Science In Real Life

Today is, of course, the American holiday of Thanksgiving, where friends and families all across the nation gather to celebrate that most favored pastime of this great land: eating absurd quantities of food. And it is in that spirit that I devote this Science In Real Life essay to the chemical process by which our body extracts and uses energy from the foods we eat. From poultry to pumpkin pie, from giblets to gravy, all of the food we eat stores chemical energy in the form of carbohydrates or fatty acids, and all multicellular animals use the same biochemical processes to function off of those fuels.

First, though, we need to understand how it is that a molecule can carry energy. Consider for a moment the Empire State Building. In this corner, weighing in at about 370,000 short tons (that is, tons of the 2000 lbs each variety), we have an edifice with most of its mass lifted up from the surface of the Earth. But gravity attracts everything – how is it not a heap of rubble? Because the structural arrangement is elegantly designed to resist exactly that process. There is energy contained in that building in a form called Gravitational Potential Energy; it’s Potential because the energy has the potential to be released if the building falls down. A quick back of the envelope calculation suggests that at current levels of American energy usage, the gravitational potential energy in the ESB is enough to fully power 20 households for a year. If the current energy crisis gets particularly unbearable and some clever chap designs a way to extract energy from falling buildings, we could blow up skyscrapers to heat our homes.

In this way do molecules contain potential energy – only this time it’s not gravitational, it’s electromagnetic. Molecules are made of atoms are made of charged particles, and a negatively charged electron in a chemical bond in a molecular arrangement contains some level of energy by being restrained “above” its positive counterparts. Left entirely to their own devices, molecules would all “fall down” into the lowest energy arrangements. But we are fortunate enough to have a source of energy which is as abundant as the sun. Sunlight becomes sugar, thanks to photosynthesis, and we ingest the sugar. You see, unlike today’s tech companies, Momma Nature has actually implemented a design credo based on interchangeable components. Glucose (C6H12O6) is the currency of choice for 99% of lifeforms on this planet; the rest accept VISA and Mastercard.

So you’ve wolfed down some glucose (or maybe some more complex sugars, or even a carbohydrate polymer or two – your body will have broken it down to glucose within minutes). Then what? Enter glycolysis, an ancient and venerated metabolic pathway. Since before time was counted, since before the sun rose over anything with limbs, even before prime time television (gasp!) there was glycolysis. Now, the actual biochemical process that is glycolysis is more complicated than I can explain here. But the upshot is exactly what I described above – the tight chemical bonds of glucose are broken, and the energy from that is used to form new molecules. In this case, the relevant products are substances called Pyruvate (C3H4O3) and a molecule called ADP, for Adenosine DiPhosphate. If glucose is the incoming mail for your body, ADP (and its relatives A-Tri-P and A-Mono-P) are the internal memorandums. They are used to transfer energy in and around the different parts of every single one of your cells.

But we still have to deal with this pyruvate business. Here is where your body really kicks it into high gear with an engine called the Krebs Cycle. This is … complicated. Here, scope this out:

( Image credit: Wikimedia commons )

Did your eyes just pop out of your head? Mine did. Doctors and biologists know this cycle like the proverbial back of the proverbial hand. I am neither of those things, but the nice thing about being a physicist is I get to cheat – the twin principles of conservation of energy and increasing entropy are always at work, throwing badly behaved misconceptions out of our heads like bouncers at an exclusive nightclub. We know, therefore, that energy comes in with the pyruvate and leaves with everything else. We also know that because the energy is going from concentrated (one molecule) to dispersed (many molecules) there are transferences of energy taking place. Where energy disperses, entropy increases. And where entropy increases, heat increases. Congratulations, you now have one warm-blooded mammalian body, ready for use. This cycle, ladies and gentlemen, is where some of your body heat comes from.

The rest of it merely happens further downstream. Those sunburst molecules of ATP and GTP (energy carriers) float away from where the Krebs cycle happens (that’d be your mitochondria) and into the rest of the cell, where they are picked up like dollar bills by so many hopeful entrepreneurs, and used to conduct the normal operations of your cell, like repairing structures, moving muscles around, reproducing, et cetera. Those processes also generate “waste” heat, which goes into warming you up. At a rough estimate, 60% of the energy you ingest goes into keeping you warm, and only 40% to the energy available for voluntary actions like moving, thinking, and writing science essays. Now if you’ll excuse me, I have to go consume large amounts of high-energy chemical bonds. Happy Thanksgiving!

It is time to take Science In Real Life back to its roots. What I am going to do with this essay, what I have been aiming at all along, is to show you a glimpse of the Universe through my eyes. Through the eyes of someone who has spent years studying that which cannot be seen, heard, or smelled directly, but which must be studied indirectly, and studied for years if proper comprehension is to be obtained. Years of effort have given me a new layer of additional information accessible to me merely on examination of an otherwise familiar object. And that, dear readers, is what I am going to share with you today. Physicist Neil deGrasse Tyson once said, “We are all connected. To each other, biologically. To the Earth, chemically. To the rest of the Universe, atomically.” I tell you now that each and every one of those connections surrounds us in every moment. I tell you now that you can see all of that and so much more in a single ordinary glass of water. Come with me, and let’s explore.

Biologically

Go ahead and pour yourself a glass of water. Set it down on the table. Stare at it. You might think that it’s just water, but you might just as well convince yourself that a school building contains only students. Yes, the students comprise most of the volume, but it is the trace elements that really make the magic happen. From a biological perspective, the water in that glass is teeming with life. Exactly what life is in it will vary from region to region, but you can be assured that bacteria of all shapes and sizes are happily doing the Bavarian backstroke in your water. Most protozoa are rougly 100 times smaller than the human eye is capable of seeing (there are visible ones, but they are quite rare by comparison). Micro-organisms by the millions are inside just eight ounces of transparent fluid. If you were to drop a few pinches of sugar in and put it in the sunlight, you could create an ecosystem that would sustain itself for thousands of years.

Speaking of sugar, all kinds of organic molecules are in our drinking water. Where do they come from? Us, of course. We are dumping food waste by the metric shit-ton – pardon the expletive, but I mean it literally. Into our water supply via our waste systems goes a lot of wasted food, both of the digested and undigested variety. In addition to whatever you rinse down the drain or wash off your plates, some portion of the food you eat simply passes through you unscathed and ends up in, for example, Puget Sound, where researchers have measured seasonal variations in runoff sufficiently fine-tuned to, if one were feeling particularly Holmesian, deduce things about the American diet. Not only food, but prescription drugs as well, although so far not in concentrations to give you anything lasting more than four hours, if you know what I mean.

Chemically

The chemistry of water is amazingly complex for such a simple molecule. But before we get to that, there are more contaminants to deal with. Minerals like calcium, magnesium, and sodium are largely responsible for most collections of water being as electrically conductive as they are. Pure H20 all by itself is not a great conductor, but scatter a few ions through it and you suddenly don’t want to be in the pool when the thunderstorm hits. Which brings us to chlorine and flourine, two substances artifically added to keep the dangerous stuff from growing in the water. Behind all the biology, your glass of water is a chemical bonanza!

And then there’s the chemistry of water itself. H20 has some remarkable properties. For such a tiny molecule, it packs a punch of polarization. Known in some circles as the universal solvent, the electrical properties of a water molecule by itself translate en masse to a substance that is as adept at pulling things apart as your three year old nephew. Water can also act as either an acid or a base (chemists call it amphoteric), making it instrumental in many of the chemical reactions so very common on planet Earth. We humans, and indeed almost all life forms on this planet, are mostly water – for a planet whose surface is also mostly water, this indeed connects us inextricably and irreversibly with our home planet. It is remarkable just how thoroughly connected everything is to everything else, by interchanging chemicals, through one simple truth: water flows. Inside your water glass are molecules, H20 and otherwise, that have been all around the world and back again.

Atomically

Here is where I could go on for far too long about a myriad of properties of this incredible liquid: its relatively high heat capacity enabling ecological mediation, its hydrogen bonding enabling so many different molecular arrangements, its astounding surface tension – here, look at the surface of the water in your glass. You will see the water rise ever so slightly when it meets the glass, as though making a bid for freedom. That is surface tension at work. The water clings to the glass and simply does not let go. Insects have evolved to take advantage of this; by being sufficiently light they are able to walk across as easily as we cross a room. Capillary action is a consequence of this. The stick-to-it-iveness of water enables 200 meter tall redwoods to siphon it up thin cellulose tubes to the highest leaves and branches.

But this is not the aspect of water that really connects us to the Universe. It is that the atoms of water, for all their extraordinary properties, are made of three very ordinary things: electrons, protons, and neutrons. They are governed by the same laws of gravity and electromagnetism and quantum mechanics that hold sway across the uncounted reaches of all of space and all of time. Everything that has ever been has helped to shape the Universe that you occupy, and you continue to shape the Universe as you live. An entire cosmos has led up to your glass of water, and an entire cosmos leads away from it.