Water, like carbon, has a special role in living things. It is needed by all known forms of life. All organisms on earth are made up mostly of water; thus, water is the biological cornerstone of life. Water is a simple molecule, containing just three atoms: two hydrogen and one oxygen. Nonetheless, water’s structure gives it unique properties that help explain why it is vital to all living organisms. In fact, without water, life would not be possible. With 70% of our earth being ocean water and 65% of our bodies being water, it is hard to not be aware of how important it is in our lives.
Unique properties of water
Water is the only substance that can exist as solid, liquid and gas in the ambient conditions that exist on the surface of the planet. All other natural substances remain in their singular state. This uniqueness confers on water a distinctive fitness for one of the most important processes on the planet: the hydrological or water cycle. Water evaporates from the oceans, cools, condenses into clouds, and then precipitates as rain, ice and snow. If water did not exist in three states there would be no water cycle and without that cycle the entire land surface of earth would be a dehydrated, lifeless waste.
Two other properties of water which are essential to keep the hydrological wheel turning are water’s low viscosity, making it highly mobile and causing it to flow easily in its liquid state, and water’s strong molecular cohesion. Both these properties mean that water molecules bond together with other water molecules and flow easily to form oceans, rivers, lakes and wetlands. The fact that fish can rapidly swim in water is also due to water’s low viscosity.
High specific heat
Water molecules are attracted to each other through hydrogen bonds. It takes a lot of energy to break these bonds. This means it takes a lot of energy to change water molecules from one state to another and, hence, water does not experience large temperature fluctuations, and this is attributed to water’s high specific heat.
Think of a lake. If the water dropped suddenly from 25°C to 0°C over the course of a few days, you would have a lot of dead fish. The slow changes in temperature allow organisms to adjust and adapt to the water around them.
Water’s high specific heat also allows us to keep our body temperature constant. If water changed temperature rapidly, we would always be changing from too hot to too cold, depending on the temperature outside. This would be detrimental for the enzymes in our bodies.
In addition to this, water has a high latent heat of vaporization. For this reason, water evaporates slowly from ponds and lakes, where many life forms are dependent on it.
Water density
Unlike most chemical substances, water in a solid state has a lower density than water in a liquid state. This is because water expands when it freezes. Again, hydrogen bonding is the reason. Hydrogen bonds cause water molecules to line up less efficiently in ice than in liquid water. As a result, water molecules are spaced farther apart in ice, giving ice a lower density than liquid water. A substance with lower density floats on a substance with higher density. This explains why ice floats on liquid water, whereas many other solids sink to the bottom of liquid water.
In a large body of water, such as a lake or the ocean, the water with the greatest density always sinks to the bottom. Water is most dense at about 4°C (39.2°F). As a result, the water at the bottom of a lake or the ocean usually has temperature of about 4°C. In climates with cold winters, this layer of 4°C water insulates the bottom of a lake from freezing temperatures. Lake organisms such as fish can survive the winter by staying in this cold, but unfrozen, water at the bottom of the lake.
In addition to this, water is transparent, thereby allowing light to penetrate up to 200m in the oceans and lakes which in turn allows plants to carry on photosynthesis under submerged conditions.
Water in cell and plant life
Water is central to two related, fundamental metabolic reactions in organisms: photosynthesis and cellular respiration. All organisms depend directly or indirectly on these two reactions. In photosynthesis, cells metabolically use the energy in sunlight to change water and carbon dioxide into glucose (C6H12O6) and oxygen (O2).
In cellular respiration, cells transfer chemical energy from glucose (by breaking it down) to ATP (a usable energy-rich molecule) in the presence of oxygen and release energy, water, and carbon dioxide. The hydrogen-bonded network within the water molecule is also critical for generating cellular energy. It provides “water wires,” long chains of linked water molecules, for moving protons around a cell. The movement of these protons generates energy within the cell.
Water has cohesive and adhesive properties. Adhesion is an attraction to unlike molecules, and cohesion is an attraction to like molecules. Water molecules have strong cohesive forces due to their ability to form hydrogen bonds with one another. Cohesive forces are responsible for surface tension, the tendency of a liquid’s surface to resist rupture when placed under tension or stress. Water also has adhesive properties that allow it to stick to substances other than itself.
Plants and trees couldn’t thrive without capillary action. It helps bring water up into the roots. With the help of adhesion and cohesion, water can work its way all the way up to the branches and leaves. Even if you’ve never heard of capillary action, it is still important in your life. Capillary action is important for moving water (and all of the things that are dissolved in it) around. It is defined as the movement of water within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension.
Capillary action occurs because water is sticky, thanks to the forces of cohesion and adhesion. The attraction of water molecules to the sides of a narrow vessel (adhesion) is stronger than the cohesion drawing water molecules together. The result is capillary action, in which the force of adhesion pulls the fluid upwards.
Water as a solvent
When the two hydrogen atoms bond with the oxygen, they attach to the top of the molecule rather like Mickey Mouse ears. This molecular structure gives the water molecule polarity, or a lopsided electrical charge that attracts other atoms.
The end of the molecule with the two hydrogen atoms is positively charged. The other end, with the oxygen, is negatively charged. Just like in a magnet, where north poles are attracted to south poles (“opposites attract”), the positive end of the water molecule will connect with the negative end of other molecules.
What does this mean? Water’s polarity allows it to dissolve other polar substances very easily. When a polar substance is put in water, the positive ends of its molecules are attracted to the negative ends of the water molecules, and vice versa. The attractions cause the molecules of the new substance to be mixed uniformly with the water molecules.
Hence water dissolves more substances than any other liquid—even the strongest acid! Because of this, it is often called the “universal solvent.” The dissolving power of water is very important for life on earth. Wherever water goes, it carries dissolved chemicals, minerals, and nutrients that are used to support living things.
Evolution has no answer as to how water came to exist on earth. One of the more popular theories is that water was brought to earth when icy comets collided with our planet. The number of comets required to cover the earth’s surface with water would be in the order of trillions and trillions and there is no evidence of such an intense bombardment. This theory simply shifts the problem further down the line—where did these comets get their water from?
The Genesis record is plain—all forms of water were created by God. As Proverbs 8:27-30 so eloquently declares, “When God prepared the heavens, I [wisdom] was there…when he established the clouds above: when he strengthened the fountains of the deep…then I was by him…” Water is just one small expression of the unfathomable wisdom and majesty of the Creator of all things.