Pond Life

Black line represents original
air bubble. Photosynthesis
in the right tube has created an
oxygen bubble.

Test tubes containing pond
water. Tube on the right
received some fertilizer.
 

To study eutrophication I set up a small scale experiment using pond water from the wetlands on the school property. This area is surrounded by athletic fields which are treated with fertilizers. In the spring and summer there is quite the alga bloom and the nasty smell of decaying matter.

One of my colleagues set up a large scale experiment in two little fish bowls, adding fertilizer to one of the bowls. After a week or so there was clearly a difference between the two bowls. The one with the fertilizer was green and becoming greener with each passing day. I did the same except in the test tubes adding a little bit of baking soda to ensure a carbon dioxide source for the growing algae. This piggy backs on my previous post about the Nitrogen cycle. The excess use of fertilizer results in the disruption of the nitrogen cycle and the introduction of excess nitrogen into bodies of water resulting in the overgrowth of algae and the depletion of oxygen in the water causing death among other species in the water. We need to rethink our obsession with thick green lawns and how to obtain them.

Enzyme Activity Lab

Hydrogen Peroxide and Raw
Potato

A very quick and easy lab to observe enzyme activity is one in which you use raw and cooked potatoes and hydrogen peroxide. Hydrogen peroxide is made as a by-product in cellular processes, it is toxic to cells and that is where the enzyme catalase comes in. The function of catalase is to decompose hydrogen peroxide into water and oxygen gas. You've observed this if you've ever used hydrogen peroxide to disinfect a cut or scrape. Students can observe the activity of the catalase by looking for the bubbles of oxygen that are released.

Enzymes which are a class of proteins are subject to the threat of denaturation, or the loss of their 3-D structure, when exposed to changes in pH or heat. In this lab I have the students mix in some vinegar into the hydrogen peroxide to lower the pH of the environment. As a result there is a visible slowing down of the reaction. We also use a baking soda solution to create an alkaline environment but the enzyme isn't impacted as much. Lastly, I have them test a piece of cooked potato. In the cooking process the catalase is denatured and there is no activity at all.

Hydrogen peroxide and
cooked potato

We have been investing in Vernier Lab Quest equipment for student data collection. Using a very crude methodology, I had the students stopper up the test tubes and use the Gas Pressure Sensor to observe any pressure changes that result from the release of the oxygen from the decomposition reaction. It worked. Clearly there was a significant pressure change with the raw potato and hydrogen peroxide, less change with the vinegar mixed in, and absolutely no change in pressure when the cooked potato was tested. Vernier does put out a series of experimental procedures that are more sophisticated and quantifiable. In this case I was focused on the students learning the key concepts of enzymes (active site, activation energy, catalyst) and the conditions that will lead to protein denaturation.

Testing for pressure change using a Vernier Lab Quest
with a Gas Pressure Sensor.