5 Steps to a 5: AP Biology - Mark Anestis 2021

Glossary

abiotic components The nonliving players in an ecosystem, such as climate and nutrients.

abscisic acid Plant hormone that inhibits cell growth, prevents premature germination, and stimulates closing of the stomata.

achondroplasia Autosomal dominant form of dwarfism seen in 1 out of 10,000 people.

ACTH See adrenocorticotropic hormone.

active site Part of the enzyme that interacts with the substrate in an enzyme—substrate complex.

active transport The movement of a particle across a selectively permeable membrane against its concentration gradient. This movement requires the input of energy, which is why it is termed “active” transport.

adaptation A trait that, if altered, affects the fitness of the organism. Adaptations are the result of natural selection and can include not only physical traits such as eyes and fingernails but also the intangible traits of organisms, such as lifespan.

adaptive radiation A rapid series of speciation events that occur when one or more ancestral species invades a new environment.

ADH See antidiuretic hormone.

adrenocorticotropic hormone (ACTH) A hormone that stimulates the secretion of adrenal cortical hormones, which work to maintain electrolytic homeostasis in the body.

aerobic respiration Energy-producing reactions in animals that involve three stages: glycolysis, the Krebs cycle, and oxidative phosphorylation; requires oxygen.

age structure Statistic that compares the relative number of individuals in the population from each age group.

agonistic behavior Behavior that results from a conflict of interest between individuals; often involves intimidation and submission.

alcohol Organic compound that contains a hydroxyl (—OH) functional group.

alcohol fermentation Occurs in fungi, yeast, and bacteria. Pyruvate is converted in two steps to ethanol, regenerating two molecules of NAD⁺.

aldehyde Carbonyl group in which one R is a hydrogen and the other is a carbon chain. Hydrophilic and polar.

aldosterone Released from the adrenal gland, this hormone acts on the distal tubules to cause the reabsorption of more Na⁺ and water. This increases blood volume and pressure.

allantois Transports waste products in mammals to the placenta. Later it is incorporated into the umbilical cord.

allele A variant of a gene for a particular character.

allopatric speciation Interbreeding ceases because some sort of barrier separates a single population into two (an area with no food, a mountain, etc.). The two populations evolve independently, and if they change enough, then, even if the barrier is removed, they cannot interbreed.

alternation of generations Plant life cycle, so named because during the cycle, plants sometimes exist as a diploid organism and at other times as a haploid organism.

altruistic behavior Behavior pattern that reduces the overall fitness of one organism while increasing the fitness of another.

alveoli Functional unit of the lung where gas exchange occurs.

amines Compounds containing amino groups.

amino acid A compound with a carbon center surrounded by an amino group, a carboxyl group, a hydrogen, and an R group that provides an amino acid’s unique chemical characteristics.

aminoacyl tRNA synthetase Enzyme that makes sure that each tRNA molecule picks up the appropriate amino acid for its anticodon.

amino group A functional group that contains —NH₂ and that acts as a base; an example is an amino acid.

amnion Structure formed from epiblast that encloses the fluid-filled cavity that helps cushion the developing embryo.

amygdala The portion of the human brain that controls impulsive emotions and anger.

amylase Enzyme that breaks down the starches in the human diet to simpler sugars such as maltose, which are fully digested farther down in the intestines.

anaerobic respiration Energy-producing reactions, known as fermentation, that do not involve oxygen. It begins with glycolysis and concludes with the formation of NAD⁺.

anemia Illness in which a lack of iron causes red blood cells to have a diminished capacity for delivering oxygen.

aneuploidy The condition of having an abnormal number of chromosomes.

angiosperm Flowering plant divided into monocots and dicots (monocotyledons and dicotyledons).

anion Ion with a negative charge that contains more electrons than protons.

anterior pituitary gland Structure that produces six hormones: TSH, STH (or HGH), ACTH, LH, FSH, and prolactin.

anther Pollen-producing portion of a plant.

antheridia Male gametangia in bryophytes and ferns designed to produce flagellated sperm that swim to meet up with the eggs produced by the female gametangia.

anticodon Region present at a tRNA attachment site; a three-nucleotide sequence that is perfectly complementary to a particular codon.

antidiuretic hormone (ADH) A hormone produced in the brain and stored in the pituitary gland; it increases the permeability of the collecting duct to water, leading to more concentrated urine content.

antigen A molecule that is foreign to our bodies and causes our immune systems to respond.

apical meristem Region at the tips of roots and shoots where plant growth is concentrated and many actively dividing cells can be found.

apoplast pathway Movement of water and nutrients through the nonliving portion of cells.

aposematic coloration Warning coloration adopted by animals that possess a chemical defense mechanism.

archaebacteria One of two major prokaryotic evolutionary branches. These organisms tend to live in extreme environments and include halophiles, methanogens, and thermoacidophiles.

archegonium Female gametangia in bryophytes, ferns, and gymnosperms.

archezoa Eukaryotic organism that allegedly most closely resembles prokaryotes.

arteries Structures that carry blood away from the heart.

artificial selection When humans become the agents of natural selection (breeding of dogs).

ascospores Haploid meiotic products produced by certain fungi.

A site Region on protein synthesis machinery that holds the tRNA carrying the next amino acid.

associative learning Process by which animals take one stimulus and associate it with another.

atom The smallest form of an element that still displays its unique properties.

ATP synthase Enzyme that uses the flow of hydrogens to drive the phosphorylation of an adenosine diphosphate molecule to produce adenosine triphosphate.

auditory communication Communication that in-volves the use of sound in the conveying of a message.

autonomic nervous system (ANS) A subdivision of the peripheral nervous system (PNS) that controls the involuntary activities of the body: smooth muscle, cardiac muscle, and glands. The ANS is divided into the sympathetic and parasympathetic divisions.

autosomal chromosome One that is not directly involved in determining gender.

autotroph An organism that is self-nourishing. It obtains carbon and energy without ingesting other organisms.

auxin Plant hormone that leads to elongation of stems and plays a role in phototropism and gravitropism.

axon A longer extension that leaves a neuron and carries the impulse away from the cell body toward target cells.

balanced polymorphism When there are two or more phenotypic variants maintained in a population.

bare-rock succession The attachment of lichen to rocks, followed by the step-by-step arrival of replacement species.

Barr bodies Inactivated genes on X chromosomes.

Batesian mimicry An animal that is harmless copies the appearance of an animal that is dangerous as a defense mechanism to make predators think twice about attacking.

behavioral ecology Science that studies the interaction between animals and their environments from an evolutionary perspective.

bile Substance that contains bile salts, phospholipids, cholesterol, and bile pigments such as bilirubin, is stored in the gallbladder, and is dumped into the small intestine on the arrival of the food.

bile salts Help to mechanically digest fat by emulsifying it into small droplets contained in water.

binary fission Mechanism by which prokaryotic cells divide. The cell elongates and pinches into two new daughter cells.

binomial system of classification System created by Linnaeus in which each species is given a two-word name: Genus + species (e.g., Homo sapiens).

biogeochemical cycles Cycles that represent the movement of elements, such as nitrogen and carbon, from organisms to the environment and back in a continuous cycle.

biomass pyramid Biomass represents the cumulative weight of all of the members at a given trophic level.

biome The various geographic regions of the Earth that serve as hosts for ecosystems.

biosphere The entire life-containing area of a planet—all ecosystems and communities.

biotic components Living organisms of an ecosystem.

biotic potential The maximum growth rate for a population given unlimited resources, unlimited space, and lack of competition or predators.

birth rate Offspring produced per a specific time period.

bivalves Mollusks with hinged shells such as oysters and clams.

blastula As a morula undergoes its next round of cell divisions, fluid fills its center to create this hollow-looking structure.

“blending” hypothesis Theory that the genes contributed by two parents mix as if they are paint colors and the exact genetic makeup of each parent can never be recovered; the genes are as inseparable as blended paint.

bottleneck A dramatic reduction in population size that increases the likelihood of genetic drift.

bronchi Tunnels that branch off the trachea that lead into the individual lungs and divide into smaller branches called bronchioles.

bronchioles Tiny lung tunnels that branch repeatedly until they conclude as tiny air pockets containing alveoli.

brush border Large numbers of microvilli that increase the surface area of the small intestine to improve absorption efficiency.

bryophytes The first land plants to evolve from the chlorophytes. Members of this group include mosses, liverworts, and hornworts.

bundle sheath cells Cells that are tightly wrapped around the veins of a leaf. They are the site for the Calvin cycle in C₄ plants.

C₄ photosynthesis Photosynthetic process that alters the way in which carbon is fixed to better deal with the lack of CO₂ that comes from the closing of the stomata in hot, dry regions.

C₄ plant Plant that has adapted its photosynthetic process to more efficiently handle hot and dry conditions.

Calvin cycle A name for the light-independent (dark) reactions of photosynthesis.

CAM (crassulacean acid metabolism) photo-synthesis Plants close their stomata during the day, collect CO₂ at night, and store the CO₂ in the form of acids until it is needed during the day for photosynthesis.

capsid A protein shell that surrounds genetic material.

carbohydrate Organic compound used by the cells of the human body in energy-producing reactions and as structural material. The three main types of carbohydrates are monosaccharides, disaccharides, and polysaccharides.

carbon cycle The movement of carbon from the atmosphere to living organisms and back to the environment in a continuous cycle.

carbon fixation The attachment of the carbon from CO₂ to a molecule that is able to enter the Calvin cycle, assisted by rubisco.

carbonyl group A functional group that is hydrophilic and polar. It has a central carbon connected to R groups on either side. If both Rs are carbon chains, it is a ketone. If one R is a hydrogen and the other a carbon chain, it is an aldehyde.

carboxyl group An acidic functional group (COOH). This functional group shows up along with amino groups in amino acids.

cardiac muscle Involuntary muscle of the heart that is striated in appearance and contains multiple nuclei.

carnivore A consumer that obtains energy and nutrients through consumption of other animals.

carotenoid A photosynthetic pigment.

carrying capacity The maximum number of individuals a population can sustain in a given environment.

casparian strip Obstacle that blocks the passage of water through the endodermis of plants.

catalase Enzyme that assists in the conversion of hydrogen peroxide to water and oxygen. Found in peroxisomes.

catalysts Molecules that speed up reactions by lowering the activation energy of a reaction.

cation Ion with a positive charge that contains more protons than electrons.

cell body The main body of the neuron.

cell cycle A cycle that consists of four stages: G₁, S, G₂, and M. G₁ and G₂ are growth stages, S is the part of the cell cycle in which the DNA is duplicated, and the M phase stands for mitosis—the cell division phase.

cell-mediated immunity This type of immunity involves direct cellular response to invasion as opposed to antibody-based defense.

cell plate Plant cell structure constructed in the Golgi apparatus composed of vesicles that fuse together along the middle of the cell, completing the separation process.

cellular slime molds Protists with a unique eating strategy. When plenty of food is available, they eat alone. When food is scare, they clump together and form a unit.

cellulose Polysaccharide composed of glucose used by plants to form cell walls.

cell wall Wall that functions to shape and protect cells. Present in plant but not animal cells.

central nervous system (CNS) The CNS is made up of the brain and the spinal cord. The CNS controls skeletal muscles and voluntary movement.

cephalization The concentration of sensory machinery in the anterior end of a bilateral organism.

cerebellum Portion of brain in charge of coordination and balance.

cerebrum Portion of the brain that controls functions such as speech, hearing, sight, and motor control. Divided into two hemispheres and four lobes per hemisphere.

cervix The uterus connects to the vaginal opening via this narrowed region.

CF See cystic fibrosis.

character A heritable feature, such as flower color, that varies among individuals.

checkpoints Stop points throughout the cell cycle where the cell verifies that there are enough nutrients and raw materials to progress to the next stage of the cycle.

chemical communication Mammals and insects communicate through the use of chemical signals called pheromones.

chemiosmosis The coupling of the movement of electrons down the electron transport chain with the formation of ATP using the driving force provided by a proton gradient. Seen in both photosynthesis and respiration.

chemoautotrophs Autotrophs that produce energy through oxidation of inorganic substances.

chitin Polysaccharide that is an important part of the exoskeletons of arthropods such as insects, spiders, and shellfish.

chlorophyll A photosynthetic pigment.

chlorophytes Green algae that are probably the common ancestors of land plants.

chloroplast The site of photosynthesis and energy production in plant cells and algae.

choanoflagellate Accepted to be the common ancestor of the animal kingdom.

choice Refers to the selection of mates by one sex (in mammals, it is usually females who exercise choice over males).

choice chamber Chamber used in scientific experiments to study kinesis.

cholesterol Steroid that is an important structural component of cell membranes and serves as a precursor molecule for steroid sex hormones.

chorion Formed from the trophoblast, it is the outer membrane of the embryo and the site of implantation onto the endometrium. It contributes to formation of the placenta in mammals.

chromatin The raw material that gives rise to the chromosomes (genetic material is uncoiled).

chromosomal translocations Condition in which a piece of one chromosome is attached to another, nonhomologous chromosome.

chromosome duplication Error in chromosomal replication that results in the repetition of a genetic segment.

chromosome inversion Condition in which a piece of a chromosome separates and reattaches in the opposite direction.

chronic myelogenous leukemia A cancer affecting white blood cell precursor cells. In this disease, a portion of chromosome 22 has been swapped with a piece of chromosome 9.

chymotrypsin Enzyme that cuts protein bonds in the small intestine.

cilia Structures that beat in rhythmical waves to carry foreign particles and mucus away from the lungs.

circadian rhythm A physiologic cycle that occurs in time increments that are roughly equivalent to the length of a day.

class I histocompatibility antigens The surface of all the cells of the human body, except for red blood cells, have these antigens, which are slightly different for each individual. The immune system accepts any cell that has the identical match for this antigen as friendly. Anything with a different major histocompatibility complex is foreign.

class II histocompatibility antigens Antigens found on the surface of the immune cells of the body. These antigens play a role in the interaction between the cells of the immune system.

classical conditioning Type of associative learning that Ivan Pavlov demonstrated with his experiments involving salivation in dogs.

cleavage divisions Developing embryo divides; cytoplasm is distributed unevenly to the daughter cells while the genetic information is distributed equally.

cleavage furrow Groove formed in animal cells between the two daughter cells; this groove pinches together to complete the separation of the two cells after mitosis.

climax community Final stable stage at the completion of a succession cycle.

clumped dispersion Scenario in which individuals live in packs that are spaced out from each other.

codominance Both alleles express themselves fully in a heterozygous organism.

codon A triplet of nucleotides that codes for a particular amino acid.

coefficient of relatedness Statistic that represents the average proportion of genes that two individuals have in common.

coelom Fluid-filled body cavity found between the body wall and the gut that has a lining and is derived from the mesoderm.

coelomates Animals that contain a true coelum.

coenocytic fungi Fungi that do not contain septae.

coevolution The mutual evolution between two species, which is exemplified by predator—prey relationships.

coleoptile Protective structure found around a grass seedling.

collenchyma cells Live plant cells that provide flexible and mechanical support.

commensalism One organism benefits from the relationship while the other is unaffected.

community A collection of populations of species in a given geographic area.

competent Describes a cell that is ready to accept foreign DNA from the environment.

competition Both species involved are harmed by this kind of interaction. The two major forms of competition are intraspecific and interspecific competition.

competitive inhibition Condition in which an inhibitor molecule resembling the substrate binds to the active site and physically blocks the substrate from attaching.

complement A protein that coats cells that need to be cleared, stimulating phagocytes to ingest them.

compounds Two or more elements combined to form an entity.

conduction Process by which heat moves from a place of higher temperature to a place of lower temperature.

conifers Gymnosperm plants whose reproductive structure is a cone.

conjugation The transfer of DNA between two bacterial cells connected by appendages called sex pili.

conservative DNA replication The original double helix of DNA does not change at all; it is as if the DNA is placed on a copy machine and an exact duplicate is made. DNA from the parent appears in only one of the two daughter cells.

convection Heat transfer caused by airflow.

convergent characters Characters are convergent if they look the same in two species, even though the species do not share a common ancestor.

convergent evolution Two unrelated species evolve in a way that makes them more similar. They both respond the same way to some environmental challenge, bringing them closer together.

cork cambium Area that produces a thick cover for stems and roots. It produces tissue that replaces dried-up epidermis lost during secondary growth.

cork cells Cells produced by the cork cambium that die and form a protective barrier against infection and physical damage.

corpus callosum Bridge that connects the two hemispheres of the brain.

cortex Outer region of the kidney or adrenal gland.

cortisol Stress hormone released in response to physiological challenges.

cotyledon Structure that provides nutrients for a developing angiosperm plant.

cri-du-chat syndrome This syndrome occurs with a deletion in chromosome 5 that leads to mental retardation, unusual facial features, and a small head. Most die in infancy or early childhood.

crossover Also referred to as “crossing over.” When the homologous pairs match up during prophase I of meiosis, complementary pieces from the two homologous chromosomes wrap around each other and are exchanged between the chromosomes. This is one of the mechanisms that allows offspring to differ from their parents.

cryptic coloration Those being hunted adopt a coloring scheme that allows them to blend in to the colors of the environment.

cuticle Waxy covering that protects terrestrial plants against water loss.

cutin Waxy coat that protects plants.

cyclic light reactions Pathway that produces only ATP and uses only photosystem I.

cyclin Protein that accumulates during interphase; vital to cell cycle control.

cystic fibrosis (CF) A recessive disorder that is the most common lethal genetic disease in the United States. A defective version of a gene on chromosome 7 results in the excessive secretion of a thick mucus, which accumulates in the lungs and digestive tract. Left untreated, children with CF die at a very young age.

cytokinesis The physical separation of the newly formed daughter cells during meiosis and mitosis. Occurs immediately after telophase.

cytokinin Plant hormone that promotes cell division and leaf enlargement, and slows down the aging of leaves.

cytoskeleton Provides support, shape, and mobility to cells.

death rate Number of deaths per time period.

deceptive markings Patterns that can cause a predator to think twice before attacking. For example, some insects may have colored designs on their wings that resemble large eyes, making individuals look more imposing than they are.

decomposer See detritivore.

dehydration reaction A reaction in which two compounds merge, releasing H₂O as a product.

deletion A piece of the chromosome is lost in the developmental process.

demographers Scientists who study the theory and statistics behind population growth and decline.

dendrite One of many short, branched processes of a neuron that help send the nerve impulses toward the cell body.

denitrification The process by which bacteria use nitrates and release N₂ as a product.

density-dependent inhibition When a certain density of cells is reached, cell growth will slow or stop. This is because there are not enough raw materials for the growth and survival of more cells.

density-dependent limiting factors Factors related to population size that come into play as population size approaches or passes the carrying capacity. Examples of density-dependent limiting factors include food, waste, and disease.

density-independent limiting factors Factors that limit population growth that have nothing to do with the population size, such as natural disasters and weather.

depolarization The electric potential becomes less negative inside the cell, allowing an action potential to occur.

desert The driest land biome on Earth, which experiences a wide range of temperatures from day to night and exists on nearly every continent.

detritivore A consumer that obtains its energy through the consumption of dead animals and plants; also known as decomposer.

dicot (dicotyledon) An angiosperm plant that has two cotyledons.

diffusion The movement of molecules down their concentration gradients without the use of energy. It is a passive process during which molecules move from a region of higher concentration to a region of lower concentration.

dihybrid cross The crossing of two different characters (BbRr × BbRr). A dihybrid cross between heterozygous gametes gives a 9:3:3:1 phenotype ratio in the offspring.

diploid (2n) An organism that has two copies of each type of chromosome. In humans, this refers to the pairs of homologous chromosomes.

diplomonads A phylum that is associated with the archezoan eukaryotes.

directional selection Occurs when members of a population at one end of a spectrum are selected against and/or those at the other end are selected for.

disaccharide A sugar consisting of two monosaccharides bound together. Common disaccharides include sucrose, maltose, and lactose.

dispersive DNA replication A theory that suggests every daughter strand contains some parental DNA, but it is dispersed among pieces of DNA not of parental origin.

disruptive selection Selection is disruptive when individuals at the two extremes of a spectrum of variation do better than the more common forms in the middle.

distribution Describes the way populations are dispersed over a geographic area.

divergent evolution Two related species evolve in a way that makes them less similar, sometimes causing speciation.

division The classification category that replaces the phylum in plant classification.

DNA methylation The addition of CH₃ groups to the bases of DNA, rendering DNA inactive.

DNA polymerase The main enzyme in DNA replication that attaches to primer proteins and adds nucleotides to the growing DNA chain in a 5′-to-3′ direction.

DNA replication The process by which DNA is copied. This process occurs during the S phase of the cell cycle to ensure that every cell produced during mitosis or meiosis receives the proper amount of DNA.

dominance hierarchy A ranking of power among the members of a group of individuals.

double helix The shape of DNA—two strands held together by hydrogen bonds.

Down syndrome A classic aneuploid syndrome affecting 1 of every 700 children born in the United States. It most often involves a trisomy of chromosome 21, and leads to mental retardation, heart defects, short stature, and characteristic facial features.

Duchenne muscular dystrophy Sex-linked dis-order caused by the absence of an essential muscle protein that leads to progressive weakening of the muscles combined with a loss of muscle coordination.

ecosystem All the individuals of a community and the environment in which it exists.

ectoderm Outer germ layer that gives rise to the nervous system, skin, hair, and nails.

ectothermic animal Animal whose basic metabolic rates increase in response to increases in temperature.

Edwards syndrome The presence of trisomy 18, which occurs in 1 out of every 10,000 live births and affects almost every organ of the body.

electron transport chain (ETC) The chain of molecules, located in the mitochondria, that passes electrons along during the process of chemiosmosis to regenerate NAD⁺ to form ATP. Each time an electron passes to another member of the chain, the energy level of the system drops.

element The simplest form of matter.

embryology The study of embryonic development.

emigration rate Rate at which individuals relocate out of a given population.

endergonic reaction A reaction that requires input of energy to occur. A + B + energy → C.

endocytosis Process by which substances are brought into cells by enclosure into a membrane-created vesicle that surrounds the substance and escorts it into the cell.

endoderm Inner germ layer that gives rise to the inner lining of the gut, digestive system, liver, thyroid, lungs, and bladder.

endodermis Cells that line the innermost layer of the cortex in plants that give rise to the casparian strip.

endometrium Inner wall of the uterus to which the embryo attaches.

endopeptidases Enzymes that initiate the digestion of proteins by hydrolyzing all the polypeptides into small amino acid groups.

endosymbiotic theory Proposes that groups of prokaryotes associated in symbiotic relationships to form eukaryotes (mitochondria and chloroplasts).

endothermic animal Animal whose body temperature is relatively unaffected by external temperature.

enhancer DNA region, also known as a “regulator,” that is located thousands of bases away from the promoter that influences transcription by interacting with specific transcription factors.

enzymes Catalytic proteins that are picky, interacting only with particular substrates. However, the enzymes can be reused and react with more than one copy of their substrate of choice and have a major effect on a reaction.

epiblast Develops into the three germ layers of the embryo: the endoderm, the mesoderm, and the ectoderm.

epidermis (plants) The protective outer coating of plants.

epididymis The coiled region that extends from the testes. This is where the sperm completes its maturation and waits until it is called on to do its duty.

episomes Plasmids that can be incorporated into a bacterial chromosome.

epistasis A gene at one locus alters the phenotypic expression of a gene at another locus. A dihybrid cross involving epistatic genes produces a 9:4:3 phenotype ratio.

esophageal sphincter Valvelike trapdoor between the esophagus and the stomach.

esophagus Structure that connects the throat to the stomach.

estrogen Hormone made (secreted) in ovaries that stimulates development of sex characteristics in women and induces the release of luteinizing hormone (LH) before the LH surge.

ETC See electron transport chain.

ethology The study of animal behavior.

ethylene Plant hormone that initiates the ripening of fruit and the dropping of leaves and flowers from trees.

eubacteria One of two major prokaryotic evolutionary branches. Categorized according to their mode of nutritional acquisition, mechanism of movement, shape, and other characteristics.

eukaryotic cell Complex cell that contains a nucleus, which functions as the control center of the cell, directing DNA replication, transcription, and cell growth. Organisms can be unicellular or multicellular and contain many different membrane-bound organelles.

evaporation Process by which a liquid changes into a vapor form. Functions in thermoregulation for humans when water leaves our bodies in the form of water vapor—sweat.

evolution Descent with modification. Evolution happens to populations, not individuals, and describes change in allele frequencies in populations with time.

excision repair Repair mechanism for DNA replication in which a section of DNA containing an error is cut out and the gap is filled by DNA polymerase.

exergonic reaction A reaction that gives off energy as a product. A + B → energy + C.

exocytosis Process by which substances are exported out of the cell. A vesicle escorts the substance to the plasma membrane, fuses with the membrane, and ejects its contents out of the cell.

exons Coding regions produced during transcription that are glued back together to produce the mRNA that is translated into a protein.

exopeptidases Enzymes that complete the digestion of proteins by hydrolyzing all the amino acids of any remaining fragments.

exponential growth A population grows at a rate that creates a J-shaped curve.

extreme halophiles Archaebacteria that live in environments with high salt concentrations.

F₁ The first generation of offspring, or the first “filial” generation, in a genetic cross.

F₂ The second generation of offspring, or the second “filial” generation, in a genetic cross.

facilitated diffusion The diffusion of particles across a selectively permeable membrane with the assistance of transport proteins that are specific in what they will carry and have a binding site designed for molecules of interest. This process requires no energy.

facultative anaerobe Organisms that can survive in oxygen-rich or oxygen-free environments.

fallopian tube See oviduct.

fats Lipids, made by combining glycerol and fatty acids, used as long-term energy stores in cells. They can be saturated or unsaturated.

fatty acid Long carbon chain that contains a carboxyl group on one end that combines with glycerol molecules to form lipids.

fermentation Anaerobic respiration pathway that occurs in the absence of oxygen; produces less ATP than aerobic respiration.

ferredoxin Molecule that donates the electrons to NADP⁺ to produce NADPH during the light reactions of photosynthesis.

fibrous root system Root system found in monocots that provides the plant with a very strong anchor without going very deep into the soil.

filtration Capillaries allow small particles through the pores of their endothelial linings, but large molecules such as proteins, platelets, and blood cells tend to remain in the vessel.

fixed-action pattern An innate behavior that seems to be a programmed response to some stimulus.

florigen Hormone thought to assist in the blooming of flowers.

fluid mosaic model Model that states that the membrane is made of a phospholipid bilayer with proteins of various lengths and sizes, interspersed with cholesterol.

fluke Parasitic flatworm that alternates between sexual and asexual reproductive cycles.

follicle-stimulating hormone (FSH) A gonadotropin that stimulates activities of the testes and ovaries. In females, it induces the development of the ovarian follicle, leading to the production and secretion of estrogen, and in males it stimulates the production of sperm.

food chain A hierarchical list of who snacks on who. For example, bugs are eaten by spiders, who are eaten by birds, who are eaten by cats.

food web Can be regarded as overlapping food chains that show all the various dietary relationships in an environment.

foraging The behavior of actively searching for and eating a particular food resource.

fossil record The physical manifestation of species that have gone extinct (e.g., bones and imprints).

F-plasmid Plasmid that contains the genes necessary for the production of a sex pillus.

frameshift mutations Deletion or addition of DNA nucleotides that does not add or remove a multiple of three nucleotides. Usually produces a nonfunctional protein unless it occurs late in protein production.

frequency-dependent selection Alleles are selected for or against depending on their relative frequency in a population.

FSH See follicle-stimulating hormone.

functional groups The groups responsible for the chemical properties of organic compounds.

G₁ phase The first growth phase of the cell cycle, which produces all the necessary raw materials for DNA synthesis.

G₂ phase The second growth phase of the cell cycle, which produces all the necessary raw materials for mitosis.

gametangia Protective covering that provides a safe haven for the fertilization of the gametes and the development of the zygote in bryophytes, ferns, and some gymnosperms.

gametes Sex cells produced during meiosis in the human life cycle.

gametophyte A haploid multicellular organism.

gastrulation Cells separate into three primary layers called germ layers, which eventually give rise to the different tissues of an adult.

gene flow The change in frequencies of alleles as genes from one population are incorporated into those from another.

generalized transduction Transduction caused by the accidental placement of host DNA into a phage instead of viral DNA during viral reproduction. This host DNA may find its way into another cell where crossover could occur.

generation time Time needed for individuals to reach reproductive maturity.

genetic code Code that translates codons found on mRNA strands into amino acids.

genetic drift A change in allele frequencies that is due to chance events.

genotype An organism’s genetic makeup for a given trait. A simple example of this could involve eye color, where B represents the allele for brown and b represents the allele for blue. The possible genotypes include homozygous brown (BB), heterozygous brown (Bb), and homozygous blue (bb).

genus Taxonomic group to which a species belongs.

gibberellin Plant hormone that assists in stem elongation and induces growth in dormant seeds, buds, and flowers.

glomerular capillaries The early portion of the nephron where the filtration process begins.

glucagon Hormone that stimulates conversion of glycogen into glucose.

glycerol Three-carbon molecule that combines with fatty acids to produce a variety of lipids.

glycogen Storage polysaccharide made of glucose molecules used by animals.

glycolysis Occurs in the cytoplasm of cells and is the beginning pathway for both aerobic and anaerobic respiration. During glycolysis, a glucose molecule is broken down through a series of reactions into two molecules of ATP, NADH, and pyruvate.

glycoprotein Protein that has been modified by the addition of a sugar.

Golgi apparatus Organelle that modifies proteins, lipids, and other macromolecules by the addition of sugars and other molecules to form glycoproteins. The products are then sent to other parts of the cell.

G-proteins Proteins vital to signal cascade pathways. These proteins directly activate molecules such as adenyl cyclase to assist in a reaction.

gradualism The theory that evolutionary change is a steady, slow process.

grana Flattened channels and disks arranged in stacks found in the thylakoid membrane.

gravitropism A plant’s growth response to gravitational force; auxin and gibberellins are involved in this response.

gross productivity The difference over time between the dissolved oxygen concentrations of the light and dark bottles calculated in primary productivity experiments.

growth factors Assist in the growth of structures.

guard cells Cells within the epidermis of plants that control the opening and closing of the stomata.

gymnosperm First major seed plant to evolve. Heterosporous plant that usually transports its sperm through the use of pollen. Conifers are the major gymnosperm to know.

habituation Loss of responsiveness to unimportant stimuli that do not provide appropriate feedback.

haploid (n) An organism that has only one copy of each type of chromosome.

Hardy-Weinberg equilibrium A special case where a population is in stasis, or not evolving.

helicase Enzyme that unzips DNA, breaking the hydrogen bonds between the nucleotides and producing the replication fork for replication.

helper T cell Immune cells that assist in activation of B cells.

hemoglobin Molecule that allows red blood cells to carry and deliver oxygen throughout the body to hardworking organs and tissues.

hemophilia Sex-linked disorder caused by the absence of a protein vital to the clotting process. Individuals with this condition have difficulty clotting blood after even the smallest of wounds.

herbivore Consumer that obtains energy and nutrients through consumption of plants.

heterosporous plant Plant that produces two types of spores, male and female.

heterotroph An organism that must consume other organisms to obtain nourishment. They are the consumers of the world.

heterotroph theory Theory that posits that the first organisms were heterotrophs (organisms that cannot produce their own food).

heterozygote advantage The situation, such as sickle cell anemia in malarial regions, in which being heterozygous for a condition provides some benefit.

heterozygous (hybrid) An individual is heterozygous (or a hybrid) for a gene if the two alleles are different (Bb).

histamine Chemical signal responsible for initiation of the inflammation response of the immune system.

holandric trait A trait inherited via the Y chro-mosome.

homeobox DNA sequence of a homeotic gene that tells the cell where to put body structures.

homeotic genes Genes that regulate or “direct” the body plan of organisms.

homologous characters Traits are said to be homologous if they are similar because their host organisms arose from a common ancestor.

homologous chromosomes Chromosomes that resemble one another in shape, size, function, and the genetic information they contain. They are not identical.

homosporous plant Plants that produce a single spore type that gives rise to bisexual gametophytes.

homozygous (pure) An individual is homozygous for a gene if both of the given alleles are the same (BB or bb).

honest indicators Sexually selected traits that are the result of female choice and signal genetic quality.

hormones Chemicals produced by glands such as the pituitary and used by the endocrine system to signal distant target cells.

host range The range of cells that a virus is able to infect. For example, HIV infects the T cells of our body.

humoral immunity Immunity involving antibodies and circulating fluids.

Huntington’s disease An autosomal dominant degenerative disease of the nervous system that appears when a person is in their 30s or 40s and is both irreversible and fatal.

hybrid vigor Refers to the fact that hybrids may have increased reproductive success compared to inbred strains. This is due to the fact that inbreeding increases the likelihood that two deleterious, recessive alleles will end up in the same offspring.

hydrolysis reaction A reaction that breaks down compounds by the addition of H₂O.

hydrophilic Water-loving.

hydroxyl group A hydrophilic and polar functional group (—OH) that is present in compounds; known as alcohols.

hypercholesterolemia Recessive disorder (hh) that causes cholesterol levels to be many times higher than normal and can lead to heart attacks in children as young as 2 years old.

hypertonic Characterizes a solution that has a higher solute concentration than does a neighboring solution.

hypha Filament found in fungi made of chitin that separates fungi into multicellular compartments.

hypoblast Forms the yolk sac, which produces the embryo’s first blood cells.

hypothalamus The thermostat and “hunger meter” of the body, regulating temperature, hunger, and thirst.

hypotonic Characterizes a solution that has a lower solute concentration than a neighboring solution.

immigration rate Rate at which individuals relocate into a given population.

imprinting Innate behavior that is learned during a critical period early in life.

inclusive fitness An individual’s fitness gain that is a direct result of his or her contribution to the reproductive effort of closely related kin. This results from the fact that close kin share copies of identical genes.

incomplete dominance Blending inheritance. The heterozygous genotype produces an intermediate phenotype rather than the dominant phenotype; neither allele dominates the other.

induced-fit model Theory that suggests that when an enzyme and a substrate bind together, the enzyme is induced to alter its shape for a tighter active-site/substrate attachment, which places the substrate in a favorable position to react more quickly.

inducer Molecule that binds to and inactivates a repressor.

induction The ability of one group of cells to influence the development of another. This influence can be through physical contact or chemical signaling.

inner cell mass Portion of the blastula that develops into the embryo.

inorganic compounds For the most part, compounds containing no carbon. There are some exceptions such as carbon dioxide, carbon monoxide, and others.

insight learning The ability to do something correctly the first time even with no prior experience.

insulin Hormone secreted in response to high blood glucose levels to promote glycogen formation.

integral proteins Proteins that are implanted within the bilayer and can extend part way or all the way across the membrane.

intermediate filaments Substances constructed from a class of proteins called keratins; function as reinforcement for the shape and position of organelles in a cell.

intermediate inheritance An individual heterozygous for a trait (Yy) shows characteristics not exactly like those of either parent. The phenotype is a “mixture” of both of the parents’ genetic input.

interneurons Function to make synaptic connections with other neurons. They work to integrate sensory input and motor output.

interphase The first three stages of the cycle, G₁, S, and G₂. Accounts for approximately 90 percent of the cell cycle.

interspecific competition Competition between different species that rely on the same resources for survival.

interstitial cells The structures that produce the hormones involved in the male reproductive system.

intraspecific competition Within-species competition that occurs because members of the same species rely on the same valuable resources for survival.

introns Noncoding regions produced during transcription that are cut out of the mRNA.

invertebrate Animal without a backbone.

ion An atom with a positive or negative charge.

isotonic solution Solution that has the same solute concentration as surrounding solutions.

karyotype A chart that organizes chromosomes in relation to number, size, and type.

ketone Carbonyl group in which both Rs are carbon chains; hydrophilic and polar.

kinesis A random change in the speed of movement in response to a stimulus. Organisms speed up in places they don’t like and slow down in places they do like.

kingdom The broadest of the classification groups.

Klinefelter syndrome (XXY) Syndrome in which individuals have male sex organs but are sterile and display several feminine body characteristics.

Krebs cycle Energy-producing reaction that occurs in the matrix of the mitochondria, in which pyruvate is broken down completely to H₂O and CO₂ to produce 3 NADH, 1 FADH₂, and 1 ATP.

K-selected populations Populations of a roughly constant size whose members have low reproductive rates. The offspring produced by K-selected organisms require extensive postnatal care.

lac operon Operon that aids in control of transcription of lactose metabolizing genes.

lactic acid fermentation Occurs in human muscle cells when oxygen is unavailable. Pyruvate is directly reduced to lactate by NADH to regenerate the NAD⁺ needed for the resumption of glycolysis.

lagging strand The discontinuous strand produced during DNA replication.

larynx Passageway from the pharynx to the trachea; commonly called the “voicebox.”

lateral meristems Cells that extend all the way through the plant from roots to shoots and provide the secondary growth that increases the girth of a plant.

lateral roots Roots that serve to hold a plant in place in the soil.

law of dominance When two opposite pure-breeding varieties (homozygous dominant vs. homozygous recessive) of an organism are crossed, all the offspring resemble one parent. This is referred to as the “dominant” trait. The variety that is hidden is referred to as the “recessive” trait.

law of independent assortment Members of each pair of factors are distributed independently when the gametes are formed. In other words, inheritance of one particular trait or characteristic does not interfere with inheritance of another trait (in unlinked genes). For example, if an individual is BbRr for two genes, gametes formed during meiosis could contain BR, Br, bR, or br. The B and b alleles assort independently of the R and r alleles.

law of multiplication Law that states that to determine the probability that two random events will occur in succession, you simply multiply the probability of the first event by the probability of the second event.

law of segregation Every organism carries pairs of factors, called alleles, for each trait, and the members of the pair segregate out (separate) during the formation of gametes. For example, if an individual is Bb for eye color, during gamete formation one gamete would receive a B and the other made from that cell would receive a b.

leading strand The continuous strand produced during DNA replication.

LH See luteinizing hormone.

LH surge Giant release of LH that triggers ovulation—the release of a secondary oocyte from the ovary.

lichen A symbiotic collection of organisms (fungus and algae) living as one.

life cycle Sequence of events that make up the reproductive cycle of an organism.

limiting factors Environmental factors that keep population sizes in check (predators, diseases, food supplies, and waste).

linkage map A genetic map put together using crossover frequencies.

linked genes Genes along the same chromosome that tend to be inherited together because the chromosome is passed along as a unit.

lipase The major fat-digesting enzyme of the human body.

lipids Hydrophobic organic compounds used by cells as energy stores or building blocks. Three important lipids are fats, steroids, and phospholipids.

logistic growth A population grows at a rate that creates an S-shaped curve.

long-day plants Plants, such as spinach, which flower if exposed to a night that is shorter than a critical period.

luteinizing hormone (LH) A gonadotropin that stimulates ovulation and formation of a corpus luteum, as well as the synthesis of estrogen and progesterone.

lymphatic system Important part of the circulatory system that functions as the route by which proteins and fluids that have leaked out of the bloodstream can return to circulation. The lymphatic system also functions as a protector for the body because of the presence of lymph nodes.

lymph nodes Structures found in the lymphatic system that are full of white blood cells, which live to fight infection. These nodes often swell up during infection as a sign of the body’s fight against the infectious agent.

lymphocyte White blood cell. There are two main types of lymphocytes: B cells and T cells. These cells are formed in the bone marrow of the body and arise from stem cells.

lysogenic cycle The virus falls dormant and incorporates its DNA into the host DNA as an entity called a provirus. The viral DNA is quietly reproduced by the cell every time the cell reproduces itself, and this allows the virus to stay alive from generation to generation without killing the host cell.

lysosome Membrane-bound organelle that specializes in digestion and contains enzymes that break down proteins, lipids, nucleic acids, and carbohydrates.

lysozyme An enzyme, present in saliva and tears, that can kill germs before they have a chance to take hold.

lytic cycle The cell actually produces many viral offspring, which are released from the cell, killing the host cell in the process.

macroevolution The big picture of evolution, which includes the study of evolution of groups of species over very long periods of time.

macronucleus A nucleus present in some protists (Ciliophora) and which controls the everyday activities of organisms.

macrospores Female gametophytes produced by heterosporous plants.

map unit Also termed centigram. Unit used to geographically relate the genes on the basis of crossover frequencies. One map unit is equal to a 1 percent recombination frequency.

matter Anything that has mass and takes up space.

mechanical digestion The physical breakdown of food that comes from chewing.

medulla Inner region of the kidney.

medulla oblongata The control center for involuntary activities such as breathing.

medusa A cnidarian that is flat and roams the waters looking for food (e.g., jellyfish).

melatonin Hormone that is known to be involved in our biological rhythms (circadian).

memory cells Stored instructions on how to handle a particular invader. When an invader returns to the body, the memory cells recognize it, produce antibodies in rapid fashion, and eliminate the invader very quickly.

meristemic cells Cells that allow plants to grow indeterminately.

mesoderm Intermediate germ layer that gives rise to muscle, the circulatory system, the reproductive system, excretory organs, bones, and connective tissues of the gut and exterior of the body.

mesophyll Interior tissue of a leaf.

mesophyll cells Cells that contain many chloroplasts and host the majority of photosynthesis.

methanogens Archaebacteria that produce methane as a by-product.

microevolution Evolution at the level of species and populations.

microfilaments Substances built from actin that play a major role in muscle contraction.

micronucleus A nucleus present in some protists (Ciliophora) and which functions in conjugation.

microspores Male gametophytes produced by heterosporous plants.

microtubules Substances constructed from tubulin; play a lead role in the separation of cells during cell division; are also important components of cilia and flagella.

migration This is a cyclic movement of animals over long distances according to the time of year.

mismatch repair Process during DNA replication by which DNA polymerase replaces an incorrectly placed nucleotide with proper nucleotide.

missense mutation Substitution of the wrong nucleotides into the DNA sequence. These substitutions still result in the addition of amino acids to the growing protein chain during translation, but they can sometimes lead to the addition of incorrect amino acids to the chain.

mitochondrion Double-membraned organelle that specializes in the production of ATP; host organelle for the Krebs cycle (matrix) and oxidative phosphorylation (cristae).

mitotic spindle Apparatus constructed from microtubules that assists in the physical separation of the chromosomes during mitosis.

monocot (monocotyledon) Angiosperm with a single cotyledon.

monohybrid cross A cross that involves a single character in which both parents are heterozygous (Bb × Bb). A monohybrid cross between heterozygous gametes gives a 3:1 phenotype ratio in the offspring.

monosaccharide The simplest form of a carbohydrate. The most important monosaccharide is glucose, which is used in cellular respiration to provide energy for cells.

morula A structure formed during the cleavage divisions of the zygote.

motor neurons Nerve cells that take the commands from the central nervous system (CNS) and put them into action as motor outputs.

M phase mitosis This is the stage during which the cell separates into two new cells.

Müllerian mimicry Two species that are aposematically colored as an indicator of their chemical defense mechanism; they mimic each other’s color scheme in an effort to increase the speed with which predators learn to avoid them.

mutant phenotypes Characters that are not the wild-type strain in fruit flies and other organisms.

mutation A random event that can cause changes in allele frequencies. It is always random with respect to which genes are affected, although the changes in allele frequencies that occur as a result of the mutation may not be.

mutualism Scenario in which two organisms benefit from an interaction or relationship.

mycelium Meshes of branching filaments formed from hyphae that function as mouthlike structures for fungi.

myelinated neurons Neurons with a layer of insulation around the axon, allowing for faster transmission. They form the cable Internet of the body.

natural selection The process by which characters or traits are maintained or eliminated in a population based on their contribution to the differential survival and reproductive success of their “host” organisms.

negative feedback Occurs when a hormone acts to directly or indirectly inhibit further secretion of the hormone of interest.

nephron The functional unit of the kidney.

net productivity Difference between the concentration of dissolved oxygen for the initial and light bottle in a primary productivity experiment.

neural plate Structure that becomes the neural groove, which eventually becomes the neural tube. This neural tube later gives rise to the central nervous system.

neural tube Embryonic structure that gives rise to the central nervous system.

neuromuscular junction The space between the motor neuron and the muscle cell.

neurotransmitter Chemical released by neurons that functions as a messenger, causing a nearby cell to react and continue the nervous impulse.

niche Term used to describe all the biotic and abiotic resources used by the organism.

nitrogen cycle The shuttling of nitrogen from the atmosphere, to living organisms, and back to the atmosphere in a continuous cycle.

nitrogen fixation The conversion of N₂ to NH₃ (ammonia).

nitrogenous bases Monomers such as adenine, guanine, cytosine, thymine, and uracil out of which DNA and RNA are constructed.

noncompetitive inhibition Condition in which an inhibitor molecule binds to an enzyme away from the active site, causing a change in the shape of the active site so that it can no longer interact with the substrate.

noncyclic light reaction Pathway that produces ATP, NADPH, and O₂. Uses both photosystem I and II.

nondisjunction The improper separation of chromosomes during meiosis, which leads to an abnormal number of chromosomes in offspring. Examples include Down syndrome, Turner syndrome, and Klinefelter’s syndrome.

nonsense mutation Substitution of the wrong nucleotides into the DNA sequence. These substitutions lead to premature stoppage of protein synthesis by the early placement of a stop codon. This type of mutation usually leads to a nonfunctional protein.

nonspecific immunity The nonspecific prevention of the entrance of invaders into the body.

notochord Structure that serves to support the body; found in the embryos of chordates.

nucleic acid Macromolecule composed of nucleotides, sugars, and phosphates that serves as genetic material of living organisms (DNA and RNA).

nucleoid Region of a prokaryotic cell that contains the genetic material.

nucleolus Eukaryotic structure in which ribosomes are constructed.

nucleus The control center of eukaryotic cells that is the storage site of the genetic material (DNA). It is the site of replication, transcription, and posttranscriptional modification of RNA.

obligate aerobe Organism that requires oxygen for respiration.

obligate anaerobe Organism that only survives in oxygen-free environments.

observational learning The ability of an organism to learn how to do something by watching another individual do it first.

oil Type of lipid.

Okazaki fragments The lagging DNA strand consists of these tiny pieces that are later connected by an enzyme, DNA ligase, to produce the completed double-stranded daughter DNA molecule.

ontogeny The development of an individual.

oogenesis Process by which female gametes are formed. Each meiotic cycle leads to the production of a single ovum, or egg.

operant conditioning Type of associative learning that is based on trial and error.

operator A short sequence near the promoter that assists in transcription by interacting with regulatory proteins (transcription factors).

operon A promoter/operator pair that services multiple genes.

opportunistic populations R-selected organisms that tend to appear when space in the region opens up due to some environmental change. They grow fast, reproduce quickly, and die quickly as well.

optimal foraging Theory that predicts that natural selection will favor animals that choose foraging strategies that maximize the differential between benefits and costs.

organic compounds Carbon-containing compounds. Important examples include carbohydrates, proteins, lipids, and nucleic acids.

osmosis The passive diffusion of water down its concentration gradient across selectively permeable membranes. It will flow from a region with a lower solute concentration (hypotonic) to a region with a higher solute concentration (hypertonic).

outbreeding Mating between unrelated individuals of the same species.

ovary The site of egg production. In animals, females often have two, one on either side of the body. Plants usually only have one ovary.

oviduct Known also as the fallopian tube, this is the site of fertilization and connects the ovary to the uterus. Eggs move through here from the ovary to the uterus (in animals only).

ovulation Stage of menstrual cycle in which the secondary oocyte is released from the ovary.

oxaloacetate Compound that plays an important role in C₄ photosynthesis of plants and the Krebs cycle in animals.

oxidative phosphorylation Aerobic process in which NADH and FADH₂ pass their electrons down the electron transport chain to produce ATP.

oxytocin Hormone that stimulates uterine contraction and milk ejection for breastfeeding.

P₁ The parent generation in a genetic cross.

palisade mesophyll Host to many chloroplasts and much of the photosynthesis of a leaf.

parallel evolution Similar evolutionary changes occurring in two either related or unrelated species that respond in a similar manner to a similar environment.

parasitism Scenario in which one organism benefits at the other’s expense.

parasympathetic nervous system Branch of autonomic nervous system that shuts down the body to conserve energy.

parathyroid hormone (PTH) Hormone that increases serum concentration of Ca²⁺, assisting in the process of bone maintenance.

parenchyma cells Plant cells that play a role in photosynthesis (mesophyll cells), storage, and secretion.

Patau syndrome Presence of trisomy 13, which occurs in about 1 out of every 12,000—16,000 live births and causes serious brain and circulatory defects.

pedigrees Family trees used to describe the genetic relationships within a family. One use of a pedigree is to determine whether parents will pass certain conditions to their offspring.

pepsin The major enzyme of the stomach, which breaks down proteins into smaller polypeptides to be handled by the intestines.

pepsinogen The precursor to pepsin that is activated by active pepsin (a small amount of which normally exists in the stomach).

peripheral nervous system (PNS) The PNS can be broken down into a sensory and a motor division. The sensory division carries information to the CNS while the motor division carries information away from the CNS.

peripheral proteins Proteins, such as receptor proteins, not implanted in the bilayer, which are often attached to integral proteins of the membrane.

peristalsis The force created by the rhythmic contraction of the smooth muscle of the esophagus and intestines.

permafrost Frozen layer of soil just underneath the upper soil layer, found in the tundra biome.

peroxisome Organelle that functions to break down fatty acids, and detoxify.

petals Structures that serve to attract pollinators.

PGAL (phosphoglyceraldehyde) Molecule important to energy-producing reactions photosynthesis and respiration.

phage A virus that infects bacteria.

phagocytes Immune cells (macrophages and neutrophils) that use endocytosis to engulf and eliminate foreign invaders.

pharynx Tube through which both food and air pass after leaving the mouth.

phenotype The physical expression of the trait associated with a particular genotype. Some examples of the phenotypes for Mendel’s peas were round or wrinkled, green or yellow, purple flower or white flower.

phenylketonuria (PKU) An autosomal recessive disease caused by a single gene defect that leaves a person unable to break down phenylalanine, which results in a by-product that can accumulate to toxic levels in the blood and cause mental retardation.

pheromones Chemical signals important to communication.

phloem Important part of plant vascular tissue that functions to transport sugars from their production site to the rest of the plant.

phosphate group An acidic functional group that is a vital component of molecules that serve as cellular energy sources: ATP, ADP, and GTP.

phospholipid Lipid with both a hydrophobic tail and a hydrophilic head; the major component of cell membranes with the hydrophilic phosphate group forming the outside portion and the hydrophobic tail forming the interior of the wall.

photoautotrophs Photosynthetic autotrophs that produce energy from light.

photolysis Process by which water is broken up by an enzyme into hydrogen ions and oxygen atoms. Occurs during the light reactions of photosynthesis.

photoperiodism The response by a plant to the change in the length of days.

photophosphorylation Process by which ATP is made during the light-dependent reactions of photosynthesis. It is the chloroplast equivalent of oxidative phosphorylation.

photorespiration Process by which oxygen competes with carbon dioxide and attaches to RuBP. Plants that experience photorespiration have a lowered capacity for growth.

photosynthesis The process by which plants generate energy from light and inorganic raw materials. This occurs in the chloroplasts and involves two stages: the light-dependent reactions and the light-independent reactions.

photosystem Cluster of light-trapping pigments involved in the process of photosynthesis.

phototaxis Reflex movement toward light at night.

phototropism A plant’s growth in response to light. Auxin is the hormone involved with this process.

phycobilin Photosynthetic pigment.

phylogeny The evolutionary history of a species.

phytochrome Important pigment in the process of flowering. Leads to the production of florigen.

pigment A molecule that absorbs light of a particular wavelength.

pioneer species A species that is able to survive in resource-poor conditions and takes hold of a barren area such as a volcanic island. Pioneer species do the grunt work, adding nutrients and other improvements to the once-uninhabited volcanic rock until future species take over.

PKU See phenylketonuria.

placenta In humans, this structure provides the nutrients for the developing embryo.

planarians Free-living platyhelminthe carnivores that live in the water.

plasma The liquid portion of the blood that contains minerals, hormones, antibodies, and nutritional materials.

plasma cells The factories that produce antibodies that eliminate any cell containing on its surface the antigen that the plasma cell has been summoned to kill.

plasma membrane Selective barrier around a cell composed of a double layer of phospholipids that controls what is able to enter and exit a cell.

plasmids Extra circles of DNA in bacteria that contain just a few genes and have been useful in genetic engineering. Plasmids replicate independently of the main chromosome.

plasmodial slime molds Nonphotosynthetic heterotrophic funguslike protists. They eat and grow as a unified clumped unicellular mass known as a plasmodium.

plasmodium This word has two meanings in this book. It can be the causative agent of malaria, or it can be the clumped unicellular mass that fungi form under certain feeding conditions.

plasmolysis The shriveling of the cytoplasm of a cell in response to loss of water in hypertonic surroundings.

platelet Blood cell involved in the clotting of blood.

pleiotropy A single gene has multiple effects on an organism.

PNS See peripheral nervous system.

polar A molecule that has an unequal distribution of charge, which creates a positive and a negative side to the molecule.

polar body Castaway cell produced during female gamete formation that contains only genetic information.

pollen Sperm-bearing male gametophyte of gymno-sperms and angiosperms.

polygenic traits Traits that are affected by more than one gene (e.g., eye color).

polymerase chain reaction Technique used to create large amounts of a DNA sequence in a short amount of time.

polyp Cylinder-shaped cnidarian that lives attached to a surface (e.g., sea anemone).

polyploidy A condition in which an individual has more than the normal number of sets of chromosomes.

polysaccharide A carbohydrate usually composed of hundreds or thousands of monosaccharides, which acts as a storage form of energy, and as structural material in and around cells. Starch and glycogen are storage polysaccharides; cellulose and chitin are structural polysaccharides.

pond succession Process by which a hole filled with water passes through the various succession stages until it has become a swamp, forest, or grassland.

population A collection of individuals of the same species living in the same geographic area.

population cycle When a population size dips below the carrying capacity, it will later come back to the capacity and even surpass it. However, the population could dip below the carrying capacity as a result of some major change in the environment and equilibrate at a new, lower carrying capacity.

population density The number of individuals per unit area in a given population.

population ecology The study of the size, distribution, and density of populations and how they change with time.

positive feedback Occurs when a hormone acts to directly or indirectly cause increased secretion of a hormone.

posterior pituitary gland Structure that produces only two hormones: ADH and oxytocin.

potometer Lab apparatus used to measure transpiration rates in plants.

predation Scenario in which one species, the predator, hunts another species, the prey.

primary consumers The consumers that obtain energy through consumption of the producers of the planet; known as herbivores.

primary immune response When a B cell meets and attaches to the appropriate antigen, it becomes activated and undergoes mitosis and differentiation into plasma cells and memory cells.

primary oocytes Cells that begin the process of meiosis and progress until prophase I, where they sit halted until the host female enters puberty.

primary plant growth Increase in the length of a plant.

primary productivity Rate at which carbon-containing compounds are stored.

primary sex characteristics The sexual organs that assist in the vital process of procreation; include the testes, ovaries, and uterus.

primary spermatocytes Produced by mitotic division, these cells immediately undergo meiosis I to produce two secondary spermatocytes, which undergo meiosis II to produce four spermatids.

primary structure The sequence of the amino acids that make up a protein.

primary succession Succession that occurs in an area that is devoid of life and contains no soil.

primer sites DNA segments that signal where replication should originate.

prion Incorrectly folded form of a brain cell protein that works by converting other normal host proteins into misshapen proteins. Prion diseases tend to cause dementia, muscular control problems, and loss of balance.

progesterone Hormone involved in menstrual cycle and pregnancy.

prokaryotic cell A simple cell with no nucleus, or membrane-bound organelles; divides by binary fission and includes bacteria—both heterotrophic and autotrophic types.

prolactin Hormone that controls the production of milk and leads to a decrease in the synthesis and release of GnRH, thus inhibiting ovulation.

promoter region A recognition site that shows the polymerase where transcription should begin.

prostate gland Structure whose function in the male reproductive system is to add a basic (pH > 7) liquid to the mix to help neutralize the acidity of the urine that may remain in the common urethral passage.

protein Organic compound composed of chains of amino acids that function as structural components, transport aids, enzymes, and cell signals, among other things.

protein hormones Hormones too large to move inside a cell, and which bind to receptors on the surface of the cell instead.

protein kinase Protein that controls the activities of other proteins through the addition of phosphate groups.

provirus A virus genome that is integrated into the DNA of a host cell that can be transmitted from one generation to the next without causing lysis.

pseudocoelomate Animal that has a fluid-filled body cavity that is not enclosed by mesoderm.

pseudopods Extensions from protists (organisms of the kingdom Protist) that assist in collection of nutrients.

P site Region in protein synthesis machinery that holds the tRNA carrying the growing protein.

PTH See parathyroid hormone.

punctuated equilibria model Theorizes that evolutionary change occurs in rapid bursts separated by large periods of stasis (no change).

purine A nitrogenous base that contains a double ring structure (adenine, guanine).

pyloric sphincter The connection point between the stomach and the small intestine.

pyramid of numbers Pyramid based on the number of individuals at each level of the biomass chain. Each box in this pyramid represents the number of members of that level. The highest consumers in the chain tend to be quite large, resulting in a smaller number of those individuals spread out over a given area.

pyrimidine A nitrogenous base that contains a single ring structure (cytosine, thymine).

Q₁₀ value Statistic that shows how an increase in temperature affects the metabolic activity of an organism.

quaternary structure The arrangement of separate polypeptide “subunits” into a single protein. Seen only in proteins with more than one polypeptide chain.

radiation The loss of heat through ejection of electromagnetic waves.

random distribution Random distribution of species in a given geographic area.

rate of reaction Rate at which a chemical reaction occurs.

reaction centers Control centers made up of pigments.

reciprocal altruism Altruistic behavior performed with the expectation that the favor will be returned.

recombinant DNA DNA that contains DNA pieces from multiple sources.

red blood cells Cells in body that contain hemo-globin and serve as the oxygen delivery system in the body.

red-green colorblindness Sex-linked condition that leaves those afflicted unable to distinguish between red and green colors.

redox reaction A reduction—oxidation reaction involving the transfer of electrons.

replication fork Fork opened in DNA strand that allows DNA replication to occur.

repolarization The lowering of the potential back down to its initial level, stopping the transmission of neural signals at that point.

repressor Protein that prevents the binding of RNA polymerase to the promoter site.

reproductive success A measure of how many surviving offspring one produces relative to how many the other individuals in one’s population produce.

RER See rough endoplasmic reticulum.

respirometer Machine that can be used to calculate the respiration rate of a reaction.

restriction enzymes Enzymes that cut DNA at specific nucleotide sequences. This results in DNA fragments with single-stranded ends called “sticky ends,” which find and reconnect with other DNA fragments containing the same ends (with the assistance of DNA ligase).

retrovirus An RNA virus that carries an enzyme called reverse transcriptase that reverse-transcribes the genetic information from RNA into DNA. In the nucleus of the host, the newly transcribed DNA incorporates into the host DNA and is transcribed into RNA when the host cell undergoes normal transcription.

reverse transcriptase Enzyme carried by retroviruses that function to convert RNA to DNA.

R_f Variable that indicates the relative rate at which one molecule migrates compared to the solvent of a paper chromatograph.

ribosomes Host organelle for protein synthesis composed of a large subunit and a small subunit. Ribosomes are built in the nucleolus.

RNA polymerase Enzyme that runs transcription and adds the appropriate nucleotides to the 3′ end of the growing strand.

RNA splicing Process that removes introns from newly produced mRNA and then glues exons back together to produce the final product.

root Portion of the plant that is below the ground.

root cap Protective structure found around the apical meristem of a root that keeps it together as it pushes through the soil.

root hairs Hairs extending off the surface of root tips that increase the surface area for absorption of water and nutrients from the soil.

root pressure Driving force that contributes to the movement of water through the xylem of a plant.

rough endoplasmic reticulum (RER) Membrane-bound organelle with ribosomes on the cytoplasmic surface of the cell. Proteins produced by RER are often secreted and carried by vesicles to the Golgi apparatus for further modification.

rRNA Ribosomal RNA, which makes up a huge portion of ribosomes.

R-selected populations Populations that experience rapid growth of the J-curve variety. The offspring produced by R-selected organisms are numerous, mature quite rapidly, and require very little postnatal care.

rubisco Enzyme that catalyzes the first step of the Calvin cycle in C₃ plants.

saprobe Organism that feeds off dead organisms.

saturated fat Fat that contains no double bonds. It is associated with heart disease and atherosclerosis.

savanna Grassland that contains a spattering of trees found all over South America, Australia, and Africa. Savanna soil tends to be low in nutrients, while temperatures tend to run high.

sclerenchyma cells Plant cells that function as protection and mechanical support.

search image Mental image that assists animals during foraging. It directs them to food of interest.

secondary consumers Consumers that obtain energy through consumption of the primary consumers.

secondary immune response Memory cells are the basis for this efficient response to invaders.

secondary oocyte An oocyte that has half the genetic information of the parent cell, but the majority of its cytoplasm.

secondary plant growth Growth that leads to an increase in plant girth.

secondary sex characteristics The noticeable physical characteristics that differ between males and females such as facial hair, deepness of voice, breasts, and muscle distribution.

secondary spermatocyte Cells formed during spermatogenesis that give rise to spermatids and eventually sperm.

secondary structure The three-dimensional arrangement of a protein caused by hydrogen bonding.

secondary succession Succession in an area that previously had stable plant and/or animal life but has since been disturbed by some major force such as a forest fire.

second messenger Molecule that serves as an intermediary, activating other proteins and enzymes in a chemical reaction.

semiconservative DNA replication Before the parent strand is copied, the DNA unzips, with each single strand serving as a template for the creation of a new double strand. One strand of DNA from the parent goes to one daughter cell; the second parent strand goes to the second daughter cell.

seminal vesicles Structures that dump fluids into the ejaculatory duct to send along with the sperm, providing three important advantages to the sperm: energy by adding fructose; power to progress through the female reproductive system by adding prostaglandin (which stimulates uterine contraction); and mucus, which helps the sperm swim more effectively.

seminiferous tubules Actual site of sperm production.

sensory neurons Nerve cells that receive and communicate information from the sensory environment.

septae Structures that divide the hypha filaments of fungi into different compartments.

SER See smooth endoplasmic reticulum.

sex pili Bacterial appendage vital to process of conjugation.

sex ratio Proportion of males and females in a given population.

sexual selection The process by which certain characters are selected for because they aid in mate acquisition.

shoots Parts of a plant that are above the ground.

short-day plants Plants, such as poinsettias, that flower if exposed to nighttime conditions longer than a critical period of length.

sickle cell anemia A recessive disease caused by the substitution of a single amino acid in the hemoglobin protein of red blood cells, leaving hemoglobin less able to carry oxygen and also causing the hemoglobin to deform to a sickle shape when the oxygen content of the blood is low. The sickling causes pain, muscle weakness, and fatigue.

sieve-tube elements Functionally mature cells of the phloem that are alive.

sink Site of carbohydrate consumption in plants.

skeletal muscle Striated muscle that controls voluntary activities and contains multiple nuclei.

smooth endoplasmic reticulum (SER) Membrane-bound organelle involved in lipid synthesis, detoxification, and carbohydrate metabolism; has no ribosomes on its cytoplasmic surface.

smooth muscle Involuntary muscle that contracts slowly and is controlled by the autonomic nervous system (ANS).

sodium—potassium pump A mechanism that actively moves potassium into the cell and sodium out of the cell against their respective concentration gradients to maintain appropriate levels inside the cell.

solute A substance dissolved in a solution.

somatotropic hormone (STH) A hormone that stimulates protein synthesis and growth in the body.

somite Structure that gives rise to the muscles and vertebrae in mammals.

source Site of carbohydrate creation in plants.

Southern blotting Procedure used to determine if a particular sequence of nucleotides is present in a sample of DNA.

specialized transduction Transduction involving a virus in the lysogenic cycle that shifts to the lytic cycle. If it accidentally brings with it a piece of the host DNA as it pulls out of the host chromosome, this DNA could find its way into another cell.

speciation The process by which new species evolve.

species A group of interbreeding (or potentially interbreeding) organisms.

specific immunity Complicated multilayered defense mechanism that protects a host against foreign invasion.

spectrophotometer Machine used to determine how much light can pass through a sample.

spermatids Immature sperm that enter the epididymis, where their waiting game begins and maturation is completed.

spermatogenesis Process by which the male gametes are formed. Four haploid sperm are produced during each meiotic cycle. This does not begin until puberty, and it occurs in the seminiferous tubules.

S phase The DNA is copied so that each daughter cell has a complete set of chromosomes at the conclusion of the cell cycle.

spongy mesophyll Region of a plant where the cells are more loosely arranged, aiding in the passage of CO₂ to cells performing photosynthesis.

sporophyte The diploid multicellular stage of the plant life cycle.

sporozoite Small infectious form that apicomplexa protists take to spread from place to place.

stabilizing selection This describes selection for the mean of a population for a given allele; has the effect of reducing variation in a given population.

stamen Male structure of a flower that contains the pollen-producing anther.

starch Storage polysaccharide made of glucose molecules; seen in plants.

start codon (AUG) Codon that establishes the reading frame for protein formation.

stem cells Cells that give rise to the immune cells of the human body.

steroid hormones Lipid-soluble molecules that pass through the cell membrane and combine with cytoplasmic proteins. These complexes pass through to the nucleus to interact with chromosomal proteins and directly affect transcription in the nucleus.

steroids Lipids composed of four carbon rings. Examples include cholesterol, estrogen, progesterone, and testosterone.

STH See somatotropic hormone.

sticky ends Single-stranded DNA fragments formed when DNA is treated with restriction enzymes. These fragments find and reconnect with other fragments with the same ends.

stigma Flower structure that functions as the receiver of pollen.

stomata Structure through which CO₂ enters a plant, and water vapor and O₂ leave.

stop codons (UGA, UAA, UAG) Codons that stop the production of a protein.

storage diseases Diseases such as Tay-Sachs that are caused by the absence of a particular lysosomal hydrolytic enzyme.

strain Groups into which bacterial species are placed.

stroma The inner fluid portion of the chloroplast that plays host to the light-independent reactions of photosynthesis.

style Pathway in a flower that leads to the ovary.

substrates Substances that enzymes act upon.

succession Shift in the local composition of species in response to changes that occur over time.

sulfhydryl group A functional group that helps stabilize the structure of many proteins.

survivorship curves A tool used to study the population dynamics of species.

symbiosis A relationship between two different species that can be classified as one of three main types: commensalism, mutualism, and parasitism.

sympathetic nervous system Branch of the autonomic nervous system that gets the body ready to move.

sympatric speciation Interbreeding ceases even though no physical barrier prevents it. Can occur as a result of polyploidy and balanced polymorphism.

symplast pathway Movement of water and nutrients through the living portion of plant cells.

synaptic knob The end of the axon. This is where calcium gates are opened in response to the changing potential, which causes vesicles to release substances called neurotransmitters (NTs) into the synaptic gap between the axon and the target cell. These NTs diffuse across the gap, causing a new impulse in the target cell.

tactile communication Communication that involves the use of touch in the conveying of a message.

taiga Biome characterized by lengthy, cold, and wet winters. This biome is found in Canada and has gymnosperms as its prominent plant life. This biome contains coniferous forests (pine and other needle-bearing trees).

tapeworm Parasitic flatworm whose adult form lives in vertebrates.

taproot system System of roots found in many dicots that starts as one thick root and divides into many smaller lateral roots, which serve as an anchor for the plant.

TATA box Group of nucleotides found in the promoter region that assists in binding of RNA polymerase to the DNA strand for transcription.

taxis The reflex movement toward or away from a stimulus.

taxonomy The field of biology that classifies organisms according to the presence or absence of shared characteristics in an effort to discover evolutionary relationships between species.

Tay-Sachs disease A fatal genetic storage disease that renders the body unable to break down a particular type of lipid.

temperate deciduous forest A biome that is found in regions that experience cold winters where plant life is dormant, alternating with warm summers that provide enough moisture to keep large trees alive.

temperate grasslands Found in regions with cold winter temperatures. The soil of this biome is considered to be among the most fertile of all.

termination site Region of DNA that tells the polymerase when transcription should conclude.

territoriality Scenario in which territorial individuals defend their territory against other individuals.

tertiary structure The 3D (three-dimensional) arrangement of a protein caused by interaction among the various R groups of the amino acids involved.

test cross Crossing of an organism of unknown dominant genotype with an organism that is homozygous recessive for the trait, resulting in offspring with observable phenotypes. Test crosses are used to determine the unknown genotype.

testis The site of sperm and testosterone production in animals; males have two testes, located in the scrotum.

testosterone Sex hormone produced in testes that stimulates the growth of male sex characteristics.

thermoacidophiles Archaebacteria that live in hot, acidic environments.

thermoregulation The process by which temperature is maintained.

thigmotropism A plant’s growth in response to touch.

thylakoid membrane system Inner membrane that winds through the stroma of a chloroplast. Site of the light-dependent reactions of photosynthesis.

thymine dimers Thymine nucleotides located adjacent to one another on the DNA strand bind together when excess exposure to UV light occurs. This can negatively affect replication of DNA and assist in the creation of further mutations.

thymosin Hormone involved in the development of the T cells of the immune system.

thyroid-stimulating hormone (TSH) A hormone that stimulates the synthesis and secretion of thyroid hormones, which regulate the rate of metabolism in the body.

thyroxin Hormone released by the thyroid gland that functions in the control of metabolic activities in the body.

tongue Structure that functions to move food around while we chew and helps to arrange the food into a swallowable bolus.

trachea The tunnel that leads air into the thoracic cavity.

tracheid cells Xylem cells in charge of water transport in gymnosperm.

tracheophytes Vascular plants.

transcription factors Helper proteins that assist RNA polymerase in finding and attaching to the promoter region.

transduction The movement of genes from one cell to another by phages.

transformation The transfer of genetic material from one cell to another, resulting in a genetic change in the receiving cell.

translocation Movement of the ribosome along the mRNA in such a way that the A site becomes the P site and the next tRNA comes into the new A site carrying the next amino acid.

translocation (plants) Movement of carbohydrates through the phloem.

transpiration Process by which plants lose water by evaporation through their leaves.

trichinosis Disease found in humans caused by a roundworm that infects meat products.

trophic levels Hierarchy of energy levels that describe the energy distribution of a planet.

trophoblast Forms the placenta for the developing fetus, and aids in attachment to the endometrium. This structure also produces human chorionic gonadotropin (hCG), which maintains the endometrium by ensuring the continued production of progesterone.

tropical forests These forests consist primarily of tall trees that form a thick cover, which blocks the light from reaching the floor of the forest (where there is little growth). Tropical rainforests are known for their rapid recycling of nutrients and contain the greatest diversity of species.

tropism Plant growth that occurs in response to an environmental stimulus such as sunlight or gravity.

tropomyosin Regulatory protein known to block the actin—myosin binding site and prevent muscular contraction in the absence of calcium.

trypsin Enzyme that cuts protein bonds in the small intestine.

TSH See thyroid-stimulating hormone.

tundra This biome experiences extremely cold winters during which the ground freezes completely. Short shrubs or grasses that are able to withstand the difficult conditions dominate.

Turner syndrome Affects females who are missing an X chromosome.

umbilical cord Structure that transports oxygen, food, and waste (CO₂) between the embryo and the placenta.

uniform distribution Scenario in which individuals are evenly spaced out across a given geographic area.

unsaturated fat Fat that contains one or more double bonds; found in plants.

uracil The nucleotide that replaces thymine in RNA.

urethra Exit point for both urine and sperm from males and urine for females.

uterus Site of embryo attachment and development in mammals.

vaccination Inoculation of medicine into a patient in an effort to prime the immune system to be prepared to fight a specific sickness if confronted in the future.

vacuole A storage organelle that is large in plant cells but small in animal cells.

vascular cambium A cylinder of tissue that extends the length of the stem and root and gives rise to the secondary xylem and phloem.

vascular cylinder Structure in plants that is composed of cells that produce the lateral roots of the plant.

vas deferens Tunnel that connects the epididymis to the urethra.

vector Agent that moves DNA from one source to another.

veins Structures that return blood to the heart.

vena cava system System of veins that returns deoxygenated blood from the body to the heart to be reoxygenated in the lungs.

vertebrate Animal with a backbone.

vessel elements Xylem cells in charge of water transport in angiosperms. More efficient than tracheid cells.

vestigial characters Characters that are no longer useful, although they once were.

viral envelope Protective barrier that surrounds some viruses but also helps them attach to cells.

viroids Plant viruses that are only a few hundred nucleotides in length.

virus A parasitic infectious agent that is unable to survive outside a host organism. Viruses do not contain enzymes for metabolism or ribosomes for protein synthesis.

visual communication Communication through the use of the visual senses.

water biomes Both freshwater and marine biomes, which occupy the majority of the surface of the Earth.

water cycle The Earth is covered in water. A lot of this water evaporates each day and returns to the clouds. This water is then returned to the earth in the form of precipitation.

water potential The force that drives water to move in a given direction. Combination of solute potential and pressure potential.

water vascular system Series of tubes and canals within echinoderms that play a role in ingestion of food, movement, and gas exchange.

wild-type phenotype The normal phenotype for a characteristic in fruit flies and other organisms.

within-sex competition Competition for mates between members of the same sex.

wobble Nucleotides in the third position of an anticodon are able to pair with many nucleotides instead of just their normal partner.

X-inactivation During the development of the female embryo, one of the two X chromosomes in each cell remains coiled as a Barr body whose genes are not expressed. A cell expresses the alleles of the active X chromosome only.

xylem The “superhighway,” or important part of the vascular tissue in plants, through which water and nutrients travel throughout the plant. Also functions as a support structure that strengthens the plant.

yolk sac Derived from the hypoblast, this is the site of early blood cell formation in humans and the source of nutrients for bird and reptile embryos.

zone of cell division Region at the tip of a root formed by the actively dividing cells of the apical meristem.

zone of elongation Cells of this region elongate tremendously during plant growth.

zone of maturation Region in the plant where cells differentiate into their final forms.