This document discusses data logging and the use of gas sensors to measure oxygen and carbon dioxide levels during photosynthesis experiments. It provides background on photosynthesis, cellular respiration, and how they relate to the consumption and production of oxygen and carbon dioxide. The document then outlines the specific procedures to set up gas sensors connected to a computer to measure these gas levels in plant leaves in both light and dark conditions. This allows calculating the rates of photosynthesis and respiration from the sensor readings. Precautions for using the sensors and interpreting the results are also described.