Biology Ch 3: Water and Life

Hydrogen Bonds and Their Importance

bonds that occur when slightly positive covalently bonded hydrogens are attracted to the slightly negative atoms of another molecule; form weak bonds between molecules

hydrogen bonds organize water molecules into higher level of structural order and contribute to the unique properties of water (cohesion, temperature regulation, density, solvent properties)

Cohesion

the ability of water molecules to cling to one another; held together by hydrogen bonds; aids in transport of water in plants from roots to leaves; allows blood plasma to fill vessels and maintains blood pressure; allows water covering surface of lungs to adhere to chest wall and keep lungs open

Surface Tension

cohesive properties of water lead to surface tension- molecules at surface are highly ordered and strongly attracted to the molecule below them; a measure of how difficult it is to stretch or break the surface of a liquid

Moderation of Temperature

water absorbs heat from the sun, which allows the surrounding air to remain cooler; water releases heat at night and winter, which warms the surrounding air (accounts for moderate temperatures year-round in coastal cities)

Molecular Movement & Specific Heat (Effect on Coastal Regions)

amount of heat absorbed or lost for 1g of a substance to change its temperature by 1 degree; water has a high specific heat due to hydrogen bonds

water absorbs heat from the sun and pulls it away from its surrounding area (water molecules speed up); when it is cool, the molecules slow down and the heat is released from the formation of hydrogen bonds

Evaporative Cooling

molecules with the greatest kinetic energy are first to change state from liquid to gas and detach, the remaining molecules have less kinetic energy and therefore have a lower temperature

maintains temperatures of bodies of water, bodies with sweat glands, and plants

Density

the amount of matter in a given volume

Density of Water vs Ice & Its Importance

-at higher temperatures (above 4 degrees C), water molecules are moving more quickly and the weak hydrogen bonds are constantly breaking a rebonding; at temperatures 0 degrees and lower, the water molecules slow down and the hydrogen bond breaking slows down, allowing more stable hydrogen bonds to form crystal structure that have less weight

-if ice did not float and instead sank, the ice would constantly be sinking and the water above it would freeze, eventually resulting in a completely frozen body of water; instead it floats and helps to insulate the water below

Solubility Terms

*solution: homogenous mixture of two or more substances

*solvent: dissolving agent (in an aqueous solution, water is the solvent)

*solute: the dissolved substance

ex: a sugar cube (solute) is dissolved in water (solvent) and forms a uniform mixture (solution)

Solubility Rules

"like dissolves like": polar solvents dissolves polar solutes; nonpolar solvents dissolve nonpolar solutes; water dissolves ionic compounds (opposite charges attract)

Water as a Solvent

water is a versatile solvent due to its polarity- oxygen will attract positive charges, hydrogen will attract negative charges

Hydrophilic/Hydrophobic

*water-loving- substance has an affinity for water (e.g. vinegar, sugar, organelles)

*water-fearing- substance does not have an affinity for water (e.g. oils)

Hydration Shell

sphere of water molecules around a dissolved ion

ex: sodium chloride (NaCl) is dissolved in water. the water molecules surround individual sodium and chloride ions, separating and shielding them from one another

pH Scale

measure of hydrogen ion concentration (equal to the negative log of the concentration of hydrogen ions) ranging in value from 0 to 14

Acid vs Base & Their Corresponding pH Numbers

*acid: substance that increased hydrogen ion concentration in solution

-pH of 0-6.9

ex: HCl --> H^+ + Cl^-

*base: substance that reduces the hydrogen ion concentration in solution( direct acceptance of H^+ and acceptance of H+ following dissociation of OH^-)

-pH of 7.1-14

ex: NaOH --> Na^+ OH^-

(note: neutral is pH of 7)

Purpose of a Buffer

substance that resists changes in pH; minimizes changes in concentrations of H^+ and OH^-

(weak acids and bases neutralize influx of acid or base in system; homeostatic blood pH mechanism)

ex: carbonic acid-bicarbonate buffer system

Heat

thermal energy in transfer from one body of matter to another

Temperature

measure of average kinetic energy of the molecules in a body of matter

increase molecular speed -> increase kinetic energy -> increase temperature

Calorie

amount of heat to raise 1 g of water 1 degree C; the amount of heat that 1 g of water released when it cools by 1 degree C

Specific Heat

the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1 degree; measure of how well a substance resists changing its temperature

Heat of Vaporization

quantity of heat a liquid must absorb for 1 g of it to be converted from a liquid to a gas- possible due to hydrogen bonds and essential for climate regulation

ex: solar heat absorbed by tropical seas is consumed during the evaporation of surface water, then condenses and releases as rain

Ocean Acidification & Consequences

-excess carbon dioxide in the atmosphere forms more carbonic acid in the ocean, and the increased hydrogen ions bind to carbonate ions

-result: fewer carbonate ions are available to corals for formation of calcium carbonate