Monthly Archives: November 2015

Leafed Behind Lab

Last Thursday, our lab group attempted to measure a plant’s production of CO2 and oxygen in photosynthesis and cellular respiration. In particular, we wanted to compare leaves with a light source to leaves in the dark. We hypothesized that leaves in the light would begin to float as they converted CO2 into less dense oxygen, while leaves in the dark would sink due formation of CO2 through cellular respiration. To quantify these reactions, we first took ivy leaves, and cut out 20 small, uniformly sized discs.   
 Next, we created a solution of baking soda (to provide CO2) and detergent (to break down the waxy surfaces of the leaves) in water. We filled a syringe with 3 mL of the solution, and added the discs. We sealed the syringe, and created a vacuum to suck out any remaining air from the leaves.

Then, we divided these leaves into two groups, each of which were placed in a cup of the solution. The half in our control group were covered in tin foil, while the other half were exposed to sunlight. 

Next, we measured the amount of discs that rose to the top of the cup each two minutes. Unfortunately, however, during out experiment, none of our leaves rose.

Multiple other groups observed that their leaves in sunlight rose after a few minutes. Though plants in the dark could only perform cellular respiration with their limited supply of oxygen and lack of light, the sunlit leaves were able to photosynthesize, thus creating oxygen gas and floating to the top of the cup. Nonetheless, after 20 minutes, still none of our group’s discs had risen. Looking back at our experiment, our group noticed a few times when our procedure might have varied. Firstly, we suspect that we might have use too little baking soda in our solution. This would have lowered the available amount of CO2 for photosynthesis, thus preventing the leaves from rising. Otherwise, we may have accidentally crushed our discs when we first put them in the syringe. Thankfully, however, many other groups were able observe their sunlit leaves rising, meaning that photosynthesis really was occurring. This experiment showed all of us the importance of running an experiment multiple times. By comparing our results with others, we were able to spot potential flaws in our procedure, instead of using most likely inaccurate results.