Photosynthesis uses light energy and CO₂ to produce glucose:

6 CO₂ + 12 H₂O - - -> C₆H₁₂O₆ + 6 O₂ + 6 H₂O

Carbon dioxide forms carbonic acid in water: CO₂ + H₂O - - -> H₂CO₃

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• OPTIONAL: Ziploc experiment on transpiration.

• PART A - CARBON DIOXIDE AS A FACTOR IN PHOTOSYNTHESIS p. 334
  • State a hypothesis regarding whether plants use CO₂ for photosynthesis.

  • Use Phenol Red as a pH indicator: red in basic and neutral solutions, turning yellow in acid.

    NOTE: dilute the Phenol Red 50%: make one solution for the class, and each group can share from that. Make a 200 ml batch: add 100 ml Phenol Red to 100 ml tap water or distilled water.

  • Have one person blow CO₂ into the diluted Phenol Red until it turns a yellow color.

  • Place Elodea in 2 screw-top test tubes with different leaf sizes (5 and 10 cm), 60 minutes exposure.

  • Note color changes.

    NOTE: Use only enough of the diluted Phenol Red (about 10 ml) to cover the largest leaves).
    Also make sure all your tubes have the same amount of Phenol Red.

    Please save the Elodea pieces; we can regrow them for later use.

• PART B - LIGHT INTENSITY AS A FACTOR IN PHOTOSYNTHESIS p. 335
  • State a hypothesis regarding the effect of light intensity on photosynthesis.

  • Use 0.5% Sodium Bicarbonate (NaHCO₃) as a supply of CO₂:
    NaHCO₃ -> NaOH + CO₂ in water; O₂ should be released as a by-product.

  • Cut 2 stems of Elodea (same size), gently crushed, and cover with the NaHCO₃.

  • Use different light treatments (light and dark), same leaf size, up to 60 minutes exposure.

  • Measure O₂ bubbles released.

• PART C - COMPUTER SIMULATION p. 336

  SKIP

• PART D - QUESTIONS p. 337