All species in an ecosystem, from critters on the forest floor to lions in the Serengeti, are directly or indirectly nourished by “dead stuff.” This organic matter, whether fallen leaves, rotting fruit, or decomposing organisms, is a crucial part of the continuous cycle of matter and energy flow in an ecosystem. While much attention is usually given to producers and consumers, an often ignored part of the food web—decomposers—play an equally vital role. These organisms break down dead matter, releasing carbon (in the form of carbon dioxide) and other nutrients back into the environment. With the Go Direct^® CO₂ Gas Sensor, students can observe this process in real-time, gaining a deeper understanding of the carbon cycle and the importance of decomposition.

The Hidden Heroes of the Ecosystem

When organic things die, they liberate carbon dioxide, water, and other compounds back into the ecosystem, but this process requires help from specialized consumers in the food web. Decomposers, such as fungi and bacteria, along with detritivores like earthworms and beetles, are essential to recycling nutrients in ecosystems by breaking down organic matter from dead plants and animals.

Carrion feeders, like vultures, are scavengers that start the larger-scale decomposition process by consuming the remains of dead animals. Detritivores consume debris (detritus), including bits of decaying matter and even feces. In terrestrial ecosystems, detritivores include certain types of beetles, earthworms, flies, millipedes, centipedes, woodlice, and even some butterflies! In aquatic ecosystems, organisms like crabs, shrimp, and sea cucumbers play this role.

This process not only cleans up the environment but also facilitates the release of carbon dioxide, which is a key component of the carbon cycle.

Experiment: Investigate Cellular Respiration in Decomposition

This simple, impactful experiment allows biology students of all levels to investigate the process of decomposition by measuring the carbon dioxide released from decaying organic material.

The remains of dead organisms—like rotting produce—still contain usable chemical energy, and this is what specialized consumers, like decomposers, are feeding on. The chemical reactions that occur include cellular respiration:

C₆H₁₂O₆ + 6 O₂(g) → 6 H₂O + 6 CO₂(g) + energy

All organisms, including decomposers, oxidize glucose for energy. Often, this energy is used to convert ADP and phosphate into ATP.

Using the CO₂ Gas Sensor and respiration chamber, students monitor the carbon dioxide produced by decomposing material.

Materials Needed

• Chromebook™, computer, or mobile device
• Vernier Graphical Analysis^® app
• Go Direct^® CO₂ Gas Sensor
• 250 mL respiration Chamber
• Decomposing plant material (e.g., banana peels, moldy bread)
• Paper towels

The Setup

This experiment is easy to conduct in a classroom, lab, or out in the field. If your students have access to a school garden or compost, a great way to contextualize this experiment is to use compost or materials they find there. But, any kind of decaying organic matter works great: banana peels, moldy fruit—even that fuzzy green cheese hiding in the back of your fridge!

Once you’ve collected your materials, launch Graphical Analysis and connect the CO₂ Gas Sensor via Bluetooth^® wireless technology or USB to your device.

The Experiment

Encourage students to make predictions about what they think that data will look like. Do they expect carbon dioxide levels to increase or decrease? Will changes occur slowly or rapidly? What is causing the changes that they predict?

Insert the decomposing material sample into the respiration chamber. Place the shaft of the CO₂ Gas Sensor in the opening of the respiration chamber and gently push it down until it stops. The sensor is designed to seal the chamber without the need for unnecessary force.

Let the sealed chamber sit for about a minute, then click or tap Collect in Graphical Analysis to start data collection. Data should be collected for 5 minutes.

Discussion Questions

Following the experiment, discuss student observations and the broader implications for food webs and ecosystems. Here are some questions you can use to extend the conversation.

• Where is the carbon coming from and what’s the process that’s starting it? 
• Why are decomposers important to ecosystems? 
• How might the decomposition process change in different environmental conditions?
• What would happen to an ecosystem if decomposers were removed from the food web?

Cleaning Up

To wrap up the experiment, remove the CO₂ Gas Sensor and the sample material from the respiration chamber. Clean out the chamber by emptying the decomposing material into the trash and then cleaning the bottle with water and soap. Thoroughly dry the inside of the respiration chamber with a paper towel.

Looking for more ways to engage students in hands-on investigations? Explore our biology resources or check out our ideas page. Questions? We’re always here to help! Reach out to biology@vernier.com, call 888‑837‑6437, or drop us a line in the live chat!