Class 6: More Molecules, for Life
Examine evaporation tray, describe & record present state - on TV if possible, & pictures for Web pages later. Get kids to describe last week's analysis of crystallization process, and dissolving. Ask them which dissolves salt faster - hot or cold water. Why?
Introduce idea of energy:
- Different kinds:
- motion, heat, Sunlight, chemical, electrical, potential,...
- interconversion: discuss ways of turning one type into another
- needed for life processes
- Fires and burning: what's needed?
- Fuel (name some types - anything that burns, including sugar)
- Air - specifically, OXYGEN
- Heat is also involved - possibly some to start, a lot coming out
Demo over TV of oxygen's diatomic molecule, and "coal" - one carbon atom (large black styrofoam sphere), and "burn" the coal, producing CO2. Then show typical "hydrocarbon" CH4, explain name, relate to oil, etc., and demo "burning" that (producing CO2 and H2O). Finally, describe "carbohydrate" - explain name, get them to give examples. "Food is fuel!"
Materials
Each group gets (click here for picture):
- 1 "carbon atom" (large black styrofoam sphere)
- 2 "hydrogen atoms" (small blue styrofoam spheres)
- 3 "oxygen atoms" (large white styrofoam spheres)
- 4 toothpicks to join them together
Hands-on Activity #1 - Burning Fuels
"Now it's your turn!" Hand out to each table (click here for picture) one O2 molecule (2 large white styrofoam spheres), and one "carbohydrate" HCOH - explain name again. Have them figure out how to "burn" sugar - manipulate the atoms to show what happens. What does a fire also release? HEAT, a type of energy.
Does anyone know how our bodies get the energy we need? Food is our fuel! Why do we have to breathe? Because we need the oxygen for the burning! What is this whole proceess called? RESPIRATION!
Take some time to draw and write up a description of what we just did, including how it's important to us and to ALL LIFE!
Hands-on Activity #2 - Photosynthesis
So food is our fuel - it gives us energy when we burn it in our bodies, using oxygen we breathe. How does the energy get into the sugar? How is the sugar made? Where does the energy come from? (Get students' answers)
Point to the aquarium tank, ask "what color do you see here?" GREEN! Why? - what is in it? Seaweed/algae, containing ...? CHLOROPHYLL! What else can you name that's green from chlorophyll? What special thing can plants and algae do that animals can't? They can capture energy (where from?? the Sun! - light is a type of energy) and store that energy by making sugar. That's what you'll do next.
Each group at each table manipulates the atoms again to show the process of PHOTOSYNTHESIS (explain name; click here for picture of molecules produced by respiration and used by photosynthesis):
- Assign roles within each group (by lot, etc.): a "Sunlight" student, a "Plant" student, and an "Animal" student
- "Sunlight" student breaks apart the CO2 and H2O into atoms
- "Plant" student then assembles the atoms into simple sugar - HCOH - and "leftovers" (discuss what is left over, make diatomic)
- "Animal" student then takes molecules produced, representing "eating" the sugar and breathing the oxygen, and reassembles atoms into products of resspiration: CO2 and H2O
- Rotate roles and repeat - any extra students without a role at first now get a chance
Note that this endless back-and-forth is happening around us all the time. Earth is an ECOSYSTEM, powered by the Sun!