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Al Stahler: Making life possible

 

We can live – or, at least, survive for a while – without food, funds … even fun. But we cannot survive without water.

You and I, plants and animals, bugs and bacteria … all life is made of water balloons. Deprived of water, a plant’s tiny balloons shrink, and it wilts. Without water, we too would wilt.

But water does more than just keep us inflated.



Water is a solvent – things dissolve in water. Sugar “likes” to dissolve in water, allowing watery blood to carry sugar molecules from gut to muscle, to fuel our movement.

But water is no ordinary solvent … it doesn’t just carry things around.



You want to break a stick, so you grasp the stick at either end, and bend it. But the stick is tough … it bends, but won’t break.

Looking closely at the stick – under a microscope – we see that, as the wood bends, it stretches. We were hoping that, as we bent it, the wood would stretch enough to snap.

The stick we’re bending – stretching – is close to snapping. We can send it over the edge by taking a knife and, where the stick is most bent – most stretched – making a small cut, weakening the wood just enough for the rest of it to snap.

We eat, in our food, all sorts of sugars. To get energy from those sugars, we’ve first got to digest them – break them apart, as one snaps a stick.

There’s a tradition, in chemistry, to give sugars names that end in “-ose.” Cellulose is a sugar found in wood (indigestible to all but the microbes that live in termite guts). Lactose is milk-sugar. Sucrose is table-sugar.

The molecular tools we use to break down sugars (and to do many other jobs) are enzymes. There’s a tradition, in chemistry, to give enzymes names that end in “-ase.” The enzyme that digests – snaps – lactose is lactase (if your body no longer makes lactase, you’re lactose-intolerant); the enzyme that digests sucrose is sucrase.

We’ve eaten a cookie. Having passed through our stomach, the “cookie” (in quotes because it no longer looks much like a cookie) enters our small intestine. Sensing sucrose, our small intestine secretes sucrase.

A sucrase molecule latches onto a molecule of sucrose. It bends the sucrose molecule, stretching it.

But sucrase cannot stretch sucrose enough to make it snap. We need something like the knife we used to slice into the bent stick.

Rub a plastic pen through your hair, a dozen times, fast (your hair must be dry for this experiment). Now hold the pen above your arm – close, but not touching. You can feel – and see – the pen attracting the fine hair on your arm. Rubbed through your hair, the pen becomes electrically-charged. The hair on your arm feels that charge, and is attracted to it. (The pen will also attract tiny bits of confetti).

Different parts of the sucrose molecule are likewise electrically-charged – some parts positive, some parts negative; when the molecule is bent, more charged parts are exposed.

The water molecule, too, is electrically-charged – some parts positive, some parts negative.

Opposites – un-like charges – attract: Positive and negative suck up to each other. Like charges (both positive, or both negative) repel.

Attracted to sucrose here, repelled there, the water molecule behaves like a knife, and makes a cut where the sucrose is most stretched. The sucrose snaps in two.

Water performs this knife trick on many different molecules, in many parts of the body. But it can do more.

Suppose we’re not snapping sticks, but splitting firewood. We raise the splitting maul, and swing it downward.

Rather than a satisfying “crack” – indicating the round has spit – the maul hits the round with a “thud” … it carves a gash into the round, but comes nowhere close to splitting the wood in two.

We place a wedge in the gash, raise the maul (now using it as a sledge) and pound on the wedge. The wedge goes deeper into the gash … pushes the wood apart … stretches the wood yet more … but still, the round refuses to split.

Adding insult to injury, the wedge is now stuck in the gash.

We place another wedge into the gash, close to the first … and pound that one in.

The gash grows wider now … but the wood still won’t split … and the second wedge is also now stuck.

We put a third wedge into the gash … pound it in. Guess what? In goes a fourth wedge … maybe a fifth …

Eventually … the damn wood is sufficiently stretched … and it snaps.

A crystal of salt is composed of bazillions of atoms, atoms we cannot live without.

We get plenty of salt in our food, but the atoms in salt hang onto each other even more tightly than the atoms in sucrose. Salt is harder to split.

Electrically-charged water molecules are just the right size, just the right shape, to work their way in, among the atoms in salt. Like pounding in one wedge after another, water molecules firmly (but gently) pry salt apart, atom-by-atom. Surrounded by water molecules, each atoms is delivered to where it’s needed.

Water inflates our water balloons. Water dissolves nutrients, hormones, wastes, and carries them where they need to go in our bodies. Water cuts molecules apart, finishing the job our enzymes begin. Water breaks things apart, atom-by-atom.

There are other molecules that can do some of these jobs, and can do the jobs sometimes well, sometimes poorly. Water is the only molecule in the universe that can do them all, and do them well.

Life evolved on Earth, some four billion years ago, from lifeless rocks and air and water. Life evolved surrounded by water. No doubt, water – and its many abilities – made it possible for rocks and air and water to come alive.

Al Stahler enjoys sharing science and nature with friends and neighbors in The Union and on KVMR-FM. He teaches classes for both kids and grown-ups, and can be reached at a.a.stahler11@gmail.com

Ours is a water planet (seen here by a robotic spacecraft orbiting the moon).
NASA/Goddard/Arizona State University

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