Explorations in Photosynthesis and Respiration

Originally posted on PASCO’s Blog. Blog is written by Bruce Taterka a teacher at West Morris Mendham High School in New Jersey

PASCO’s Wireless CO2 Sensor provides a powerful opportunity for students to explore the effects of photosynthesis and respiration in their local environment. This blog will describe how students can use a “Pretzel Barrel CO2 Chamber” to design experiments to measure rates of photosynthesis and respiration in a wide variety of settings and circumstances.

Background

Soil plays an important role in the carbon cycle and global climate because it acts as a carbon sink, sequestering CO2 from the atmosphere in the form of organic matter. The upper layers of soil contain organic matter that is actively decomposed by the soil community: microbes, insects, worms and other animals.
While respiration by soil organisms decomposes organic matter and releases CO2, the plant community is photosynthesizing and taking in CO2 from the atmosphere. So in this part of the earth’s carbon cycle, CO2 is moving in two directions – into the atmosphere from soil, and out of the atmosphere into plants. We refer to this transfer of carbon as “CO2 flux.” With PASCO’s Wireless CO2 Sensor, students can explore the carbon cycle, plant and soil biology and climate change by measuring CO2 flux.

The rate of CO2 flux depends on a wide variety of factors. For soil, the rate of CO2 production may be affected by:

  • The content and type of organic matter in the soil
  • Temperature
  • Moisture
  • Sunlight
  • Soil chemistry

For the plant community, the rate of CO2 production may be affected by:

  • Type and density of plants
  • Temperature
  • Moisture
  • Sunlight
  • Soil chemistry

Carbon flux will vary with the weather, throughout the day, and throughout the year as the seasons change. Measuring CO2 flux provides an excellent jumping-off point for engaging in NGSS practices regarding the earth’s carbon cycle.

 

Creating a model of the Earth's carbon cycle

Figure 1. Collect data, and construct explanations. Integrating a range of analytical results can form the basis for creating a model of the earth’s carbon cycle and designing solutions to problems such as climate change and food production.

Students can define their own research questions and problems, analyze the results, and generate designs to conduct a variety of controlled experiments using the chamber. Most experiments will identify the CO2 concentration inside the chamber as the dependent variable and will test the effect of an independent variable of students’ choice.

On land students can compare CO2 flux on soil, lawn, forest, sunny vs. shady areas, and in a wide variety of other situations. In general, when the chamber is on bare soil or leaf litter, the CO2 concentration inside the chamber will be expected to increase, usually within a short time period such as 5 or 10 minutes. Figure 1. For longer investigations the sensor can be placed in logging mode (storing data to internal memory) and left for ~24hrs before the batteries will be depleted.

The chamber can be placed over plants that can fit inside it, in which case CO2 concentration inside the chamber should decrease, although it may be counteracted by respiration. The chamber can even be used on water by wrapping a piece of foam insulation around it, allowing it to float.

In any type of environment, students can design their own studies to investigate the effect of different variables on CO2 flux.

How to make a Pretzel Barrel CO2 Chamber

The chamber is made of a plastic pretzel container available in supermarkets.

  • Draw a straight line around the container, then cut it in half using a razor knife to form two large plastic chambers open at the bottom and closed on top.
  • You have two options here. You can cut a hole in the top for a CO2 sensor using an electric drill or a razor knife. The hole should allow the CO2 sensor to fit snugly, keeping the container airtight; the hole can be adjusted with tape if necessary to create a tight seal around the sensor. Alternatively, the sensor can be placed inside the container since it’s wireless!
  • The chamber is now ready to be used by placing it on top of soil and measuring CO2 flux.

For aquatic environments, wrap a piece of foam pipe insulation around it.

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