Photosynthesis: Molecule Models
Class Copy. Please leave in class.
Introduction
Plants photosynthesize when they are in the light. Plants
need to take in water and carbon dioxide and rearrange the
atoms from these molecules to make glucose, which is food
for plants. Oxygen gas is another product of this chemical
reaction. Photosynthesis requires an input of light energy.
Light energy is transformed into chemical energy, which is
stored in the high-energy bonds of glucose: C-C and C-H
bonds. Use the molecular models to show how this happens.
Set-up:
1. Get the following materials:
a. Whiteboard, marker, and eraser
b. 6 Carbon atoms
c. 12 Hydrogen atoms
d. 18 Oxygen atoms
e. 12 spring bonds
f. 24 wood bonds
g. 12 pipe cleaner pieces
2. Set up your whiteboard like the visual shown here.
Reactants
Products
Procedure:
1. Work with your partner to make molecule models of the reactant molecules:
a. Make models of 6 carbon dioxide (CO2) molecules and 6 water (H2O) molecules. Put these
molecules on the reactant side of your whiteboard.
b. When you are finished creating the reactant molecules, carbon dioxide and water, put
away any extra pieces that you didn’t use into your bin. This is an important step!
c. Place 12 pipe cleaners in the “reactants” square on your whiteboard and write “Light
Energy” under these pipe cleaners. Pipe cleaners represent light energy coming from the
Sun.
d. Fill out your data chart for the reactants.
Get checked off by Ms. Wang or Ms. Anne for Step 1.
2. Show how the atoms of the reactant molecules can recombine into product molecules and show
what happens to energy.
a. Disassemble all of your carbon dioxide (CO2) and water (H2O) molecules and recombine
them into glucose (C6H12O6) and oxygen gas (O2) molecules. Use ALL the atoms from your
reactants. Put these molecules on the product side of your whiteboard. Some things to
notice and discuss with your partner:
i. How many carbon dioxide molecules were used?
ii. How many water molecules were used?
iii. How many glucose molecules were produced?
iv. How many oxygen molecules were produced?
a. Energy lasts forever, so move the twist ties to the product side of your whiteboard. Glucose
has high-energy bonds (C-C and C-H). Add a pipe cleaner to all the C-C- and C-H bonds in the
products. What form of energy did the light energy change into? (Re-read the introduction
if you aren’t sure.) Write the correct form of energy under the pipe cleaners.
b. Fill out your data chart for the products.
Get checked off by Ms. Wang or Ms. Anne for Step 2.
Atoms last forever!! Check yourself: did your number and type of atoms stay the same at the
beginning and end of the chemical change?
Energy lasts forever! Check yourself: did the number of pipe cleaners stay the same at the beginning
and end of the chemical change?
Writing the chemical equation. Use the molecular formulas (C6H12O6, O2, CO2, H2O) and the yield sign
() to write a balanced chemical equation on your worksheet.
Check in with another pair. Can everyone explain the
transformations of matter and energy in photosynthesis?
3. Plant Biosynthesis: After plants make glucose, some of the glucose is used to make either starch or
cellulose. Starch is stored energy for plants (like fat for animals); cellulose helps give plants their
structure. Show how two or more glucose molecules can combine to form starch.
a. Remove a hydrogen atom from one glucose molecule, and an –OH from another glucose
molecule.
b. There will be an empty bond space when you remove these atoms. Link the two glucose
molecules together at this space using a bond.
c. Combine the –H and –OH together into a water molecule.
d. Answer the questions below your data chart.
4. Clean up: Disassemble all the molecule models and return the pieces to your bin. Count all pieces
to make sure you have everything ready for the next class to use, and replace any missing pieces.
Name: ____________________________________________ Per. _____ Date: _____________
Photosynthesis: Molecule Models
Use this sheet to summarize your learning from the molecule models.
Matter
Number
of Carbon
atoms
Number of
Molecules Made
Number
of Oxygen
atoms
Energy
Number of
Hydrogen
atoms
Reactants
Carbon Dioxide
Forms of energy:
Water
Number of
Molecules Made
Number
of pipe
cleaners:
Initial:
Total atoms in
reactants
Products
Glucose (sugar)
Oxygen gas
Forms of energy:
Number
of pipe
cleaners:
Total atoms in
products
1. What is the balanced chemical equation for photosynthesis?
2. In the space below, DRAW the reaction of photosynthesis that you modeled. You may use the simple
shape for glucose, but draw the molecular structures of the other molecules.
Initial:
(over)
3. According to the molecule models, what happens to matter during photosynthesis?
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4. How do you know that matter is conserved in photosynthesis?
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5. What happens to energy during photosynthesis?
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6. How do you know that energy is conserved in photosynthesis?
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7. In your own words, what do you think is the purpose of photosynthesis?
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8. When you constructed starch, what process were you modeling?
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9. Besides in plant cells, where else does the process you named in Question 8 happen, and with which
molecules?
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