Hands-On with Photosynthesis and Cellular Respiration

Photosynthesis is a topic that many students need help understanding. Using a hands-on experiment to demonstrate the process helps reinforce the concepts with students, especially your kinesthetic learns. Combining the lab with images and video found on the Internet targets your audio and visual learners as well. Below are simple activities that use Elodea to help teach this topic.

Observing photosynthesis

Before describing what we are doing, we will briefly discuss what we are not doing—as in a much-repeated experiment that uses Elodea to produce gaseous O₂ in the presence of light. The usual procedure requires gas collection over a relatively long time period. Approaching this experiment differently provides a more rapid response in volume change of gas produced, relative to light intensity. Using this simple system, students observe the immediate effects in variations of physical factors, such as temperature and light intensity, on Elodea producing gaseous O₂.

Cellular respiration and photosynthesis

Create another twist to this activity by comparing Elodea exposed to light with Elodea that is not. Using bromthymol blue as an indicator, students expose a sprig of Elodea to light while covering another sprig to keep out light. The plant exposed to light produces oxygen, so the water remains basic and its color turns blue. The covered sprig respires, releasing carbon dioxide. The carbon dioxide reacting with the water forms carbonic acids and lowers the pH, causing the indicator to remain yellow.