Water and Life

The Hydrologic Cycle Water cycles through both biotic and abiotic Water exists on Earth in 3 states at the same time: solid, liquid and gas. Of all the water cycling through the environment only about 1% is available for living systems….

Which apply to all living organisms?

Chemical Properties 2 hydrogen and 1 oxygen covalently bonded. H2O Due to atom size difference H’s valence electrons spend more time around the O, as a result, the H’s become net (+) The O, gaining 2 electrons from each H, becomes net (-). The molecule acts like a magnet with a (+) and a (-) end…it is POLAR.

The Universal Solvent Water dissolves more polar substances than other liquid and all without reacting to them! Ions like Ca+, Fe+; necessary for nerves, muscles Ionically bonded substances like NaCL Organic molecules like sugars, that are required for the processes of life…

Physical Properties Due to its polarity, water is strongly attracted to itself. This results in the many unique physical characteristics of water that enable life to exist.

DENSITY Density is the amount of matter in a given space. Water is the only substance who’s solid state is LESS dense than its liquid state. As a result, ice floats! WHY? As water freezes the polar molecules form a lattice shape which increases its volume, but, decreases its density. This is why water pipes crack in winter! Ice layers help to insulate the water beneath allowing life in temperatures well below freezing, floating ice sheets moderate climate by reflecting heat back into the atmosphere…

TEMPERATURE One of the most important roles of water is the ability to retain enormous amounts of energy with only a little change in its own temperature. WHY? As water absorbs heat energy its molecules increase in motion, only until all the H bonds between the molecules are broken will water change phase, and that takes time. As a result… Large bodies of water retain large amounts of heat which ensures the survival of marine life. Chemical reactions and solubility rates increase. Internal temperatures of organisms remain more stable even when external temperatures vary… which means ENERGY does not have to be expended by the cell or organism to maintain homeostasis.

Dissolved Oxygen One negative effect of higher water temperatures is that it holds less dissolved oxygen. Even though the water molecule is composed of the element oxygen, this is not what the organisms that live in water use…they need dissolved free oxygen. The cooler the water the more oxygen it can hold. WHY? Cooler water traps dissolved O2 whereas warm water allows more spaces where dissolved O2 can escape into the atmosphere.

COHESION As stated earlier, water is a polar molecule. As a result water is attracted to itself. When water molecules are attracted to water molecules the force that results is called COHESION. Water is highly cohesive. WHY? When water comes in contact with the atmosphere the attraction between the molecules becomes uneven so they ‘pull’ together more, drawing the molecules in tighter forming a sphere.

Surface Tension The cohesive force of water is high where water comes in contact with the atmosphere. This results in the phenomenon; surface tension. The surface of the water is slightly “thicker” than the water below. WHY? The molecules at the surface do not have other water molecules on all sides of them and consequently they cohere more strongly to those directly below and to the sides.

ADHESION As water molecules cohere to each other, they also are attracted to different polar materials. When water molecules are attracted to polar molecules of different substances the force that results is called ADHESION.

CAPILLARITY The height to which capillarity will Capillarity occurs due to the forces of cohesion and adhesion. Adhesion of water to the walls of a vessel will cause an upward force on the liquid at the edges resulting in a meniscus. Capillary action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules. The height to which capillarity will take water in a uniform circular tube is limited by surface tension and, of course, gravity. Why is this important to life?

Capillary Action in Living Systems Allows water to move high into trees. Blood to continue to flow great distances from heart Moss to ‘wick’ moisture into cells Lizards to ‘drink’ without moving http://www.arkive.org/thorny-devil/moloch-horridus/video-10.html Capillary Action, as well as, the unique properties of water allow materials to be dissolved and transported without the cell, or organism, expending ENERGY! RINGMASTER