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AP Biology Free Response Question Rubrics
Essay #3
1. Carbon is a very important element in living systems.
a.
Describe the various characteristics of the carbon atom that makes possible
the building of a variety of biological molecules.
b.
The following structures are examples of different categories of biological
compounds. Describe how each category of compounds is important to the structure and
function of living systems.
STANDARDS:
A. CHARACTERISTICS OF CARBON ATOMS:
(Max of 4 points)
__Ready availability, abundance
__Atom small in size, outer (valence) electrons close to nucleus, so forms stable
(strong) bonds
__4 electrons in a valence-capacity of 8, forms 4 bonds to 4 other atoms
__Forms covalent bonds
__Can bond to other carbon atoms, no upper limit to size of carbon compounds
__Bond angles form tetrahedron, resulting in 3-D structures, chains, rings, not just
planar
__Can form multiple C-C, C=C, C=C bonds
__Can form isomers, different structures - same number and kind of atoms
__Functional groups/combine with a variety of other elements
__BONUS POINT: if get 3 above - Uniqueness, only Carbon has all of these
characteristics
B.
BIOLOGICAL MOLECULES:
(Max of 5 points)
(Cannot get 10 points for this question without mentioning both category I and II)
CATEGORY I:
__Identification of molecule / category:
Phospholipid, phosphoglyceride, fat, lipid,
phosphatidylethanolamine / polypeptide.
__Characteristics of molecule:
Hydrophobic/hydrophilic, polar/nonpolar,
amphipathic, or non-water soluble, high E bonds,
sat/unsat C-C bonds.
__Structural uses of molecule:
membrane, lipid bilayer, fluid mosaic.
__Functions of molecule (for example):
(2 Max) Phospholipids: Regulation of membrane permeability, fluidity
Fats:
Structural, insulation, energy storage, water-proofing
Steroids/Sterols:
Hormonal, membrane fluidity
Cholesterol:
Animal membranes
Fat soluble Vitamins:
Coenzymes
Prostaglandins:
Neural modulators
Waxes:
Water-proofing
CATEGORY II:
__Identification of molecule / category:
Amino acid / protein / cysteine
__Recognizing cysteine's role in disulfide bond formation
__Characteristics of molecule:
Side chains variable
Peptide bonds may be formed
Subunit (monomer, building block) of protein
Levels of protein structure / zwitterion / as buffers
__Structural roles:
__Functional roles:
(2 Max)
Keratin, collagen, cytoskeletal (tubulin, actin), etc.
Enzymatic - speed reactions
(pepsin, glucose oxidase, etc.)
Transport (Hb, Myb, permeases, HDL/LDL)
Regulatory (oligopeptides, ex. hypothalamic releasing
factors, insulin, glucagon, etc.)
Contractile - actin, myosin
Protection - antibodies
Essay # 2. The unique properties (characteristics) of water make life possible on Earth. In 3 paragraphs, 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.
Water FRQ (1996) Rubric
Identification (1pt)
Definition (1pt)
Elaboration (1pt)
Example (1pt_)
POLARITY
Unequal charge distribution
Electronegativity, Hd+, Od-,
unequal sharing
Various
Hydrogen Bonding
Weak, intermolecular, transient,
electrostatic attraction
Attraction between Hd+ and Od-
Various
Cohesion
Attraction of water molecules to
each other
H-bonding explained
Transpiration, surface tension,
e.g., water striders
Surface tension
Resistance to being stretched
H-binding explained
Water walking, water held by
soil particles
Adhesion
Attraction of water molecules for
other molecules
H-bonding explained
Capillarity, transpiration
High Specific Heat
Absorbs 1 cal/g/oC
Water absorbs heat; heat
buffering; many H-bonds; high
boiling point
Moderates temperature effects
on organisms
(circadian/seasonal) and
environmental temperature
High Heat of
Vaporization
Energy req’d for liquid  gas;
540 cal/g/oC
Breaking H-bonds; good
coolant; high boiling point
Sweating; evaporation from
body surface results in cooling;
water cycles/rain; transpiration
Versatile solvent
Dissolves many compounds
Dissolves by
ionization/ionization shells, e.g.,
salts, minerals, gases
Any valid biological example;
spheres of hydration,
bioorganics, etc; acid rain
effects;
hydrophobic/hydrophilic
Essay #1.Chemical bonds are essential to building the molecules of life.
a. In 3 paragraphs, describe the following bond types and how they are significant to life on earth: ionic, covalent
(polar and non-polar), hydrogen, and Van der Wahls (interactions).
b. How is energy transferred between these bonds and what role does oxygen play in the formation and breaking of
bonds?
Rubric
Identification (1pt)
Ionic
Definition (1pt)
Bonding between cation and anion, This
inequality is brought to an extreme in a
bonding arrangement called an ionic bond.
Elaboration (1pt)
In an ionic bond, one atom
pulls the shared electrons
away from the other atom
entirely. Ionic bonds are
stronger than polar bonds.
Covalent P&NP
Bonds formed through the more or less equal
sharing of electrons between atoms are known
as covalent bonds.
Hydrogen
a weak bond between two molecules resulting
from an electrostatic attraction between a
proton in one molecule and an electronegative
atom in the other.
If the electrons in a
covalent bond are shared
equally, the resulting bond
is called a
nonpolar covalent bond.
When one atom pulls the
shared electrons toward
itself a little more tightly
than the other, the
resulting covalent bond is
said to be a polar bond.
In a polar bond, the atom
that pulls electrons toward
itself gains a slight
negative charge (because
electrons have a negative
charge). Since the other
atom partially loses an
electron, it gains a slight
positive charge.
A hydrogen bond is a
dipole dipole interaction
that occurs between any
molecule with
a bond between a
hydrogen atom and any
of
oxygen/fluorine/nitrogen. it
is a force of attraction
between a hydrogen atom
in one molecule and a
small atom of
high electronegativity in
another molecule. That is,
it is an intermolecular
force, not an
Example (1pt_)
One example of
ionic bonding is
the reaction
between sodium
(Na) and
chlorine (Cl) to
form table salt
(NaCl). The
chlorine atom
steals an
electron from
the sodium
atom. Because
it loses an
electron, the
sodium atom
develops a
charge of +1.
The chlorine
atom has a
charge of –1,
since it gained
an electron.
For example,
the atoms in
water form polar
bonds because
oxygen, which
has eight
protons in its
nucleus, has a
greater pull on
electrons than
hydrogen, which
has only one
proton.
Hydrogen
bonds are
responsible for
the bonding of
water molecules
in liquid and
solid states, and
are weaker than
covalent and
ionic bonds.
Van de Wahls
Van der Waals forces include attraction and
repulsions between atoms, molecules, and
surfaces, as well as other intermolecular
forces. They differ
from covalent and ionic bonding in that they
are caused by correlations in the fluctuating
polarizations of nearby particles (a
consequence of quantum dynamics[3]).
Bond energy
Ionic and covalent
bonds between elements require energy to
break. Ionic bonds are not as strong as
covalent, which determines their behavior in
biological systems. However, not all bonds are
ionic or covalent bonds. Weaker bonds can
also form between molecules. Two weak
bonds that occur frequently are hydrogen
bonds and van der Waals interactions.
Weak interactions are the key means by which
molecules interact with one another—
enzymes with their substrates, hormones with
their receptors, antibodies with their antigens.
intramolecular force as in
the common use of the
word bond.
are the residual attractive
or repulsive forces
between molecules or
atomic groups that do not
arise from a covalent
bond, or electrostatic
interaction of ions or of
ionic groups with one
another or with neutral
molecules.[1] The resulting
van der Waals forces can
be attractive or repulsive.
Oxygen is a very
electronegative element,
which means it attracts
electrons as is seen in
water. So It is kind of a
vacuum for electrons,
which result in bonds
breaking.
Gekko lizard
and wall of
aquarium
The strength
and specificity
of weak
interactions are
highly
dependent on
the medium in
which they take
place, and the
majority of
biological
interactions take
place in water.
Two properties
of water are
especially
important
biologically: