Abstract:
In this experiment, my partner, Chris
Jung, and I explored the effects that pH had on the cell respiration of yeast.
We altered the pH of 3 different yeast/water/glucose solutions, while keeping a
control solution. Thus, we ended up with one acidic solution with a pH of 1-2,
our control at a pH of 7, and two basic solutions with a pH of 8 and 9. We
measured the rate of cell respiration by the amount of CO2 created.
The results showed that the optimum pH for the cellular respiration of yeast is
more acidic than basic, and is closer to 7 than 1 or 2.
Background:
Cellular Respiration is a process
that is essential to all life. Through cell respiration, ATP is captured from
the chemical energy released after digesting foods like carbohydrates, fats,
and proteins.
The process
of Cellular Respiration uses the fuel of glucose/fructose/galactose and oxygen
to create carbon dioxide, water, and 36-38 ATP, which is then used to normal
bodily functions. This can be seen in the chemical formula, C6H12O6 +6O2 → 6CO2
+ 6H2O + 36-38 ATP.
There are three parts to Cellular
Respiration: Glycolysis, Krebs cycle, and oxidative phosphorylation. In
glycolysis, which occurs in the cytosol of the cell, the 6 carbon
(glucose/fructose/galactose) is broken down, through the investment of 2 ATP,
into 2 three carbon chains a.k.a pyruvate. The pyruvate molecules are then
oxidized and both lose one Carbon in the form of Carbon Dioxide. These 2 two
carbon chains, acetyl coA, are then taken into the matrix of the mitochondria
to participate in the krebs cycle. Here, NADH and FADH2 are formed
and carry electrons off to the Christae and Electron Transport Chain. In this
last phase of Cellular respiration, the electrons are transferred through
carriers from one protein to another, with oxygen being the final acceptor.
Each time, hydrogen is attracted and led out the membrane. Eventually, a higher
concentration of Hydrogen is formed on the outside compared the inside. This
group of protons goes through chemiosmosis, and is pumped through the membrane
by the ATP synthase. Once pumped through, the hydrogen join oxygen to create
water. The energy released during this process is used to form ATP.
However, we know that because yeast
is unable to go through aerobic respiration, it goes through fermentation a
form of anaerobic respiration. In fermentation,
C6H12O6 (glucose)
→ 2 C2H5OH (ethanol) + 2 CO2 (carbon dioxide),
Glucose is
changed into energy, with ethanol and carbon dioxide as the waste products. In
yeast, there the enzyme zymase is responsible for breaking glucose
anaerobically to ethanol and CO2.
Hypothesis:
Because yeast is able to go through
cellular respiration in solutions with plain water, the farther away the pH in
a yeast solution is from 7 the slower the rate of cellular respiration will be.
Out of all our experiments, our control will have the best results.
Materials:
·
4
test tubes
·
Salt
·
Glucose
·
Yeast
·
Warm
water
·
4
test tube stoppers with holes and pipes in them
·
4
syringes that connect to the test tubes pipes
·
Timer
·
Test
tube rack
·
HCL
·
NaOH
Procedure:
1.
Before
you start, collect the 3 solutions that your teacher so kindly created for you,
because you were too slow. These solutions should then be labeled with their
appropriate pH levels: 1-2, 8, and 9. These solutions were created by a mixture
of water and HCL or NaOH.
2.
Collect
4 test tubes and label them, 1, 2, 3, and 4.
3.
Fill
each test tube with 1 gram of yeast and 1 gram of salt each.
4.
Fill
test tube # 1 with 35 mL of warm water
5.
Fill
test tube #2, with 35 ml of the solution with a pH of 1-2, test tube #3 with
35mL of the solution with a pH of 8, and test tube 4 with 35 mL of the solution
with a pH of 9.
6.
Connect
each test tube with a stopper, tube, and a syringe.
7.
Make
sure each syringe is starting around 2.0 ml
8.
Wait
5 minutes for the process of cell respiration/fermentation to begin.
9.
After
the 5 minutes, every minute measure the amount of CO2 produced.
a.
To
measure how much CO2 is being released, push down the syringe, then wait for it
to rise, and read the new number.
10. Do this for 10 minutes, or as long as
you can to get some clear results.
Results:
Time (min) \ pH
|
7 (control)
|
1-2
|
8
|
9
|
1
|
2.3
|
2.4
|
2.0
|
2.1
|
2
|
2.4
|
2.2
|
2.2
|
2.4
|
3
|
2.4
|
2.0
|
2.4
|
2.4
|
4
|
2.5
|
1.9
|
2.5
|
2.4
|
5
|
2.6
|
1.2
|
2.6
|
2.4
|
6
|
2.8
|
0
|
2.6
|
2.4
|
7
|
2.9
|
0
|
2.8
|
2.6
|
 |
All four lines should have started 2.0 and should have continued to 7 minutes. There were some technical difficulties.
The Title of this chart is effects of pH on production of CO2 |
In this experiment, the pH of the
environment of the yeast was changed. The results matched my hypothesis.
Because of fact that yeast can release carbon dioxide normally with simple tap
water already, it was hypothesized that the amount of co2 produced would be
greatest the closer to the pH of 7, like our control.
The results show that our control,
the yeast solution made with only water (pH of 7), had the greatest amount of
carbon dioxide emission. Solution 3 and 4 had the next greatest amounts of CO2 emission,
in that order. This makes sense seeing as how solution 3 (pH of 8), which is
closer to solution 1 in terms of pH instead of solution 4, had a greater
emission than solution 4. Solution 2, with a pH of 1, had the lowest amount of emission;
in fact, there was absorption of CO2 apparently. This, however, may have been a
result of a leak. Still, if it was intentional, it makes sense, for the enzymes
in the yeast, zymase, was denatured, and forced into a habitat far from its optimal level.
After some research, I found that
the optimal pH level for zymase is 6 (5-7), proving the results of my
experiment. Though there were many small errors in my lab report, like not
capping the test tubes immediately, the results were still able to be
conclusive, and accurate.
For future experiments, I would hope
to use more solutions, one for the pH levels of 1-14. I would also like to take
measurements every 10 minutes, for I had run out of time during this
experiment.
