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1. State the Problem: How much carbon dioxide does the plant Elodea absorb and how much oxygen does it release?

Why are two investigations needed to show gas exchange during photosynthesis?

How will we measure the amount of carbon dioxide that Elodea has absorbed?

How will we measure the amount of oxygen Elodea has released?

2. Hypothesis
Independent Variable:
IF_______________________________________________,

THEN____________________________________________

________________________________________________.
Dependent Variable:

3. Experiment
Control:
Materials:
Procedures (list steps)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.

Watch the video in Lesson 3, page 10 before moving forward.
4. Describe the data you expect to collect in this investigation by answering the questions. You can also insert a sample data table if you wish.

How will you determine whether photosynthesis has occurred? What color does BTB make the water to begin with? What color do you expect the water to be IF photosynthesis has occurred?

Answer the following questions.
If you place an Elodea plant in the BTB + baking soda solution overnight and in the morning it is yellow. What does that mean? Do you think there would be oxygen bubbles present?

Examine the example table to the right and answer the question that follows.

Content of Test Tube: Baking soda + BTB, Color when left in the light: yellow, Color when left in the dark: yellow
Content of Test Tube: Baking soda, BTB, & Elodea, Color when left in the light: Green, Color when left in the dark: greenish yellow
Content of Test Tube: Baking soda, BTB, & Elodea, Color when left in the light: Green, Color when left in the dark: yellow

Which trial performed photosynthesis when left in the light? Which trial performed photosynthesis when left in the dark?

Examine the table to the right and answer the following questions.

Time Elapsed (minutes) Test Tube 1 – Number of bubbles Test Tube 2 – Number of Bubbles
0 0 0
1 20 23
2 31 31
3 32 35
4 31 32
5 32 33

Make a graph of the number of oxygen bubbles that are released per minute for 5 minutes. Plot the time in minutes on the horizontal axis and the number of bubbles on the vertical access.
If you cannot make the graph directly in this document, you will need to create your graph on paper and then upload a picture. If you cannot get it into this box, add it to the end of this lab report or attach a separate submission to the drop box.

5. Conclusion: written explanation of what you learned. This should be one paragraph explaining what you learned about photosynthesis (5-6 sentences, 250 words). Be sure to include ALL required vocab words below and underline them.
Photosynthesis
Cellular Respiration
Oxygen
Water
Glucose
Carbon Dioxide
Roots
Stem
Sunlight/Energy
Release
Absorb
Leaves
Chlorophyll
Chloroplast
ATP
Product
Reactant

Information to include:
Did your data support or refute your hypothesis?
What would you do to improve the experiment in the future?
What did you learn about this topic?

1 answer

1. State the Problem:

How much carbon dioxide does the plant Elodea absorb and how much oxygen does it release?

Two investigations are needed to show gas exchange during photosynthesis because one investigation can focus on the absorption of carbon dioxide, while the other can focus on the release of oxygen. These separate measurements provide a clearer understanding of the photosynthesis process.

How will we measure the amount of carbon dioxide that Elodea has absorbed?

We will measure the amount of carbon dioxide absorbed by observing the color change of Bromothymol Blue (BTB) in a solution containing the Elodea plant. BTB will change colors based on the acidity of the solution, indicating the amount of carbon dioxide present.

How will we measure the amount of oxygen Elodea has released?

The amount of oxygen released will be measured by counting the number of oxygen bubbles produced by the Elodea plant during photosynthesis in the presence of light.

2. Hypothesis:

Independent Variable: IF the amount of light exposure is increased,
THEN the rate of photosynthesis will increase,
which will result in a greater release of oxygen bubbles and more significant absorption of carbon dioxide.

Dependent Variable: The rate of oxygen bubbles produced and the color change in the BTB solution.

3. Experiment

Control: Use a test setup without light (dark environment) to compare the results.

Materials:

  • Elodea plant
  • BTB solution
  • Baking soda
  • Test tubes
  • Light source (lamp)
  • Stopwatch
  • Ruler
  • Thermometer

Procedures (list steps):

  1. Prepare two test tubes.
  2. Fill each test tube with a solution of baking soda and BTB.
  3. Place a piece of Elodea in one of the test tubes.
  4. Leave the second test tube without the Elodea as a control.
  5. Place both test tubes under a light source.
  6. Observe and record the color of the BTB solution over time in both test tubes.
  7. Count the number of oxygen bubbles produced in the test tube containing Elodea every minute for five minutes.
  8. After five minutes, record the data.
  9. Repeat the experiment in the dark for comparison.
  10. Analyze the results and draw conclusions.

4. Expected Data and Analysis

If photosynthesis has occurred, we would expect to see a color change in the BTB solution. Initially, the BTB will be blue-green, indicating a neutral pH. If photosynthesis occurs, the solution will turn green or yellow, indicating a decrease in carbon dioxide and an increase in pH.

If the Elodea plant is placed in the BTB + baking soda solution overnight and the next morning it is yellow, it means that the carbon dioxide levels decreased significantly, indicating that photosynthesis occurred. Yes, there should be oxygen bubbles present as a byproduct of this process.

Analysis of Color Changes:

  • Trial with BTB + baking soda: Yellow in both light and dark indicates no photosynthesis.
  • Trial with BTB, baking soda, & Elodea: Green in light indicates photosynthesis occurred; greenish-yellow in the dark indicates no photosynthesis.

Bubble Count Data Table

| Time Elapsed (minutes) | Test Tube 1 – Number of Bubbles | Test Tube 2 – Number of Bubbles | |-----------------------|--------------------------------|--------------------------------| | 0 | 0 | 0 | | 1 | 20 | 23 | | 2 | 31 | 31 | | 3 | 32 | 35 | | 4 | 31 | 32 | | 5 | 32 | 33 |

Graph: (Note: please create and attach a graph based on the data provided above.)

5. Conclusion

Through this investigation into photosynthesis, I learned how plants such as Elodea perform key processes to survive. Photosynthesis is a critical process where plants absorb carbon dioxide from the environment and use water, along with energy from sunlight, to produce glucose and release oxygen. The presence of chlorophyll in the leaves and chloroplasts of the plant allows it to capture this light energy. Our findings supported the hypothesis; increased light exposure resulted in a higher rate of oxygen bubble production, indicating successful photosynthesis. The data collected showed clear evidence of gas exchange, where Elodea absorbs carbon dioxide and releases oxygen. To improve this experiment, consider varying the distance of the light source or exploring different conditions such as temperature. Overall, understanding how plants absorb and release gases during cellular respiration deepens comprehension of their essential roles in ecosystems.