The Effects of UV Light on
Yeast Cell Respiration
1
Problem
-Ultraviolet light is an inherent risk for many terrestrial
organisms.
-UV light exposure varies due to altitude, shade, and
ozone shield.
-What cell activities are compromised by UV exposure?
2
Ultraviolet Light
- Electromagnetic radiation with a wavelength ranging from 100 nm to
400 nm.
- Can cause sun burn, lead skin cancer, increase the appearance of
aging, harm eyes, and damage DNA.
- To prevent these effects, it is suggested to wear sunglasses, hats,
protective clothing, and sun screen.
- Sources include the sun, tanning beds, and fluorescent lamps.
3
Stressed Cells
- UV light can stress
cells and interfere
with their ability to
carry out basic
functions.
- Oxidative stress is a
condition where
oxidant production
increases, free
radicals accumulate,
and cellular
degeneration occurs.
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Yeast
- Unicellular eukaryotic micro-organism in the kingdom Fungi.
- Common model organism in the research of modern cell biology.
- Similar cell cycle, DNA replication, recombination, cell division,
and metabolism to humans.
- Saccharomyces cerevisiae (baker’s yeast) is a species of budding
yeast and is often used in the food industry.
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Aerobic Cellular Respiration
- Set of metabolic reactions.
- Includes glycolysis, Kreb’s cycle, and the electron
transport chain.
- Process in which the cell yields energy in the form of
ATP.
- Substances such as FADH2, NADH, and CO2 are also
yielded.
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Aerobic Cellular Respiration (cont.)
7
Effects of Different Isomers of
Sugar on Yeast Respiration
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Purpose
To determine if ultraviolet light has an effect on
the aerobic cellular respiration of Saccharomyces
cerevisiae.
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Hypotheses
Hypothesis:
Ultraviolet light will significantly decrease the cellular
respiration of yeast.
Null Hypothesis:
Ultraviolet light will have no significant effect on the
cellular respiration of yeast.
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Materials
- Packs of Red Star® Quick
Rise Yeast
- 125 mL Erlenmeyer flasks
- Party Express helium quality
balloons (9 in.)
- Plastic Weigh boats
- Sugar
- Plastic tubs
- Large plastic bin
- 250 mL graduated
cylinders
- 250 mL graduated
cylinders
- Laminar Flow Hood UV
Light
- Plastic wrap
- Water
- Deionized water
- Pipettes
- Incubator
- YEPD agar plates (1% yeast
extract, 2% peptone, 2%
dextrose, 1.5% sugar)
- Spreader bars
- Sterile dilution fluid (SDF)
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Procedure
1. 4.00 grams of Red Star® Quick Rise yeast granules were spread
into a monolayer on the plastic weigh boats.
2. Plastic weigh boats were positioned underneath a Laminar Flow
Hood UV Light. The different exposure times for each group were 0
seconds, 30, 90, and 150 seconds.
3. UV light was turned on and each group of yeast received its
designated exposure before being removed.
4. 0.60 grams of sugar (sucrose table sugar) and 30.0 mL of
deionized water were added to each Erlenmeyer flask.
5. Flasks were swirled to dissolve sugar.
6. Yeast samples were transferred into flasks with the water and
sugar.
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Procedure (cont.)
7. Immediately, Party Express helium quality balloons were affixed
to the rims of the flasks.
8. Flasks were gently swirled to suspend the yeast.
9. The flasks were transferred to a 30 °C water bath and incubated
for one hour.
10. The displacement of water was used to determine the amount of
gas produced.
(250 mL graduated cylinders were filled with water and inverted
into a half filled tub of water. The nozzle of the balloon was
pinched and placed in the inverted graduated cylinder. The air
from the balloon was released slowly. The volume of the gas was
recorded.)
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Pictures of the Experiment
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Procedure (UV Survivorship)
1. 0.2 grams of Red Star® Quick Rise yeast granules were
spread into a monolayer on the plastic weigh boats.
2. Plastic weigh boats were positioned underneath a
Laminar Flow Hood UV Light. The different exposure
times for each group were 0, 30, 90, and 150 seconds.
3. UV light was turned on and each group of yeast
received its designated exposure before being removed.
4. Yeast was poured into a tube containing 10 mL sterile
dilution fluid (SDF).
5. After vortexing, serial dilution was performed to yield
a countable number of colonies.
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Procedure (UV Survivorship cont.)
100 uL
Weigh Boat
YEPD
Plates
10 mL SDF
8. Solution from tube was spread out into YEPD plates.
9. Plates were incubated for one day.
10. Colonies in YEPD plates were counted.
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UV Stressed Yeast Survivorship
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UV Stressed Yeast Survivorship (cont.)
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UV Exposure Time Selection
- The yeast used in finding the effects of UV light on
cellular respiration of yeast were granules.
- However, the yeast used in UV light survivorship
experiments were suspended in fluid and plated.
- The granular form is thought to be more resistant to
radiation and thus UV exposure range was increased.
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The Effects of UV Light on Yeast
Respiration
Amount of CO2 (mL)
120
P-Value is
0.013807
106.25
100
94.25
93.75
30
90
88.25
80
60
40
20
0
0
150
Time of UV Light Exposure (Seconds)
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Dunnett’s Test Chart
The T critical value is 2.68.
Exposure
Times
T Value
Interpretation
30 seconds
2.60
2.73
3.90
Not Significant
90 seconds
150 seconds
Significant
Significant
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Respiration and Survivorship
(Relative to the Control)
30
90
150
seconds seconds seconds
Cell
Respiration
88.7%
88.2%
83.1%
Survivorship
103%
83.0%
20.4%
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Conclusion
Hypothesis:
ACCEPTED
The total amount of cellular respiration that occurred
in the ultraviolet light exposed yeast samples was
significantly less than the amount in the control.
However, this could be because the yeast died and the
rate of cell respiration was not affected.
Null Hypothesis:
REJECTED
The total amount of cellular respiration that occurred
in the yeast samples was significantly affected by the
ultraviolet light.
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Interpretation
Puzzle (?)
Why did the 150 second exposure cells yield such a large
volume of CO2?
- The data suggests that (1) the cell respiration increased
dramatically in the individual cells for that group, or (2)
that the cells were able to survive for the short remaining
time of the respiration experiment, but did not survive
for the one day toxicity incubation.
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Limitations: Extensions:
- Amount of time allowed
for the yeast to perform
cell respiration.
- The temperature
conditions during the
experiment were not ideal
for the respiration.
- Amount of trials and
different UV exposure
times.
- Test the effect UV light has on
some of the other functions of
an organism.
- Investigate the effects UV
light has on the cell respiration
of other organisms.
- Observe yeast cell respiration
in other potentially harmful
circumstances.
- Stress the yeast cells, perform
the respiration experiment and
immediately perform a Trypan
Blue exclusion assay.
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Works Cited
Nelson, Andrew. "Saccharomyces Cerevisiae." BioWeb Home. Web. 22 Jan.
2011. <http://bioweb.uwlax.edu/bio203/s2007/nelson_andr/>.
Bailey, Regina. "Cellular Respiration." Biology. Sat. 15 Jan. 2011.
<http://biology.about.com/od/cellularprocesses/a/cellrespiration.htm>.
"UV Radiation." NASA Advanced Supercomputing (NAS) Division Home Page.
Web. 15 Jan. 2011.
<http://www.nas.nasa.gov/About/Education/Ozone/radiation.html>.
Zeman, Gary. "Ultraviolet Radiation." Health Physics Society. Web. 23 Jan.
2011. <http://www.hps.org/hpspublications/articles/uv.html>.
Schuster, Tom, Rosalie Van, and Harold Coller. "Yeast Respiration." California
State University, Northridge. Web. 27 Jan. 2011.
<http://www.csun.edu/scied/2-longitudinal/schuster/index.html>.
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