Properties of Water


Captions are on! Click CC at bottom right to turn off. Follow us on Twitter (@AmoebaSisters) and Facebook! We have a riddle for you. Ok, not really a riddle. We’re bad at riddles. More like clues about our favorite molecule. It’s polar. It’s shaped like an outstretched V. Its
properties are awesome. We have a riddle for you. Ok, not really a
riddle. We’re bad at riddles. More like clues about our favorite molecule. It’s
polar. It’s shaped like an outstretched V. Its properties are awesome. Also, it makes
up ¾ of the Earth’s surface. That one always gives it away. Our favorite molecule is water. And we’re not going to lecture you about
how important water is and the fact that all life as we know it could not survive without
it, because yeah that’s true, but we really want to talk about what makes water so unique
for biology itself. What are these awesome properties? We mentioned the shape of water and the fact
that it is polar. It has one very electronegative oxygen that is always trying to keep the electrons
closer to it than to the hydrogens it is bonded to. This actually gives the oxygen a slightly
negative charge—because of the electrons that are spending more time next to it—and
it gives the hydrogens a slightly positive charge. Well that means that other water molecules
have an easy time bonding together. Why? Because the hydrogen of one water molecule with its
slightly positive charge can bond to another water molecule’s oxygen with a slightly
negative charge. These bonds among the water molecules are hydrogen bonds, and these very
bonds are what allow water to do these things that it can do…which we are about to talk
about. Have you ever looked at a really tall tree
and wondered, “How does the water get all the way up there?” I mean, it’s got to
go against gravity. Gravity! Well in our plant video, we talk about the xylem. It’s vessels
within certain types of plants, like trees, that transports water. But what’s really
neat about water is that—it sticks to the xylem walls in what is known as adhesion.
This helps fight gravity. But water molecules, with their hydrogen bonding, also bond to
each other in something called cohesion. In almost a “beads on a string” kind of fashion,
as water molecules evaporate from a leaf—the next water molecule in line is pulled upwards
and so on. Cohesion is also a reason that water striders,
one of our favorite insects, can skate on water. Cohesion contributes to the surface
tension of water. Water actually has quite a bit of surface tension compared to other
liquids. And it’s not just water striders. There are a lot of insects, spiders, and even
larger animals like reptiles and birds that can walk on water. So to the Google
for that. With water being polar, it also is a powerful
solvent for other molecules. That means that water can dissolve many other molecules especially
polar molecules and ionic compounds. Why does that matter? This is important because many
of the processes occurring in organisms use water as a solvent. Just consider the need
for water for your kidneys in their filtering properties and all different types of body
fluids. I’ll never forget when I was little, my
father built us a pond. We had some goldfish in there. We loved our pond. Well in West
Texas where we’re from—it can freeze in the winter. And one morning I went outside,
terrified, to find that the top of my pond had frozen. I thought my fish were goners.
Only to find them swimming and doing their…fish activities…under the ice layer. See most
substances actually contract when they freeze and become more dense. But water expands when
it freezes and becomes less dense when frozen. Resulting in floating ice where it can actually
make an insulated surface layer that makes a difference for many organisms. This is due
to the hydrogen bonds. At freezing level, the breaking and reforming of hydrogen bonds—which
is usually happening often—is not happening very much. The molecules are set into a lattice
of hydrogen bonded molecules just far enough apart that it is less dense in ice form than
in water form. That is all going to be very important for aquatic life. Speaking of temperature, water resists changing
its temperature. It has what is called a high specific heat. Specific heat is a measurement
of heat that needs to be absorbed or lost for 1 g of a substance to change its temperature
by 1C. That’s why, on the first day that school is out in the summer, it may be super
hot outside but the water can still be pretty cold. It’s really good that water is like
this for life—it is stabilizing for aquatic environment temperatures. It also means that
water can absorb a lot of heat in the summer without reaching as high of temperatures itself—which
is useful when the winter comes along. The water can release heat as it cools in the
winter. Still on the topic of temperature, consider
evaporation. Many animals rely on evaporation to cool them. Think of water molecules. They
are moving, but those that have more energy—are “hotter” per se—are moving the fastest.
They are more likely to make the phase change to gas. As these molecules leave, their energy—their
heat—is no longer on your skin. By the way, all of this is not just animals too. Plants
use evaporative cooling to aid them in hot temperatures. Excessive high temperatures
can be dangerous for many different processes in both plants and animals—it can be damaging
to the enzymes in many of those processes. Well we went through a lot of features of
water—definitely something to consider next time you encounter it. Which based on how
much we depend on it…will likely be soon. Well that’s it for the Amoeba Sisters and
we remind you to stay curious.

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