Experiment on the Rate of Photosynthesis Using Elodea

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Elodea is an aquatic plant that occurs naturally in lakes, ponds and streams. It lives underwater but its flowers blossom on water surfaces. The plant provides a habitat for some invertebrates. Photosynthesis is how plants manufacture carbohydrates using sunlight. The carbohydrates are manufactured from carbon dioxide, and light has to be present for photosynthesis to take place. The levels of carbon dioxide present and light intensity determine the rate of photosynthesis, which is shown by the number of bubbles produced by the elodea stem during an experiment.

Things You'll Need

  • Elodea
  • Test tube
  • Distilled water
  • Test tube holder
  • Metal stand
  • Baking soda
  • 40-watt lamp
  • Single-edge razor blade
  • Tape
  • Timer
  • Metric ruler
  • Pen and paper

Remove a few leaves from the sprig of elodea. Cut off a section of the plant’s stem with the razor blade and crush it. The cut should be at an angle.

Put the room-temperature distilled water into the test tube. Fill the tube to the brim.

Place the elodea into the test tube with its stem facing up.

Put the test tube in the test tube holder and secure it using adhesive tape. When the test tube is secured, place it in a test tube rack.

Turn on the 40-watt lamp and place the 40-watt lamp about 5 centimeters from the elodea.

Count the number of bubbles that rise from the stem. Wait for a minute after placing the lamp near the plant to start counting. Record the number of bubbles that you can see rising from the stem within five minutes. Count the number of bubbles produced for another five minutes and write down the findings.

Add the two results and divide the total by two to get an average.

Move the 40-watt lamp and place it 20 centimeters away from the plant. Wait for a minute and count the number of bubbles that are produced from the stem in five minutes. Record the number of bubbles that you see.

Put 0.5 gram baking soda in the test tube and put the lamp 5 centimeters away. The baking soda is used to increase the level of carbon dioxide in the water. Wait for a minute and record the number of bubbles that are produced by the stem in five minutes. Observe the number of bubbles produced for another five minutes and record the findings.

Tips & Warnings

  • The higher the rate of photosynthesis, the more bubbles that elodea will produce in a given time.

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