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

---

• OPTIONAL: Ziploc experiment on transpiration.

• PART A - CARBON DIOXIDE AS A FACTOR IN PHOTOSYNTHESIS p. 68
  • 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: make one 500 ml Phenol Red solution for the class, and each group can share from that.
    Have one person blow CO₂ into a 500 ml batch of Phenol Red until it turns a yellow color.

    NOTE: wear goggles; exhale only, do not inhale (drink)!

  • Place aquatic plant (Cabomba) in 2 screw-top test tubes with same leaf sizes (10 cm). Use different light treatments for the tubes:
    • One tube is placed under a light source (use overhead projector).
    • One tube is placed in the dark.

    60 minutes exposure (or as long as time permits). p. 69

  • If there is enough Cabomba, put additional pieces in tubes under the light, wrapped in red or green cellophane filters (see PART C).

  • Note color changes.

    NOTE: Use enough of the Phenol Red (about 10 ml) to completely cover the leaves.
    Also make sure the tops are securely screwed tight, so that no CO₂ from the atmosphere leaks into your tubes.

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

• PART B - LIGHT INTENSITY AS A FACTOR IN PHOTOSYNTHESIS p. 69

  SKIP (note any bubbles as oxygen is released - you can observe this in PART A)

• PART C - COLOR OF LIGHT AS A FACTOR IN PHOTOSYNTHESIS p. 70

  OPTIONAL (unless there is enough Cabomba to perform this experiment at the same time as PART A).

• Questions p. 71

  NOTE:

  • "light dependent" reactions are called "photo" reactions in the Phelan book.
  • "light independent" reactions are called "synthesis" reactions in the Phelan book.