Biology Molecule
Unit 1 -man is high 50ís to 60% water -distribution in body divided into 3
compartments: 1) intracellular - 28 litres 2) intercellular/interstitial fluid -

11 litres - 80% 3) blood plasma - 3 litres - 20% -women contain less water than
men -organisms can contain 60-80% water -bacteria have lots of water -fat cells
have little -waterís properties result from its structure and molecular
interactions -water is polar -polar covalent bonds and asymmetrical shape give
it opposite charges on opposite sides -electrons spend more time around O giving

H a slight positive charge -hydrogen bonds form between the oxygen of one
molecule and the hydrogen of another -cohesion: substance being held together by
hydrogen bonds -hydrogen bonds are transient yet enough is always held together
to give water more structure than almost any other liquid -beads and meniscus
formed by cohesion (also helps upward transport of water in plants) -adhesion
counteracts downward pull of gravity -water has greater surface tension than
most liquids -surface molecules are hydrogen bonded to molecules below and
around them -surface tension can hinder life (i.e. beading in the alveoli of
lungs) -makes water "unwettable" -surfactants used to counteract this -water
has a high specific heat which allows it to resist extreme temperature changes
-has a high heat of vaporization that causes it to require alot of energy to
change states -when sweating, heat energy is utilized to change states from
liquid to gas, causing a drop in temperature -as a solid water is less dense
than as a liquid and will float -charged regions of molecules have an electrical
attraction to charged ions -water surrounds ions separating and shielding them
from one another -polar compounds are generally soluble -charged regions of
water are attracted to oppositely charged regions of other polar molecules
-polar molecules are miscible in other polar liquids -most water molecules
donít dissociate ( 1/554 million do) -hydrogen atom in hydrogen bond between
the two water molecules may shift from the oxygen atom it is covalently bonded
to the unshared orbitals of the oxygen that it is hydrogen bonded to -hydrogen
ion is transferred creating a hydronium ion and leaving a hydroxide ion -the
solvent is water itself -at equilibrium water is not dissociated -at equilibrium
in pure water at 25oC [H+] = [OH-] -pH of this solution is 7 (neutral) -high pH
= low acidity -acids are substances that increase the relative [H+] and remove

OH- because it tends to combine with H+ to form water - if [H+] * [OH-] , it is
acidic and has a pH between 0 and 7 -bases are substances that reduce the
relative [H+] in a solution -it may increase the [OH] -if [H+] * [OH-] , it is
basic and has a pH greater than 7 -buffers are important in the body to keep the
pH range between 6 and 8 -pH of blood is between 7.34 and 7.44 -mustnít shift
below 7.2 or acidosis will occur -some body zones may have a pH as low as 0.5 or
as high as 10 -buffers minimize sudden changes and are a combo of hydrogen
donors and hydrogen acceptors -ions are accepted when in excess and donated when
in short supply -in biological systems an example is the bicarbonate buffer -in
response to a rise in pH, the carbonic acid dissociates to form a carbonate ion
and a hydrogen proton -if there is a drop, it is reversed (pH up = to right, pH
down = to left) -equilibrium is established but it is always moving to the left
or the right -a balance is the optimum pH -other body buffers include protein
molecules which donate and accept amino acids to stabilize pH -most of the rest
of organisms is made up of carbon based compounds like carbs, lipids, proteins,
nucleic acids -carbon compounds are known as organic -vitalism is the belief in
a life force outside the control of chemical laws -this has been disproved as
water, ammonia, hydrogen and methane have been combined in a lab to form organic
substances -C+O+H = carbohydrates -C+H+N = amino acids, urea, proteins, lipids
-carbon atoms are the most versatile building blocks -each has 4 valences where
bonds can form -carbon chains form the skeleton of most organic molecules -may
be straight or branched, long or short, or in closed rings -hydrocarbons contain
only hydrogen and carbon -they form when organic matter decomposes and
functional groups break off leaving a skeleton -hydrocarbon chains, branches,
and rings can be modified by other elements which are joined on in a particular
matter -these are components of organic molecules