AP Biology Lab: Cellular Respiration
Adeel Kadeer
Per. 5
1/21/09
Background Information
Cellular respiration is the process of oxidizing food molecules, like glucose, to
carbon dioxide and water. The energy released is trapped in the form of ATP for use by
all the energy-consuming activities of the cell. Mitochondria are membrane-enclosed
organelles distributed through the cytosol of most eukaryotic cells. Their main function is
the conversion of the potential energy of food molecules into ATP. Because respiration
causes the release of CO2, plants have to respire because plant cells use the CO2 during
photosynthesis to form new carbohydrates. Also in the process of cellular respiration,
oxygen gas is required to serve as an acceptor of electrons. This oxygen is identical to the
oxygen gas given off during photosynthesis. Also, plants use cellular respiration to
produce energy to transporting sugars, and also for growth and development.
In this experiment, we were required to research seeds. A seed is a small
embryonic plant enclosed in a covering called the seed coat, usually with some stored
food. There are two types of seeds, gymnosperm and angiosperm. Gymnosperms are
plants whose seeds are not enclosed in an ovule (like a pine cone). Gymnosperm means
as "naked seed". Angiosperms are plants in which the mature seed is surrounded by the
ovule (think of an apple). A typical seed includes three basic parts: (1) an embryo, (2) a
supply of nutrients for the embryo, and (3) a seed coat.
The embryo is an immature plant from which a new plant will grow under proper
conditions. The radicle is the embryonic root. The plumule is the embryonic shoot. The
embryonic stem above the point of attachment of the cotyledon(s) is the epicotyl. The
embryonic stem below the point of attachment is the hypocotyls.
One important function of most seeds is delaying germination, which allows time
for dispersal and prevents germination of all the seeds at one time. The staggering of
germination safeguards some seeds and seedlings from suffering damage or death from
short periods of bad weather or from transient herbivores; it also allows some to
germinate when competition from other plants for light and water might be less. Many
species of plants have seeds that germinate over many months or years, and some seeds
can remain in the soil seed bank for more than 50 years before germination. This is
referred to as dormancy.
Statement of Problem
We will determine the effect of temperature and germination vs. no germination on
cellular respiration.
Hypothesis
If we allow the germinated peas to sit in room temperature for a period of time, then the
peas will respire, by producing CO2, because plant cells also contain mitochondria and
need to respire for additional energy.
Experimental Design
Variable
Independent Variable: Germinating Peas and temperature (room vs. cold
Dependent Variable: Percent of light transmittance after 4 days
Control: Glass Beads
Constants: Time, Amount of Bromothymol Blue in each plastic container, number of
peas, percentage of light transmittance at beginning of experiment, paper towel.
Materials
 25x Germinated peas
 25x Non-Germinated peas
 25x Glass beads
 Graduated cylinder
 Bromothymol Blue
 Plastic cups
 Glass container
 Water
 Large Plastic containers
 Paper towel
 Paper cups
 Refrigerator
 Spectrophotometer
Procedure
1. Using water displacement, determine the volume of 25 germinating peas. To do this
place 20 mL of water into a graduated cylinder. Drop 25 germinating peas into
cylinder and record the change in volume. Remove the water without losing any peas.
2. Remove peas onto a piece of paper towel, cover the peas and place in paper cup.
3. Add 10 ml of water to the paper towel to aid in respiration.
4. Repeat steps 1 and 2 for 25 non-germinating peas
5. Repeat steps 1-3 for 25 glass beads.
6. Repeat steps 1-5 once more.
7. Fill 6 small plastic cups with 20 mL of bromothymol blue.
8. Place one plastic cup and one paper cup to each of the 6 larger plastic containers.
9. Label each of the large plastic containers as follows:
 1-Germinating peas-Room Temperature
 2-Non-Germinating peas-Room Temperature
 3-Glass beads-Room Temperature
 4-Germinating peas-Cold Temperature
 5-Non-germinating peas-Cold Temperature
 6-Glass Beads- Cold Temperature
10. Close each container. Place Containers 4-6 in the refrigerator.
11. After 4 days, open first container and take 10 mL of bromothymol blue into special
glass container for spectrophotometer. Make sure to zero out spectrophotometer.
12. Measure and record the light transmittance of the bromothymol blue.
13. Repeat steps 11-12 for every container.
14. Graph your table.
Results
Type of Pea
Volume Before
Volume After
Germinating Peas
20 mL
27 mL
Non-Germinating Peas
20 mL
23 mL
Number of Container
Light Transmittance
Before
Light Transmittance
After
1
18%
76%
2
18%
16%
3
18%
19%
4
18%
72%
5
18%
18%
6
18%
21%
Conclusion and Validity
At the end of this experiment, it can be determined that plant cells respire as well
as photosynthesize. The bromothymol blue is used to determine whether there is CO2
released or not. This was demonstrated the day before the lab when we were told to blow
into a neutral bromothymol blue solution. The result was that it changed color from blue
to green/yellow demonstrating that there was CO2 present. As you can see from our data,
both the room temperature container and cold temperature container (with germinating
peas) showed a dramatic change of color. What it shows is that the peas were releasing
CO2. The question is why? The answer is that plants also respire which is also stated in
my hypothesis. Plant cells contain mitochondria just like in humans so plants use the
mitochondria to create energy as well. They use this energy for cellular functions and
keep the plant stable. Therefore, a plant could not live without respiration.
As for cold temperature, there was not a dramatic effect of temperature on the
respiration of the peas. In fact most of the results were the same whether they were room
temperature or cold temperature. Even the non germinating peas remained the same.
Therefore, I conclude that cold temperature would not have a great effect on the
respiration of the peas.
There were many hidden variables in this experiment that could have caused the
data to become invalid. For example, when we put the 20 mL of bromothymol blue into
the large plastic container, we were continuously breathing onto the bromothymol blue
which may have caused it to slightly change color. Then when we closed the tops of the
containers, the CO2 may have still been trapped in the container causing slight distortions
to our data. If I were to perform this experiment again, I would add face masks to the list
of materials for the students to wear. This would prevent our breath from getting into the
bromothymol blue.
Another error that may have occurred was measuring the percent light
transmittance of the bromothymol blue and after the experiment. As you can see from our
data, the light transmittance for container number 2 (the non germinating room
temperature peas) went from 18% to 16%. The expected result was that it would stay the
same because non germinating peas do not respire. One reason this may have occurred
was that there was an error in measuring the light transmittance before we started the
experiment. Perhaps the bromothymol blue was not at its most neutral form in the
beginning of the experiment. Or perhaps the glass container for the spectrophotometer
was dirty when we were measuring the light transmittance. If I were to repeat this
experiment, I would measure the light transmittance for EACH of the 6 containers and
make sure to wipe the glass container before putting it into the spectrophotometer.