Cellular Respiration in Plants
Cellular respiration occurs within the mitochondria of each cell and is the process by which the cells of
organisms convert sugars into energy and release waste products. Cellular respiration involves a series of
enzyme-mediated reactions. The equation below shows the simplified reaction.
C6H12O6 + 6O2 -----> 6 CO2 + 6 H2O
In this experiment, the CO2 produced during cellular respiration will be removed by sodium hydroxide
(NaOH) and will form solid sodium bicarbonate (NaHCO3) according to the following reaction.
CO2 + NaOH --> NaHCO3
Since the carbon dioxide is being removed, the change in the volume of gas in the respirometer will be
directly related to the amount of carbon dioxide consumed. Each respirometer is in a petri dish of water. The
net result is a decrease in gas volume within the tube and a related decrease in pressure in the tube. This will
cause the water (from the petri dish) to move toward the region of lower pressure (up the tube).
Germination is the process where a plant emerges from a seed and begins to grow. In this experiment, the
relative volume of CO2 consumed by germinating and non-germinating (dead) radish seeds will be measured.
The amount of carbon dioxide consumed will be measured over a period of time by measuring the rate of
water uptake.
Procedure:
1. Cut off the tips of four plastic pipets so that there is a wide opening. Be sure all pipets are the same
length.
2. Put 5 drops of a 1% solution of NaOH in each pipet.
3. Stuff dry cotton in each pipet so that the cotton absorbs all of the NaOH and the NaOH solution will not
touch the seedlings.
4. Add 10 (3 day) germinating seedlings to one pipet.
5. Add 10 non-germinating seedings to one pipet.
6. Add 10 (2 day) germinating seedlings to one pipet.
7. Add 20 (2 day) germinating seedlings to one pipet.
8. Cut four holes in a cardboard square. Label which pipet will be in which slot.
9. Put the pipets into the cardboard stabilizer and set them on the petri dish that is half-filled with water.
10. Label, with a permanent marker, the starting point of the level of water.
11. Record the movement of water up the pipets in a data table.
Questions:
1. Why do plants perform both photosynthesis
and cellular respiration?
2. Explain the effect of germination on radish
seed respiration.
3. What was the purpose of NaOH?
4. If respiration had been studied in 5 day old
germinating seedlings, what results could
be predicted? Explain your reasoning.
Why is this lab an example of rigorous and relevant instruction?
Students perform the above lab during the Photosynthesis and Cellular Respiration Unit.
The purpose of the lab is to see the correlation between the age of seedlings and the amount of cellular respiration that
they perform. Students create respirometers that will allow them to determine which seedlings create the most carbon
dioxide by performing cellular respiration by measuring the amount of water pulled into a vacuum created inside the
respirometer by sodium hydroxide absorbing the carbon dioxide. The more water that is pulled into the respirometer, the
more cellular respiration that is occurring.
This is a difficult lab for students to do analysis on. They need to understand why the vacuum is being created and tie
that to the amount of cellular respiration that is being performed by the dead, 1 day, 2 day, and 3 day old seedlings.
They inherently understand that an older seed will do more cellular respiration, but not why. When they write their
discussion section of their lab report, I have them dig deep into the reasons why. They will eventually end up discussing
things like the fact that the seed is larger and therefore, has more cells. And since there are more cells, there are more
mitochondria which perform cellular respiration. So it makes sense for there to be more cellular respiration in older
seedlings. They will also have to do some error analysis, most likely. If they have an outlier data point, they need to
review their procedure and determine what could have affected their lab adversely. One of the major things that affects
their lab is that they allow the sodium hydroxide to touch their seedlings which kill some of the seeds.
Lesson Plan:
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Students are provided with the lab instructions the day before the lab to familiarize themselves with the
background and to create a materials list, hypothesis, and data collection table.
Students are quizzed prior to performing the lab about major components.
Perform the lab.
After the lab, but before students leave class, they will discuss with their lab partners what they saw and make
sure they all have thoroughly detailed measurements and observations.
Following lab day, students can bring rough drafts of their discussion for review from the teacher. This helps
them focus in on where they need more detail. They are never told what to add, but are asked leading questions.
Once all labs for the semester are graded, the highest graded lab of theirs is counted as a summative grade to
show mastery in technical writing.
Labs are a great way for us to practice technical writing. It gives us an opportunity to provide incremental feedback, show
examples of exemplary work, ask thought provoking questions without giving away the answers, and to practice writing
for unit exams (which always have essay questions).