Properties of Water

All organisms require H2O

Background

H2O Life evolved in the early oceans Vital to history of life on Earth

3/4’s of Earth is covered with H2O

Human’s are 2/3’s H2O

Polarity of H2O

O

HH+ +

-

108°

Oxygen is very electronegative.

i.e. It likes e-s.

Polarity of H2O (cont.)

e-s are shared unequally b/t H’s & O’s

H2O molecules are polar!

Hydrogen Bonding

Weak chemical associations w/ other molecules, like little magnets sticking together

Accounts for much of the organization of living chemistry

A lot of bonds work together for strength

Generally indicated by dashed lines

Do the water molecule shuffle!

The structure of water leads to some interesting properties of water……

Water is the Universal Solvent

Like dissolves like

Anything with a charge or polar will dissolve in water

Anything nonpolar will not dissolve in water

– eg. NaCl + H20

Na+ Cl-

OO

H

H

HH

+

Some examples:

Hard water Caves Salty ocean Hydrophobic vs. Hydrophilic molecules

Hydrophobic & Hydrophilic Interactions

Very important in biological systems

– ex. Cell membranes

Cell Membrane

Cohesion and Adhesion

Water molecules stick to one another Examples:

Surface tension Water molecules stick to other charged

substancesExamples:

MeniscusCapillary Action

Boating Spiders

Water Walking Spiders

Water has a high specific heat

1kcal/1goC Absorbs a lot of heat to raise T Must break H bonds to pull the

molecules apart

A comparison…. (No need to copy this in your notes!)

2 X oil or alcohol 4 X air or Al 9 X iron Only ammonia is greater

“So what,” you may be asking?

Temperature regulation- large thermal capacity

Oceans

Body Temperature

Thermal Conductivity-disperses heat evenly throughout a body

Water has a high boiling point

Liquid Gas + 540 cal.

Evaporation is a cooling process

Freezing Point of water is high

Water is less dense as a solid than a liquid (that is really weird!)

Solid water floats on its liquid form So, what does this mean to aquatic life?

To summarize---

Life is dependent on water

Life Evolved in water

50-90% of wt. Of any living thing is water

70% human is water Blood plasma cytoplasm

Medium of transport

Molecules/nutrients Wastes Sex Cells Development of fetus

Temperature Regulation

Sweat Blood

Buoyance

Movement Predation/Prey

Waterproofing

Integument