Lab 5

Photosynthesis in Elodea

(Note: Your completed lab report should include title, problem, pre-lab questions, data table, answers to questions, and conclusion.)


Problem: Is photosynthesis taking place in the aquatic plant Elodea?


Background Information:


     Elodea is a common “exotic” aquarium plant that has also escaped into some local waterways. Elodea is an excellent plant for our studies of photosynthesis and cells because it is easy to grow, and readily available. The leaves are only a few cells thick so they will be easy for us to observe under the microscope to look at cells and cell parts.

     Recall from the reading that photosynthesis requires certain raw materials and produces certain products, one of which is released by the cells as a gas. You have read about the process of photosynthesis, and now you will act as any scientist would and ask to see the proof! How can you see the proof however, since gases are colorless and oxygen and carbon dioxide are both odorless too? Read the Procedure at this point.


Book Reference: pages 88-90 (pages 94 – 96 in the new light green version)


Pre-lab Questions: (Read Procedure before answering.)


  1. How and what will we measure to see if photosynthesis is taking place?
  2. Why would we use an aquatic plant for this experiment instead of a terrestrial plant?


Materials: (per group)

Sprig of Elodea

Distilled Water w /Baking Soda

Graduated Cylinder or Test Tube

Timer or Watch

60 watt Spotlight

Safety Goggles



 Before you begin, create a data table.


  1. Fill test tube with distilled water. Add 0.5 g. of baking soda.
  2. Cut the end of the sprig of Elodea.
  3. GENTLY crush the freshly cut end.
  4. Place the Elodea in the Graduated Cylinder or test tube. Be sure the freshly cut end of the Elodea is toward the top of the tube or cylinder.
  5. With the light off, observe the freshly cut end of Elodea. Count the number of oxygen bubbles that are released in a minute. Record for each minute for 10 minutes.
  6. Now place the Elodea in front of the light and turn it on. Wait a few minutes.
  7. Over the next ten minutes count the number of bubbles that are released each minute. Record the results.


Safety Considerations:

  • Wear goggles
  • Be very careful not to crush the stem of Elodea too much.
  • Be cautious with glassware; report breakage to the teacher immediately!
  • The spotlights and the metal shades become extremely hot and can cause serious burns.


Clean-up all materials as your instructor directs.


Post-Lab Questions: (Answer each in a 1-paragraph answer.)


1. Is Photosynthesis taking place in Elodea? Use evidence from your investigation to support your answer.


2. Consider these facts:
            - Elodea is green. This is because its leaves contain the chlorophyll, which is the chemical that carries out photosynthesis.

            - The light we are using is white and thus contains all the colors of the rainbow.

            - When each color of light reaches an object, the light energy is either absorbed into the object or reflected back out.

            - The color of an object is actually the color of the light that is reflected back out.
   Using these facts to support your answer, predict what colors of light are actually used by the plant in photosynthesis.


3. Using this investigation as a basis, design an experiment to test the effect of an environmental factor on the rate of photosynthesis. Some possible independent variables include: distance from light, different light intensities (wattages), different colors, or temperature.


4. Bonus: Why did we use the baking soda?


(In your conclusion, you should briefly summarize the problem and what you did. Then answer the problem referring to the data and background information including your pre and post lab questions).