Molecular modelling of respiration and photosynthesis

Use molecule models to show how living things use sugar and oxygen for energy, and how plant photosynthesis reverses the process.
Science content
Biology: Features, Adaptations of Living Things (K, 1, 3, 7)
Biology: Food Webs, Ecosystems, Biomes (3, 4)
Chemistry: Atoms, Molecules (3-7)
Chemistry: Chemical Changes (2, 7)
  • molecule models (see resource) to build one glucose (C6H12O6) and six oxygen molecules (6 X O2), as many sets as possible for student groups to each have a set

This models how animals combining oxygen (from the air) with sugar (that they eat), to give them energy. The chemical reaction generates carbon dioxide and water. So animals (and plants also), when they respire, put carbon dioxide into the air.

Plants, when they photosynthesize, do the opposite: they take carbon dioxide from the air, and combine it with water to make sugar (which they use to build their structures) and oxygen. Hence, planting trees helps pull carbon from the atmosphere.

Give student groups a set of molecules (one sugar and 6 oxygens).
Ask them to take apart the sugar molecule and combine it with the oxygens to make 6 water molecules (tell them H2O) and 6 identical other molecules.
Students will eventually arrive at carbon dioxide as the second product molecule.

All living things do the same thing - they use food energy (sugar molecules) and oxygen to make energy, and put carbon dioxide into the atmosphere.

Plants, as well as respiring like animals, also do photosynthesis. This is the opposite chemistry.
Demonstrate (or students can build) 6 carbon dioxide and 6 water molecules combining together to make the reverse chemical reaction, producing a sugar molecule (glucose, C6H12O6) and 6 oxygen molecules.

Grades taught
Gr 5
Gr 6