Biology: April 2009 Archives


April 23, 2009

OK, so this is pretty clever:
Biological molecules exhibit homochirality and are optically active. Therefore, it is possible that the scattering of light by biological molecules might result in a macroscopic signature in the form of circular polarization. If this is the case, then circular polarization spectroscopy, which may be utilized in remote sensing, can offer a powerful indicator of the presence of a universal biosignature, namely homochirality. Here, we describe laboratory experiments designed to investigate this idea. We focus on photosynthetic microorganisms, and also show results from macroscopic vegetation and control minerals. In the microorganisms, we find unambiguous circular polarization associated with electronic absorption bands of the photosynthetic apparatus. Macroscopic vegetation yields a stronger and more complex signature while the control minerals produce low-levels of circular polarization unrelated to their spectra. We propose a heuristic explanation of our results, which is that the polarization is produced by circular dichroism in the material after the light has undergone its last scattering event. The results are encouraging for the use of circular polarization spectroscopy in remote sensing of a generic biomarker from space or the ground.

Writeup here. I don't know if it will work, but clever...


April 20, 2009

Look if John Boehner wants to believe that global warming isn't happening or isn't bad or whatever, then fine. But can we at least be spared this kind of stupidity:
STEPHANOPOULOS: So what is the responsible way? That's my question. What is the Republican plan to deal with carbon emissions, which every major scientific organization has said is contributing to climate change?

BOEHNER: George, the idea that carbon dioxide is a carcinogen that is harmful to our environment is almost comical. Every time we exhale, we exhale carbon dioxide. Every cow in the world, you know, when they do what they do, you've got more carbon dioxide. And so I think it's clear...

OK, so this is, as Wolfgang Pauli is supposed to have said "not even wrong". First, nobody is claiming that CO2 is a carcinogen. The reason people want to reduce CO2 emissions isn't that they give you cancer, it's that CO2 causes global warming. So, the fact that you exhale it hardly leads to the conclusion that it's somehow a great idea to radically increase the CO2 content of the atmosphere.

Even if the reason to restrict CO2 was that it was bad for humans instead of the environment (like, say mercury) this wouldn't follow. Have you noticed that you're inhaling CO2? It's a waste product from aerobic respiration (look up the Krebs Cycle). Boehner's argument is like suggesting that feces isn't bad for you because you emit it regularly, as do cows, etc., but I'm assuming he'd like to minimize his feces consumption.

Interestingly, while CO2 is a waste product, it's not actually toxic. You wouldn't want to breathe an all CO2 atmosphere, but CO2 is what stimulates the breathing reflex. Oxygen, on the other hand, is fairly toxic once you get too far above the normal partial pressures in the atmosphere.