Water and Life

The Hydrologic CycleWater cycles throughboth biotic and abiotic environmentWater exists on Earthin 3 states at the same time:solid, liquid and gas.Of all the water cyclingthrough the environmentonly about 1% is available for living systems….

Which apply to all living organisms?

CHEMICAL PROPERTIESThe chemistry of water makes it a

very unique compound.

Chemical Structure2 hydrogen and 1 oxygencovalently bonded. H2ODue to atom size differenceH’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 magnetwith a (+) and a (-) end…it is POLAR.

The Universal SolventWater 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 NaCLOrganic polar molecules like sugars, that

are required for the processes of life…

PHYSICAL PROPERTIESDue to its polarity, water is strongly

attracted to itself. This results in the many unique physical characteristics of water

that enable life to exist.

DENSITYDensity 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…

TEMPERATUREOne of the most important roles of water is the ability to

retain enormous amounts of heat 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

moderating climate 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 OxygenAs atmospheric temperatures increase water

temperatures also increase…one negative effect of higher water temperatures is that it holds less dissolved oxygen. The cooler the water the more oxygen it can hold. WHY?

Cooler water traps dissolved O2 whereas warm water breaks H bonds allowing more trapped O2 to escape into the atmosphere.

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, so moderate water temperatures are best.

COHESIONAs stated earlier, water is a polar molecule. As a result water is strongly attracted to itself. When water molecules are attracted to water

molecules the force that results is called COHESION. Water is highly cohesive. WHY?

Where water molecules come in contact with the atmosphere

the attraction between the water molecules becomes uneven

The polarity ‘pulls’ them together tighter drawing the molecules in toward center… this is why water drops are spheres.

BUMBLE BEE

Surface TensionThe 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.

ADHESIONAs water molecules cohere to each other, they are

also highly attracted to different polar materials and surfaces.

When water molecules are attracted to polar molecules of different substances the force that results is called ADHESION.

CAPILLARITYCapillarity occurs due to the interaction of cohesive

and adhesive forces. 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 of water molecules to a curved surface is stronger than the cohesive forces between the water 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 heartMoss to ‘wick’ moisture into cells

Lizards to ‘drink’ without movinghttp://www.arkive.org/thorny-devil/moloch-horridus/video-10.html

All of the unique properties of water enable materials to be dissolved and transported, heat to be conserved and all without the cell, or organism, expending ENERGY to do it!