Ecocycles - Photosynthesis and Respiration
This activity gives students (and/or teachers!) an opportunity to realize visually and tactilely the molecular processes involved in photosynthesis and respiration.
Materials
- styrofoam sphere atoms: (suggested colors - change if necessary)
- 1 C (large black)
- 2 H (small blue)
- 3 O (large white)
- chemical bond materials
- 2 toothpicks
- 4 pipecleaner segments about 2" (or 2 more toothpicks if double bonds not considered)
- (optional, but highly recommended) 1" square or so slips of yellow paper with small holes in the center, to represent solar energy ("energy token")
- (optional, but highly recommended) a yellow, a green, and a red (or pink) slip of paper: yellow for Sun, green for Plant, red for Animal
- pencil and paper - as usual, recording is important!
- (optional) digital camera to webify the activity
Procedure
The class breaks up into groups (3 students per group is ideal), and each group receives a materials set as listed above. The students pick a colored slip to choose their (initial) role. Students start their datasheets with an inventory of materials. Then each group uses the materials to assemble the "input" molecules that plants (and algae and other chlorophyll-bearing organisms) use in photosynthesis, i.e. CO2 and H2O. Written descriptions and drawings should be recorded on the datasheets, as well as chemical formulas for the molecules.
The student representing the Sun gives one of the small, holed yellow paper slips to the student representing the Plant. This energy enables the Plant to disassemble the molecules H2O and CO2, then reassemble the atoms into "carbohydrate" CH2O and oxygen O2; the yellow "energy token" should be skewered on one of the carbohydrate's bonds (C-H toothpick is easiest). All should ponder the fact that the process could not happen without the solar energy - energy is like the "money" of an ecosystem, and nothing can happen if there is none.
Plant now gives Animal (student with red/pink paper slip) the carbohydrate (food to eat) and O2 (air to breathe); Animal (and all others) should ponder the eating, digestion, and breathing processes as Animal "digests" the carbohydrate by breaking it apart, and recombining it with the oxygen atoms to return to water and carbon dioxide (products of burning). Respiration is a type of burning. The "energy token" is freed and Animal keeps it separate from the new molecules - it represents energy liberated by respiration, and available for Animal to use for other activities. Animal hands the H2O and CO2 back to Plant, who can then repeat the process if Sun gives another energy token. Repeat the cycle as many times as there are energy tokens... Students can rotate roles if time permits. Multiple repetitions underscore the cyclic nature of the processes in an ecosystem. The reuse of the same atoms, but new energy tokens, relates directly to how a closed mini-aquarium can survive on just sunlight.