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Name: ________________________
Teacher’s Name: ________________
Class: ________________________
Date: ________________________
TITLE
How To Use This Lab Skeleton:
The instructions are in ORANGE.
The content is in BLACK. Take out the
orange and type in your responses in
black. You are finished when no
ORANGE remains!
(change this to an original title that sums up the lab)
Prelab Information:
The production of food from carbon dioxide and water in the presence of
chlorphyll utilizing light energy and releasing oxygen is called photosynthesis.
Plants produce food in the form of simple sugars (carbohydrate). In order for
photosynthesis to occur, sunlight and chlorophyll must be present. There are
different types of chlorophyll, but the one involved in photosynthesis is called
chlorophyll-A. Chlorophyll is a pigment which is stored in chloroplasts.
In this lab, students will observe the production of one of the end products of
photosynthesis, which is oxygen. The reagent Bromothymol Blue is an “indicator
reagent”. This means that it can appear as two different colors in two different
conditions. Bromothymol Blue is the color blue when the pH is above 7.6 and yellow
when the pH is below 6.0. In this lab, students will first fill a liquid solution with
the gas carbon dioxide, dropping the pH and changing the indicator to yellow. Then
the student will add a sprig of the plant Elodea, and allow it to photosynthesize. If
the plant is successful, the carbon dioxide should be used up in the photosyntheis
reaction, thus raising the pH. Results will be obtained after 24 hours.
Students are also reminded to use proper scientific experimental technique
with the utilization of a “control” group. A “control” group is treated the same as
the “experimental” group with one very important difference. It does not contain
the experimental variable. The control group should show no reaction, therefore
any reaction that the experimental group has can be compared to it.
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PURPOSE: The purpose is the reason why the lab is being done. You type the
purpose of the lab (in your own words) here.
HYPOTHESIS: You type your hypothesis here. A hypothesis is a testable
statement about what you think is going to happen when the experiment is
performed. It should include both a guess AND a reason why you think that guess
is correct.
MATERIALS:
You add a list of what you used.
PROCEDURE:
1.
2.
3.
4.
5.
6.
7.
Obtain two glass test tubes. Using masking tape and a sharpie marker, label one “control
group” and the other “experimental group”. Put the names of the members of the group on
the tubes as well. Place the test tubes in a beaker to ensure that they remain upright.
Add 10mL water plus 1-2 drops of bromothymol blue to each test tube.
Gently blow into the tube using a straw until the indicator changes color to yellow. This will
ensure that the tubes are each full of carbon dioxide gas.
Carefully add 5mL seltzer to get a more significant color change to yellow.
Place a piece of Elodea in the “experimental” test tube. Record the pH and the color of
both test tubes.
Expose both test tubes to sunlight by leaving them near a window for at least 24 hours.
After the 24 hour incubation period, record the pH and the color of both test tubes.
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DATA: Neatly type your data below. Be sure that EVERY number has a unit and
the correct number of significant figures is used for all calculations.
Initial pH
Final pH
pH
Initial
Color
Final Color
Color
Control
Experimental
For a visual representation, you will always want to graph your data. Pay attention
to where the independent and dependent variables go. You can make a computergenerated graph, or you can print the graph grid below and hand-draw your graph
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(use colored pencils to make it look really nice). For this experiment, you should
have two lines on your line graph. Construct a legend so that the reader knows
which line is which.
Figure 1: Title (look back in your “How To Make A Graph” notes to see how to write a
good title for a graph)
LEGEND
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Remember to
label your axes!
CONCLUSION:
Use your answers to the following Analysis Questions (which you worked out on
your Rough Copy) to construct a conclusion paragraph. YOU SHOULD NOT SHOW
THE QUESTIONS IN YOUR FINAL DRAFT! Your interesting and well-written
paragraph should contain the answers to all of the questions below. Remember to
use scientific writing (passive voice, no personal pronouns).
1.
Was the hypothesis supported or rejected? Why?
2. What does a yellow tube indicate?
3. What does a blue tube indicate?
4. Explain what occurred in the “control” test tube.
5. Explain what occurred in the “experimental” test tube.
6. How can a scientist be sure that a blue color change indicates that photosynthesis
occurred?
7. Imagine this experiment was repeated in the same manner, however instead of filling the
liquid solution with carbon dioxide (CO2), the student filled it with helium gas (He). What
would the outcome of the experiment be?
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8. Imagine this experiment was repeated in the same manner, however the test tubes were put
into a dark closet instead of a sunny window. What would the outcome of the experiment
be?
9. What changes or improvements could be suggested for a related experiment?
After you have finished writing the Conclusion, go back and write the Title. The
Title should be a short statement that sums up what the entire lab was about. Be
creative – but make sure the title represents the experiment! You cannot use the
title that your instructor used!
Last-minute check! Did you use the spellchecking feature to make sure your words
are spelled correctly? Have you removed ALL of the instructions from the lab
skeleton? Are you going to make sure your lab report prints neatly (do not cut the
data section or the graphs across two sheets of paper!) and is stapled in the upperleft hand corner?