Properties of Water All organisms require H 2 O

Background nH2OnH2O n Life evolved in the early oceans n Vital to history of life on Earth

n 3/4’s of Earth is covered with H 2 O

n Human’s are 2/3’s H 2 O

Polarity of H 2 O O H H ++ ++ -- 108° Oxygen is very electronegative. i.e. It likes e - s.

Polarity of H 2 O (cont.) n e - s are shared unequally b/t H’s & O’s n H 2 O molecules are polar!

Hydrogen Bonding n Weak chemical associations w/ other molecules, like little magnets sticking together n Accounts for much of the organization of living chemistry n A lot of bonds work together for strength n 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 n Like dissolves like n Anything with a charge or polar will dissolve in water n Anything nonpolar will not dissolve in water

–eg. NaCl + H 2 0 Na + Cl - O O H H H H +

Some examples: n Hard water n Caves n Salty ocean n Hydrophobic vs. Hydrophilic molecules

Hydrophobic & Hydrophilic Interactions n Very important in biological systems –ex. Cell membranes

Cell Membrane

Cohesion and Adhesion n Water molecules stick to one another n Examples: Surface tension n Water molecules stick to other charged substances Examples: Meniscus Capillary Action

Boating Spiders

Water Walking Spiders

Water has a high specific heat n 1kcal/1g o C n Absorbs a lot of heat to raise T n Must break H bonds to pull the molecules apart

A comparison…. (No need to copy this in your notes!) n 2 X oil or alcohol n 4 X air or Al n 9 X iron n Only ammonia is greater

“So what,” you may be asking? n Temperature regulation- large thermal capacity Oceans Body Temperature n Thermal Conductivity-disperses heat evenly throughout a body

Water has a high boiling point n Liquid Gas cal. n Evaporation is a cooling process

Freezing Point of water is high n Water is less dense as a solid than a liquid (that is really weird!) n Solid water floats on its liquid form n So, what does this mean to aquatic life?

To summarize--- n Life is dependent on water

Life Evolved in water n 50-90% of wt. Of any living thing is water n 70% human is water n Blood plasma n cytoplasm

Medium of transport n Molecules/nutrients n Wastes n Sex Cells n Development of fetus

Temperature Regulation n Sweat n Blood

Buoyance n Movement n Predation/Prey

Waterproofing n Integument