Water and Life. The Hydrologic Cycle. Water cycles through both biotic and abiotic cycles 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….
both biotic and abiotic
in 3 states at the same time:
solid, liquid and gas.
through the environment
only about 1% is available
for living systems….
2 hydrogen and 1 oxygen
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.
Water dissolves more polar substances than other liquid and all without reacting to them!
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 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…
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…
which means ENERGY does not have to be expended by the cell or organism to maintain homeostasis.
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.
Cooler water traps dissolved O2
whereas warm water allows more
spaces where dissolved O2 can
escape into the atmosphere.
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.
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.
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 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?
distances from heart
moisture into cells
Capillary Action, as well as, the unique properties of water allow materials to be dissolved and transported without the cell, or organism, expending ENERGY!