Investigating Photosynthesis with Algae Balls
Student Materials
Introduction ................................................................................................................................2
Lab Protocol ...............................................................................................................................4
Data Collection Worksheet .......................................................................................................5
Pre-Lab Questions .....................................................................................................................6
Post-Lab Analysis ......................................................................................................................7
Students
You should read the Introduction and Lab Protocol and then answer the Pre-Lab Questions.
Also be sure to answer the questions that are embedded in the Introduction. Completion of the
questions will help you understand the concepts and procedures of the lab. Once you have
completed the lab, complete the Post-Lab Questions and Analysis.
Investigating Photosynthesis with Algae Balls
Introduction
Introduction: Biofuel is an energy source derived from biological materials, most commonly plants.
What is the biological process that plants use to create biofuels?
What is the energy source for this process?
Where do the carbon molecules contained in the biofuel come from?
http://www.key4biz.it/biocarburanti-in-grecia-si-coltivano-quelli-per-gli-aerei-video/
Over the past decade, interest and controversy about growing microalgae for biofuels has surged.
These unicellular photosynthetic organisms appear to be an attractive alternative to fossil fuels
because of their ability to grow solely on sunlight and carbon dioxide from the atmosphere without
taking up valuable farmland. Algae growers harvest the lipids from their algae and convert the lipids
into biodiesel. However, there are still significant hurdles in both engineering and biology before largescale microalgae farms become economically viable. An important component to their future success
is a thorough understanding of algal metabolism and physiology.
What do you already know?? List five facts you already know about photosynthesis.
As you read below, underline anything that you listed above.
In this lab, you will lead your own
scientific inquiry about environmental
factors that affect the rate of
photosynthesis in microalgae.
Photosynthesis is the process by
which primary producers fix CO2 into
carbohydrates. Some of the
carbohydrates produced are used by
the algae for respiration, other
carbohydrates are used in other
metabolic pathways to create carboncontaining compounds necessary for
life. Some will be converted into the
lipids harvested for biodiesel.
http://www.nytimes.com/2011/10/27/business/energy-environment/
farming-for-energy-starts-to-gain-ground.html?pagewanted=all
Chemically, you can summarize photosynthesis as follows:
CO2 + 6H2O + light
 C6H12O6 + 6O2
This equation glosses over the many chemical intermediates on the path from carbon dioxide to
glucose. In the light-dependent reactions, photons of light excite electrons within chlorophyll
molecules. The excited electrons pass through the electron transport chain and ultimately wind
up with the electron carrier NADP+. This process generates ATP and NADPH, both of which are
required to power the light-independent reactions, called the Calvin-Benson cycle, that convert
CO2 into carbohydrates. Each reaction in this process is catalyzed by a specific enzyme. Factors
such as temperature, light, and the presence of pollutants directly influence enzyme activity and
affect how quickly these reactions can take place. In this lab, you will measure photosynthesis
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using single-celled algae immobilized in balls of calcium alginate. Calcium alginate consists of
negatively charged alginate that can be cross-linked by positively charged calcium ions when in
solution. This creates a gelatinous polymer that will be used to make the algae balls. On Day 1 of
this two-day lab, you will learn how to make the algae balls and how to use a color-changing dye
to monitor the progress of photosynthesis. Your group will then design an experiment to
investigate the effect of a particular independent variable on the photosynthetic reaction of your
algae balls. On Day 2, you will conduct your own experiments. You will be able to choose
between four different variables, but if you have a different idea for an experiment, talk to the
teacher to see whether the classroom is equipped with the equipment needed.
Measuring pH: As your algae photosynthesize, they will be using carbon dioxide and producing
oxygen and glucose. But we can’t see these chemicals – so how do we know anything is actually
happening?
There are machines that can analyze the composition of gases in a sample, but these tools are
expensive and calibrating them can be very difficult. Instead, we will be using a technique called
titration in order to watch in real-time as our algae balls cause an indicator solution to change
color from yellow to purple, due their uptake of CO2.
When carbon dioxide is dissolved in water, it changes the pH (a.k.a. acidity) of the solution by
producing carbonic acid, H2CO3. The more CO2 there is in the solution, the more H2CO3 is
produced, which decreases the pH (lower pH means more acidic). Conversely, if CO2 is taken
out of the solution, less H2CO3 is around, and the pH increases.
Draw the pH scale and label where acids and bases are indicated.
There are a number of different chemicals that change color in response to changes in pH.
These are called chemical indicators. The indicator that we will be using is called hydrocarbonate.
This indicator is sensitive to changes within the pH range that we are measuring.
Change in color of the hydrocarbonate
indicator solution in response to changes in pH
In which tube do you think the concentration of H+ ions is higher?
What evidence do you have to support your answer?
There are two main ways to correlate the color of the hydrocarbonate
indicator solution in your experiment to a specific pH value. You can
estimate an the unknown solution’s pH by comparing the color of the
sample to the color of a set of standards of known pH values.
http://www.vernier.com/products/sensors/
spectrometers/visible-range/svis-pl/
Alternatively, a more accurate method is to use a machine called a
spectrophotometer. This machine works by passing a beam of light
through a solution and measuring how much light of a particular wavelength is absorbed by the
solution. For this experiment, we would measure the absorbance of our indicator solution at a
wavelength of 550 nanometers. High absorbance corresponds to high pH, while low absorbance
corresponds to low pH.
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Investigating Photosynthesis with Algae Balls Student Lab
Student Protocol
Materials:
5 X 1 mL transfer pipettes
2 X small beaker (50-100 mL) or 1 oz portion cups
4 X plastic/paper cups
2 X 2.0 mL microcentrifuge tubes (avoid colored tubes)
1 tea strainer or mesh filter
Plastic spoon
2 X 1 dram (3.9 mL) vials
Sodium alginate
Calcium chloride
Concentrated algae solution
1X Hydrocarbonate indicator solution
dH2O
Permanent marker
Procedure:
Preparing Algae Balls
1. Check your station to make sure you have all materials.
2. Use a marker to label one beaker “Algae.” Pour approximately 20 mL of calcium chloride
solution into the beaker.
3. Use a marker to label one microcentrifuge tube “Algae.” Using a
plastic transfer pipette to transfer 1 mL of sodium alginate into the
microcentrifuge tube.
4. Using a clean transfer pipette, add 1 mL of the concentrated algae
solution to the tube you prepared in Step 3. Gently mix the alginate and
algae by drawing up and dispensing the liquid back into the tube.
TIP!!!
Sodium alginate is very goopy.
Pipette slowly and stir carefully
to avoid trapping air bubbles in
your solutions.
5. Reuse the transfer pipette you used to measure the algae to carefully suck up a few mL of the
algae/alginate solution you made in Step 4. Slowly add drops of the alginate/algae solution to the
calcium chloride solution in the beaker.
TIP!!
6. Wait 5 minutes for the algae balls to harden, then pour the algae balls
While you’re making the balls,
and calcium chloride through a tea strainer into a cup. The calcium
gently swirl the beaker of CaCl2
chloride in the cup can be reused to make the water balls in step 9.
so the algae balls don’t clump
7. Gently rinse the algae balls with tap water.
together.
8. Using a plastic spoon transfer 35 algae balls to one of the vials, Label it “algae.”
You are now going to repeat the process using water instead of algae.
Preparing Water Balls
9. Use a marker to label one beaker “Water.” Pour approximately 20 mL of calcium chloride
solution into the beaker.
10. Use a marker to label one microcentrifuge tube “Water.”
11. Using a plastic transfer pipette to transfer 1 mL of sodium alginate into the microcentrifuge
tube. 12. Using a clean transfer pipette, add 1 mL of dH2O to the tube containing sodium alginate.
Gently mix the alginate and water by drawing up and dispensing the liquid back into the tube.
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13. Reuse the transfer pipette you used to measure the water to carefully suck up a few mL of
the water/alginate solution you made in Step 12. Slowly add drops of the water/alginate solution
to the calcium chloride solution in the beaker.
14. Wait 5 minutes for the water balls to harden, and then pour the contents of the beaker
through a tea strainer into a cup. The calcium chloride in the cup can be poured down the sink.
15. Gently rinse the algae balls with tap water.
16. Using a plastic spoon transfer 35 of the water balls to one of the vials, Label it “water.”
Indicator Assay
17. Use a clean transfer pipette to add 2.5 mL of the 1X indicator solution to each vial. Put the
cap on and gently invert it to mix. Let the vials sit for 3 minutes to allow for the indicator solution
to equilibrate.
18. Compare the color of each reaction vial to known standards or to the color chart provided by
your teacher. Estimate the pH to the nearest tenth and record the pH values in the data table
below. A spectrophotometer may also be used to measure the pH. (see “Measuring pH Using a
Spectrophotometer”)
19. Place both tubes under a light source for approximately 30 minutes.
20. During the light incubation step, pour the remaining algae balls and water into a conical tube.
If necessary, add a little extra water to the tube so that the algae balls are completely submerged.
Label the tube with the date and the initials of your group members (or some other identifier).
21. Repeat with any extra water balls and a second clean conical.
22. While your experiment proceeds, plan your student-centered lab investigation using the
handout provided by your teacher.
23. When the 30-minute light incubation is complete, measure the pH of each sample and record
the pH values in the table below.
24. Return the samples so they are under the light source and incubate overnight. Record the pH
after 24 hours.
Data Table
pH
Time
Algae Balls in Light
Water Balls in Light
0
30 min
24 hours
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Investigating Photosynthesis with Algae Balls
Pre-Lab Questions
Directions: After reading through the introduction and protocol for the Algae Ball lab, answer the
questions below.
1. Summarizing Briefly summarize the process of photosynthesis.
2. Remembering What is the purpose of an experimental control?
3. Applying Which tube was your control in this experiment? Explain how the tube you chose acts as a
control.
4. Predicting Describe what you think will happen in each tube during the 30 minute incubation. What
about after 24 hours?
Algae ball tube:
30 minutes:
24 hours:
Water ball tube:
30 minutes:
24 hours:
5. Understanding Explain how the indicator is used to measure the process of photosynthesis. (Hint: your
answer to question #1 might be useful)
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Investigating Photosynthesis with Algae Balls
Post-Lab Questions
Directions: After completing the Investigating Photosynthesis lab, answer the questions below.
1. Analyzing In the initial lab, did the results from the algae ball tube and the control tube match
your prediction from the pre-lab questions?
2. Analyzing In general, you would assume that increasing the amount of light increases the rate
of photosynthesis. Explain how you measured the increase in photosynthesis in all of your
experiments.
3. Analyzing Does the data you collected in your student designed experiment support your
predictions? If not, offer some possible explanation for the variance.
4. Creating If the algae was boiled before making algae balls, and you repeated the
experiments, would you expect the that the results obtained would be the same? Explain your
answer.
5. Applying If the water used to make the water balls was contaminated with bacteria, would
they give you the same results as the water ball control used in this experiment? Explain your
answer.
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