Life-Supporting Properties of Water

Water’s Life Supporting Properties

We previously defined the chemical formula for waterThe universal solvent essential for life. as H2O.We looked at the structure of water moleculesGroups of atoms bonded together. being something like Mickey Mouse Heads.  We also found that there are slightly negatively charged poles and slightly positively charged poles of water molecules that come together in a weak attraction known as a hydrogen bond.  Hydrogen bonds are pretty much the cause of all of water’s life-supporting properties.  The things we are going to define in this mini-lecture are the properties of water that allow living organisms to exist here on Earth. 

Water moderates temperature

Water has this incredible ability to moderate temperature.  This means that water can absorb a lot of energyThe capacity to do work or cause change. with only small changes in temperature. Many of us have observed this in something we’ve been doing for a long time. Think about heating up water in a saucepan on the stovetop.  You place a pan of water on the stove and turn the burner to high and wait about a minute.  Which would more likely burn you at this point: the pan made from steel or the water inside it? The pan reaches burning temperatures much faster than the water does. Before the temperature can increase in water some energy is absorbed by the hydrogen bondsWeak attractions between hydrogen and electronegative atoms like oxygen or nitrogen. to separate water molecules from each other. Energy is therefore put into breaking the hydrogen bonds between water molecules rather than raising the temperature.  This ability to resist temperature change is called heat capacityThe amount of heat needed to raise the temperature of a substance..

Heat capacity and
evaporative cooling

There are so many ways in which this impacts your life.  If you live near a body water like an ocean or large lake, you may have noticed that the temperatures are cooler near the water.  Defrosting frozen meat in water takes a shorter amount of time, reducing the amount of time your uncooked meat spends in the ideal temperature for bacterial reproductionThe process of producing offspring..  And, most importantly, your water-based blood does not boil and evaporate when you walk out into the sun.  Your body uses water-based sweat to bring heat to the surface of your body for evaporation just as dogs pant to do the same.  As a personal example, I grew up at the Jersey Shore, surfing year-round.  Like, I remember walking to the ocean through the snow on the beach.  So, as a surfer, I acquired wetsuits of variable thickness.  But the best thing I found was a two-wetsuit combo.  By wearing two suits, you’d get this insulating layer of water between the two.  And, since your urineThe liquid waste excreted by the kidneys. is water based, and pretty hot, wearing two suits and peeing as soon as you get out into the water was guaranteed to keep you warm for hours. 

The Density of Water

Solid water (known as ice) is less dense than liquid water. In other words, ice floats. Do you realize how unique this is? For almost all known substances, the solid form is denser than the liquid form. If you were to make frozen gasoline cubes, for example, the solid gasoline would sink to the bottom of a glass of gasoline.

The key to understanding water’s different states of matter (solid, liquid, gas) is in the orientation of the hydrogen bonds.  Solid water, or ice, has a precise arrangement to take advantage of the maximum possible hydrogen bonds. This just means that the hydrogen bonds are fixed, like a crystalline lattice.  Liquid water has hydrogen bonds that are constantly breaking and reforming, which might help you understand why water can take the shape of its container.  Water vapor, or water in its gaseous state, has no hydrogen bonds.  It’s kinda like little floating Mickey Mouse heads.  Possibly a nightmare for some people.

Frozen Lake

Ice floating is especially significant to life in temperature zones such as the biome in which I live, here in upstate New York.  We experience relatively hot summers that encourage growthAn increase in size and number of cells. of organisms, and particularly cold winters that can kill many animals and plants.  Because ice floats, a thin layer of ice insulates the rest of a lake, allowing aquatic life to survive the winter.  The ice acts like an insulating blanket, containing the heat generated by the life forms.  Alternatively, the ice reflects the sun’s heat, relating to the shrinking polar ice caps and increasing global temperature.

Solution = Solvent + Solute

Water has an incredible ability to dissolve many substances and is known as the Universal Solvent.  Let’s review for a moment: solutes dissolve into solvents to make solutions.  By dissolving carbon dioxide into water, we have seltzer.  Adding salt makes club soda, and adding quinine makes tonic water.  Seawater and blood are both solutions with water as the solvent and ionsCharged atoms or molecules., biomolecules, and other substances as the solutes.  Your cellsThe basic structural and functional units of life. are essentially small packets of water that contain a complex solutionA homogeneous mixture of two or more substances. of molecules dissolved within the water.

Hydrophilic                       Hydrophobic

Substances that dissolve in water or are attracted by water are called hydrophilic. Think of all the substances that dissolve in water or absorb water: rice, pasta, bread, cotton towels, paper towels. These substances are known as hydrophilic, or water-loving.  Two substances you are familiar with that do not dissolve in water are waxes and oils. Water beads up on waxy surfaces and the oil in salad dressing rises above the watery vinegar.  This is why you should use a blender to emulsify your salad dressings.   Think of all the substances that are hydrophobic: olive oil, butter, many lotions, cleaners, and rain-proof clothing.  Substances that do not dissolve in water or repel water are called hydrophobic. Both hydrophilic and hydrophobic substances can be found in living systems. 

Adhesion  Cohesion

Water exhibits the two properties of cohesion and adhesionThe tendency of water molecules to stick to other substances..  What’s the difference?  Think of the root words.  Ad: adjacent, adjunct, additional.  And Co: cohabitate, coordinate, co-captains.  Cohesion is a water molecule’s ability to stick to another water molecule, causing surface tension.  This is what causes that nasty skinThe body’s largest organ, providing protection and regulation. on the soup in a cafeteria.  The solutes like seasonings in the soup are attracted to the surface tension at the air-water interface.  This surface tension forms a boundary layer that is stout enough to serve as a surface habitat for small insects, snails, and other small organisms. Adhesion is water’s ability to stick to something else, like the cotton of your jeans, the sides of a capillary tube, or a hydrophilic paper towel. 

Capillary action

In factA statement based on direct observation that is repeatedly confirmed., this property can cause capillary action where a water-based substance rises through a small tube.  The cotton of your jeans are essentially small tubes.  On your way to class you step in a puddle and get the bottom of your jeans wet.  As you sit in class, the wet mark seems to rise up your jeans, defying gravity. When you get up to leave, it looks like you stepped in a puddle that was two feet deepAway from the surface of the body.. This mechanism is also at work in the large redwoods, allowing them to draw water and nutrients from the soil and transport them to the leave without an active pump.