To Breathe, Or Not To Breathe: Observing Photosynthesis

We all know that plants take in water and sunlight -- after all, anyone who has ever worked in a windowless office knows how difficult it is to keep a plant alive without sunlight, and we've all seen how plants that aren't watered shrivel up and die.

But we also all know that plants produce oxygen, even though most of us have never actually seen it for ourselves. With this simple experiment, a plant's formation of oxygen from water and sunlight (a.k.a. photosynthesis) can been seen.

Place a small amount of pond weed in the center of the bottom of a beaker. Place an upside down funnel over the pond weed. Carefully fill the beaker with water so that the pond weed is fully immersed. Next, fill a test tube with water, and carefully invert it and place it over the stem of the funnel. Place the set up in natural light. 

Over time, the water in the test tube will be displaced by oxygen.

This is because the plant has the water and the sunlight that it needs to create its food, and is therefore producing waste from this process. In the case of plants, this waste biproduct is oxygen.

Why pond weed? Why not a regular plant leaf? The reason this experiment calls for pond weed is because pond weed is an underwater plant. Land plants (such as most office plants like Ivy and spider plants) not only produce oxygen, but require carbon dioxide to live as well. These plants "breath" in carbon dioxide through pores on their leaves. While there is some carbon dioxide available in the water for these plants, it is easier and faster to produce oxygen underwater using plants that are naturally found there.

Congratulations super-scientist! You can now prove that plants produce gases from just water and sunlight!