Question 1 1996
1. The unique properties (characteristics) of water make life possible on Earth.
Select three properties of water and
a) for each property, identify and define the property and explain
it in terms of the physical/chemical nature of water.
b) for each property, describe one example of how the property affects
the functioning of living organisms.
Identification [1 pt] Definition-------------[2 pts]-----------Elaboration Example [1 pt]
polarity unequal charge distribution electronegativity, tetrahedron, various
Hd+, Od-, unequal
sharing
hydrogen bonding weak, intermolecular, transient, attraction between Hd+ and Od- various
electrostatic attraction
cohesion attraction of water molecules H-bonding explained transpiration, surface tension,
for each other e.g., water striders
surface tension resistance to being H-bonding explained water walking; water held by
stretched soil particles
adhesion attraction of water molecules for H-bonding explained capillarity, transpiration
other molecules
high specific heat absorbs 1 cal/g/ìC (or K) water temp slowly, moderates temperature effects
absorbs heat, heat
buffering, on organisms (circadian/
many H-bonds; high seasonal) and environmental
boiling point temperature
high heat of energy reqd for liquid > gas; breaking H-bonds; good sweating, evaporation from body
vaporization 540 cal/g/ìC coolant; high boiling point surfaces results in cooling;
water cycles/rain; transpiration
versatile solvent dissolves many compounds dissolves by ionization; any valid biological example,
ionization shells;
spheres e.g., salts, minerals, gases,
of hydration bioorganics, etc.; acid rain
effects; hydrophobic/hydrophilic
unusual phase change solid >liquid >gas ice floats (less dense); change
in thermal mixing; nutrient upwelling;
characteristics at same temperature crystal lattice; water
molecules insulation of ice layer on ponds/
farther apart; more H-bonds/ ocean; snow effects on
molecule; 4ìC most
dense organisms
dissociation/ionization 2H2O < > H3O+ + OH- pH scale based on H2O buffers work; specific cellular or
H2O < > H+ + OH- H2O pH = 7.0 (neutral) organismal example; metabolic
water; e- source in
photosynthesis; hydrolysis rxns
Less Commonly Cited Properties
Identification [1 pt] Definition-------------[2 pts]--------Elaboration Example [1 pt]
incompressibility resists changes in volume H-bond influence hydrostatic skeleton; amniotic
due to pressure fluid; CSF; blood pressure
sound conduction;
turgor
viscosity resistance to flow fish swimming; aquatic
propulsion
poor conductivity ability to allow e- flow requires conducting solutes electric fish, eel
heat of fusion 80 cal/g/ìC
size 3 atoms; diagram of water rapid diffusion (osmosis) various; imbibition; turgor,
molecule osmoregulation; contractile
vacuole
chemically stable
(good place for
reactions)
light penetration
Other Properties [Abiotic] ...........melting point heat of fusion specific gravity
Question Overview
A. Standards /criteria for judging students responses
Question 1 was composed of two parts... Part a asked for the student to identify, define and
explain (in terms of the physical/chemical nature of water) three properties of water. Part b asked
the student to describe one example of how the selected property affects the functioning of living
organisms. For convenience of grading the question was divided into four parts; identification,
definition, elaboration, and example, and each part was awarded 1 point. (3 properties x 4
parts x 1 pt each = 12 possible ways to achieve a score of 10).