AP Biology, Chapter 3
Water and the Fitness of the Environment

INTRODUCTION
EFFECTS OF WATER’S POLARITY
	Intro
		1. Describe how water contributes to the fitness of the environment to support life.
			a. Solvent for molecules to interact
			b. Moderates Earth's climate
	The polarity of water molecules results in hydrogen bonding
		2. Describe the structure and geometry of a water molecule, and explain what properties 
		emerge as a result of this structure.
			a. Outer shell of O has four orbitals as a tetrahedron
			b. Two need filling, two O-H bonds form at two corners of the tetrahedron
			c. O is very electronegative, hogs electrons, is negative
			d. H side of the molecule is positive
		3. Explain the relationship between the polar nature of water and its ability to form 
		hydrogen bonds.
			a. Polar = one side positive, one negative
			b. O-side negative attracted to H-side positive
		4. List four characteristics of water that are emergent properties resulting from hydrogen 
		bonding.
			a. Cohesion
			b. High heat capacity
			c. Expands upon freezing
			d. Versatile solvent
	Organisms depend on the cohesion of water molecules
		5. Describe the biological significance of the cohesiveness of water.
			a. Evaporation out the leaves pulls water upward
	Water moderates temperatures on Earth
		6. Distinguish heat and temperature.
			a. Heat is energy content as total kinetic energy
			b. Temperature is the average kinetic energy of the molecules
		7. Explain how water's high specific heat, high heat of vaporization, and expansion upon 
		freezing affect both aquatic and terrestrial ecosystems.
			a. Specific heat: helps dampen drastic temperature changes
			b. Heat of vaporization: absorbs and disperses a lot of heat when it evaporates
			c. Expansion
				i. Liquid water molecules slid randomly over one another
				ii. Water molecules in ice are lined up by H-bonds
				ii. Crystals are less dense
	Oceans and lakes don’t freeze solid because ice floats
	Water is the solvent of life
		8. Distinguish solute, solvent, and solution.
			a. Solute = dissolved substance
			b. Solvent = dissolving agent
			c. Solution = homogeneous mixture	
		9. Explain how the polarity of the water molecule makes it a versatile solvent.
			a. Each molecule has a positive H side and a negative O side
			b. Opposite charges are attracted to polar and ionic solutes
		10. Distinguish hydrophilic and hydrophobic substances.
			a. Hydrophilic; "water-loving", polar, usually contain O/N/S
			b. Hydrophobic; "water-fearing", non-polar
		11. Distinguish a mole and the molecular weight of a substance.
			a. Mole = a set number of molecules of a substance
			b. Molecular weight = mass of one mole of a substance

DISSOCIATION OF WATER MOLECULES
	Intro
		12. Write the equation for the dissociation and re-formation of water.
			a. H2O  H+ + OH-
	Organisms are sensitive to changes in pH
		13. Explain the basis for the pH scale.
			a. pH = negative log of the hydrogen ion concentration
			b. Example: pH 3 = 10-3 M H+
			c. In water, [H+] and [OH-] are complementary, when one goes up the other 
			goes down proportionally
			d. [H+][OH-] = 10-14 M2
			e. Example: pH 3 = 10-3 M H+ and 10-11 M OH-
		14. Explain how acids and bases directly or indirectly affect the hydrogen ion 
		concentration of a solution.
			a. Acids dissociate in water to release H+
			b. Bases
				i. Indirectly by releasing OH- (like NaOH)
				ii. Directly by absorbing H+ (like ammonia)
		15. Using the bicarbonate buffer system as an example, explain how buffers work.
			a. H2CO3 releases H+ when the pH falls
			b. HCO3- absorbs H+ when the pH rises
	Acid precipitation threatens the fitness of the environment
		16. Describe the causes of acid precipitation and explain how it harms the environment.
			a. Causes
				i. Dissolved CO2 reduces rain pH to 5.6
				ii. Sulfur dioxide and nitrogen oxides from combustion make it more 
				acidic
			b. Effects
				i. Kills fish, plants, eggs
				ii. Depletes minerals from soil