P0: parental generation in a cross
p21: cell-cycle regulatory protein that inhibits the cell cycle; its levels are controlled by p53
p53: cell-cycle regulatory protein that regulates cell growth and monitors DNA damage; it halts the progression of the cell cycle in cases of DNA damage and may induce apoptosis
P680: reaction center of photosystem II
P700: reaction center of photosystem I
Pacinian corpuscle: encapsulated mechanoreceptor in the skin that responds to deep pressure and vibration
Paleognathae: ratites; flightless birds, including ostriches and emus
paleontology: study of life’s history by means of fossils
palmately compound leaf: leaf type with leaflets that emerge from a point, resembling the palm of a hand
Pan: genus of chimpanzees and bonobos
pancreas: gland that secretes digestive juices
pancreas: organ located between the stomach and the small intestine that contains exocrine and endocrine cells
pandemic: widespread, usually worldwide, epidemic disease
papilla: one of the small bump-like projections from the tongue
paracentric: inversion that occurs outside the centromere
paracrine signal: signal between nearby cells that is delivered by ligands traveling in the liquid medium in the space between the cells
parafollicular cell: thyroid cell that produces the hormone calcitonin
parapodium: fleshy, flat, appendage that protrudes in pairs from each segment of polychaetes
parasite: organism that uses resources from another species, the host
parasitic plant: plant that is dependent on its host for survival
parasitism: symbiotic relationship in which one member of the association benefits at the expense of the other
parasympathetic nervous system: division of autonomic nervous system that regulates visceral functions during rest and digestion
parathyroid gland: gland located on the surface of the thyroid that produces parathyroid hormone
parathyroid hormone (PTH): hormone produced by the parathyroid glands in response to low blood Ca2+ levels; functions to raise blood Ca2+ levels
Parazoa: group of animals without true differentiated tissues
parenchyma cell: most common type of plant cell; found in the stem, root, leaf, and in fruit pulp; site of photosynthesis and starch storage
parent material: organic and inorganic material in which soils form
parental types: progeny that exhibits the same allelic combination as its parents
parietal lobe: part of the cerebral cortex involved in processing touch and the sense of the body in space
Parkinson’s disease: neurodegenerative disorder that affects the control of movement
parthenogenesis: form of asexual reproduction where an egg develops into a complete individual without being fertilized
partial pressure: amount of pressure exerted by one gas within a mixture of gases
particulate matter: small particle such as dust, dirt, viral particles, and bacteria that are in the air
passive immunity: transfer of antibodies from one individual to another to provide temporary protection against pathogens
passive transport: method of transporting material through a membrane that does not require energy
patella: (also, kneecap) triangular bone that lies anterior to the knee joint
pathogen: agent with the ability to cause disease
pathogen: an agent, usually a microorganism, that causes disease in the organisms that it invades
pathogen-associated molecular pattern (PAMP): carbohydrate, polypeptide, and nucleic acid “signature” that is expressed by viruses, bacteria, and parasites but differs from molecules on host cells
pattern recognition receptor (PRR): molecule on macrophages and dendritic cells that binds molecular signatures of pathogens and promotes pathogen engulfment and destruction
peat moss: Sphagnum
pectoral girdle: bones that transmit the force generated by the upper limbs to the axial skeleton
pedipalp: second pair of appendages in Chelicerata
peer-reviewed manuscript: scientific paper that a scientist’s colleagues review who are experts in the field of study
pelagic realm: (also, pelagic zone) open ocean waters that are not close to the bottom or near the shore
pellicle: outer cell covering composed of interlocking protein strips that function like a flexible coat of armor, preventing cells from being torn or pierced without compromising their range of motion
pelvic girdle: bones that transmit the force generated by the lower limbs to the axial skeleton
penis: male reproductive structure for urine elimination and copulation
pepsin: enzyme found in the stomach whose main role is protein digestion
pepsinogen: inactive form of pepsin
peptide bond: bond formed between two amino acids by a dehydration reaction
peptide hormone: hormone composed of a polypeptide chain
peptidoglycan: material composed of polysaccharide chains cross-linked to unusual peptides
peptidyl transferase: RNA-based enzyme that is integrated into the 50S ribosomal subunit and catalyzes the formation of peptide bonds
perception: individual interpretation of a sensation; a brain function
perforin: destructive protein that creates a pore in the target cell; used by NK cells and killer T cells
perianth: part of the plant consisting of the calyx (sepals) and corolla (petals)
perianth: (also, petal or sepal) part of the flower consisting of the calyx and/or corolla; forms the outer envelope of the flower
pericardium: membrane layer protecting the heart; also part of the epicardium
pericarp: collective term describing the exocarp, mesocarp, and endocarp; the structure that encloses the seed and is a part of the fruit
pericentric: inversion that involves the centromere
pericycle: outer boundary of the stele from which lateral roots can arise
periderm: outermost covering of woody stems; consists of the cork cambium, cork cells, and the phelloderm
periodic table: organizational chart of elements indicating each element's atomic number and atomic mass; provides key information about the elements' properties
peripheral protein: protein at the plasma membrane's surface either on its exterior or interior side
peripheral resistance: resistance of the artery and blood vessel walls to the pressure placed on them by the force of the heart pumping
perirenal fat capsule: fat layer that suspends the kidneys
peristalsis: wave-like movements of muscle tissue
peristome: tissue that surrounds the opening of the capsule and allows periodic release of spores
peritubular capillary network: capillary network that surrounds the renal tubule after the efferent artery exits the glomerulus
permafrost: perennially frozen portion of the Arctic tundra soil
permanent tissue: plant tissue composed of cells that are no longer actively dividing
permissive: cell type that is able to support productive replication of a virus
peroxisome: small, round organelle that contains hydrogen peroxide, oxidizes fatty acids and amino acids, and detoxifies many poisons
petal: modified leaf interior to the sepals; colorful petals attract animal pollinators
petiole: stalk of the leaf
Petromyzontidae: clade of lampreys
pH paper: see litmus paper
pH scale: scale ranging from zero to 14 that is inversely proportional to the hydrogen ions' concentration in a solution
phage therapy: treatment of bacterial diseases using bacteriophages specific to a particular bacterium
phagolysosome: cellular body formed by the union of a phagosome containing the ingested particle with a lysosome that contains hydrolytic enzymes
phalange: one of the bones of the fingers or toes
pharmacogenomics: study of drug interactions with the genome or proteome; also called toxicogenomics
pharyngeal slit: opening in the pharynx
pharynx: throat; a tube that starts in the internal nares and runs partway down the neck, where it opens into the esophagus and the larynx
phenotype: observable traits expressed by an organism
pheromone: substance released by an animal that can affect the physiology or behavior of other animals
phloem: tissue responsible for transport of sugars, proteins, and other solutes
phosphatase: enzyme that removes the phosphate group from a molecule that has been previously phosphorylated
phosphoanhydride bond: bond that connects phosphates in an ATP molecule
phosphodiester: linkage covalent chemical bond that holds together the polynucleotide chains with a phosphate group linking neighboring nucleotides' two pentose sugars
phosphodiesterase: enzyme that degrades cAMP, producing AMP, to terminate signaling
phosphodiesterase (PDE): enzyme that deactivates cAMP, stopping hormone activity
phospholipid: membranes' major constituent; comprised of two fatty acids and a phosphate-containing group attached to a glycerol backbone
phosphorylation: addition of a high-energy phosphate to a compound, usually a metabolic intermediate, a protein, or ADP
photic zone: portion of the ocean that light can penetrate
photoact: ejection of an electron from a reaction center using the energy of an absorbed photon
photoautotroph: organism capable of producing its own organic compounds from sunlight
photomorphogenesis: growth and development of plants in response to light
photon: distinct quantity or “packet” of light energy
photoperiodism: occurrence of plant processes, such as germination and flowering, according to the time of year
photosystem: group of proteins, chlorophyll, and other pigments that are used in the light-dependent reactions of photosynthesis to absorb light energy and convert it into chemical energy
photosystem I: integral pigment and protein complex in thylakoid membranes that uses light energy to transport electrons from plastocyanin to NADP+ (which becomes reduced to NADPH in the process)
photosystem II: integral protein and pigment complex in thylakoid membranes that transports electrons from water to the electron transport chain; oxygen is a product of PSII
phototroph: organism that is able to make its own food by converting solar energy to chemical energy
phototropin: blue-light receptor that promotes phototropism, stomatal opening and closing, and other responses that promote photosynthesis
phototropism: directional bending of a plant toward a light source
phyllotaxy: arrangement of leaves on a stem
phylogenetic tree: diagram showing the evolutionary relationships among various biological species based on similarities and differences in genetic or physical traits or both; in essence, a hypothesis concerning evolutionary connections
phylogenetic tree: diagram that reflects the evolutionary relationships among organisms or groups of organisms
phylogeny: evolutionary history and relationship of an organism or group of organisms
phylum: (plural: phyla) kingdom division in the taxonomic classification system
physical map: representation of the physical distance between genes or genetic markers
physical science: field of science, such as geology, astronomy, physics, and chemistry, that studies nonliving matter
physiological dead space: (also, physiological shunt) region of the lung that lacks proper ventilation/perfusion due to a physiological change in the lung (like inflammation or edema)
phytochrome: plant pigment protein that exists in two reversible forms (Pr and Pfr) and mediates morphologic changes in response to red light
pia mater: thin membrane layer directly covering the brain and spinal cord
pigment: molecule that is capable of absorbing certain wavelengths of light and reflecting others (which accounts for its color)
pilidium: larval form found in some nemertine species
pilus: surface appendage of some prokaryotes used for attachment to surfaces including other prokaryotes
pinacocyte: epithelial-like cell that forms the outermost layer of sponges and encloses a jelly-like substance called mesohyl
pinnately compound leaf: leaf type with a divided leaf blade consisting of leaflets arranged on both sides of the midrib
pinocytosis: a variation of endocytosis that imports macromolecules that the cell needs from the extracellular fluid
pioneer species: first species to appear in primary and secondary succession
pistil: fused group of carpels
pith: ground tissue found towards the interior of the vascular tissue in a stem or root
pituitary dwarfism: condition caused by underproduction of GH in children
pituitary gland: endocrine gland located at the base of the brain composed of an anterior and posterior region; also called hypophysis
pituitary stalk: (also, infundibulum) stalk that connects the pituitary gland to the hypothalamus
pivot joint: joint with the rounded end of one bone fitting into a ring formed by the other bone
placenta: organ that supports the diffusion of nutrients and waste between the pregnant person’s and fetus’ blood
plagiarism: using other people’s work or ideas without proper citation, creating the false impression that those are the author’s original ideas
planar joint: joint with bones whose articulating surfaces are flat
planktivore: animal species that eats plankton
plankton: diverse group of mostly microscopic organisms that drift in marine and freshwater systems and serve as a food source for larger aquatic organisms
planospiral: shell shape coiled around a vertical axis
plantar flexion: bending at the ankle such that the heel is lifted, such as when standing on the toes
planuliform: larval form found in phylum Nemertea
plasma: liquid component of blood that is left after the cells are removed
plasma cell: immune cell that secrets antibodies; these cells arise from B cells that were stimulated by antigens
plasma membrane: phospholipid bilayer with embedded (integral) or attached (peripheral) proteins, and separates the cell's internal content from its surrounding environment
plasma membrane hormone receptor: a hormone receptor on the surface of the plasma membrane of a cell
plasmid: extrachromosomal, covalently closed, circular DNA molecule that may only contain one or a few genes; common in prokaryotes
plasmodesma: (plural = plasmodesmata) channel that passes between adjacent plant cells' cell walls, connects their cytoplasm, and allows transporting of materials from cell to cell
plasmogamy: fusion of cytoplasm
plasmolysis: detaching the cell membrane from the cell wall and constricting the cell membrane when a plant cell is in a hypertonic solution
plastid: one of a group of related organelles in plant cells that are involved in the storage of starches, fats, proteins, and pigments
platelet: (also, thrombocyte) small cellular fragment that collects at wounds, cross-reacts with clotting factors, and forms a plug to prevent blood loss
Platyrrhini: clade of New World monkeys
Plesiadapis: oldest known primate-like mammal
pleura: tissue layer that surrounds the lungs and lines the interior of the thoracic cavity
pleurisy: painful inflammation of the pleural tissue layers
plumule: shoot that develops from the germinating seed
pneumatic bone: air-filled bone
point mutation: mutation that affects a single base
polar covalent bond: type of covalent bond that forms as a result of unequal electron sharing, resulting in creating slightly positive and negative charged molecule regions
polar nuclei: found in the ovule sac; fusion with one sperm cell forms the endosperm
pollen grain: structure containing the male gametophyte of the plant
pollen tube: extension from the pollen grain that delivers sperm to the egg cell
pollination: transfer of pollen from the anther to the stigma
pollination: transfer of pollen to the stigma
poly-A tail: modification added to the 3' end of pre-mRNAs to protect mRNA from degradation and assist mRNA export from the nucleus
poly-A tail: a series of adenine nucleotides that are attached to the 3' end of an mRNA to protect the end from degradation
polyandry: mating system where one female mates with many males
polycarpic: plants that flower several times in their lifetime
polygenic: phenotypic characteristic caused by two or more genes
polygyny: mating system where one male mates with many females
polymer: chain of monomer residues that covalent bonds link; polymerization is the process of polymer formation from monomers by condensation
polymerase chain reaction (PCR): technique to amplify DNA
polymorphic: possessing multiple body plans within the lifecycle of a group of organisms
polynucleotide: long chain of nucleotides
polyp: stalk-like sessile life form of a cnidarians with mouth and tentacles facing upward, usually sessile but may be able to glide along surface
polypeptide: long chain of amino acids that peptide bonds link
polyploid: individual with an incorrect number of chromosome sets
polysaccharide: long chain of monosaccharides; may be branched or unbranched
polysome: mRNA molecule simultaneously being translated by many ribosomes all going in the same direction
polyspermy: condition in which one egg is fertilized by multiple sperm
polytomy: branch on a phylogenetic tree with more than two groups or taxa
Pongo: genus of orangutans
population: all of the individuals of a species living within a specific area
population density: number of population members divided by the area or volume being measured
population genetics: study of how selective forces change the allele frequencies in a population over time
population growth rate: number of organisms added in each reproductive generation
population size (N): number of population members in a habitat at the same time
population variation: distribution of phenotypes in a population
Porifera: phylum of animals with no true tissues, but a porous body with rudimentary endoskeleton
positive feedback loop: feedback to a control mechanism that continues the direction of a stimulus
positive gravitropism: growth toward Earth’s gravitational center
positive polarity: ssRNA virus with a genome that contains the same base sequences and codons found in their mRNA
positive regulator: protein that increases transcription
post-anal tail: muscular, posterior elongation of the body extending beyond the anus in chordates
post-transcriptional: control of gene expression after the RNA molecule has been created but before it is translated into protein
post-translational: control of gene expression after a protein has been created
posterior pituitary: extension of the brain that releases hormones produced by the hypothalamus; along with the infundibulum, it is also referred to as the neurohypophysis
postzygotic barrier: reproductive isolation mechanism that occurs after zygote formation
potential energy: energy type that has the potential to do work; stored energy
potocytosis: variation of pinocytosis that uses a different coating protein (caveolin) on the plasma membrane's cytoplasmic side
precapillary sphincter: small muscle that controls blood circulation in the capillary beds
predator: organism that kills and consumes another organism
preinitiation complex: cluster of transcription factors and other proteins that recruit RNA polymerase II for transcription of a DNA template
presbyopia: visual defect in which the image focus falls behind the retina, thereby making images in the distance clear, but close-up images blurry; caused by age-based changes in the lens
prezygotic barrier: reproductive isolation mechanism that occurs before zygote formation
primary active transport: active transport that moves ions or small molecules across a membrane and may create a difference in charge across that membrane
primary bronchus: (also, main bronchus) region of the airway within the lung that attaches to the trachea and bifurcates to each lung where it branches into secondary bronchi
primary consumer: trophic level that obtains its energy from the primary producers of an ecosystem
primary electron acceptor: pigment or other organic molecule in the reaction center that accepts an energized electron from the reaction center
primary feather: feather located at the tip of the wing that provides thrust
primary growth: growth resulting in an increase in length of the stem and the root; caused by cell division in the shoot or root apical meristem
primary producer: trophic level that obtains its energy from sunlight, inorganic chemicals, or dead and/or decaying organic material
primary structure: linear sequence of amino acids in a protein
primary succession: succession on land that previously has had no life
primase: enzyme that synthesizes the RNA primer; the primer is needed for DNA pol to start synthesis of a new DNA strand
Primates: order of lemurs, tarsiers, monkeys, apes, and humans
primer: short stretch of nucleotides that is required to initiate replication; in the case of replication, the primer has RNA nucleotides
prion: infectious particle that consists of proteins that replicate without DNA or RNA
probe: small DNA fragment to determine if the complementary sequence is present in a DNA sample
product: molecule that is result of chemical reaction
product rule: probability of two independent events occurring simultaneously can be calculated by multiplying the individual probabilities of each event occurring alone
productive: viral infection that leads to the production of new virions
progesterone: reproductive hormone in females; assists in endometrial regrowth and inhibition of FSH and LH release
prognathic jaw: long jaw
progymnosperm: transitional group of plants that resembled conifers because they produced wood, yet still reproduced like ferns
prokaryote: single-celled organism that lacks organelles and does not have nuclei surrounded by a nuclear membrane
prokaryote: unicellular organism that lacks a nucleus or any other membrane-bound organelle
prolactin (PRL): hormone produced by the anterior pituitary that stimulates milk production
prolactin-inhibiting hormone: hormone produced by the hypothalamus that inhibits the release of prolactin
prolactin-releasing hormone: hormone produced by the hypothalamus that stimulates the release of prolactin
prometaphase: stage of mitosis during which the nuclear membrane breaks down and mitotic spindle fibers attach to kinetochores
promoter: DNA sequence to which RNA polymerase and associated factors bind and initiate transcription
pronation: movement in which the palm faces backward
proofreading: function of DNA pol in which it reads the newly added base before adding the next one
prophage: phage DNA that is incorporated into the host cell genome
prophase: stage of mitosis during which chromosomes condense and the mitotic spindle begins to form
proprioception: sense about how parts of the body are oriented in space
proprioception: sense of limb position; used to track kinesthesia
prosimian: division of primates that includes bush babies and pottos of Africa, lemurs of Madagascar, and lorises of Southeast Asia
prostate gland: structure that is a mixture of smooth muscle and glandular material and that contributes to semen
prosthetic group: (also prosthetic cofactor) molecule bound to a protein that facilitates the function of the protein
protease: enzyme that breaks down proteins
proteasome: organelle that degrades proteins
protein: biological macromolecule comprised of one or more amino acid chains
protein signature: set of uniquely expressed proteins in the diseased state
proteome: entire set of proteins that cell type produces
proteomics: study of proteomes' function
proto-oncogene: normal gene that when mutated becomes an oncogene
proton: positively charged particle that resides in the atom's nucleus; has a mass of one amu and a charge of +1
protonema: tangle of single-celled filaments that forms from the haploid spore
protostome: blastopore develops into the mouth of protostomes, with the second opening developing into the anus
protraction: anterior movement of a bone in the horizontal plane
proventriculus: glandular part of a bird’s stomach
proximal convoluted tubule (PCT): part of the renal tubule that lies close to the glomerulus
PrPc: normal prion protein
PrPsc: infectious form of a prion protein
pseudocoelomate: animal with a body cavity located between the mesoderm and endoderm
pseudopeptidoglycan: component of archaea cell walls that is similar to peptidoglycan in morphology but contains different sugars
pseudostratified: layer of epithelia that appears multilayered, but is a simple covering
psychrophile: organism that grows at temperatures of -15 °C or lower
pulmocutaneous circulation: circulatory system in amphibians; the flow of blood to the lungs and the moist skin for gas exchange
pulmonary circulation: flow of blood away from the heart through the lungs where oxygenation occurs and then returns to the heart again
pump: active transport mechanism that works against electrochemical gradients
punctuated equilibrium: model for rapid speciation that can occur when an event causes a small portion of a population to be cut off from the rest of the population
Punnett square: visual representation of a cross between two individuals in which the gametes of each individual are denoted along the top and side of a grid, respectively, and the possible zygotic genotypes are recombined at each box in the grid
pupil: small opening though which light enters
pure culture: growth of a single cell type in the laboratory
purine: type of nitrogenous base in DNA and RNA; adenine and guanine are purines
pyrimidine: type of nitrogenous base in DNA and RNA; cytosine, thymine, and uracil are pyrimidines
pyruvate: three-carbon sugar that can be decarboxylated and oxidized to make acetyl CoA, which enters the citric acid cycle under aerobic conditions; the end product of glycolysis
quadrat: square made of various materials used to determine population size and density in slow moving or stationary organisms
quaternary structure: association of discrete polypeptide subunits in a protein
quiescent: refers to a cell that is performing normal cell functions and has not initiated preparations for cell division
quorum sensing: method of cellular communication used by bacteria that informs them of the abundance of similar (or different) bacteria in the environment
r-selected species: species suited to changing environments that produce many offspring and provide little or no parental care
radial cleavage: cleavage axes are parallel or perpendicular to the polar axis, resulting in the alignment of cells between the two poles
radial glia: glia that serve as scaffolds for developing neurons as they migrate to their final destinations
radial symmetry: type of symmetry with multiple planes of symmetry, with body parts (rays) arranged around a central disk
radiation hybrid mapping: information obtained by fragmenting the chromosome with x-rays
radicle: original root that develops from the germinating seed
radioisotope: isotope that emits radiation comprised of subatomic particles to form more stable elements
radioresistant: organism that grows in high levels of radiation
radius: bone located along the lateral (thumb) side of the forearm; articulates with the humerus at the elbow
radula: tongue-like organ with chitinous ornamentation
raphe: slit in the silica shell of diatoms through which the protist secretes a stream of mucopolysaccharides for locomotion and attachment to substrates
reactant: molecule that takes part in a chemical reaction
reaction center: complex of chlorophyll molecules and other organic molecules that is assembled around a special pair of chlorophyll molecules and a primary electron acceptor; capable of undergoing oxidation and reduction
reading frame: sequence of triplet codons in mRNA that specify a particular protein; a ribosome shift of one or two nucleotides in either direction completely abolishes synthesis of that protein
reception: receipt of a signal (such as light or sound) by sensory receptors
receptive field: region in space in which a stimulus can activate a given sensory receptor
receptor: protein in or on a target cell that bind to ligands
receptor potential: membrane potential in a sensory receptor in response to detection of a stimulus
receptor-mediated endocytosis: variation of endocytosis that involves using specific binding proteins in the plasma membrane for specific molecules or particles, and clathrin-coated pits that become clathrin-coated vesicles
recessive: trait that appears “latent” or non-expressed when the individual also carries a dominant trait for that same characteristic; when present as two identical copies, the recessive trait is expressed
recessive lethal: inheritance pattern in which an allele is only lethal in the homozygous form; the heterozygote may be normal or have some altered, nonlethal phenotype
reciprocal cross: paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross
recombinant DNA: combining DNA fragments that molecular cloning generates that do not exist in nature; also a chimeric molecule
recombinant protein: a gene's protein product derived by molecular cloning
recombination frequency: average number of crossovers between two alleles; observed as the number of nonparental types in a progeny's population
recombination nodules: protein assemblies formed on the synaptonemal complex that mark the points of crossover events and mediate the multistep process of genetic recombination between nonsister chromatids of a homologous pair
recruitment: process of opening airways that normally remain closed when the cardiac output increases
rectum: area of the body where feces is stored until elimination
red blood cell: small (7–8 μm) biconcave cell without mitochondria (and in mammals without nuclei) that is packed with hemoglobin, giving the cell its red color; transports oxygen through the body
redox reaction: chemical reaction that consists of the coupling of an oxidation reaction and a reduction reaction
reduction: gain of electron(s) by an atom or molecule
reduction division: nuclear division that produces daughter nuclei each having one-half as many chromosome sets as the parental nucleus; meiosis I is a reduction division
reflex action: action in response to direct physical stimulation of a nerve
refractory period: period after an action potential when it is more difficult or impossible for an action potential to be fired; caused by inactivation of sodium channels and activation of additional potassium channels of the membrane
regulatory T (Treg) cell: specialized lymphocyte that suppresses local inflammation and inhibits the secretion of cytokines, antibodies, and other stimulatory immune factors; involved in immune tolerance
reinforcement: continued speciation divergence between two related species due to low fitness of hybrids between them
relative fitness: individual’s ability to survive and reproduce relative to the rest of the population
relative species abundance: absolute population size of a particular species relative to the population sizes of other species within the community
renal artery: branch of the artery that enters the kidney
renal capsule: layer that encapsulates the kidneys
renal column: area of the kidney through which the interlobar arteries travel in the process of supplying blood to the renal lobes
renal corpuscle: glomerulus and the Bowman's capsule together
renal fascia: connective tissue that supports the kidneys
renal pelvis: region in the kidney where the calyces join the ureters
renal pyramid: conical structure in the renal medulla
renal tubule: tubule of the nephron that arises from the glomerulus
renal vein: branch of a vein that exits the kidney and joins the inferior vena cava
renin: enzyme produced by the juxtaglomerular apparatus of the kidneys that reacts with angiotensinogen to cause the release of aldosterone
renin-angiotensin-aldosterone: biochemical pathway that activates angiotensin II, which increases blood pressure
replication fork: Y-shaped structure formed during initiation of replication
replicative intermediate: dsRNA intermediate made in the process of copying genomic RNA
repressor: protein that binds to the operator of prokaryotic genes to prevent transcription
reproductive cloning: entire organism cloning
reproductive isolation: situation that occurs when a species is reproductively independent from other species; behavior, location, or reproductive barriers may cause this to happen
residence time: measure of the average time an individual water molecule stays in a particular reservoir
residual volume (RV): amount of air remaining in the lung after a maximal expiration
resilience (ecological): speed at which an ecosystem recovers equilibrium after being disturbed
resistance: measurement of lung obstruction
resistance (ecological): ability of an ecosystem to remain at equilibrium in spite of disturbances
resorption: process by which osteoclasts release minerals stored in bones
respiratory bronchiole: terminal portion of the bronchiole tree that is attached to the terminal bronchioles and alveoli ducts, alveolar sacs, and alveoli
respiratory distress syndrome: disease that arises from a deficient amount of surfactant
respiratory quotient (RQ): ratio of carbon dioxide production to each oxygen molecule consumed
respiratory rate: number of breaths per minute
restriction endonuclease: enzyme that can recognize and cleave specific DNA sequences
restriction fragment length polymorphism (RFLP): variation between individuals in the length of DNA fragments, which restriction endonucleases generate
restrictive disease: disease that results from a restriction and decreased compliance of the alveoli; respiratory distress syndrome and pulmonary fibrosis are examples
results: section of a scientific paper in which the author narrates the experimental findings and presents relevant figures, pictures, diagrams, graphs, and tables, without any further interpretation
resuscitation: process by which prokaryotes that are in the VBNC state return to viability
retina: layer of photoreceptive and supporting cells on the inner surface of the back of the eye
retinoblastoma protein (Rb): regulatory molecule that exhibits negative effects on the cell cycle by interacting with a transcription factor (E2F)
retraction: movement in which a joint moves back into position after protraction
reverse genetics: method of determining the gene's function by starting with the gene itself instead of starting with the gene product
reverse transcriptase: enzyme found in Baltimore groups VI and VII that converts single-stranded RNA into double-stranded DNA
reverse transcriptase PCR (RT-PCR): PCR technique that involves converting RNA to DNA by reverse transcriptase
reversible chemical reaction: chemical reaction that functions bidirectionally, where products may turn into reactants if their concentration is great enough
review article: paper that summarizes and comments on findings that were published as primary literature
rhizobia: soil bacteria that symbiotically interact with legume roots to form nodules and fix nitrogen
rhizoids: thin filaments that anchor the plant to the substrate
rhizome: modified underground stem that grows horizontally to the soil surface and has nodes and internodes
rhizosphere: area of soil affected by root secretions and microorganisms
rho-dependent termination: in prokaryotes, termination of transcription by an interaction between RNA polymerase and the rho protein at a run of G nucleotides on the DNA template
rho-independent: termination sequence-dependent termination of prokaryotic mRNA synthesis; caused by hairpin formation in the mRNA that stalls the polymerase
rhodopsin: main photopigment in vertebrates
rhynchocoel: cavity present above the mouth that houses the proboscis
rib: one of 12 pairs of long, curved bones that attach to the thoracic vertebrae and curve toward the front of the body to form the ribcage
ribonuclease: enzyme that breaks down RNA
ribonucleic acid (RNA): single-stranded, often internally base paired, molecule that is involved in protein synthesis
ribosomal RNA (rRNA): RNA that ensures the proper alignment of the mRNA and the ribosomes during protein synthesis and catalyzes forming the peptide linkage
ribosome: cellular structure that carries out protein synthesis
ring of life: phylogenetic model where all three domains of life evolved from a pool of primitive prokaryotes
RISC: protein complex that binds along with the miRNA to the RNA to degrade it
RNA editing: direct alteration of one or more nucleotides in an mRNA that has already been synthesized
RNA stability: how long an RNA molecule will remain intact in the cytoplasm
RNA-binding protein (RBP): protein that binds to the 3' or 5' UTR to increase or decrease the RNA stability
rod: strongly photosensitive, achromatic, cylindrical neuron in the outer edges of the retina that detects dim light and is used in peripheral and nighttime vision
root cap: protective cells covering the tip of the growing root
root hair: hair-like structure that is an extension of epidermal cells; increases the root surface area and aids in absorption of water and minerals
root system: belowground portion of the plant that supports the plant and absorbs water and minerals
rooted: single ancestral lineage on a phylogenetic tree to which all organisms represented in the diagram relate
rotational movement: movement of a bone as it rotates around its own longitudinal axis
rough endoplasmic reticulum (RER): region of the endoplasmic reticulum that is studded with ribosomes and engages in protein modification and phospholipid synthesis
roughage: component of food that is low in energy and high in fiber
Ruffini ending: (also, bulbous corpuscle) slowly-adapting mechanoreceptor in the skin that responds to skin stretch and joint position
ruminant: animal with a stomach divided into four compartments
runner: stolon that runs above the ground and produces new clone plants at nodes
S phase: second, or synthesis, stage of interphase during which DNA replication occurs
S-layer: surface-layer protein present on the outside of cell walls of archaea and bacteria
S-shaped growth curve: shape of a logistic growth curve
saddle joint: joint with concave and convex portions that fit together; named because the ends of each bone resemble a saddle
sagittal plane: plane cutting through an animal separating the individual into right and left sides
salamander: tailed amphibian that belongs to the clade Urodela
salivary amylase: enzyme found in saliva, which converts carbohydrates to maltose
saltatory conduction: “jumping” of an action potential along an axon from one node of Ranvier to the next
sand: soil particles between 0.1–2 mm in diameter
saprobe: organism that derives nutrients from decaying organic matter; also saprophyte
saprophyte: plant that does not have chlorophyll and gets its food from dead matter
sarcolemma: plasma membrane of a skeletal muscle fiber
sarcomere: functional unit of skeletal muscle
Sarcopterygii: lobe-finned fish
Sargassum: type of free-floating marine seaweed
satellite glia: glial cell that provides nutrients and structural support for neurons in the peripheral nervous system
saturated fatty acid: long-chain hydrocarbon with single covalent bonds in the carbon chain; the number of hydrogen atoms attached to the carbon skeleton is maximized
sauropsid: reptile or bird
scapula: flat, triangular bone located at the posterior pectoral girdle
scarification: mechanical or chemical processes to soften the seed coat
schizocoelom: coelom formed by groups of cells that split from the endodermal layer
schizocoely: during development of protostomes, a solid mass of mesoderm splits apart and forms the hollow opening of the coelom
schizophrenia: mental disorder characterized by the inability to accurately perceive reality; patients often have difficulty thinking clearly and can suffer from delusions
Schwann cell: glial cell that creates myelin sheath around a peripheral nervous system neuron axon
science: knowledge that covers general truths or the operation of general laws, especially when acquired and tested by the scientific method
scientific method: method of research with defined steps that include observation, formulation of a hypothesis, testing, and confirming or falsifying the hypothesis
scion: the part of a plant that is grafted onto the root stock of another plant
sclerenchyma cell: plant cell that has thick secondary walls and provides structural support; usually dead at maturity
sclerocyte: cell that secretes silica spicules into the mesohyl
scrotum: sac containing testes; exterior to the body
scutellum: type of cotyledon found in monocots, as in grass seeds
sebaceous gland: in mammals, a skin gland that produce a lipid mixture called sebum
second messenger: small, non-protein molecule that propagates a signal within the cell after activation of a receptor causes its release
secondary active transport: movement of material that results from primary active transport to the electrochemical gradient
secondary consumer: usually a carnivore that eats primary consumers
secondary feather: feather located at the base of the wing that provides lift
secondary growth: growth resulting in an increase in thickness or girth; caused by the lateral meristem and cork cambium
secondary plant compound: compound produced as byproducts of plant metabolic processes that is usually toxic, but is sequestered by the plant to defend against herbivores
secondary structure: regular structure that proteins form by intramolecular hydrogen bonding between the oxygen atom of one amino acid residue and the hydrogen attached to the nitrogen atom of another amino acid residue
secondary succession: succession in response to environmental disturbances that move a community away from its equilibrium
secretin: hormone which stimulates sodium bicarbonate secretion in the small intestine
seed: structure containing the embryo, storage tissue, and protective coat
seedless vascular plant: plant that does not produce seeds
segmental artery: artery that branches from the renal artery
selective pressure: environmental factor that causes one phenotype to be better than another
selectively permeable: membrane characteristic that allows some substances through (also known as semipermeable)
self-pollination: transfer of pollen from the anther to the stigma of the same flower
semelparity: life history strategy characterized by a single reproductive event followed by death
semen: fluid mixture of sperm and supporting materials
semi-permeable membrane: membrane that allows only certain solutes to pass through
semicircular canal: one of three half-circular, fluid-filled tubes in the vestibular labyrinth that monitors angular acceleration and deceleration
semilunar valve: membranous flap of connective tissue between the aorta and a ventricle of the heart (the aortic or pulmonary semilunar valves)
seminal vesicle: secretory accessory gland in males; contributes to semen
seminiferous tubule: site of sperm production in testes
senescence: process that describes aging in plant tissues
sensory receptor: specialized neuron or other cells associated with a neuron that is modified to receive specific sensory input
sensory transduction: conversion of a sensory stimulus into electrical energy in the nervous system by a change in the membrane potential
sensory-somatic nervous system: system of sensory and motor nerves
sepal: modified leaf that encloses the bud; outermost structure of a flower
septa: cell wall division between hyphae
septum: structure formed in a bacterial cell as a precursor to the separation of the cell into two daughter cells
sequence mapping: mapping information obtained after DNA sequencing
serendipity: fortunate accident or a lucky surprise
serotype: strain of bacterium that carries a set of similar antigens on its cell surface, often many in a bacterial species
Sertoli cell: cell in seminiferous tubules that assists developing sperm and makes inhibin
serum: plasma without the coagulation factors
sesamoid bone: small, flat bone shaped like a sesame seed; develops inside tendons
sessile: leaf without a petiole that is attached directly to the plant stem
set point: midpoint or target point in homeostasis
seta: stalk that supports the capsule in mosses
seta/chaeta: chitinous projection from the cuticle
sex-linked: any gene on a sex chromosome
sexual dimorphism: phenotypic difference between a population's males and females
sexual reproduction: mixing of genetic material from two individuals to produce genetically unique offspring
shared ancestral character: describes a characteristic on a phylogenetic tree that all organisms on the tree share
shared derived character: describes a characteristic on a phylogenetic tree that only a certain clade of organisms share
Shine-Dalgarno sequence: (AGGAGG); initiates prokaryotic translation by interacting with rRNA molecules comprising the 30S ribosome
shoot system: aboveground portion of the plant; consists of nonreproductive plant parts, such as leaves and stems, and reproductive parts, such as flowers and fruits
short bone: bone that has the same width and length, giving it a cube-like shape
shotgun sequencing: method used to sequence multiple DNA fragments to generate the sequence of a large piece of DNA
sickle cell anemia: genetic disorder that affects the shape of red blood cells, and their ability to transport oxygen and move through capillaries
sieve-tube cell: phloem cell arranged end to end to form a sieve tube that transports organic substances such as sugars and amino acids
signal: method of communication between animals including those obtained by the senses of smell, hearing, sight, or touch
signal integration: interaction of signals from two or more different cell-surface receptors that merge to activate the same response in the cell
signal sequence: short tail of amino acids that directs a protein to a specific cellular compartment
signal transduction: propagation of the signal through the cytoplasm (and sometimes also the nucleus) of the cell
signaling cell: cell that releases signal molecules that allow communication with another cell
signaling pathway: (also signaling cascade) chain of events that occurs in the cytoplasm of the cell to propagate the signal from the plasma membrane to produce a response
silent mutation: mutation that is not expressed
silt: soil particles between 0.002 and 0.1 mm in diameter
simple epithelia: single layer of epithelial cells
simple fruit: fruit that develops from a single carpel or fused carpels
simple leaf: leaf type in which the lamina is completely undivided or merely lobed
simulation model: ecosystem model that is created with computer programs to holistically model ecosystems and to predict the effects of environmental disturbances on ecosystem structure and dynamics
single nucleotide polymorphism (SNP): variation between individuals in a single nucleotide
single-strand binding protein: during replication, protein that binds to the single-stranded DNA; this helps in keeping the two strands of DNA apart so that they may serve as templates
sink: growing parts of a plant, such as roots and young leaves, which require photosynthate
sinoatrial (SA) node: the heart’s internal pacemaker; located near the wall of the right atrium
siphon: tubular structure that serves as an inlet for water into the mantle cavity
sister taxa: two lineages that diverged from the same branch point
skeletal muscle tissue: forms skeletal muscles, which attach to bones and control locomotion and any movement that can be consciously controlled
skull: bone that supports the structures of the face and protects the brain
sliding clamp: ring-shaped protein that holds the DNA pol on the DNA strand
small 40S ribosomal subunit: ribosomal subunit that binds to the RNA to translate it into protein
small intestine: organ where digestion of protein, fats, and carbohydrates is completed
small nuclear RNA: molecules synthesized by RNA polymerase III that have a variety of functions, including splicing pre-mRNAs and regulating transcription factors
smooth endoplasmic reticulum (SER): region of the endoplasmic reticulum that has few or no ribosomes on its cytoplasmic surface and synthesizes carbohydrates, lipids, and steroid hormones; detoxifies certain chemicals (like pesticides, preservatives, medications, and environmental pollutants), and stores calcium ions
smooth muscle tissue: occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels
soil: outer loose layer that covers the surface of Earth
soil profile: vertical section of a soil
solar intensity: amount of solar power energy the sun emits in a given amount of time
solute: substance dissolved in a liquid to form a solution
solvent: substance capable of dissolving another substance
somatic cell: all the cells of a multicellular organism except the gametes or reproductive cells
somatosensation: sense of touch
somatostatin: hormone released to stop acid secretion when the stomach is empty
somite: group of cells separated by small spaces that form from the mesoderm and give rise to connective tissue
soredia: clusters of algal cells and mycelia that allow lichens to propagate
source: organ that produces photosynthate for a plant
source water: point of origin of a river or stream
Southern blotting: DNA transfer from a gel to a nylon membrane
speciation: formation of a new species
species: group of populations that interbreed and produce fertile offspring
species dispersion pattern: (also, species distribution pattern) spatial location of individuals of a given species within a habitat at a particular point in time
species richness: number of different species in a community
species-area relationship: relationship between area surveyed and number of species encountered; typically measured by incrementally increasing the area of a survey and determining the cumulative numbers of species
specific heat capacity: the amount of heat one gram of a substance must absorb or lose to change its temperature by one degree Celsius
spectrophotometer: instrument that can measure transmitted light and compute the absorption
spermatheca: specialized sac that stores sperm for later use
spermatogenesis: process of producing haploid sperm
spermatophyte: seed plant; from the Greek sperm (seed) and phyte (plant)
Sphenodontia: clade of tuataras
sphere of hydration: when a polar water molecule surrounds charged or polar molecules thus keeping them dissolved and in solution
sphincter: band of muscle that controls movement of materials throughout the digestive tract
spicule: structure made of silica or calcium carbonate that provides structural support for sponges
spinal cord: thick fiber bundle that connects the brain with peripheral nerves; transmits sensory and motor information; contains neurons that control motor reflexes
spinal nerve: nerve projecting between skin or muscle and spinal cord
spiral cleavage: cells of one pole of the embryo are rotated or misaligned with respect to the cells of the opposite pole
spirometry: method to measure lung volumes and to diagnose lung diseases
splicing: process of removing introns and reconnecting exons in a pre-mRNA
spongocoel: central cavity within the body of some sponges
spongy bone tissue: forms the inner layer of all bones
spontaneous mutation: mutation that takes place in the cells as a result of chemical reactions taking place naturally without exposure to any external agent
sporangium: reproductive sac that contains spores
spore: haploid cell that can produce a haploid multicellular organism or can fuse with another spore to form a diploid cell
spore: a haploid cell that can undergo mitosis to form a multicellular, haploid individual
sporocyte: diploid cell that produces spores by meiosis
sporophyll: leaf modified structurally to bear sporangia
sporophyte: a multicellular diploid life-cycle stage that produces haploid spores by meiosis
sporophyte: multicellular diploid stage in plants that is formed after the fusion of male and female gametes
sporopollenin: tough polymer surrounding the spore
Squamata: clade of lizards and snakes
squamous epithelia: type of epithelia made of flat cells, specialized in aiding diffusion or preventing abrasion
stabilizing selection: selection that favors average phenotypes
stamen: structure that contains the male reproductive organs
standard metabolic rate (SMR): metabolic rate at rest in ectothermic animals
stapes: (also, stirrup) third of the three bones of the middle ear
starch: storage carbohydrate in plants
start codon: AUG (or rarely, GUG) on an mRNA from which translation begins; always specifies methionine
statolith: (also, amyloplast) plant organelle that contains heavy starch granules
stele: inner portion of the root containing the vascular tissue; surrounded by the endodermis
stereocilia: in the auditory system, hair-like projections from hair cells that help detect sound waves
stereoscopic vision: two overlapping fields of vision from the eyes that produces depth perception
sternum: (also, breastbone) long, flat bone located at the front of the chest
steroid: type of lipid comprised of four fused hydrocarbon rings forming a planar structure
stigma: uppermost structure of the carpel where pollen is deposited
stipule: small green structure found on either side of the leaf stalk or petiole
stolon: modified stem that runs parallel to the ground and can give rise to new plants at the nodes
stoma: opening that regulates gas exchange and water evaporation between leaves and the environment, typically situated on the underside of leaves
stomach: saclike organ containing acidic digestive juices
stratified epithelia: multiple layers of epithelial cells
streptophytes: group that includes green algae and land plants
strigolactone: hormone that promotes seed germination in some species and inhibits lateral apical development in the absence of auxins
strobili: cone-like structures that contain the sporangia
strobilus: plant structure with a tight arrangement of sporophylls around a central stalk, as seen in cones or flowers; the male strobilus produces pollen, and the female strobilus produces eggs
stroke volume: the volume of blood pumped into the aorta per contraction of the left ventricle
stroma: fluid-filled space surrounding the grana inside a chloroplast where the light-independent reactions of photosynthesis take place
stromatolite: layered sedimentary structure formed by precipitation of minerals by prokaryotes in microbial mats
structural isomers: molecules that share a chemical formula but differ in the placement of their chemical bonds
style: long, thin structure that links the stigma to the ovary
subduction: movement of one tectonic plate beneath another
substituted hydrocarbon: hydrocarbon chain or ring containing an atom of another element in place of one of the backbone carbons
substrate: molecule on which the enzyme acts
substrate-level phosphorylation: production of ATP from ADP using the excess energy from a chemical reaction and a phosphate group from a reactant
sucrase: enzyme that breaks down sucrose into glucose and fructose
sulcus: (plural: sulci) indents or “valleys” in the cortex
sum rule: probability of the occurrence of at least one of two mutually exclusive events is the sum of their individual probabilities
summation: process of multiple presynaptic inputs creating EPSPs around the same time for the postsynaptic neuron to be sufficiently depolarized to fire an action potential
superior colliculus: paired structure in the top of the midbrain, which manages eye movements and auditory integration
superior vena cava: drains blood from the jugular vein that comes from the brain and from the veins that come from the arms
supination: movement of the radius and ulna bones of the forearm so that the palm faces forward
suprachiasmatic nucleus: cluster of cells in the hypothalamus that plays a role in the circadian cycle
surface tension: tension at the surface of a body of liquid that prevents the molecules from separating; created by the attractive cohesive forces between the liquid's molecules
surfactant: detergent-like liquid in the airways that lowers the surface tension of the alveoli to allow for expansion
survivorship curve: graph of the number of surviving population members versus the relative age of the member
suspensor: part of the growing embryo that makes connection with the maternal tissues
sutural bone: small, flat, irregularly shaped bone that forms between the flat bones of the cranium
suture: short fiber of connective tissue that holds the skull bones tightly in place; found only in the skull
swim bladder: in fishes, a gas filled organ that helps to control the buoyancy of the fish
symbiont: plant in a symbiotic relationship with bacteria or fungi
symbiosis: close interaction between individuals of different species over an extended period of time that impacts the abundance and distribution of the associating populations
sympathetic nervous system: division of autonomic nervous system activated during stressful “fight or flight” situations
sympatric speciation: speciation that occurs in the same geographic space
symphysis: hyaline cartilage covers the end of the bone, but the connection between bones occurs through fibrocartilage; symphyses are found at the joints between vertebrae
symporter: transporter that carries two different ions or small molecules, both in the same direction
synapse: junction between two neurons where neuronal signals are communicated
synapsid: mammal having one temporal fenestra
synapsis: formation of a close association between homologous chromosomes during prophase I
synaptic cleft: space between the presynaptic and postsynaptic membranes
synaptic signal: chemical signal (neurotransmitter) that travels between nerve cells
synaptic vesicle: spherical structure that contains a neurotransmitter
synaptonemal complex: protein lattice that forms between homologous chromosomes during prophase I, supporting crossover
synarthrosis: joint that is immovable
synchondrosis: bones joined by hyaline cartilage; synchondroses are found in the epiphyseal plates of growing bones in children
syndesmosis: joint in which the bones are connected by a band of connective tissue, allowing for more movement than in a suture
synergid: type of cell found in the ovule sac that secretes chemicals to guide the pollen tube towards the egg
synovial joint: only joint that has a space between the adjoining bones
systematics: field of organizing and classifying organisms based on evolutionary relationships
systemic circulation: flow of blood away from the heart to the brain, liver, kidneys, stomach, and other organs, the limbs, and the muscles of the body, and then the return of this blood to the heart
systems biology: study of whole biological systems (genomes and proteomes) based on interactions within the system
systole: contraction phase of cardiac cycle when the ventricles are pumping blood into the arteries
Biology 2e, March 28, 2018, OpenStax, https://openstax.org/books/biology-2e/pages/1-introduction