Investigating Photosynthesis
By Morgan Marsh
Adapted from Eva Carswell
Original found at http://www.theaps.org/education/k12curric/activities/pdfs/carswell.pdf
Overview: To provide students with a situation in which they can explore photosynthesis.
Standards: B-3.1 Summarize the overall process by which photosynthesis converts solar
energy into chemical energy and interpret the chemical equation for the process.
Performance Objectives:
Students will be able to:
realize that the very same carbon molecules that heterotrophs breathe out are the carbon
molecules that make up the backbone of the glucose molecule.
write the equations for photosynthesis with coefficients and subscripts (study time is
required).
Hook: How and why do leaves change color?
Materials:
 three pieces of blue construction paper (cut each piece in half so you have six
pieces on which to write “C” to represent carbon [six molecules of carbon])
 six pieces of red construction paper (cut each piece in half so you have 12 pieces
on which to write “H” to represent hydrogen [12 molecules of hydrogen])
 nine pieces of green construction paper (cut each piece in half so you have 18
pieces on which to write “O” to represent oxygen [18 molecules of oxygen])
 one piece of yellow construction paper (draw a sun to represent energy coming
from the sun)
 one piece of white construction paper with a “+” on it
 one piece of white construction paper with an arrow to represent the yields sign in
the equation
 posterboard with the equation for photosynthesis on one side
 one piece of construction paper that reads “carbon dioxide”
 one piece of construction paper that reads “water”
 one piece of construction paper that reads “glucose”
 one piece of construction paper that reads “oxygen”
Concept Exploration
Procedure:
Each student is given the role of a molecule of carbon, hydrogen, or oxygen. Depending
on the size of your class, some students may need to be assigned the role of two
molecules of the same element. For example, you may need to give one student two
“H’s” instead of one “H.” If you have a large open area in your classroom, you can
conduct this part of the activity inside. Otherwise, you will need to plan to go outdoors,
into the hallway, or even to the school gymnasium or cafeteria. Once you arrive at your
destination, hold up the posterboard with the equation for photosynthesis facing the
students. First, instruct the students to position themselves so that they represent the
reactants of the photosynthesis equation. (Remember to assign a student to the role of
“sun,” “+” and “yields”.) Once students have gotten into the correct positions give each
group of molecules the name of the substance that they represent (carbon dioxide or
water). Next, have the students position themselves so that they represent the products of
the photosynthesis equation. Once the students have positioned themselves correctly
give each group of molecules the name of the substance they represent (glucose or
oxygen). The idea is that students will realize that the very same carbon atoms that make
up carbon dioxide make up the backbone for the glucose molecule.
Questions to ask during activity:
1. How many molecules of carbon dioxide and how many molecules of water are needed
for green plants to synthesize one molecule of glucose and six molecules of oxygen?
2. Name three ways that animals lose water.
3. What type of nutrient is glucose (carbohydrate, protein, nucleic acid or lipid)?
4. What are other sources of carbon dioxide (besides animals exhaling)?
5. What gas do you exhale?
6. What gas do plants give off?
Concept Introduction:
The teacher introduces the concept by covering the following:



All organisms need a constant source of energy to survive. The ultimate source of
energy for most life on Earth is the Sun.
Photosynthesis is the overall process by which sunlight (solar energy) chemically
converts water and carbon dioxide into chemical energy stored in simple sugars
(glucose).
This process occurs in two stages.
o The first stage is called the light-dependent reactions because they require
solar energy.
 During the light-dependent reactions, solar energy is absorbed by
chloroplasts and two energy storing molecules (ATP and NADPH)
are produced.
 The solar energy is used to split water molecules which results in
the release of oxygen as a waste product, an essential step in the
process of photosynthesis.
o The second stage is called the dark (light-independent) reactions because
they do not require solar energy.
 During the dark (light-independent) reactions, energy stored in
ATP and NADPH is used to produce simple sugars (such as
glucose) from carbon dioxide. These simple sugars are used to
store chemical energy for use by the cells at later times.
 Glucose can be used as an energy source through the process of
cellular respiration or it can be converted to organic molecules
(such as proteins, carbohydrates, fats/lipids, or cellulose) by
various biologic processes.
The process of photosynthesis is generally represented using a balanced chemical
equation. However, this equation does not represent all of the steps that occur during the
process of photosynthesis.
Solar energy
6CO2 + 6H2O  C6H12O6 + 6O2




In general, six carbon dioxide molecules and six water molecules are needed to
produce one glucose molecule and six oxygen molecules.
Each of the reactants (carbon dioxide and water) is broken down at different stages of
the process.
Each of the products (oxygen and glucose) is formed in different stages of the
process.
Solar energy is needed to break down the water molecules.
Concept Application
Complete worksheet
Student Worksheet
Photosynthesis and Respiration
You will act out the equations for photosynthesis 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
C O
+
H O

C H O
+
O
Answer the following questions.
1. How many molecules of carbon dioxide and how many molecules of water are needed
for green plants to synthesize one molecule of glucose and six molecules of oxygen?
2. Name three ways that animals lose water.
3. What type of nutrient is glucose (carbohydrate, protein, nucleic acid or lipid)?
4. What are other sources of carbon dioxide (besides animals exhaling)?
5. What gas do you exhale?
6. What gas do plants give off?