Photosynthesis and Light Lab B 50 minutes

Name
Date
Class
Chapter 2 Lesson 4
Lab B
50 minutes
Photosynthesis and Light
You might think of photosynthesis as a process of give and take. Plant cells take in water
and carbon dioxide and, powered by light energy, make their own food. Plants give off
oxygen as a waste product during photosynthesis. Can you determine how the intensity
of light affects the rate of photosynthesis?
Ask a Question
How does the intensity of light affect photosynthesis?
Materials
test tube
lamp
Elodea
watch or clock
scissors
thermometer
beaker
Safety
Make Observations
1. Read and complete a lab safety form.
2. Cut the bottom end of an Elodea stem at an angle and lightly crush the cut end. Place
3. Place the beaker containing your test tube on a circle drawn on a sheet of paper under a
lamp. Measure the temperature of the water in the beaker. Record the temperature.
4. When bubbles of oxygen begin to rise from the plant, start counting the number of
bubbles per minute. Continue to record data for 10 minutes.
5. Record the temperature of the water in the beaker at the end of the test.
6. Calculate the average number of bubbles produced per minute by your plant.
7. Compare your data with your classmates’ data.
84
Cell Structure and Function
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
the Elodea in a test tube with the cut side at the top. Fill the test tube with water. Stand
the test tube and a thermometer in a beaker filled with water. (The water in the beaker
keeps the water in the test tube from getting too warm under the lamp.)
Name
Date
Class
Lab B continued
Sample Data Table
Number of Bubbles per Minute
Time
Control
Dimmer Light
1
2
3
4
5
6
7
8
9
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
10
Form a Hypothesis
8. Use your data to form a hypothesis relating the amount of light to the rate of
photosynthesis.
Test Your Hypothesis
9. Repeat the experiment, changing the light variable so that you are observing your
plant’s reaction to getting more or less light. Keep all other conditions the same.
10. Record your data in the data table, and calculate the average number of bubbles per
minute.
Cell Structure and Function
85
Name
Date
Class
Lab B continued
Lab Tips
To calculate the average number of bubbles per minute,
add the total number of bubbles observed in 10 minutes,
and then divide by 10.
Analyze and Conclude
11. Use Variables How does the intensity of light affect
photosynthesis? What is your evidence?
Remember to use scientific
methods.
Make Observations
Ask a Question
Form a Hypothesis
Test your Hypothesis
Analyze and Conclude
Communicate Results
12.
The Big Idea How do plant cells make food?
What do they take in and what do they give off?
What source of energy do they use?
Compile all the class data on one graph to show the
effects of varying amounts of light on the rate of
photosynthesis.
Extension
What other variables might affect the rate of photosynthesis? For example, how does
different-colored light or a change in temperature affect the rate of photosynthesis?
To investigate your question, design a controlled experiment.
86
Cell Structure and Function
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Communicate Your Results