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AP Biology Exam Review
PART I: MOLECULES AND CELLS (25%)
Chemistry of Life (7%)
Water is a highly polar molecule due to the electronegativity of oxygen: the oxygen side has a
slightly negative charge while the hydrogen side has a slightly positive charge, which allows for
hydrogen bonding the strong hydrogen attractions between molecules of water.
Characteristics of water –
Cohesion is due to hydrogen bonds holding water molecules together. Adhesion is the
clinging of one substance to another. Capillary action results from their combined
forces and is important in the movement of water up a tree.
Greater surface tension than most other liquids.
High specific heat results in a stable environmental temperature for marine organisms.
High heat of vaporization evaporating water requires relatively greater amount of heat.
Ice is less dense than water, allowing fish and other organisms to survive beneath a
frozen pond in the winter.
Organic compounds are compounds that contain carbon. The four classes of organic
compounds are as follows:
Carbohydrates consist of carbon, hydrogen, and oxygen. Monosaccharides include
glucose and fructose. A disaccharide consists of two monosaccharides joined through
condensation (removal of water), with hydrolysis (addition of water) being the reverse
of condensation. Polysaccharides include cellulose (structure, plants), starch (storage,
plants), chitin (structure, animals), and glycogen (storage, animals).
Lipids includes fats, oil, waxes, and steroids. All are hydrophobic. Most lipids consist of
one glycerol molecule and three fatty acid tails (saturated or unsaturated hydrocarbon
chains with a carboxyl group at the end). Steroids are lipids with four fused rings.
Proteins carry out many functions in the body, such as signaling and catalyzing chemical
reactions. Smallest units are amino acids which join together with peptide bonds to
create a polypeptide chains. Be familiar with the four levels of protein structure: 1) linear
sequence of amino acids, 2) alpha helices or beta pleated sheets, 3) interactions between
side chains, such as hydrogen bonding, ionic bonding, Van der Waals, hydrophobic
interactions, or disulfide bonds, 4) optional, refers to proteins consisting of more than
one polypeptide chain.
Nucleic acids ribonucleic (RNA) or deoxyribonucleic (DNA), responsible for carrying
heredity information. Made of nucleotides, which consist of phosphate, a 5-carbon
sugar deoxyribose or ribose, and a nitrogen base: adenine, cytosine, guanine, or thymine
(DNA), or uracil (RNA). 1 http://guidesbyjulie.blogspot.com/
AP Biology Exam Review
The first law of thermodynamics states that energy cannot be created or destroyed, only
transferred – otherwise known as the law of conservation of energy. The second law of
thermodynamics states that in the course of energy conversions, the entropy (disorder) in the
universe decreases. Gibb’s free energy equation: G = H – T S, where G represents free
energy change, H represents change in heat content, T represents absolute temperature, and
S represents entropy.
An exergonic reaction results in a net release of free energy, with G being negative – the
reactants have more energy than the products. This models a spontaneous or “downhill”
reaction. An endergonic reaction absorbs free energy, storing it in products, resulting in a
positive G – the reactants have less energy than the products. This is an “uphill” reaction.
ATP adenosine triphosphate, powers cellular work by coupling exergonic reactions to
endergonic reactions. In other words, through phosphorylation the transfer of a phosphate
group from ATP to another molecule, an otherwise endergonic reaction can become exergonic.
Catabolism is the breaking down of molecules, while the building of molecules is anabolism
Enzymes are catalytic proteins that speed up reactions by lowering the energy of activation
Characteristics of Enzymes:
Enzymes are substrate specific Only the active site of an enzyme will bind to the
The induced-fit model states that as substrates enter the active site, they induce the
inducedenzyme to alter its shape slightly so that the substrate fits better.
Enzymes remain unchanged during a reaction and are reused. They catalyze reactions in
Enzymes are affected by temperature and pH. Enzymes are inactive in low
temperatures, with activity reaching a peak point at a certain temperature. After this
peak, enzymes will begin to denature Too low or too high pH levels can also denature
In competitive inhibition compounds resembling the substrate compete with the
substrate for the same active site. In noncompetitive inhibition binding of one
substrate to another active site may block the other active site, preventing the other
substrate from binding. In allosteric inhibition the enzyme will have two active sites:
one for a substrate and one for an inhibitor. The enzyme will oscillate between an active
form and an inactive form, with an activator/inhibitor stabilizing the respective form.
In feedback inhibition the end product of a series of reactions serves as the allosteric
inhibitor of an enzyme earlier in the pathway. 2 http://guidesbyjulie.blogspot.com/
AP Biology Exam Review
The cell theory has three basic tenets: all living things are made of cells, cells are the basic unit
of all organisms, and all cells arise from preexisting cells.
Prokaryotic cells have no nucleus or internal membranes. DNA is not enclosed by a nuclear
membrane and is circular, concentrated in the region called the nucleoid. They are mainly
unicellular, with small cells. Eukaryotic cells are larger and more complex, with distinct
organelles, DNA enclosed in the nuclear membrane and wrapped around histones into
Cell membranes consist of a phospholipid bilayer. A phospholipid is ampipathic, meaning it has
both hydrophobic and hydrophilic region. Membrane proteins include integral proteins which
penetrate the hydrophobic core of the lipid bilayer, and peripheral proteins which are loosely
bound to the surface of the membrane. They are important in transport, enzymatic activity,
signal transduction, intercellular joining, cell-cell recognition, and attachment to the
cytoskeleton and extracellular matrix. Cholesterol molecules are embedded in the interior of
the bilayer to stabilize the membrane. Carbohydrates attached to the external surface are
important for cell-to-cell recognition
It is important to remember that animal cells do not have chloroplasts, a central
vacuole/tonoplast, cell wall, and plasmodesmata. Plant cells do not have lysosomes, centrioles,
or flagella (except in some plant sperm).
Nucleus contains chromosomes, surrounded by selectively permeable nuclear
Ribosomes the site of protein synthesis, found free in the cytoplasm or attached to
The Endomembrane System
- Endoplasmic reticulum (ER) Smooth ER lacks ribosomes, while Rough ER has
ribosomes located on its outer surface. Smooth ER synthesizes lipids,
metabolizes carbohydrates, and detoxifies the cell of drugs and poison. Rough ER
makes proteins and membranes.
- Golgi apparatus the “FedEx” of the cell, modifying, packaging, and directing
G olgi apparatus:
products to the appropriate sites.
Lysosomes: sacs of hydrolytic enzymes the principal site of intracellular digestion.
Play a role in apoptosis programmed cell death. Not found in plant cells.
Peroxisomes: contain catalase which converts hydrogen peroxide into water with the
release of oxygen atoms.
Mitochondria: double-membraned, site of cellular respiration
AP Biology Exam Review
Chloroplasts: double-membraned, site of photosynthesis
Vacuoles: single, membrane-bound structures for storage.
Cytoskeleton: network of protein filaments that extend throughout the cytoplasm in
order to give the cell its shape
- Microtubules hollow tubes, made of tubulin, found in cilia and flagella
- Microfilaments (actin filaments): two intertwined strands of actin, found in
pseudopodia, cell division, muscle contraction, and cytoplasmic streaming
- Intermediate filaments: fibrous proteins coiled into thicker cables, anchors
organelles and found in the nuclear lamina
Mitosis produces two genetically identical daughter cells, while meiosis occurs in sexually
reproducing organisms and results in haploid cells. The cell cycle consists of five major phases:
G 1, S, and G 2, which comprise interphase, and mitosis and cytokinesis which make up the cell
Meiosis results in genetic variation:
Independent assortment of chromosomes: homologous pairs of chromosomes separate
depending on the random way they line up on the metaphase plate during metaphase I.
There is an equal chance that a particular gamete will receive a maternal chromosome or
a paternal chromosome.
Crossover: crossover produces recombinant chromosomes combining genes inherited
from both parents.
Random fertilization: any sperm can fertilize any egg
cyclinDensityCyclins and cyclin-dependent kinases are responsible for controlling the cell cycle. Densitydependent growth factors prevent cells from continuing to divide if there are no longer any
sites upon which to anchor. Cancer cells do not exhibit such inhibition and have escaped form
cell cycle controls.
Cellular Energetics (8%)
Cellular respiration involves glycolysis, the Krebs cycle, and the ETC/oxidative phosphorylation.
Glycolysis is the conversion of glucose into two molecules of pyruvate. The net energy yield
from glycolysis is 2 ATP and 2 NADH. After glycolysis, pyruvate will be converted into acetyl
coenzyme A (Acetyl CoA). The Krebs cycle will then decompose Acetyl CoA into carbon dioxide,
producing 2 NADH per glucose molecule. For every glucose molecule, there are 6 NADH
produced, 2 FADH2 produced, and 2 ATP produced. Any ATP produced so far has been through
substrate-level phosphorylation At this point, NADH and FADH2 will be shuttled to the
electron transport chain for oxidative phosphorylation The total of 10 NADH will enter the
electron transport chain at the beginning, while the two FADH2 enter further along. Oxygen
functions as the final electron acceptor. As the electrons release energy, this energy is used to
AP Biology Exam Review
pump protons (H+) from the mitochondrial matrix to the intermembrane space, resulting in a
concentration gradient. H+ will only be able to diffuse back across to the mitochondrial matrix
through ATP synthases In chemiosmosis the H+ will pass through a channel in ATP synthase
and cause the oxidative phosphorylation of ADP, creating ATP. Chemiosmosis is an energy- coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane
to drive cellular work. A maximum of 38 ATP can be created from one glucose molecule in
Fermentation, anaerobic respiration is an alternate pathway that will recycle NAD+ and create
a minimal amount of ATP. Pyruvate is converted to ethanol in alcohol fermentation and is
converted to lactic acid in lactic acid fermentation
Photosynthesis is the conversion of light energy from the sun to chemical energy stored in
sugar and other organic molecules. Chloroplasts are the site of photosynthesis in plants, with
the light reactions taking place in the thylakoid membranes and dark reactions taking place in
The purpose of the light reactions is to convert light energy to the chemical energy stored in
NADPH and ATP. Photosystem II absorbs light at the same time that Photosystem I does.
When Photosystem II absorbs light, an electron excited to a higher energy level will be captured
by the primary electron acceptor. This electron will pass down an ETC to Photosystem I.
Electrons excited in Photosystem I will be accepted by another primary electron acceptor and
pass to a second ETC and finally, to NADP+ reductase, which creates NADPH Electrons are
replaced in Photosystem II through photolysis the splitting of water. As electrons fall down
the ETC, ATP will be created in noncyclic photophosphorylation providing energy for the
synthesis of sugar during the Calvin cycle. In some cases, cyclic electron flow which uses
photosystem I but not photosystem II, will be used to compensate for the large amount of ATP
consumed in the Calvin cycle.
The Calvin Cycle uses ATP and NADPH to convert CO2 into sugar. Three molecules of CO2 are
required for the net synthesis of one molecule of glyceraldehyde-3 -phosphage (G3P) First,
CO2 is fixed by the enzyme rubisco to ribulose biphosphate (RuBP), creating an extremely
unstable 6-carbon molecule that immediately splits into two molecules of 3 -phosphoglycerate
(3 -PGA) Thus, there are now 6 molecules of 3-PGA. These molecules are then phosphorylated
and given a pair of electrons each from NADPH, creating 6 molecules of G3P. However, only
one molecule will be used to create glucose, with the other five being incorporated back into the
cycle to create RuBP for future use.
Alternate methods of carbon fixation exist to prevent excessive water loss in hot, arid climates.
These are the C 4 pathway and CAM pathway The C4 pathway uses bundle-sheath cells as a
confined environment for CO2 to be fixed, while CAM plants open stomata during the night.
AP Biology Exam Review
PART II: HEREDITY AND EVOLUTION
See page 4 for information about genetic variation through meiosis. In spermatogenesis, four
mature sperm cells will result. In oogenesis only one daughter cell results from meiosis, with
the rest becoming polar bodies that will degenerate.
DNA molecules are packaged into chromosomes DNA is first wrapped around proteins called
histones Each DNA-wrapped histone and the DNA around it will form a nucleosome The
string of nucleosomes coils to form a chromatin fiber which then become looped domains
attached to a scaffold of nonhistone proteins. The chromatin folds further to result in the
Important heredity concepts:
Incomplete dominance is the blending of two characteristics to form an intermediate
characteristic, such as in red and white carnations.
Codominance: both traits will show, such as in roan cattle, with patches of red and
M ultiple alleles:
Multiple alleles: occurs when there are more than two allelic forms of a gene, such as in
ABO blood types
Pleiotropy: the ability of one single gene to affect an organism in several or many ways,
causing a “cascade” of symptoms
Epistasis: two separate genes control one trait, with one gene masking the expression
of the other gene. For example, a gene for production of melanin can be epistatic to one
for the deposition of melanin
Polygenic Inheritance: characters varying along a continuum, such as height or skin
tone. There is no either-or option.
Genes that are on the same chromosome are linked genes One map unit distance on a
chromosome is the distance within which recombination occurs 1 percent of the time.
Molecular Genetics (9%)
DNA is a double helix consisting of two strands running in opposite directions (antiparallel
One runs 5’ to 3’, while the other is 3’ to 5’. Each nucleotide consists of a five-carbon sugar
(deoxyribose) a phosphate and a nitrogen base The nucleotides are connected by
phosphodiester linkages Adenine and guanine are purines, with two rings, while thymine and
cytosine are pyrimidines, with one ring. Adenine always pairs with thymine (uracil in RNA), and
guanine always pairs with cytosine. Nitrogenous bases are connected by hydrogen bonds. 6 http://guidesbyjulie.blogspot.com/
AP Biology Exam Review
DNA replication is semiconservative as proved by Meselsohn and Stahl Each strand of a
DNA double helix will be incorporated into a new strand of DNA.
1. Replication begins at the origins of replication forming replication bubbles
2. Replication proceeds in both directions, forming a replication fork
3. DNA polymerase catalyzes the elongation of the DNA strands, going in the 5’ to 3’
direction. This is the leading strand
4. Elongation of the lagging strand in the 3’ to 5’ direction, must be accomplished with the
assistance of Okazaki fragments. These are small segments of DNA synthesized, with
ligase going back to join together the Okazaki fragments.
DNA synthesis is primed using RNA primer (RNA nucleotides joined together by primase).
The machinery that uses DNA to synthesize proteins read nucleotide sequences in triplet code
with each three nucleotides being one codon Each codon will code for an amino acid. In
transcription DNA is transcribed into messenger RNA (mRNA). The RNA will be processed,
given a 5’ cap and poly (A) tail after having its introns excised by snRNPs (small nuclear
ribonucleoproteins) and spliceosomes
Translation is the process by which the codons are changed into a sequence of amino acids.
Transfer RNA (tRNA) holds an amino acid corresponding to the anticodon that will match to
the codon on a strip of mRNA. As a ribosomal RNA (rRNA) unit proceeds along a piece of mRNA,
tRNAs will bring their amino acids to the translation machinery as necessary, forming a
Gene mutations include point mutations, in which only one base pair is changed. An insertion
or deletion is more detrimental, as it will cause a frameshift mutation altering the series of
codons downstream of the mutation. This can either cause a missense (mutated polypeptide
formed) or nonsense mutation (no polypeptide formed).
A virus consists of DNA or RNA enclosed in a protein coat called a capsid Viruses can only
reproduce within a host cell. The bacteriophage can reproduce using the lytic cycle or the
lysogenic cycle In the lytic cycle, the phage will enter a host cell, replicate itself, and cause the
cell to lyse, releasing more infectious phages. In the lysogenic cycle, the phage DNA will
integrate with the host genome, becoming a prophage that is replicated each time the host cell
replicates. At a certain point, the prophage will switch to the lytic phase.
Biotechnology uses recombinant DNA techniques for practical purposes. Scientists have been
able to clone genes by isolating a gene of interest, inserting it into a plasmid, and then inserting
the plasmid into a vector, such as a bacterium. As the bacteria reproduce themselves, copies of
the plasmid and gene of interest will also be reproduced. Restriction enzymes can be used to
cut out desired genes. Gel electrophoresis separates large molecules of DNA based on their
AP Biology Exam Review
rate of movement through agarose gel in an electric field. The polymerase chain reaction
(PCR) is an automated technique to rapidly copy a small piece of DNA. Restriction fragment
length polymorphisms (RFLPs) are noncoding regions in human DNA that are as a DNA
Evolutionary Biology (8%)
Life originated between 3.5 and 4.0 billion years ago, with ancient prokaryotes such as
stromatolites About 2.7 billion years ago, oxygen began to accumulate as photosyntehsis
developed. Eukaryotic life began about 2.1 billion years ago, with multicellular eukaryotes
evolving by 1.2 billion years ago. The Miller -Urey model has shown to be somewhat successful
Millerin producing organic compounds from gases that would have been prevalent on early Earth.
RNA may have been the first genetic material.
Evidence for evolution:
Fossil Record – shows that species have become extinct or evolved into other species.
There are transitional forms linking older fossils to modern species.
Homology – anatomical homologies show structures with anatomical similarities may
have had a common ancestor. Vestigial organs are historical remnants of structures
that had important functions in ancestors. Embryological homologies show homologies
that are not obvious in adult organisms. Molecular homologies help relate distantly
related organisms by going as deep as the universality of the genetic code.
Biogeography – species tend to be more closely related to other species from the same
area than to other species with the same way of life but living in different areas.
Darwin’s theory of natural selection proposes that populations tend to grow exponentially,
overpopulate, and exceed their resources, resulting in a competition and struggle for existence.
In any population, there is genetic variation resulting in an unequal ability of individuals to survive
and reproduce. Only the fittest individuals survive and are able to pass on their traits to
offspring. Evolution occurs as advantageous traits accumulate in a population.
Types of selection:
Stabilizing Selection: eliminates the extremes, favoring the more common intermediate
forms. Leads to greater numbers of an average phenotype.
Disr uptive/Diversifying Selection: increases the extreme types, with lower numbers of
intermediates. Balanced polymorphism one population divided into two distinct types,
Directional Stabilization: moves toward one extreme phenotype.
Sexual sel ection: competition for mates
Artificial selection: humans breeding for certain desired traits
AP Biology Exam Review
PART III: Organisms and Populations (50%)
Diversity of Organisms (8%)
Hierarchical classification uses binomial nomenclature to identify species, using their genus and
species epithet. The hierarchical classification that is most often used is the three-domain,
five-kingdom system, in which domain separate into phyla, which separate into classes, which
separate into orders, which separates into families, which separate into genera, and finally, into
Bacteria: all are single-celled prokaryotes with many being pathogens have a thick,
rigid cell wall containing peptidoglycan
Archaea: unicellular, prokaryotic, includes the extremophiles no peptidoglycan
Eukarya: all organisms have a nucleus and internal organelles
In Eukarya, there are four kingdoms: protista, fungi, plantae, and animalia.
Specialized cells, tissues, and organs larger and more complex animals will have more
Germ layers: Porifera and Cnidaria have only two cell layers, while other animals have
ectoderm mesoderm and endoderm
Bilateral symmetry: the body is organized along a longitudinal axis with right and left
sides mirroring one another.
Cephalization: sensory apparatus and a brain will be clustered at the anterior.
Coelom: There is a progression from acoelomates which have no coelom, to
pseudocoelomates which have a coelom partly lined by mesoderm, and coelomates
which have a coelom completely lined by mesoderm.
Protostomes and deuterostomes: coelomates are divided into these two categories. In
protostomes the first opening becomes the mouth, while in deuterostomes the first
opening becomes the anus with the second opening becoming the mouth.
Structure and Function of Plants and Animals (32%) Plants
Plants are multicelled, eukaryotic, photosynthetic autotrophs. They store extra carbohydrates
as starch, and their cells have cell walls and central vacuoles. Bryophytes are plants without
transport vessels. Tracheophytes have xylem and phloem for support, lignified transport 9 http://guidesbyjulie.blogspot.com/
AP Biology Exam Review
vessels to support the plant, roots, leaves, and a life cycle with a dominant sporophyte
generation. They are divided into gymnosperms and angiosperms
Angiosperms are divided into the monocots and the dicots Monocots have one cotyledon,
scattered vascular bundles in the stem, parallel leaf venation, floral parts in multiples of 3, and
fibrous root systems. Dicots have two cotyledons, vascular bundles arranged in a rung, netlike
leaf venation, floral parts in 4s and 5s, and taproots.
Primary growth involves elongation of the plant down into the soil and up into the air. Be
familiar with the zone of cell division zone of elongation and zone of differentiation
Secondary growth involves increase in girth.
Dermal: endodermis, epidermis, and cells that produce a waxy cuticle. It covers and
protects the plant.
Vascular consists of xylem and phloem Xylem consists of tracheids and vessel
elements, they are used for the transport of water and minerals. Phloem consists of
chains of sieve tube members connected to companion cells. They carry sugars form
the leaves to the rest of the plant by active transport.
Ground: any tissue that is not dermal nor vascular is ground tissue, which functions in
support, storage, and photosynthesis. They consist of parenchymal cells,
collenchymal cells, and sclerenchymal cells.
Roots are responsible for absorbing nutrients from the soil, anchoring the plant, and storing
food. The transpirational pull-cohesion theory states that for each molecule of water that
pullevaporates from a leaf by transpiration, another molecule of water is drawn in at the root to
replace it. Phloem sap is transported using translocation as phloem moves from the sugar
source to the sugar sink
Auxin responsible for phototropisms apical dominance and stimulates stem
Cytokinins: stimulates cytokinesis and cell division, delay senescence by inhibiting
Gibberellins: promote stem and leaf elongation
Abscisic Acid: inhibits growth, enables plants to withstand drought, closes stomata in
time of stress, promotes seed dormancy
Ethylene: promotes fruit ripening, facilitates apoptosis, promotes leaf abscission.
abscission 10 http://guidesbyjulie.blogspot.com/
AP Biology Exam Review Animals
Digestion can either occur in a gastrovascular cavity which has only one opening, or in an
alimentary canal (gastrointestinal tract), which has two openings. In humans, the breakdown
of starch begins in the mouth. The stom ach churns food mechanically and secretes gastric
juice to begin the digestion of proteins. Digestion is completed in the duodenum, where bile will
be used to break down fats. Peptidases continue to break down proteins, nucleases will break
down nucleic acids, and lipases break down fats. Projections called villi absorb the released
nutrients, and a lacteal will absorb fatty acids and glycerol. The large intestine removes
undigested waste, excess water, and produces vitamins.
Gas exchange occurs passively by diffusion, and respiratory surfaces must be thin, moist, and
have large surface area Less complex respiratory systems are external, involving gas exchange
at the skin. Arthropods and crustaceans have internal systems with spiracles. Aquatic animals
have gills that take advantage of countercurrent exchange In humans, air enters the naval
cavity, passing through the larynx and down the trachea and bronchi to bronchioles. Diffusion of
respiratory gases occurs in the alveoli. Oxygen is carried in the human blood by hemoglobin A
drop in pH lowers the affinity of hemoglobin for oxygen (Bohr shift
In the circulatory system, arteries and arterioles carry blood away from the heart under high
pressure, with walls made of thick, elastic, and smooth muscle. Veins and venules carry blood
back to the heart under little pressure. They have thin walls with valves to prevent back flow.
Capillaries allow for the diffusion of nutrients and wastes between cells and blood.
Beginning with the pulmonary circuit, the right ventricle pumps blood to the lungs via the
pulmonary arteries. As the blood flows through capillary beds, it will load oxygen and unload
carbon dioxide. Oxygen-rich blood returns via the pulmonary veins to the left atrium of the
heart. Next, the oxygen-rich blood will flow into the left ventricle, which will pump it out to
body tissues in the systemic circuit.
Blood leaves the left ventricle via the aorta, which conveys blood to arteries leading
throughout the body. First branches supply blood to the heart, and then to the head and
forelimbs. The aorta will then supply oxygen-rich blood to the abdominal organs and legs,
picking up carbon dioxide. Capillaries will rejoin to form venules, which convey blood back to
the veins. Oxygen-poor blood is emptied into the right atrium, where it will flow into the
Osmoregulation is the management of the body’s water and solute concentration. Excretion is
the removal of metabolic wastes, including carbon dioxide and water from cell respiration and
nitrogenous wastes from protein metabolism. The kidneys are responsible for filter blood and
producing urine. The functional unit of the kidney is the nephron
AP Biology Exam Review
The central nervous system (CNS) consists of the brain and spinal cord. The peripheral
nervous system consists of all nerves outside the CNS. The peripheral nervous system is
further divided into the sensory system and motor system. The simplest nerve response is a
reflex arc such as the knee-jerk reflex, which only consists of a sensory neuron and motor
neuron. An action potential can be generated in the axon of a neuron, which will result in
depolarization of the membrane as potassium floods out of the cell. This causes an impulse to
move along the axon.
The first line of nonspecific defense prevents pathogens from entering the body and includes
skin, mucous membranes, cilia, and stomach acid. The second line of defense is also
nonspecific, and includes the inflammatory response, phagocytes, interferons, and natural killer
cells. The third line of defense is specific and consists of lymphocytes – B lymphocytes and T
lymphocytes. B lymphocytes produce the humoral response by producing antibodies T antibodies.
lymphocytes fight pathogens in the cell -mediated response They kill body cells that have
been infected by recognizing protein fragments displayed by MHC molecules
Fertilization, the fusion of sperm and ovum nuclei, begins with the acrosome reaction when
the head of the sperm releases hydrolytic enzymes that penetrate the egg. This will cause the
cortical reaction as the vitelline layer hardens. Embryonic development consists of cleavage
gastrulation and organogenesis Cleavage is the rapid mitotic division. Protostomes have
spiral, determinant cleavage. Deuterostomes have radial and indeterminate cleavage.
Gastrulation involves the formation of the blastopore. Organogenesis involves differentiation of
Ecology is the study of the interactions of organisms with their physical environment and with
each other. A population is a group of individuals of one species living in one area at one time.
Two models of population growth are exponential growth, modeled by the J-curve, and logistic
growth modeled by the S-curve. The logistic growth model involves a limit the number of
individuals that can occupy one area in a particular time, known as the carrying capacity (K)
Limiting factors to population growth are either density-dependent or density-independent
There are two growth patterns: r -strategists which have many young, little or no parenting,
rapid maturation, small young, and one-time reproduction, versus K-strategists which have
few young, intensive parenting, slow maturation, large young, and reproduction many times.
Symbiosis is an important element in interactions between organisms and can be either
mutualistic (both benefit), parasitic (one is helped, one is harmed), or commensal (one is
helped, one is neither helped nor harmed). Other means of interactions are competition and
AP Biology Exam Review
The food chain is the pathway along which food is transferred from one trophic level to
another. Energy transfer is very inefficient, with only about 10% being transferred to the next
Primary ecological succession occurs in an area where an ecosystem has been completely
destroyed. The first organisms will be pioneer organisms such as lichen and mosses. Soil must
develop through the weathering of rock and accumulation of organic material. Secondary
succession occurs when an existing community is cleared, but the soil is intact.
Biomes are very large regions of the earth whose distribution depends on rainfall and
temperature Each biome has different vegetation and plant life. The basic groupings are
marine, tropical rainforest, desert, temperate grasslands, temperate deciduous forest, taiga, and
Chemical cycles are nature’s way of recycling. In the water cycle water evaporates form the
earth, forms clouds, and rains over oceans and land. In the carbon cycle cellular respiration
adds carbon dioxide to the air and removes oxygen. Photosynthesis will remove the carbon
dioxide from the air and add oxygen. In the nitrogen cycle atmospheric nitrogen is fixed into a
form usable by plants. Bacteria will then convert the nitrates back into atmospheric nitrogen.
Humans have had an effect on the biosphere through eutr ophicat ion of lakes , air pol lution
causing acid rain, t ox i ns, gl obal warming, and int roduci ng new s pecies.
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