This lab is typically done with whole leaves (from spinach or other plants) that are placed in our small BioChamber.

In the presence of sufficient light of the correct wavelengths, the leaves in the chamber should produce O₂ and should consume CO₂. The opposite should happen in the dark or if the leaves are not illuminated with sufficient light.

There are a number of issues that can make getting good results with this lab difficult. Typically, the problem is that significant changes in O₂ are not seen during this experiment. There are several issues that need to be addressed to see a significant change in oxygen concentration.

1. The small chamber is not ideal for this exercise. To get good results use the Large Bio Chamber. Spinach leaves (or other leaves) should be placed on the bottom of the chamber. Cover as much of the bottom of the chamber as possible without ‘overlapping’ the leaves on top of each other. The idea is to maximize the amount of leaf surface area that will be exposed to the light.
2. Do not use starter plants that contain soil. Soil contains bacteria and other microorganisms that will respire regardless of whether the lights are on or off. Use only leaves (fresh if possible) in the chamber.
3. The change in O₂ concentration is going to be very small relative to the starting level of O₂ in the chamber. Make sure that you are are recording data in ppm or ppt for O₂, not % O₂.
4. Do a control run with the leaves in the dark first. It will help if you do a control run first with the leaves in the dark or without illumination. The leaves should begin to respire and this should increase the level of CO₂ in the chamber while decreasing the level of O₂. After completing the control run, turn on the light and repeat the experiment. You should now see a decrease in CO₂ and a decent increase in O₂.
5. It is important to use proper illumination. A small 60 watt bulb will not produce enough photosynthetic active radiation to produce really good data. Use a 12-inch fluorescent ring lamp for maximum light in the photosynthetically active radiation (par) wavelength range, but with minimal heat emission. Insufficient light and/or excessive heat can contribute to poor results. You can also do this experiment next to a window when it is sunny.
6. It takes time to see a good response. Changes in O₂ and CO₂ typically lag by about 5 minutes from when the lights are turned on or off. You can decrease this ‘wait’ time by ‘priming’ the leaves in the dark or the light for 5 minutes, wait to see an increase or decrease begin, and then begin recording your data.
7. The O₂ and CO₂ sensor are sensitive to altitude. If you are doing an experiment above 4,000 ft. Please make sure you re-calibrate your O₂ and CO₂ sensor at altitude before you conduct this experiment.

For tips on how to get good results using the CO₂ sensor see How to get good results with photosynthesis experiments when using a CO₂ Gas Sensor.

Please note that this is not in reference to the DPIP lab that looks at isolated chloroplasts that is found in the lab books Biology with Vernier and Advanced Biology with Vernier.