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Chapter 3

BIOL 1201 Chapter Notes - Chapter 3: Sodium Chloride

Biological Sciences
Course Code
BIOL 1201

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Chapter 3 Notes
Water and the Fitness of the Environment
Cells are 70-90% water
Water covers 70% of the earth’s surface
Water is the only common substance to exist in all 3 states of matter: solid, liquid, and gas
Life on earth began in water and evolved there for 3 billion years before it spread to land
All living organisms require water more than any other substance
Human beings can survive for several weeks without food, but no more than 1 week without water.
The polarity of water molecules makes water a good solvent for molecules that have charged
regions (i.e. polar molecules) or atoms that are charged (i.e. ions)
Concept 3.2
Four emergent properties of water that contribute to Earth’s fitness for life
Cohesive behavior
Ability to moderate temperature
Expansion upon freezing
Versatility as a solvent
Emergent property 1: Cohesive behavior
Cohesion: attraction between like molecules (Ex: water molecules being held together by H bonds)
Adhesion: attraction between unlike molecules (water molecules being held to cell walls by H
Surface Tension:
the force that allows the surface of a liquid to stretch without breaking
Due to the ordered arrangement of water molecules hydrogen-bonded to one another at the
surface of the water
Greater in water than most liquids
Example: overfilling a glass of water, or the ability of some organisms to walk on water
Emergent property 2: The water’s ability to moderate temperature
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