (Lactic Acid
Fermentation) or 2 moles of CO2 and a mole of ethanol.

9. I. Introduction
The experiment conducted aims to study the cellular
respiration in yeast by observing the results and taking note
of the condition at which they occur. Also, this experiment
aims to enumerate factors in cellular respiration by analyzing
and varying the reagent in each smith fermentation tube.

10. II. Methodology
• 5 Smith Fermentation tubes were filled with 20
ml of different reagents. (Glucose for the first
3 tubes, Starch for the 4th and water for the test
tube
• 20 ml water was added to each of the
tubes.
• 20 ml of yeast suspension was added to tubes
1,4 and 5 while 20 ml of boiled yeast suspension
was added to tube 3.
• Each tube were checked for air bubbles in the
tube and titled the tube horizontally while
covering the opening to remove them.
• The opening of each tube was covered with
cotton.
• The evolution of CO2 in each tube were recorded
and compared.

11. III. Results and Discussion
Cellular Respiration is spontaneous chemical process
wherein a cell makes energy by the transformation of energy
molecules such as sugars and fatty acids into ATP and certain
by-products. Cellular Respiration is divided mainly into
Aerobic Respiration and Anaerobic Respiration.

12. III. Results and
Discussion
Aerobic Respiration is the creation of
36/38 units of ATP, 6 moles of CO2 and 6
moles of H2O from the breaking down of
glucose through certain processes. It is
given by the equation:
C6H12O6 + 6O2  6CO2 + 6H2O+ 36/38 ATP

13. III. Results and
Discussion
Aerobic Respiration is divided into 3
major processes: Glycolysis, the Krebs
Cycle and the Electron Transport Chain.
The first step of any type of Cellular
Respiration is Glycolysis where the glucose
molecules are transformed into 2 moles of
pyruvic acid in the cytosol at the
consequence of using 2 units of ATP.
The energy input and output of glycolisis

14. III. Results and
Discussion
In this process, 4 units of ATP is produced for a
net total of 2 (subtracted from the 2 used), 2 units of
NADH+H and as said, 2 moles of pyruvic acid. The
pyruvic acid produced goes into a transitional stage
where the pyruvic acid is transformed into Acetyl CoA.
This product then goes into the Kreb’s cycle
where Acetyl CoA goes through numerous
transformations which will result into 8 units of NADH,
2 units of FADH2 and 4 units of ATP. This whole process
occurs inside the mitochondrial matrix of the cell.
Overview of pyruvate oxidation and Citric Acid
Cycle

15. III. Results and
Discussion
Lastly, the units of NADH and FADH2 proceed to
the cristae of the mitochondria where these products
are passed through certain pigments called cytochrome.
These carriers are then transformed into ATP.
The total units of ATP produced is 36 or 38 units
this is called the Electron Transport Chain. The reason for
the difference is due to the transportation of the NADH
produced in the cytosol to the mitochondrion of the cell.
There are 2 transportation systems: malate aspartate and
glycerol phosphate.
Free-energy change during electron transport

16. III. Results and Discussion
Under malate aspartate NADH can pass through the complete
Transport chain thus producing 6 for the two NADH while in glycerol
phosphate it will produce 4.
Anaerobic Respiration on the other hand is the production of
Energy from the enzymatic breakdown of Glucose to produce energy
this process is done without oxygen.

17. III. Results and Discussion
Unlike its oxygen using counterpart, Anaerobic Respiration is much
more inefficient in the production of ATP producing just 2 units of ATP. In
Anaerobic Respiration, only glycolysis takes place and the NADH produced
will be used in the repetition of glycolysis. This process has two different
types: Alcoholic Fermentation and Lactic Acid Fermentation. Alcoholic
Fermentation is the production of Ethyl Alcohol, 2 moles of CO2 and 2 units
of ATP.

18. C6H12O6  2CO2 + C2H5OH + 2 ATP
This type of respiration occurs in yeast and some plant cells.

19. III. Results and Discussion
The other type of Anaerobic Respiration is Lactic acid Fermentation
which is the enzymatic breakdown of glucose into Lactic acid and 2 units of
ATP. It is given by the equation:
C6H12O6 → C3H6O3 + 2 ATP
This type of respiration is seen in bacteria and muscle cells. This is
the main reason for cramping in our muscles

20. III. Results and Discussion
In Cellular Respiration, there are two processes which can be observed in the
production of energy. The first is called substrate phosphorylation. It occurs when a
molecule of ADP reacts with a phosphate group from a substrate to produce ATP. This
type of Phosphorylation is seen in Glycolysis and also in the Kreb’s Cycle.
The other type of phosphorylation is called Oxidative Phosphorylation. This is
the process that creates the most number of ATP. This is only seen in Aerobic
Respiration and it occurs when an ADP combines with a phosphate group in the
electron transport chain.

21. In the experiment, mixtures were placed in separate
Smith Fermentation tubes. The diameter of the circle was
measured to compare the amount of carbon dioxide formed.
Tube No. Contents (excluding H2O)
1 Glucose +Yeast
2 Glucose
3 Boiled Yeast + Glucose
4 Starch Solution + Yeast
5 Yeast
min. 1 2 3 4 5
5m 0.02mm n/a 0.15mm 0.08mm 0.1mm
10m 0.03mm n/a 0.18mm 0.10mm 0.1mm
15m 0.04mm n/a 0.20mm 0.10mm 0.1mm
20m 0.05mm n/a 0.21mm 0.14mm 0.1mm
25m 0.05mm n/a 0.24mm 0.15mm 0.1mm
30m 0.05mm n/a 0.25mm 0.15mm 0.1mm
35m 0.5mm n/a 0.25mm 0.20mm 0.1mm
40m 0.5mm n/a 0.26mm 0.20mm 0.1mm

22. III. Results and
Discussion
After shaking vigorously, spontaneous
production of CO2 was observed. Since it
produced bubbles instead of one big bubble, the
amount was then just compared to one another.
Content Amt. of bubbles
Glucose +Yeast Large production
Glucose No Bubbles
Boiled Yeast + Glucose 1 small bubble
Starch Solution + Yeast 2 large bubbles with a
small prod of bubbles
Yeast No Bubbles

23. III. Results and
Discussion
The production of CO2 was observed in
Tube 1, Tube 3 and Tube 4.
The evolution of CO2 is very fast and the
bubbles were numerous in tube 1 this was
because glucose was readily available for the
respiration of the yeast. In tube 3, there should
be no CO2 because yeast dies in high
temperature. The presence of CO2 in tube 3 is
probably due to the incomplete heating of the
yeast suspension.

24. III. Results and Discussion
Lastly, in tube 4 there was little evolution of CO2 this is because
to respire, yeast must secrete amylase to break down the starch into
glucose and not all yeast can produce amylase and even if they could
this will take more time. For tubes 2 and 5 Respiration was not present
because one of the essential factors was absent (yeast in tube 2 and
glucose in tube 5).

25. III. Results and Discussion
There are several factors in which respiration will occur, let’s
discuss them one by one:

26. III. Results and
Discussion
Amount of
Nutrients
The more nutrients that is available to transform, the
more energy results in the cellular respiration process. The
types of nutrients that can go through the cellular respiration
process and transform into energy are namely fat, proteins
and carbohydrates. This also includes amino acids and fatty
acids. The carbohydrates converts to glucose, the fats go
through the citric acid cycle and the proteins break down and
go through glycolysis. The amount of nutrients available to
transform into energy depend on the diet of a person. The
nutrients go through three processes in cellular respiration.
The processes are glycolysis, Kreb’s cycle and the cytochrome
system.

27. III. Results and
Discussion
Temperature
Another factor affecting the cellular
respiration is the temperature of the
environment. Usually, the rate of cellular
respiration quickens if the temperature is
warmer. The lower the temperature, the slower
the rate of cellular respiration is. People who live
in warmer environments find it easier to restore
their energy as long as there are nutrients
available to convert in the body.

28. III. Results and
Discussion
Temperature
The reason for this is the enzymes that
are present in the cellular respiration process.
Enzymes break down easier and then transform
into energy quicker when the temperature is
higher. Although the temperature affects the
rate of cellular respiration, there are no studies
that prove more energy production with higher
temperatures. The temperature factor just
affects the rate of the cellular respiration
process.

29. III. Results and
Discussion
State of
Cell
The state of a cell undergoing the cellular respiration
process is a factor that affects the rate of transforming
nutrients into energy. Working cells, such as neurons or roots
of the human hair, have a higher cellular respiration rate
compared with dormant cells like seeds. This is because
working cells can store extra energy in the body while dormant
cells tend to stay non-motile. For this reason, plant cells do
not need to store as much energy as human cells or animal
cells do. This is the reason why cellular respiration in plants is
a bit different from the cellular respiration process human
and animal cells go through.

30. III. Results and
Discussion
Substrate
Present
As seen with the experiment the type of
substrate to be used in Respiration is quite
important. As for the case of the yeast, if glucose,
starch and maltose are placed in different tubes,
glucose will still be the fastest. Though there are
numerous glucose molecules in both maltose and
starch, the yeast will need to release enzymes which
may not be available to them and even if they are it
would take time compared to an environment
where glucose is readily available.

31. III. Results and
Discussion
Substrate
Present
In the experiment, yeast was observed to use
energy through Alcoholic Fermentation.
Though yeast can produce through both
Aerobic and Alcoholic Fermentation, it can be
deduced that it is anaerobic because the cotton was
placed to block any oxygen had there been oxygen
the amount of CO2 would have been much greater.

32. IV. Conclusion
The rate of cellular respiration is affected by the conditions in
which it takes place. When yeast and a simple sugar such as glucose is
present during the cellular respiration, the production of CO2 will form
more prominently than the others

33. References
Biology 10 (General Biology) Laboratory Manual. Department of
Biology - College of Arts and Sciences - University of the Philippines,
Manila. Print.
Campbell, N.A., Reece, J.B. & Meyers, N. (2006). Biology. Frenchs
Forest: Pearson Education
Delos Reyes, J. (2006). Introduction to Biology: Principles and
Processes (6th ed.). Department of Biology, College of Arts and
Sciences, University of the Philippines Manila.