Lesson Plan

Climate Change #2 - Photosynthesis/Respiration

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Grade Level:
Upper Elementary: Third Grade through Fifth Grade
Lesson Duration:
60 Minutes
Additional Standards:
ESS2.A, ESS2.C, ESS3.D, LS1.C, LS2.A, LS2.B, PS1.A, PS1.B, PS3.D
Thinking Skills:
Analyzing: Break down a concept or idea into parts and show the relationships among the parts. Creating: Bring together parts (elements, compounds) of knowledge to form a whole and build relationships for NEW situations.


By the end of this activity:
1. Students will be able to identify atoms as the smallest building block of materials (matter). 
2. They will be able to explain that atoms, in different combinations, form different materials.
3. They will be able to differentiate between photosynthesis and respiration.


The students have probably heard about climate change, but most do not yet have the chemical background to understand what is happening. This activity is designed to give them a basic chemical understanding of the carbon cycle and thereby giving them an understanding of why healthy plants are essential to a healthy habitat. While other greenhouse gases (besides carbon dioxide) are also important, carbon is the example covered here. It is also important for the students to understand that there are other greenhouse gases.

The story of Democritus’ definition of the atom can be used to set a basic understanding. Using cheese (or something similar) as a prop when you talk will maintain the student’s curiosity. Democritus stated that if you take a piece of cheese and cut it in half, you still have cheese. If you take that half and cut it again, the smaller piece is still cheese. If you take that tiny piece and cut it again the tinier piece is still cheese. If you could continue cutting the cheese into tinier and tinier pieces you would eventually come down to the most basic of all particles that still have all the qualities of cheese.

Democritus called that fundamental particle the atom. Now cheese is not a fundamental particle, but you can explain that atoms combine in various arrangements to form different materials. They are the fundamental particles or building blocks from which all matter is made. The atom that is found in all living things on earth is carbon. In the upcoming activities, direct special attention to where the carbon atoms are going.



Materials: Provided sign templates, Chalk/Ribbon/Rope (something to make a circle with) (green and brown)


1. Print off signs to be pinned to each student. (See Step 5 for a simpler equation)
You will need:

  •  6 black carbon atom sign (6 pages)
  • 12 white hydrogen atom sign (4 pages)
  •  18 red oxygen atom sign (6 pages)
  •  1 big yellow energy sign

2. These will be used to act out the processes of photosynthesis and respiration. Post the equations of these processes where the students can see them. The equations are as follows:

  • Photosynthesis: 6CO2 + 6 H2O + energy -> C6H12O6 +6O2
    oCarbon dioxide plus water plus energy yields sugar and oxygen
  • Respiration: C6H12O6 +6O2 -> 6CO2 + 6 H2O + energy
    oSugar plus oxygen yields carbon dioxide plus water plus energy

3. Make a large circle on the floor with green chalk or a green piece of ribbon. The circle needs to be large enough for the student groups to step into. This will represent a plant. Feel free to get creative if a circle seems boring!


4. Make a second large circle on the floor with brown chalk or with a brown piece of ribbon. The circle needs to be large enough for the student groups to step into. This will represent an animal.


5. To make this activity easier, feel free to divide the number of atoms in half and just explain to the kids that the sugar molecule is usually twice as big.

Possible easier equation: 3CO2 + 3H2O +Energy -> C3H6O3 + 3 O2


Includes ones for this lesson and following lessons.

Download Name tags for students


1. Give each student one sign to wear. There are 36 different atoms and the energy sign. 


2. At this point you may wish to have students come up and model each of the molecules. i.e. bring three students up to the front and have them form a CO2 molecule so everyone in the class can see what it looks like.  Show them how the carbon and oxygen (for water) have to be in the center of the group.


3. Have students group themselves into six (three) carbon dioxide molecules and six (three) water molecules by holding hands or linking arms to form the chemical bonds.

  • Have the water molecules pretend that they are being drawn into the plant through the roots.
  • Have the carbon dioxide molecules pretend that they are being drawn into the plant through the leaves.
  • Once they are all in the plant, have the yellow energy person come in to break the bonds by pulling their hands apart. Make the point that it takes energy to break the bonds.
  • Energy stays in the plant circle while the atoms regroup themselves into sugar and oxygen molecules, holding hands or linking arms to show that new bonds have formed.
  • Have the oxygen molecules drift off into the air, as the plant does not need it.

4. Now explain that an animal, such as a human, is going to eat the plant. Have the students pretend they are eaten by stepping as a molecule (with hands still held), along with the energy, into the brown ribbon that represents an animal.

  • Have the students who are the oxygen molecules pretend they are being breathed into the animal.
  • Now have everyone regroup into carbon dioxide and water. The energy will be released as “heat” when the CO2 and H2O bonds form and those students who represent energy will leave the animal by stepping outside the circle.
  • Tell the students that the energy is used by the animal to live and that is why the animal ate the plant. They can feel their own body heat as evidence. Ask them what happens when they are active – like when they are playing a sport. They will probably respond that they feel energized and warm/hot.
  • Have them pretend that the water is released as sweat or urine, the water student molecules step out of the brown circle, and the carbon dioxide is breathed out, the carbon dioxide student molecules step out of the circle.


5. Repeat the cycle about two more times until the students can do it without help. For advanced students you can lead to the understanding that plants both photosynthesize and respire.

Assessment Materials

Discussion Questions

What is an atom?
(An atom is the smallest particle that can exist and still have the properties of the parent material. A material made of all of one kind of atom is called an element.)


What are the elements in the molecules? How many atoms of each type are in each molecule?

(The reactants in photosynthesis are CO2, and H2O. The carbon dioxide is made of one carbon atom between two oxygen atoms. The water is made of one oxygen atom between two hydrogen atoms)


What happened to the reactant molecules? Where did the atoms go? How many of each atom are the new product molecules?

(The reactants molecules came apart into their component atoms. Those atoms recombined to form sugar. No atoms were lost or gained in the process.)


Is it atoms or molecules that break into pieces to form new things?
(It is molecules that break apart into individual atoms.)


Where did the plants get the carbon from?
(The plants get the carbon from the carbon dioxide in the air.)


Explain how a plant, a solid, can be made from the gas, carbon dioxide.
(When the atoms recombine into a different molecule the new material has different physical and chemical properties than the original molecule. So an atom of carbon in carbon dioxide has the molecular properties of a gas, but the same atom in a sugar molecule has the molecular properties of a solid.)


What happened to the energy trapped by the plants?
(The energy was stored in the plant until the plant decomposed or was eaten.)

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