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.

It's working...

While Stumbling one day I came across a blog that described growing or should I say Re-growing celeryfrom its stalk. I decided to give it a try. It took some time but the first thing I noticed was the "greening" of the stalks as the exposure to the sunlight and access to water stimulated photosynthesis. Then from the base I began to see the formation of roots which have continued to elongate and multiply. Lastly, from the center is evidence of leaf formation. I have been keeping it on a sunny sill or what can be called a sunny sill as we approach the winter solstice. I'm also making sure to keep it well watered. Eventually I will transfer it to soil and hopefully come spring time put it out in the garden. Since I will be having the students doing an osmosis lab later this week using celery perhaps we will set one of these experiments in the lab to watch the process.

Here you can see the roots forming
at the base of the stalk

Notice the small leaf formation in
the very center.

The Nitrogen cycle

One of the books that I read this summer was Thomas Hager's The Alchemy of Air. This was a fascinating piece of writing mixing science, history and biography in a well woven tale about one of the essential elements of life. Nitrogen is needed for the production of amino and nucleic acids which all living things require. Our planet's atmosphere is 78% nitrogen yet with the rare exception of some bacteria found in soil and cyanobacteria/algae in aquatic ecosystems, living organisms can not use this inert gas directly. Through the activity of nitrogen fixation and the formation of nitric oxide from atmospheric nitrogen and oxygen gases using the energy from lightning to drive the reaction, nitrogen takes on a form that plants and other photosynthetic organisms can absorb and convert into amino and nucleic acids. Nitrogen is returned to the atmosphere by the activity of decomposing bacteria.

 

You're wondering where the book comes in. At the turn of the twentieth century the call went out to find a way to synthesize nitrogen based fertilizers to help feed the growing human population. I bet they never thought we would reach the 7 billion now on the planet, but I digress. The point being that Fritz Haber took up the challenge and designed a way to convert nitrogen and hydrogen gases into ammonia. It took the genius of Carl Bosch to engineer the necessary equipment to make it possible to make ammonia in a profitable large scale way. Today the Haber-Bosch process continues to produce the majority of inorganic fertilizers used in agriculture. According to Hager 50% of the nitrogen in our bodies comes from this process and from the foods we have consumed which have been at one time treated with fertilizers.

 

The problem now is too much nitrogen in the cycle. Excess nitrogen from fertilizers now enters into the soil and water systems. Eutrophication of lakes and the ocean occurs from the over growth of algae which impacts the oxygen levels of the water and kills other aquatic life. Excess nitric oxide in the atmosphere contributes to the formation of acid rain which can lead to pH changes in soil and bodies of water impacting the plants and animals in the affected regions. Too much of a good thing can be a problem.

 

My Ecology class recently did a unit on the geochemical cycles and we discussed the impact of human activity on the nitrogen cycle. The focus has been on the carbon cycle and climate change, that the nitrogen cycle and its disruption often goes unnoticed. The nitrogen cycle's disruption may become part of the next major ecological worries. The background knowledge I gained from this book allowed me to share how science and the development also played a role in the course of history primarily World War II when the Nazi war machine used the technology developed by Haber and Bosch to make synthetic fuel. 

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.

Concept mapping

In the never ending quest to assist students (high school sophomores in a college prep biology class) in learning new and difficult material, like macromolecules for example, my colleague and I developed a list of key terms for the students to map. Concept maps can take several different forms such as a top down flow chart or a web. Here I show just one portion of a larger map. As we moved through the unit I would have the students take their maps out and add new details to them. Tomorrow is the big unit test, they will be allowed to use the map on the test and turn it in for a classwork grade. Keep your fingers crossed for good results. The biggest challenge will be can they retain it as we move on in our curriculum and succeed on the mid-year exams?

Concept Map featuring terms about Lipids, includes key terms, examples, functions, etc.