Ecology: CO2 Cycle - Photosynthesis and Respiration

See real-time evidence that CO2 is taken up by a plant during photosynthesis and released from a plant during cellular respiration.

Motion Sensors

CO2 levels rise when the light is off and decrease dramatically when the light is turned on, providing students evidence that CO2 is both given off by plants during respiration and used by plants during photosynthesis. Enlarge graph.

Lab Summary:

In this activity, students will use a Carbon Dioxide Gas sensor and a mini-terrarium to explore the cycle of CO2 as the plant engages in the process of photosynthesis and then when photosynthesis is not occurring.

Students will see in real time that when photosynthesis is occurring and CO2 is being trapped by the plant into energy-storage molecules (carbohydrates, including sugars and starches), the concentration of CO2 decreases in the air of the terrarium. Students will see that when photosynthesis is not occurring (and CO2 is no longer being trapped into energy-storage molecules), the plant’s cellular respiration processes (which produce CO2 as a byproduct) cause the concentration of the CO2 gas in the air of the terrarium to increase.

Download Free Lab  (PDF, 548 KB)

(student version)

Method:

Use the Carbon Dioxide Gas Sensor and a mini-terrarium to explore the cycle of CO2 as the plant engages in the processes of photosynthesis and respiration.

Here's What You Need:

Probeware

Other Materials

  • Bright light source, such as a lamp with a 100-watt Fluorescent Bulb
  • Erlenmeyer Flask, 250-mL
  • Dark Cloth, (1) m2
  • Small Plant
  • Water, 50.0 mL

Lab Manual:

This activity is included in Explorations in Biology (PS-2807), complete with Teacher Information pages, student instructions and handouts, and sample data for a total of 25 probeware-based labs. For your convenience, we offer bundles which provide the probeware necessary for the activities in the manual. For more information on these resources and bundles, click here.