LESSON DESCRIPTION: Intro to Photosynthesis
Teacher:
Linda Arnoldi
Unit Theme: Cell Energy
Date/Course: November 21, 2009/Biology
Idea for activity came from
Eva Carswell
Westside High School
Macon, GA
RATIONALE:
Some of my students have already been introduced to the concept of photosynthesis and
respiration, while others might not have. So I will start with the basics from what they know
about the importance of plants and incorporate this into what they’ve learned recently about
molecules and cells.
This activity will reinforce what has already been taught, while providing a more detailed
understanding of the number of elements needed to make up a specific number of molecules in
the reactions. This is also a kinesthetic and visual exercise that will provide a memorable
experience.
OVERVIEW:
Each student will represent an atom from the photosynthesis reactants. Students will model
the rearrangement of atoms during photosynthesis. If there is time, they will also model
respiration. They will be able to write the balanced chemical formula for the reactions as a
result of their formations.
STANDARD/EALR:
9-11 LS1A
Carbon-containing compounds are the building blocks of life. Photosynthesis is
the process that plant cells use to combine the energy of the sunlight with molecules of carbon
dioxide and water to produce energy-rich compounds that contain carbon (food) and release
oxygen.
 Explain how plant cells use photosynthesis to produce their own food. Use the
photosynthesis equation to illustrate how plants rearrange atoms during
photosynthesis.
 Explain the importance of photosynthesis for both plants and animals, including
humans.
9-11 PS2G
Chemical reactions change the arrangement of atoms in the molecules of
substances. Chemical reaction release or acquire energy from their surroundings and result in
the formation of new substances.
 Use a chemical equation to illustrate how the atoms in molecules are arranged before
and after a reaction.
PREPARATION:
Make signs on construction paper:
6 C’s, 18 O’s, 12 H’s, 1 Sun,
1 “Carbon Dioxide” with chemical formula
1 “Water” with chemical formula
1 “Glucose” with chemical formula
1 “Oxygen” with chemical formula
1 “Energy as ATP”
Materials:
 Overhead
 Construction paper signs
INSTRUCTIONAL SEQUENCE:
Intro (X Min):
Q. Why are plants so important to humans for survival? (On over head when they walk in)
Food, oxygen
Give an example of a plant we eat.
Q. Where did the (plant) get it’s food from? (Sun)
Q. Does the (plant) eat the Sun? What’s happening there?
Someone offers photosynthesis as an explanation
Perfect! This leads me to what I’d like to explore more with you today, photosynthesis!
Discuss root meaning of term
Q. Anyone have an idea what the reactants are? (Cake analogy if needed)
Water, carbon dioxide, light
Write these on the overhead
Q. Does anyone remember the chemical formula for these?
Start to construct the chemical formula.
Once it’s complete, point out how to count the number of atoms and molecules. Point out how
the numbers don’t make sense.
POINT OF ACTIVITY:
You are going to discover the correct number and arrangement of these atoms and molecules
reaction and what happens to each atom in a photosynthesis reaction.
Activity (X Min):
Distribute signs while telling them that they are going to start out forming the reactants of
photosynthesis.
Once they form, count with them the number of each molecule of water (6) and carbon dioxide
(6). Put these numbers on the reactants on the overhead
Then, hold up sun sign and instruct them to use this light energy to rearrange and form the
products glucose and oxygen.
Once they form, count with them the number of each molecule of glucose (1) and oxygen (6).
Put these numbers on the products on the overhead.
While you are standing there, tell me what animals like humans need to breathe, in other
words, perform respiration. (Oxygen…) Write it on overhead. Why do we eat food? (For energy)
Energy-rich glucose molecules are found in the cells of our food, but we need to perform
respiration to release that energy. So, the other reactant in respiration is…(wait 5 seconds for
their answer)…glucose.
Draw yield arrow and energy on the other side. What do we breathe out? (Carbon dioxide) If
they don’t think of water. Go right into modeling it, recording their calculations of molecule
number. When they get to the products, help them see H2Os (hint at the fog you might blow on
a window)
Wrap-up:
Great job! Now head back to your seats and fill out the worksheet. When you finish, you’ll get a
stamp.
If there is time after stamping, invite them to share their answer to the last question of their
worksheet.
ASSESMENT:
Students will be able to write the chemical reaction of photosynthesis and respiration with
coefficients and subscripts.
Their exit slip will be their worksheet, complete with respiration and photosynthesis chemical
equations with their coefficients and subscripts, and questions answered.
MODIFICATIONS:
If students are still confused, I can help them model and count at their desk or as a mini group.
Name:
Date:
Photosynthesis and Respiration Worksheet
You will act out the equations for photosynthesis and respiration (listed
below) as a molecule or molecules of the same element.
The equation for ______________ is written below. Fill in the missing
coefficients and subscripts. Also write the words that can be used to
describe the chemical formulas.
sunlight
CO + H O → C H O + O
The equation for______________ is written below. Fill in the missing
coefficients and subscripts. Also write the words that can be used to
describe the chemical formulas.
O + C H O → CO + H O + energy
In your own words, how do plants make their own food?
Compare the reactants of the photosynthesis equation to the products of
the equation for respiration. What do you notice?
Compare the reactants of the respiration equation to the products of the
photosynthesis equation. What do you notice?
How many molecules of carbon dioxide and how many molecules of
water (reactants) are needed to make 1 molecule of glucose (product)?
Story Time! What would happen if a meteor hit Earth and shrouded
everything in a thick cloud of dust, leaving plants unable
photosynthesize?