Using Light Energy to Build Matter
Name
Photosynthesis Protocol
Tape this into your journal.
INTRODUCTION
There are several ways to measure the rate of photosynthesis. This protocol will help you determine how quickly photosynthetic
reactions use carbon dioxide (CO2). You will do this by measuring the decrease in CO2 concentration in a water environment by
measuring the pH of the surrounding water. Your test subject will be sprigs of a common aquatic plant, Elodea.
Focus Question: How does the environmental factor of [place your group’s chosen
variable here] affect the rate of photosynthesis?
Pre-Lab Questions
1.
The presence of CO2 in the water causes the water’s pH to do what? (Hint: What happens to blood with added CO2?)
2.
On the pH scale below, label where you would find the lowest pH, highest pH, most basic, most acidic, and neutral
solutions.
0
1
2
3
4
5
6
7
8
9
10
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12
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14
Collect some background information:
3.
Read essay, Whose Discovery is This? on or around page 365 in your textbook. Write down the main point of this article.
4. Skim the first page of the essay, Getting Energy and Matter into Biological Systems on or around page 367. With your
group, address the following:
- What do plants need in order to photosynthesize?
- List two or more factors that might affect the rate at which plants photosynthesize.
HYPOTHESIS
Refer to the focus question above to form your hypothesis. Create one hypothesis with your group that
you can test in lab.
Hypothesis:
Variables:
M:
R:
C:
AVAILABLE MATERIALS (i.e., you do not need to use all of these – just list what your group will need and any additions)
Elodea, an aquatic plant
Beakers, test tubes, etc.
Water
Timers/clocks
pH probes and computer program
Any other material your group would need
PROCEDURE
Design a set of detailed steps (list or flowchart – it’s up to you) in order to answer your question above. You can
use some or all of the materials listed above in order to carry out your procedure. You will need to run your
experiment as long as possible, as photosynthesis may take a while.
DATA
Set up both data tables in your journal and be sure to include the title and all appropriate labels.
GRAPHS
Graph both data tables in your journal and be sure to include the title and all axes labels.
CONCLUSION
You may be asked to write this in your journal or on a separate sheet of paper. Stay posted.
Debrief Questions – in journals (some to be done after Photosynthesis Lecture)
Refer to the essay on or around pg. 367 and/or notes from the lecture.
1.
2.
3.
4.
5.
What gas was in the bubbles produced by the Elodea?
The Earth’s early atmosphere had no oxygen. Use your understanding of plant photosynthesis to explain how
photosynthetic organisms made the evolution of aerobic organisms possible.
How does the trapping of light energy provide energy for carbon fixation?
Light energy is absorbed during photosynthesis and stored as potential energy in the form of carbohydrates. Explain the
connection to the endothermic/exothermic reactions that we studied in previous labs.
Do plants carry out cellular respiration? Web search this or read about it in your textbook. What effect may this concept
have on the experiment and therefore the interpretation of data?