Friday, February 25, 2005

Metabolic Energy Clock

Live fast and die young. Although there are exceptions, most big animals live a long time, while small ones live fast and die young. Metabolic rates, the speed at which an organism gets energy from food, seem to be proportional to body mass raised to the 3/4 power.
"It appears as if we've been gifted with just so much life, you can spend it all at once or slowly dribble it out over a long time."
-Brian Enquist, ecologist, University of Arizona, Tucson
An article published last summer in Ecology describes a "Metabolic Theory of Ecology" which argues that metabolic rates depend on the efficiency with which resources can be transferred into cells. That efficiency, the authors contend, is related to the "animal's effective surface area." Specifically they're taking about the area of all surfaces (in the digestive and circulatory systems) that nutrients have to pass through before they reach the cells. This equation (originally put forth in 1883, corrected in 1932, justified by the same authors in 1997) holds true for organisms ranging in size from microbes to whales.

The new breakthrough here is the inclusion of temperature as a second variable in their metabolic equations. Up until this point, the equations really only worked well for mammals and birds. Since most chemical reactions slow down when the temperature is decreased, animals that have cooler body temperatures should have slower metabolisms, which is exactly what the authors find.

The figure shown is a plot of the metabolic equation (including body temperature) versus mass. There a few important things to notice here: One, it's a great line that includes plants, mammals, and bats - organisms that have little in common and probably shouldn't fall on the same line (but do!). Two, the axes are both ln, or natural log. Be skeptical of log-log plots; engineers joke that any data set plotted on log-log paper will give a line.

Although it's easy to be skeptical of this theory because it attempts to explain so much (see the full paper or the link below for the rest of their claims), such amazingly large patterns can only be seen if you step back far enough and look.

Via: ScienceNews
Also covered at NuSapiens and Roland Piquepaille's Technology Trends.

Old Blood, Young Blood

Death and taxes. We all age and unless Aubrey de Gray's Strategies for Engineered Negligible Senescence actually do work soon, we're all going to die. As we age, bodily functions begin to break down - memories fade and muscles strain. A recent publication in Nature uncovers another piece of the puzzle of how our cells age.

Thomas Rando and coworkers at the Stanford University School of Medicine uncovered that old muscles can repair themselves if they are provided a source of young blood. To show this, the authors connected the circulatory systems of young and old mice muscles, and provided them either young or old mouse blood. They then measured the ability of the muscle tissues to regenerate after being damaged.

Let's look at the cells in all four possible environments to see what happened. The red and green colors in the images below come from dyes and markers added to the tissue cultures to visualize certain portions of the cells (it's not really important to understand what they are; just look at them qualitatively).

1. Young tissues connected to young tissues.2. Young tissues connected to old tissues.
3. Old tissues connected to old tissues.4. Old tissues connected to young tissues.

So one of these is not like the other ones, #3, and that's the sample with no young parts. Important, as seen in #4, old muscle cells can repair themselves when provided with young blood. These observations suggest that there is something in the young blood that helps keep those cells fix themselves. Determining which of the components is responsible for this regeneration is going to be a monumental task since there are thousands and thousands of components in blood. Still, this work shows that the environment of a cell may be as important as the cell itself. But don't hold your breath for a Fountain of Youth just yet, Aubrey.

Via: Eurekalert
Wired covered this here.

Friday, February 11, 2005

Gliding Ants

In the most current issue of Nature, scientists from the University of Texas Medical Branch, UC Berkeley, and University of Oklahoma report their finding on the "Directed aerial descent in canopy ants." The ants under investigation, the species Cephalotes atratus, can direct themselves back to their tree should they fall, or dropped from a pair of tweezers in this study. This is pretty important for them, considering their entire colony lives in one tree, and a free fall from the canopy likely means certain death for the bugs (either due to ground-dwelling predators, the sheer impact, or the fact that the rainforest floor is flooded for half of the year).

The video of this phenomenon is worth a watch. You'll see what the authors did to collect data on these gliding ants. One ant is taken in a pair of tweezers (they appear blurry in the first few seconds) and dropped from a short distance from the trunk of the tree. Part of the ant was painted white to aid in following the falling insect. The authors even painted over the eyes of a few of their subjects to see if they were actually responding to visual cues to direct their fall. Most of those ants plummeted to the forest floor, while 85% of their seeing-eye cousins made it safely back to the tree. The ants even climbed back to the original elevation within 10 minutes. This is the first case of directional gliding recorded in the insect kingdom. I have to agree with the authors that this is quite a remarkable evolved behavior.

Via: EurekAlertAlso covered at: Boingboing, Dean's world

Friday, February 04, 2005

The O-Ring

You've all heard of ozone (O3) before; it's a reactive gas found in the upper atmosphere of our planet that blocks lots of harmful solar radiation. Discovered first by Christian Schönbein, ozone is used industrially to disinfect bottled water, and clean and bleach clothing. That's all well and good, but not really worth getting into now.

What is news worthy is that a, as-of-yet unobserved, cyclic form of ozone has been predicted to be stable by theorists. It has almost twice as much energy as normal (acyclic) ozone, which means that when the same amount of cyclic ozone combines with hydrogen in a jet engine it produces more energy. That makes it an excellent candidate for the next best rocket fuel for our trips to Mars. If only we had a tank to test.
Temple University's Center for Advanced Photonics Research is trying to make cyclic ozone with their ultrafast lasers. The idea is to take very specifically shaped laser pulses to manipulate single molecules to do what they want. Somewhere in the 10^40 possibilities of pulses there's a path to cyclic ozone. They're relying on a "evolutionary search strategy" to cover this vast search space; how they're doing that we'll have to wait to hear about.

What's really interesting about this molecule is not the promise of being able to make a microgram in a laser system and record its absorbance spectrum (though that would get plenty of chemists hot and bothered). This unknown form of ozone has been predicted to actually be stable. Roald Hoffman (1981 Nobel Prize in Chemistry) discusses some of the reasons for this in a recent article in American Scientist. Coincidentally, some of the reasons that cyclic ozone is likely to be stable are based on the Woodward-Hoffman Rules, for which Hoffman was awarded the Nobel Prize. Hoffman, along with Peter Wolczanski, also recently published a theoretical paper in the Journal of the American Chemical Society discussing the possibility of stabilizing cyclic ozone by complexation to a transition metal.

If the search works out, and this does help put man on Mars, it'll be quite the chemical success story.