chemistry review ap biology. chapter 2: the chemical context of life
TRANSCRIPT
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Chemistry Review
AP Biology
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Chapter 2: The Chemical Context of Life
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Matter, Elements, and Compounds• Matter
• Anything that takes up space or has mass
• Element• “Pure” substance that cannot be broken
down• 92 naturally occurring in nature
• Compound• Two or more elements combined in a fixed
ratio
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Life’s chemical requirements
• 25 of 92 elements are required• Carbon, nitrogen, hydrogen and oxygen
make up 96% of living matter
• Trace elements• Required in minute quantities• Some needed by all life forms• Others only by certain species
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Atomic StructureWhat are these called?
These have what charge?
These have what charge?
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Reading the periodic table
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Isotopes and Radioisotopes• Isotopes
• Different forms of element due to # of neutrons
• Radioisotopes• Nucleus decays
spontaneously• Date fossils• Used to trace atoms
through metabolisms• Can damage cellular
molecules
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Electron configuration• Energy levels
• Closest shell = least energy
• Farthest shell = most energy
• Energy is gained/lost by moving shells
• Orbital• 3-D place where e- are
usually found• 2 e- per orbital
• Valence electrons and shell• Outermost e-• Complete outer shell =
non-reactive
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Chemical Bonding
• Interactions between atoms• Covalent – shared e-
• Non-polar covalent• Polar covalent
• Ion – charged atom• Anion (-)• Cation (+)
• Ionic bond – “steals” e-
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Weak chemical bonds• Hydrogen bonds
• Hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom
• Hydrogen bonds, ionic bonds and other weak bonds help form proteins
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Reactants and Products
• Chemical reactions• Make and break chemical bonds, change composition of
matter• Reactants and products
• Starting and ending materials of chem rxns• Matter cannot be destroyed, but rearranged
• Most chemical rxns are reversible• Chemical equilibrium
• When reactions offset one another• Rxns still happening, but no effect on reactant/product
concentrations• Reactants and products are NOT equal in concentration
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Chapter 3: Water and the Fitness of the Environment
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Polarity and Hydrogen Bonding
• Polar molecule• Has opposite charges
at different ends
• Each water molecule can bond to a max of 4 others
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Water Properties and Organisms• Water molecules stick together
due to hydrogen bonds• In liquid form, bonds are fragile• Each bond lasts one trillionth a
second
• Cohesion – bonds collectively hold substance together• How plants transport water• Hydrogen molecules tug on
molecules further down the vessel• http://faculty.pingry.org/thata/
pingry_upload/movies/water_macromolecules/cohesion_transport.mov
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• Adhesion• Clinging of one
substance to another
• Surface tension• Measure of how
difficult it is to break the surface of a liquid
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Water & Earth
• Moderates temperatures, contributing to habitability
• Kinetic energy• Energy of motion
• Heat• Measure of total kinetic energy due to
molecular motion
• Temperature• Intensity of heat due to avg. kinetic
energy
• Celsius scale
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Water and Earth, cont.• Calorie
• Amount of heat energy needed to raise 1g of water by 1°C
• Kilocalorie• Amount of heat energy
needed to raise 1kg of water by 1°C
• Joule• = 0.239 calories (one
calorie = 4.184 J)
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Water and Earth, cont.• Specific heat
• Amount of heat absorbed or lost for 1g of substance to change 1°C
• Specific heat of water is 10x that of iron
• Water resists change in temp
• High specific heat of water makes ocean temp stable for life
• Organisms made mostly of water resist temp changes
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Water and Earth, cont.• Liquid molecules moving
fast to overcome bonds enter air as gas• Vaporization or
evaporation• Takes 580 calories of heat
to evaporate 1g of room temp water
• Evaporative cooling• As substance evaporates,
surface of remaining substance cools down
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Ice Floats
• Why oceans and lakes don’t freeze
• Water is less dense as a solid than as a liquid• Expands when frozen• Reaches its greatest density at 4°C
• If ice sank, all ponds, lakes, and oceans would freeze solid
• How would this affect life?
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Water is the solvent of life• Solution
• Solvent + solute
• Solvent• Does dissolving
• Solute• What dissolves
• Aqueous solution• Solution with water as solvent
• Water works well, but not for everything, otherwise could not be stored
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Water is the solvent of life, cont.• Hydrophilic
• Has affinity for water• Hydrophobic
• Repels water• Mole
• Equal in # to molecular weight of substance in grams
• Molecular weight• Sum of all weights of all atoms in
a molecules• Avagadro’s number = 6.02 x 1023
(# molecules/mole)• Molarity
• Moles of solute per liter of solution
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Organisms and pH• Organisms are sensitive to
pH
• Hydrogen ion• (H+) single proton with charge
of +1
• Hydroxide ion• (OH-) charge of -1
• Dissociation • Transfer of hydrogen atoms
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pH• Acid
• Substance that increases H+ concentration of a solution
• Donate H+ to a solution• When hydrochloric acid is added to water HCl H+ +
Cl-
• Base• Substance that increases OH- of a solution
• Concentrations of H and OH• Products of OH- and H+ concentrations are always
10-14
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pH, cont.• pH scale
• Range from 0-14, expresses OH- and H+ concentrations
• Defined as –log[H+]• pH declines as H+ concentration increases• Each pH unit represents 10-fold difference in
OH- and H+ concentrations
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pH, cont.• Buffers
• Substances that minimize changes in pH• Accepts and donates ions in solution when
needed• Ex: carbonic acid
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Acid Precipitation & Environment
• Threatens the fitness of environment
• Acid precipitation• Rain, snow, or fog more acidic than pH 5.6
• Harms environment by killing plants and animals
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Chapter 4: Carbon and the Molecular Diversity of Life
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Carbon• Prominent role in evolution of life
• Can form molecules that are large, complex, and diverse
• Complexity is demonstrated in hemoglobin
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Organic Chemistry• Study of carbon compounds
• 30% of a cell is carbon based compounds
• Common ingredients in carbon compounds: H, O, N, S, P
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Carbon atoms are a versatile building block
• Carbon has 6 electrons• Little tendency to gain or lose
e- and form ionic bonds• Completes valence shell by
making 4 covalent bonds• Makes large, complex
molecules possible• Carbon is compatible with
many different elements• CO2 is the source of carbon for
all the organic molecules found in organisms
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Variation = Diversity• Variation in carbon
skeletons contributes to the diversity of organic molecules
• Carbon chains form the skeletons of organic molecules
• Hydrocarbons• Organic molecules
consisting only of carbon and hydrogen
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Variation = Diversity, cont.
• Isomers• Compounds with same
molecular formula, but different structures, hence different properties
• Structural isomers• Differ in the covalent
arrangements of their atoms
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Variation = Diversity, cont.
• Geometric isomers• All have same
covalent partnerships, differ in their spatial arrangements
• Stereoisomers• Molecules are mirror
images of each other
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Functional Groups• Contribute to the molecular diversity of
life• Hydroxyl group
• H atom bonded to a O atom, in turn bonded to the C skeleton
• Alcohol: organic compounds containing hydroxyl groups
• Polar because of electronegative oxygen
• Carboxyl• O double bonded to a C, bonded to
hydroxyl
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Functional Groups, cont.
• Amino• N bonded to 2 H atoms
• Sulfhydral• S bonded to H
• Phosphate• P ion convalently attached by O atom to C
skeleton
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Chemical Elements of Life: Review
• Living matter consists of mainly C, H, O
• Chemical behavior of carbon makes it a versatile building block