Water and Life Chapter 3 Unit 1

Contributions to Life on Earth Evoulution of Life Cells are 70%-95% water Covers about ¾ of the Earth solid, liquid, and gas

Water’s Polarity Polar molecule: overall charge is unevenly distributed (+) of hydrogen attracted to (–) of oxygen Maximum of 4 bonds with other water molecules Hydrogen bonds between water molecules Covalent bonds between O and H2

4 Emergent Properties Cohesive behavior Moderation in Temperature Floating of Ice on Liquid Solvent of Life

Cohesive Behavior Cohesion Adhesion Surface Tension Measure of how difficult to stretch or break surface

Moderates Temp. on Earth High specific heat Amt. of heat absorbed or lost for 1g of a substance to change its temp. Large bodies of water act as Heat Sinks Absorb heat from sunlight during day and release heat during night

Moderates earth’s climate Evaporative Cooling High Heat of Vaporization (Boiling point) Quantity of heat a liquid must absorb to be converted into gaseous state Moderates earth’s climate Tropical air moves pole ward, vapor releases heat as condenses into rain Keeps organisms from overheating

Floating of Ice on Liquid Less dense as a solid than as a liquid Prevents deep bodies of water from freezing As freezes, releases heat to water below Freeze-> H bonds release heat Melts-> H bonds break absorbing heat

Versatile Solvent Caused by polarity Solution: homogenous mixture of 2 or more substances Solvent Solute Hydrophilic: affinity for water (polar) Hydrophobic: does not have affinity for water (nonpolar and nonionic)

pH Scale Acids: pH < 7 Bases: pH > 7 Increases relative H+ of a solution HCL  H+ + Cl- Bases: pH > 7 Reduces the relative H+ of a solution NAOH  NA++ OH-

Buffers Minimize wide fluctuations in pH Combinations of H+ donor and H+ acceptors