Photosynthesis and cellular respiration are perhaps the two most important chemical reactions on the planet and underpin the carbon cycle. The model I'm going to demonstrate makes clear the role that
oxygen plays in storing the energy from sunlight that drives life. The talk provides implications for teaching and for understanding climate change.
The attached video shows the model in use. Also available at
https://www.youtube.com/watch?v=oKeQw3yKb_k
All will be revealed in the talk - useful for Biologists, Chemists and our Physics friends too.
Why is the model important? It shows the importance of
oxygen when energy is stored during photosynthesis. Energy is NOT stored in the food, but in the
fuel-oxygen system. We say "food 'contains' energy" but it is only when it combines with oxygen that energy becomes available**. Oxygen is a dangerously reactive gas, with weak chemical bonds holding the atoms together. Fuels and food by contrast are strongly bonded. The energy comes from replacing the weak bonds in oxygen with the strong bonds in carbon dioxide and water, which are the products of respiration and the starting materials for photosynthesis.
Download
www.scienceissues.org.uk for a full science programme and search for photosynthesis or look in the 'energy' section. View the linked Fuseschool video on Photosynthesis and respiration here:
https://www.youtube.com/watch?v=3XIyw...(**Except in anearobic respiration where a small amount of energy is available by re-arranging the bonds in eg glucose.)
HCOH is not the normal formula for carbohydrates?I have obviously greatly simplified the two processes, photosynthesis and respiration. Text books are eager to point out that the oxygen comes from the water and that the carbon dioxide is reduced in a later reaction. In fact both reactions are extremely complex and this complexity only gets in the way of a basic understanding.
C6H12O6 is an end product of the complex process so why not keep it simple: Carbo (C) hydrate (HOH) hence CHOH or HCOH. The overall result is that energy from the sun pulls oxygen away from the oxides, leaving carbohydrate in the green plant for the plant to use for growth and for its own fuel supply. Like almost all living things, when it needs energy it allows a little oxygen to spring back to join the fuel and release carbon dioxide and water once more, transferring energy for the plant to use.
Making the model The templates "Bottom" and "Top" should be printed on A4 paper and stuck on stiff card (or print directly on stiff white card). Now cut away
carefully the marked bits from the "Top" moving part. Staple large thick elastic bands, which have been cut open, to the "Top" card. Lay the two cards together and fix the other ends of the elastic bands, tight but not yet stretched, round to the rear of the fixed "Bottom" card. Use plastic file clasps to act as ‘runners’ for the moving part which needs to be glued or taped to the fixed "Bottom" card, allowing the "Top" card to slide out. Fix handles on the back of the fixed "Bottom" card and the moving "Top" card to make operating easier.
All will be revealed in the talk - useful for Biologists, Chemists and our Physics friends too.
