Carbon Cycle Model
Carbon constitutes 12% to 19% of the mass of a living organism. It is a main ingredient in a lot
of compounds important to life on earth. Specifically, carbon is a main ingredient of glucose, which is
one of the simplest molecules that store chemical energy in living organisms. Living organisms then use
this glucose whenever they need energy, either to grow or move around. It is important to know then
how glucose fits in the global carbon cycle.
Glucose is first formed when plants or cyanobacteria take in carbon dioxide and water from the
atmosphere and change these molecules to glucose and oxygen gas. This process is called
photosynthesis and only occurs in the presence of sunlight. The chloroplasts in plant cells or
cyanobacteria absorb energy from the sun and use this energy to rearrange atoms from carbon dioxide
and water into glucose and oxygen gas.
Glucose is then used by the plants or organisms that eat the plants as a source of energy to grow
or to move. The cells in the living organisms that need energy break the glucose molecule and turn it
back into carbon dioxide and water, extracting the energy that was stored in the glucose molecule. This
process is called cellular respiration.
Cellular respiration and photosynthesis can be illustrated by the following two chemical
equations:
Cellular respiration: C6H12O6 + 6O2 → 6H2O + 6CO2 + energy
Photosynthesis:
energy + 6H2O + 6CO2 → C6H12O6 + 6O2
The carbon cycle is the global movement of carbon between different reservoirs following
specific flows. Carbon is present in four major reservoirs on earth, which are the four spheres of earth,
the geosphere, the atmosphere, the hydrosphere and the biosphere. Here, we have decided to model the
movement of carbon between the atmosphere and biosphere because this branch of the carbon cycle can
be demonstrated by photosynthesis and cellular respiration.
A. Cellular Respiration Model
Materials
 250 ml Erlenmeyer flask
 1 packet active dry yeast (Saccharomyces cerevisiae)
 100 ml apple juice
 1 balloon
Procedure
1. Heat the juice until it is 50 °C
2. Mix yeast and juice in the Erlenmeyer flask
3. Secure balloon over the Erlenmeyer flask
4. Balloon will inflate after a couple hours
Analysis and Interpretation
Discuss the different parts of the model and explain how each part integrates to demonstrate cellular
respiration. For example, what do the yeast, apple juice and balloon represent in this model, and why
may these parts be good examples of carbon reservoirs? Also, which flow of the carbon cycle is
illustrated in this experiment?
B. Photosynthesis Model
Materials
 250 ml Erlenmeyer flask
 large test tube
 1 stopper
 1 funnel
 1straw
 100 ml distilled water
 bromthymol blue
 leafy aquatic plant (Echinodorus bleheri)
Procedure
1. Fill the Erlenmeyer flask with the 100 ml distilled water
2. Add bromthymol blue to the water until the water turns dark blue
3. Blow into the Erlenmeyer flask until the water and bromthymol blue turn yellow
4. Pour the yellow solution into a large test tube using the funnel
5. Place a sprig of the leafy aquatic plant in the test tube
6. Stopper the test tube and place in a sunny location
7. Observe the solution in the test tube every 15 minutes until the color changes
Analysis and Interpretation
Discuss the different parts of the model and explain how each part integrates to demonstrate cellular
respiration. For example, what is the source of carbon in this model? What do the bromthymol blue and
Echinodorus bleheri represent in this model? Why are these components good examples of parts of the
carbon cycle? Also, which flow is illustrated in this experiment?
C. Carbon Cycle Model
Design an experiment that models cellular respiration and photosynthesis working hand in hand. The
carbon dioxide produced by cellular respiration must be used by a plant that will change it to glucose.
You must include a materials list and method section in your lab report for part C. Carbon Cycle. Finally
answer the following questions in your Analysis and Interpretation and Question for Further Thoughts
section.
Analysis and Interpretation
Discuss the different parts of this model and explain how each part integrates to demonstrate cellular
respiration and photosynthesis working hand in hand.
Question for Further Thoughts section
 Why is energy a reactant in the photosynthesis chemical equation and a product in the cellular
respiration chemical equation?
 Why is an aquatic plant used in the photosynthesis model instead of a terrestrial plant?
 Will the model you created in C. cycle carbon in perpetuity? Explain your answer.
C. Carbon Cycle Model
Materials
 250 ml Erlenmeyer flask
 250 ml boiling flask
 elbow-tube
 2 one-hole stopper
 large test tube
 1 stopper
 1 funnel
 ring stand
 1 packet active dry yeast (Saccharomyces cerevisiae)
 100 ml orange juice
 100 ml apple juice
 100 ml distilled water
 bromthymol blue
 leafy aquatic plant (Echinodorus bleheri)
Procedure
1. Heat the juice until it is 50 °C
2. Mix yeast and juice in boiling flask
3. Stopper the boiling flask with an elbow-tube
4. Place the boiling flask on the ring stand and immerse the end of the elbow-tube in the
Erlenmeyer flask filled with water and bromthymol blue
5. Wait until the water and bromthymol blue turn yellow
6. Pour the yellow solution into a large test tube using the funnel
7. Place a sprig of the leafy aquatic plant in the test tube
8. Stopper the test tube and place in a sunny location
9. Observe the solution in the test tube after 15 minutes