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Exploration Lab
Measuring the Rate of Photosynthesis
OBJECTIVES
Measure the amount of oxygen produced by an elodea sprig.
Determine the rate of photosynthesis for elodea.
PROCESS SKILLS
•
•
•
•
making observations
measuring
collecting data
graphing
MATERIALS
• 500 mL of 5% baking-soda-and-water
• glass funnel
• test tube
• metric ruler
solution
• 600 mL beaker
• 20 cm long elodea sprigs (2–3)
Background
1. Summarize the main steps of photosynthesis.
2. State the source of the oxygen produced during photosynthesis.
3. Identify factors that can affect the rate of photosynthesis.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Modern Biology
37
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Measuring the Rate of Photosynthesis continued
Procedure
PART A: SETTING UP THE EXPERIMENT
CAUTION Always wear safety goggles and a lab
apron to protect your eyes and clothing. Glassware
is fragile. Notify the teacher of broken glass or cuts. Do not clean up broken glass or spills with broken glass unless the teacher tells you to do so.
Wear disposable polyethylene gloves when handling any plant. Do not eat
any part of a plant or plant seed used in the lab. Wash hands thoroughly
after handling any part of a plant.
1. Add 450 mL of baking-soda-and-water solution to a
beaker.
2. Put two or three sprigs of elodea in the beaker. The
baking soda will provide the elodea with the carbon dioxide it needs for photosynthesis.
3. Place the wide end of the funnel over the elodea
as shown at right. The end of the funnel with the
small opening should be pointing up. The elodea
and the funnel should be completely under the
solution.
4. Fill a test tube with the remaining baking-soda-andwater solution. Place your thumb over the end of
the test tube. Turn the test tube upside down,
taking care that no air enters. Hold the opening of
the test tube under the solution, and place the test
tube over the small end of the funnel. Try not to let any solution leak out of
the test tube as you do this.
5. Place the beaker setup in a well-lighted area near a lamp or in direct sunlight.
PART B: COLLECTING DATA
6. Record your data for steps 7–9 in the table below.
Amount of Gas Present in the Test Tube
Days of exposure to light
Total amount of gas present (mm)
Amount of gas produced per day (mm)
0
1
2
3
4
5
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Modern Biology
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Measuring the Rate of Photosynthesis continued
7. Record that there was 0 mm gas in the test tube on day 0. (If you were unable
to place the test tube without getting air in the tube, measure the height of the
column of air in the test tube in millimeters. Record this value for day 0.) In
this lab, change in gas volume is indicated by a linear measurement expressed
in millimeters.
8. For days 1 through 5, measure the amount of gas in the test tube. Record the
measurements in your data table under the heading “Total amount of gas
present (mm).”
9. Calculate the amount of gas produced each day by subtracting the amount of
gas present on the previous day from the amount of gas present today. Record
these amounts under the heading “Amount of gas produced per day (mm).”
Analysis and Conclusions
1. Using the data from your table, prepare a graph.
2. Using information from your graph, describe what happened to the amount of
gas in the test tube.
3. How much gas was produced in the test tube after day 5?
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Modern Biology
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Measuring the Rate of Photosynthesis continued
4. Write the equation for photosynthesis. Explain each part of the equation. For
example, which ingredients are necessary for photosynthesis to take place?
Which substances are produced by photosynthesis? Which gas is produced
that we need in order to live?
5. What may happen to the oxygen level if an animal, such as a snail, were put in
the beaker with the elodea sprig while the elodea sprig was making oxygen?
Further Inquiry
Design an experiment for predicting the effects of temperature on the amount of
oxygen produced or rate of photosynthesis by elodea.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Modern Biology
40
Datasheets for In-Text Labs