Nov 02 2010
The Carbon Cycle
So…I forgot to make sure there was a scribe for this lesson, so I got this one. Maybe a model of what those that handle other cycles can do?
Since we are all “carbon-based life forms,” this cycle is crucial to life. We reviewed a little biochemistry in class, noting that carbs, lipids, nucleic acids, and proteins are all made primarily of carbon chains or rings. If you were to ask for the basic ingredients for each macromolecule, then the recipe for each might look like this:
Carbs: CHO (usually a 1:2:1 ratio)
Lipids: CHO (but usually in longer chains, includes P when considering phospholipids in cell membranes)
Nucleic Acids: CHONP
Proteins: CHON (with a few amino acids containing S).
*Note: I’ve embedded a little biology review powerpoint in “the box” if you were absent or want a refresher.
For each cycle, I want you to focus on main reservoirs, how the elements travel (flux)from sphere to sphere (includes chemical reactions), unique characteristics, and human impacts. Study the global carbon cycle pictured below:
Notice the main reservoirs of carbon are sedimentary rocks (in solid form in the Earth’s crust or lithosphere), the oceans (as CO2 or bicarbonate), then fossil fuels (also in the lithosphere). In class, we used balloons of different colors and quantities to represent the size of each reservoir. We think of the living things being made of carbon, but the biosphere is not the main reservoir! Living things play a critical role in cycling carbon in and out of the atmosphere through photosynthesis and respiration. I showed a video clip of carbon dioxide levels in the atmosphere based on the Kneeling Curve–It’s almost as if you can see the Earth “breathing” carbon over the course of a few seasons…If interested, you can find the current CO2 readings (and historical data) at Mauna Loa, Hawaii at this NOAA website.
We also spent a some time tracing the path of CO2 into and out of the oceans. You can find a nice summary of carbon’s path in the oceans here:
As for unique characteristics, I would note that carbon does not enter the biosphere (ecosystems) via the roots of plants. You all learned last year that carbon dioxide enters plants by diffusion via their stomata.
Finally, human impacts on the cycle:
1. Burning of fossil fuels (adding “excess” to the atmosphere beyond historical averages). Don’t forget your combustion reactions (handout is once again in “the box”) for the quiz. This particularly worrisome as carbon dioxide is a warming gas, and it’s build up in the atmosphere can trigger a number of positive feedback loops.
2. Deforestation (removing sinks that could store carbon allows it to build in the atmosphere)–if trees are burned then the problem is even worse.
The goal is for you to be able to trace the movement of an element of carbon from each sphere to the others. There are many interactive diagrams and animations of this cycle (and the others) online. There is a more ecosystem level diagram at the text website under chapter 7 animations. Here are a few that may also help you learn the carbon cycle:
The Carbon Cycle Game (travel from reservoir to reservoir)
The Carbon Cycle (interactive diagram)
PBS Cartoon Series on carbon’s role in “global warming” (we’ll do a whole unit on this in the spring)