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Biology LibreTexts

Glossary

  • Page ID
    22673
  • A

    abdominopelvic cavity

    body cavity that fills the lower half of the trunk and holds the kidneys and the digestive and reproductive organs

    abiotic factor

    nonliving aspect of the environment such as sunlight, air, or water

    ABO blood group system

    system of red blood cell antigens controlled by a single gene with three common alleles on chromosome 9 that produces types A, B, AB, and O blood

    absolute dating

    carbon-14 or other method of dating fossils that gives an approximate age in years

    absorption

    process in which substances such as nutrients pass into the blood or lymph

    accessory organ of digestion

    digestive organ that releases substances into the duodenum for chemical digestion but through which food does not pass; liver, gallbladder, or pancreas

    acclimatization

    development of reversible changes to environmental stress over a relatively short period of time

    acid

    solution with a pH lower than 7

    acid rain

    low-pH precipitation that forms when certain primary pollutants in the atmosphere combine with water

    acne

    common skin disorder in which pimples, blackheads, nodules, or other skin lesions occur when bacteria infect sebum-clogged pores

    acquired immunodeficiency syndrome (AIDS)

    disorder characterized by frequent opportunistic infections that may eventually develop in people who are infected with human immunodeficiency virus (HIV)

    actin

    thin protein filament in muscle cells that slides over a thick myosin filament to produce a muscle contraction

    action potential

    reversal of electrical charge across the membrane of a resting neuron that travels down the axon of the neuron as a nerve impulse

    activation energy

    energy needed to start a chemical reaction

    active immunity

    ability to resist a specific pathogen that results when an adaptive immune response to the pathogen produces memory lymphocytes for that pathogen

    active transport

    movement of substances across a plasma membrane that requires energy

    acute disease

    short-term illness

    adaptation

    genetically based trait that has evolved because it helps living things survive and reproduce in a given environment

    adaptive immune system

    subset of the immune system that makes tailored attacks against specific pathogens or tumor cells such as the production of antibodies that match specific antigens

    adaptive radiation

    process by which a single species evolves into many new species to fill available niches

    Addison’s disease

    disorder characterized by hyposecretion of the adrenal cortex hormone cortisol, generally because the immune system attacks and destroys the adrenal gland

    adhesion

    in the context of human reproduction, process in which a sperm "sticks" to an egg due to sperm-receptor proteins on the egg

    adipose tissue

    type of connective tissue that is composed mainly of fat-storage cells called adipocytes; also called body fat

    admixture

    situation in which new DNA sequences enter a population’s gene pool through interbreeding with individuals in another population

    adolescence

    period of transition between childhood and adulthood during which significant physical, cognitive, and psychosocial changes occur

    adolescent growth spurt (AGS)

    period of rapid physical growth that occurs during puberty

    adrenal cortex

    outer layer of the adrenal gland that produces steroid hormones such as cortisol and aldosterone

    adrenal gland

    one of a pair of glands located on top of the kidneys that secretes hormones such as cortisol and adrenaline

    adrenaline

    non-steroid catecholamine hormone produced by the medulla of the adrenal glands that stimulates the fight-or-flight response

    adrenal medulla

    central part of an adrenal gland that is surrounded by the adrenal cortex and that produces catecholamine hormones including adrenaline

    adulthood

    life stage of the human organism between adolescence and death

    aerobic

    referring to anything, such as a process or an organism, that requires oxygen

    aerobic exercise

    any physical activity in which muscles are used well below their maximum contraction strength but for a relatively long period of time, consuming a large amount of oxygen

    age-related macular degeneration (AMD)

    common cause of blindness that occurs because cells of the macula die

    age-sex structure

    number of individuals of each sex and age or age group in a population

    agonist

    any psychoactive drug that increases the activity of particular neurotransmitters

    Air Quality Index (AQI)

    assessment of the levels of pollutants in the outdoor air that is based on their human health effects

    alcoholic fermentation

    type of anaerobic respiration that includes glycolysis followed by the conversion of pyruvic acid to ethanol and carbon dioxide and the formation of NAD+

    algal bloom

    excessive growth of algae in bodies of water because of high levels of nutrients, usually from fertilizer in runoff

    allele

    one of two or more different versions of the same gene

    allele frequency

    how often an allele occurs in a gene pool relative to the other alleles for that gene

    Allen’s rule

    ecogeographic rule stating that animals living in hotter climates generally have longer extremities than closely related animals living in colder climates

    allergen

    any substance, typically an antigen, that causes an allergy

    allergy

    disorder in which the immune system makes an inflammatory response to a harmless antigen

    allopatric speciation

    evolution of a new species that occurs when some individuals become geographically separated from the rest of their species

    alveolus (plural, alveoli)

    one of a cluster of tiny sacs at the ends of bronchioles in the lungs where pulmonary gas exchange takes place

    amino acid

    small molecule that is a building block of proteins

    amnion

    membrane forming a fluid-filled sac that surrounds and protects an embryo and fetus

    anabolic reaction

    endothermic reaction in organisms

    anaerobic

    referring to anything, such as a process or an organism, that does not require oxygen

    anaerobic exercise

    any physical activity in which muscles are used at close to their maximum contraction strength but for a relatively short period to time, consuming a small amount of oxygen

    anaerobic respiration

    type of cellular respiration, such as fermentation, that does not require oxygen

    analogous structure

    structure that is similar in unrelated organisms because it evolved to perform the same function and not because it was inherited from a common ancestor

    anaphase

    third phase of mitosis during which sister chromatids separate and move to opposite poles of the cell

    anaphylaxis

    severe, systemic allergic reaction that is considered a medical emergency

    anatomically modern human

    any early member of the species Homo sapiens who was virtually indistinguishable in physical traits from humans today but was not necessarily behaviorally modern

    anatomy

    study of the structure of the body

    androgen

    general term for a male sex hormone such as testosterone

    anemia

    disorder in which the blood has an inadequate volume of red blood cells, which are needed to carry oxygen to cells

    angina

    chest pain or pressure that occurs when heart muscle cells do not receive adequate blood flow and become starved of oxygen

    animal

    heterotrophic, multicellular eukaryote with cells that lack cell walls; member of the Animal Kingdom

    anorexia nervosa

    eating disorder in which people consistently eat very little, resulting in extremely low body weight and often other signs and symptoms of starvation

    antagonist

    any psychoactive drug that decreases the activity of particular neurotransmitters

    anterior pituitary

    front lobe of the pituitary gland that synthesizes and secretes pituitary hormones

    anthropogenic biome

    human-made terrestrial biome such as cropland, rangeland, or a dense settlement

    anthropoid

    any non-prosimian primate; monkey, ape, or human

    antibiotic drug

    drug that kills bacteria and usually cures bacterial infections and diseases

    antibiotic resistance

    ability to withstand antibiotic drugs that has evolved in some bacteria

    antibody

    large, Y-shaped protein produced by B cells that recognizes and binds to a nonself antigen in a humoral immune response

    anticodon

    string of three nucleotide bases that are complementary to the three nucleotide bases of a codon for an amino acid

    antigen

    molecule that the immune system identifies as either self or nonself and, if the latter, may respond to by forming antibodies

    anus

    final part of the large intestine with an opening to the outside for feces to pass through

    anxiolytic

    type of psychoactive drug that has a tranquilizing effect and inhibits anxiety

    Apgar test

    simple assessment given to an infant immediately after birth to evaluate its transition from the uterus to the outside world

    aphotic zone

    water in an aquatic biome that is deeper than 200 meters and where too little sunlight penetrates for photosynthesis to take place

    appendicular skeleton

    bones of the upper and lower limbs, shoulder girdle, and pelvic girdle

    appendix

    vestigial organ that projects from the colon of the large intestine and has no apparent function in adults

    aquatic biome

    any water-based biome; may be a freshwater or saltwater biome

    aquifer

    underground layer of rock that stores water

    arboreal

    referring to trees, as in arboreal, or tree-living, animal

    Archaea

    one of two prokaryotic domains; includes organisms that live in extreme environments

    archaic human

    member of any now-extinct species of Homo that existed between about 500,000 years ago and the evolution of Homo sapiens, including the species Homo neanderthalensis, Homo floresiensis, and Homo denisova

    areolar connective tissue

    common form of loose connective tissue found in the skin and mucous membranes and around blood vessels and internal organs

    artery

    type of blood vessel that carries blood away from the heart and toward the lungs or body

    artificial selection

    process in which organisms evolve traits useful to humans because people select which individuals are allowed to reproduce and pass on their genes to successive generations

    assisted reproductive technology (ART)

    collection of medical procedures in which eggs and sperm are removed from an infertile couple and manipulated in ways that increase the chances of fertilization occurring, such as in vitro fertilization

    asthma

    chronic inflammatory disease of the respiratory system in which airways periodically become inflamed, causing swelling and narrowing of the airways, which makes breathing difficult

    atherosclerosis

    condition in which plaque builds up inside arteries, eventually causing the lumen inside to narrow and the arterial walls to stiffen

    athlete’s foot

    infection of the skin between the toes by the fungus Trichophyton

    atom

    smallest particle of an element that still has the properties of that element

    ATP (adenosine triphosphate)

    energy-carrying molecule that cells use to power their metabolic processes

    atrium (plural, atria)

    one of the two upper chambers of the heart that pumps blood to the ventricle below it

    atrophy

    decrease in the size of a structure, such as a decrease in the size of a muscle through nonuse

    Australopithecus

    genus of early hominins that is thought to be ancestral to the human genus Homo

    autoimmune disease

    type of disease, such as type 1 diabetes, in which the immune system attacks the body’s own cells as though they were pathogens

    autonomic nervous system

    division of the peripheral nervous system that controls involuntary activities

    autosomal trait

    any genetic trait controlled by a gene on an autosome

    autosome

    any of the chromosomes numbered 1 to 22 in humans that contains genes for characteristics unrelated to sex determination

    autotroph

    organism that uses energy directly from the sun or from chemical bonds to produce organic compounds from simple inorganic molecules

    axial skeleton

    division of the skeleton that includes the skull, rib cage, and vertebral column

    axon

    long extension of the cell body of a neuron that transmits nerve impulses to other cells

    B

    baby boom

    period marked by a temporary but dramatic increase in the birth rate

    Bacteria

    one of two domains of prokaryotes, some of which cause human diseases

    balance

    ability to sense and maintain an appropriate body position

    bariatric surgery

    weight-loss surgery for obesity that modifies the digestive system to limit the intake of food and/or absorption of nutrients from food

    barrier method

    type of contraception in which a device such as a condom or diaphragm is used to physically block sperm from entering the uterus

    basal cell carcinoma

    most common type of skin cancer that occurs in basal cells of the epidermis and rarely metastasizes

    basal metabolic rate (BMR)

    amount of energy needed to keep the body functioning at rest

    base

    solution with a pH higher than 7

    B cell

    type of lymphocyte that fights infections by forming antibodies

    Bergmann’s rule

    ecogeographic rule stating that, within a broadly distributed taxonomic group, populations or species of larger size are found in colder environments, whereas populations or species of smaller size are found in warmer environments

    bile

    fluid produced by the liver and stored in the gall bladder that is secreted into the small intestine to help digest lipids and neutralize acid from the stomach

    bilirubin

    brown pigment secreted into bile by the liver that is a byproduct of catabolism of dead red blood cells and is excreted in feces by the large intestine

    binding site

    region of a protein responsible for binding with another molecule

    binge eating disorder

    eating disorder in which people repeatedly binge on a large amount of food, followed by feelings of guilt but not purging and usually leading to excessive weight gain

    binomial nomenclature

    method of naming species with two names, consisting of the genus name and species name

    bioaccumulation

    increasing concentration of a nonbiodegradable substance as it passes from lower to higher trophic levels in an ecosystem

    biochemical compound

    any carbon-based chemical compound that helps make up the cells of living things or carry out life processes

    biochemical reaction

    chemical reaction that occurs inside living things

    biodegradable

    referring to a substance such as a pollutant that breaks down in the environment due to natural processes

    biodiversity

    all of the variety of life that exists on Earth, including the diversity of genes, species, and ecosystems

    biodiversity hotspot

    area with a high level of biodiversity that is under serious threat from human actions

    biogeochemical cycle

    interconnected pathways through which water or a chemical element such as carbon or nitrogen is continuously recycled through the biotic and abiotic components of ecosystems

    biogeography

    study of how and why organisms live where they do

    biomass

    amount of organic matter present in an individual organism or in all the organisms at a given trophic level

    biomass energy

    energy obtained from living or recently living things, such as wood or biogas made from crops such as sugarcane

    biome

    group of similar ecosystems with the same general type of physical environment anywhere in the world

    biopsy

    surgical removal of a tissue specimen for analysis in a medical laboratory, usually to diagnose cancer

    biosphere

    every part of Earth where life exists, including land, water, and air

    biotechnology

    use of technology to change the genetic makeup of living things in order to produce useful products

    biotic factor

    living aspect of the environment, including any organism of the same or different species

    bipedalism

    walking on two legs

    birth rate

    number of births in one year per 1,000 people in a population

    birthweight

    weight of a baby at birth

    Black Death

    mid-14th century Eurasian plague pandemic that was one of the deadliest pandemics in human history

    bladder infection

    common type of urinary tract infection in which the bladder becomes infected, usually by bacteria but occasionally by fungi

    blastocoele

    fluid-filled cavity within a blastocyst

    blastocyst

    fluid-filled ball of cells that develops a few days after fertilization in the process of blastulation

    blastulation

    process during the germinal stage in which the solid ball of cells called the morula changes into a fluid-filled ball of cells called the blastocyst

    blind experiment

    scientific experiment in which subjects do not know in which experimental group they have been placed to help avoid bias in the outcome

    blood

    fluid connective tissue that circulates throughout the body through blood vessels

    blood-brain barrier

    highly selective membrane formed of epithelial cells that separates circulating blood from extracellular fluid in the brain and spinal cord

    blood group system

    all of the genes, alleles, and possible genotypes and phenotypes that exist for a particular set of blood type antigens

    blood pressure

    measure of the force exerted by circulating blood on the walls of arteries

    blood type

    genetic characteristic associated with the presence or absence of antigens on the surface of red blood cells

    blood vessel

    hollow, tube-like structure through which blood flows in the cardiovascular system; vein, artery, or capillary

    body cavity

    fluid-filled space inside the body that holds and protects internal organs

    body mass index (BMI)

    estimate of the fat content of the body that is calculated by dividing a person’s weight (in kilograms) by the square of the person’s height (in meters)

    bolus

    lump of swallowed food

    bone marrow

    soft connective tissue in spongy bone that produces blood cells

    bone remodeling

    continuous, lifelong process in which existing bone is resorbed by osteoclasts and new bone is made by osteoblasts

    bone repair

    process in which bone heals itself following a bone fracture

    bone tissue

    hard connective tissue in bones that consists mainly of mineralized collagen matrix; also called osseous tissue

    Bowman’s capsule

    structure surrounding the glomerulus of a nephron in a kidney into which substances that are filtered out of blood are passed to the renal tubule

    brain

    central nervous system organ inside the skull that is the control center of the nervous system

    brain stem

    lowest part of the brain that connects the brain with the spinal cord and controls unconscious functions such as heart rate and breathing

    Broca’s area

    speech center in the brain that controls speech production

    bronchus (plural, bronchi)

    one of many tubes of various sizes that carry air between the trachea and the alveoli in the lungs

    bulbourethral gland

    one of a pair of glands in the male reproductive system that secretes a fluid to help lubricate the urethra and neutralize any urine it may contain before ejaculation occurs; also called Cowper’s gland

    bulimia nervosa

    eating disorder in which people recurrently binge on large amounts of food, following by purging the food from the body, for example, by vomiting

    C

    calcitonin

    endocrine hormone secreted by the thyroid gland that helps regulate calcium homeostasis by stimulating bones to absorb calcium from the blood

    Calorie

    unit used to measure the energy in food, where 1 Calorie is the amount of energy needed to raise 1 kilogram of water by 1 degree Celsius; also called kilocalorie

    Cambrian explosion

    spectacular burst of new life that occurred at the start of the Paleozoic Era

    cancer

    disease that occurs when the cell cycle is no longer regulated and cells divide out of control

    cancer staging

    classifying cancer based on such factors as how large a tumor is and the extent to which the cancer has spread

    candidiasis

    infection of the mouth or vagina that is caused by the yeast Candida

    canine tooth

    one of four pointed teeth on either side of the front teeth that are used for tearing foods

    capillary

    smallest type of blood vessel that connects arterioles and venules and that transfers substances between blood and tissues

    carbohydrate

    major class of biochemical compounds that includes sugars, starches, glycogen, cellulose, and chitin

    carbon cycle

    biogeochemical cycle through which carbon is recycled through the biotic and abiotic components of ecosystems

    carcinogen

    anything that can cause cancer

    cardiac cycle

    contraction of the heart’s atria and ventricles to produce a single heartbeat, consisting of diastole and systole

    cardiac muscle

    involuntary, striated muscle found only in the walls of the heart; also called myocardium

    cardiovascular disease (CVD)

    class of diseases that involve the heart or blood vessels

    cardiovascular system

    organ system consisting of the heart, blood vessels, and blood that transports materials to and from cells of the body

    carnivore

    consumer that eats animals

    carotene

    pigment in the epidermis that gives skin a yellowish tint, especially in skin with low levels of melanin

    carpal tunnel syndrome

    musculoskeletal disorder that occurs when a nerve becomes compressed between carpal bones in the wrist, leading to reduced innervation of the thumb and first two fingers

    carrying capacity (K)

    largest population size that can be supported in an area without harming the environment

    cartilage

    dense connective tissue that provides a smooth surface for the movement of bones at joints

    cartilaginous joint

    partly movable joint in which bones are joined by cartilage

    case-control study

    observational study in which a group of subjects with a trait (cases) is compared retrospectively with a group of subjects without the trait (controls)

    catabolic reaction

    exothermic reaction in organisms

    catecholamine

    any non-steroid hormone, such as adrenaline, that is produced by the medulla of the adrenal gland and that stimulates the fight-or-flight response

    cell

    basic unit of structure and function of living things

    cell body

    central part of a neuron that contains the nucleus and other cell organelles

    cell cycle

    repeating series of events that a cell goes through during its life including growth,

    DNA replication, and cell division

    cell division

    process in which a parent cell divides to form two daughter cells

    cell theory

    theory that all living things are made of cells, all life functions occur within cells, and all cells come from pre-existing cells

    cellular respiration

    process in which cells break down glucose and make ATP for energy

    cellulose

    complex carbohydrate (polysaccharide) that is an important structural component of the cell walls of plants and many algae

    Cenozoic Era

    era of "modern life," also called the age of mammals, which began about 65 million years ago and still continues in the present

    central nervous system (CNS)

    one of two main divisions of the nervous system that includes the brain and spinal cord

    central obesity

    type of obesity in which most of the excess fat is stored in the abdomen, placing the obese person at greater risk of adverse health consequences of obesity, such as type 2 diabetes and cardiovascular disease

    centriole

    organelle in eukaryotic cells that helps organize the chromosomes before cell division occurs, so that each daughter cell has the correct number of chromosomes after the cell divides

    centromere

    region of sister chromatids where they are joined together

    cerebellum

    part of the brain below the cerebrum and behind the brain stem that coordinates body movements

    cerebral cortex

    highly folded, thin outer layer of the cerebrum where most information processing in the brain takes place

    cerebrospinal fluid

    clear fluid produced by the brain that forms a thin layer within the meninges and provides protection and cushioning for the brain and spinal cord

    cerebrum

    largest part of the brain that controls conscious functions such as reasoning and sight

    cervical cancer

    cancer of the cervix of the uterus, usually caused by infection with human papillomavirus (HPV)

    cervix

    neck of the uterus that protrudes down into the vagina and through which a canal connects the vagina and uterus

    Chargaff’s rules

    observations by Erwin Chargaff that concentrations of the four nucleotide bases in nucleic acids differ among species and that, within a species, the concentrations of adenine and thymine are always about the same, as are the concentrations of cytosine and guanine

    chemical bond

    force holding together atoms in a molecule that occurs when atoms share electrons

    chemical digestion

    chemical breakdown of large, complex food molecules into smaller, simpler nutrient molecules that can be absorbed by blood or lymph

    chemical equation

    symbolic way of showing what happens in a chemical reaction

    chemical reaction

    molecular process that changes some chemical substances into others

    chemoautotroph

    producer that uses energy in chemical bonds to produce organic molecules by chemosynthesis

    chemoreceptor

    type of sensory receptor that responds to chemicals

    chemosynthesis

    process of using the energy in chemical bonds to make organic molecules from inorganic substances

    chemotaxis

    movement of a living structure in response to a chemical signal, as when chemical signals from an egg direct the movement of sperm toward the egg

    chemotherapy

    treatment of cancer using one or more drugs that kill cancer cells

    childhood

    stage of the human organism between birth and adolescence

    chitin

    tough, complex carbohydrate (polysaccharide) that makes up the cell walls of fungi and the exoskeletons of insects and other arthropods

    chlamydia

    sexually transmitted infection by the bacterium Chlamydia trachomatis that is the most common bacterial STI in the United States

    chorion

    membrane formed from extraembryonic cells that helps form the fetal portion of the placenta

    chromatid

    one of two identical copies of a chromosome that are joined together at a centromere before a cell divides

    chromatin

    grainy material that DNA forms when it is not coiled into chromosomes

    chromosomal alteration

    mutation that changes chromosome structure

    chromosome

    coiled structure made of DNA and proteins that is the form in which the genetic material of a cell goes through cell division

    chronic disease

    long-term or lifelong disease

    chronic obstructive pulmonary disease (COPD)

    lung disease characterized by chronic poor airflow, most often following years of tobacco smoking

    chyme

    thick, semi-liquid mixture that food in the gastrointestinal tract becomes by the time it leaves the stomach

    cilia (singular, cilium)

    short, hairlike projections that extend from some cells, such as cells lining the airways

    circadian rhythm

    regular change in biology or behavior that occurs in a 24-hour cycle

    clade

    group of related organisms that includes an ancestor and all of its descendants

    cladogram

    branching diagram representing related organisms in which each branch represents the emergence of new traits that separate one group of organisms from the rest

    cleavage

    first several mitotic divisions of a fertilized egg that lead to the formation of a solid ball of cells called a morula

    climate

    average weather in an area over a long period of time

    climate change

    any change in average weather condition on Earth that lasts for at least several decades; often used to refer to ongoing global warming

    cline

    line on a map connecting populations that have the same frequency of an allele or of a genetic trait, showing the geographic distribution of the allele or trait

    clitoris

    small, sensitive external female organ that is part of the vulva and may lead to sexual arousal when stimulated

    coagulation

    process by which blood changes from a liquid to a gel to form a blood clot

    coal

    naturally occurring renewable solid fossil fuel that produces the most pollution and greenhouse gases when it is burned

    cochlea

    coiled, fluid-filled tube in the inner ear that changes mechanical sound vibrations and positional information to nerve impulses that travel to the brain

    codominance

    relationship between two alleles for the same gene in which both alleles are expressed equally in the phenotype of the heterozygote

    codon

    group of three nitrogen bases in nucleic acids that makes up a code "word" of the genetic code

    coevolution

    process in which two interacting species evolve together, with each species influencing the other’s evolution

    coextinction

    phenomenon in which extinction of one species causes a second species to go extinct because the first species is a necessary resource for the second species

    cohort study

    observational study in which a group of subjects selected at the start of the study (the cohort) is followed prospectively into the future

    collecting duct

    one of a network of ducts in a kidney where additional water may be reabsorbed from urine

    colon

    main part of the large intestine between the small intestine and rectum where water and salts are removed from liquid food wastes to form feces

    commensalism

    symbiotic relationship between two species in which one species benefits while the other species is unaffected

    community

    all the populations of all the species that live and interact in an ecosystem

    compact bone

    dense outer layer of bone that is very hard and strong

    comparative anatomy

    study of the similarities and differences in the structures of different species

    comparative embryology

    study of the similarities and differences in the embryos of different species

    competitive exclusion principle

    principle of ecology stating that two different species cannot occupy the same niche in the same place for very long

    complementary base pair

    pair of nucleotide bases that bond together; either adenine and thymine (or uracil) or cytosine and guanine

    complement system

    innate immune response that consists of a cascade of proteins that complement the killing of pathogens by antibodies

    complex carbohydrate

    polysaccharide such as starch, glycogen, cellulose, or chitin

    compound

    substance with a unique, fixed composition that consists of two or more elements

    connective tissue

    tissue made up of cells that form the body’s structure, such as bone and cartilage, and in which cells are separated by non-living material called extracellular matrix

    consensus science

    science undertaken in areas in which a great deal of evidence has already accumulated

    consumer

    organism that consumes other organisms to obtain organic compounds

    contraception

    any method or device used to prevent pregnancy; also called birth control

    control center

    component of a homeostatic control mechanism that monitors a variable and sends signals to the effector as needed to keep the variable in homeostasis

    coronary artery

    one of two arteries that supply the cells of the heart with oxygen and nutrients

    coronary artery disease

    class of diseases that result from atherosclerosis of coronary arteries; includes angina and myocardial infarction

    corpus luteum

    ovarian structure that forms from a follicle after it matures and ovulates an egg

    correlation

    association between variables in which a change in one variable is associated with a change in the other variable

    cortical bone tissue

    type of bone tissue that is smooth and dense and makes up the outer layer of bones

    corticosteroid

    any steroid hormone produced by the cortex of the adrenal gland; includes mineralocorticoids, glucocorticoids, and androgens

    cortisol

    glucocorticoid hormone produced by the cortex of the adrenal gland that helps control metabolic rate, suppression of the immune system, and other functions

    cranial cavity

    cavity that fills most of the upper part of the skull and contains the brain

    cranium

    upper part of the skull that encloses and protects the brain; also called braincase

    Crohn’s disease

    inflammatory bowel disease that may affect any part of the gastrointestinal tract from the mouth to the anus

    crossbridge cycling

    sequence of molecular events that forms crossbridges between myosin and actin filaments in muscle fibers, allowing for muscle contraction

    cross-contamination

    contamination of a food by microbes in another food with which it comes into contact either directly or indirectly

    crossing-over

    exchange of genetic material between homologous chromosomes when they are closely paired during meiosis I

    cross-sectional study

    observational study in which data are collected from a sample of subjects just once at a certain point in time

    culture

    entire way of life of a group of people

    Cushing’s disease

    disorder in which there is hypersecretion of the adrenal cortex hormone cortisol, most commonly due to a tumor of the pituitary gland

    cystic fibrosis

    autosomal recessive genetic disease that causes the production of sticky mucus that clogs respiratory and digestive organs, causing frequent lung infections and malabsorption of nutrients

    cytokine

    chemical released by injured, infected, or immune cells that triggers inflammation or other immune responses

    cytokinesis

    splitting of the cytoplasm to form daughter cells when a cell divides

    cytoplasm

    all of the material inside the plasma membrane of a cell (excluding organelles), consisting largely of cytosol

    cytoskeleton

    structure of filaments and tubules in the cytoplasm that provides a cell with an internal framework

    cytosol

    watery substance that makes up cytoplasm inside cells

    D

    data (singular, datum)

    observations collected in a scientific investigation in order to test a hypothesis

    dead zone

    area in the ocean or other body of water where low oxygen levels following excessive growth of algae have killed virtually all aquatic organisms

    death rate

    number of deaths per year per 1,000 people in a population

    deciduous teeth

    first set of 20 teeth that emerge in infancy and early childhood and are lost and replaced by permanent teeth during middle childhood; also called baby teeth

    decomposer

    organism that breaks down the remains of dead organisms or other organic wastes

    demographic transition

    major population shift in which the death rate falls and the population growth rate increases, followed later by the birth rate falling and the population growth rate decreasing

    demography

    scientific study of human populations

    dendrite

    extension of the cell body of a neuron that receives nerve impulses from other neurons

    dependent variable

    variable in a scientific experiment that is affected by another variable, known as the independent variable; also called outcome variable

    depressant

    type of psychoactive drug that calms the brain, reduces anxious feelings, and induces sleepiness

    dermis

    inner layer of skin that is made of tough connective tissue and contains blood vessels, nerve endings, hair follicles, and glands

    desalination

    process in which salt is removed from ocean water to produce fresh water for human use

    descriptive statistics

    statistics such as the mean and standard deviation that describe and summarize data

    developmental adjustment

    nongenetic phenotypic change that occurs during development in infancy or childhood and that may persist into adulthood and become irreversible

    diabetes mellitus

    disease caused by problems with the pancreatic hormone insulin, which lead to high blood glucose levels and symptoms such as excessive thirst and urination; includes type 1 and type 2 diabetes

    diabetic nephropathy

    progressive kidney disease caused by damage to capillaries in the glomeruli of the kidneys due to poor blood sugar control in people with diabetes

    diaphragm

    large, dome-shaped muscle below the lungs that allows breathing to occur when it alternately contracts and relaxes

    diastole

    part of a heartbeat in which the atria contract and pump blood into the ventricles, while the ventricles relax and fill with blood from the atria

    differentiation

    process by which unspecialized cells become specialized into one of many different types of cells, such as neurons or epithelial cells

    diffusion

    type of passive transport that does not require the help of transport proteins

    digestion

    process of breaking down food into nutrients that can be absorbed by blood or lymph

    digestive system

    organ system that breaks down food, absorbs nutrients, and eliminates any remaining wastes

    diploid

    having two of each type of chromosome, or twice the number of chromosomes as a haploid gamete

    directional selection

    type of natural selection for a polygenic trait in which one of two extreme phenotypes is selected for, resulting in a shift in the phenotypic distribution toward that extreme

    disaccharide

    sugar consisting of two monosaccharides

    disease

    condition associated with impairment of normal body functioning, generally causing signs or symptoms of illness

    disease burden

    impact of a disease on a population as measured by financial cost, mortality, morbidity, or other indicators

    disease outbreak

    event in which two or more people contract an infectious disease from a common source of infection

    disruptive selection

    type of natural selection for a polygenic trait in which phenotypes in the middle of the phenotypic distribution are selected against, resulting in two overlapping phenotypes, one at each end of the distribution

    diverticulitis

    disease in which one or more pouches (diverticula) in the large intestine become infected and inflamed

    diverticulosis

    condition in which pouches called diverticula form in the wall of the large intestine

    DNA (deoxyribonucleic acid)

    double-stranded DNA that makes up genes and chromosomes

    DNA replication

    natural process of copying DNA prior to cell division

    domain

    taxon in the revised Linnaean system that is larger and more inclusive than the kingdom

    dominant

    referring to an allele that masks the presence of another allele for the same gene when the two alleles occur together in a heterozygote, or referring to a trait that is controlled by such an allele

    dormancy

    state in which a plant slows down cellular activity and may shed its leaves

    dorsal cavity

    major human body cavity that includes the head and the posterior (back) of the trunk and holds the brain and spinal cord

    double-blind experiment

    scientific experiment in which neither the subjects nor the researchers know in which group subjects have been placed to help avoid bias in the outcome

    double helix

    double spiral shape of the DNA molecule

    doubling time

    time it would take a population to double in size at its current rate of growth

    drowning

    respiratory impairment from being in or under a liquid, whether or not death results

    drug abuse

    use of a drug without the advice of a medical professional and for reasons not originally intended

    drug addiction

    compulsive use of a substance such as a psychoactive drug despite negative consequences that such use may entail

    drug dependence

    condition in which stopping use of a substance such as a psychoactive drug produces physical and/or psychological symptoms

    duodenum

    first and shortest of three parts of the small intestine where most chemical digestion occurs

    E

    ear

    special sensory organ that collects and amplifies sound waves and information on body position and transforms them into nerve impulses that travel to the brain

    early adulthood

    first stage of human adulthood that coincides more or less with the 20s and early 30s

    early childhood

    stage of a human organism between infancy and middle childhood that covers the ages 1-5 years

    early modern human

    any member of the species Homo sapiens who lived prior to about 10,000 years ago

    eating disorder

    mental illness in which people feel compelled to eat in a way that causes physical, mental, and/or emotional health problems

    ecological succession

    changes through time in the numbers and types of species in an ecosystem

    ecology

    study of how living things interact with each other and their environment

    ecosystem

    all the biotic and abiotic factors in an area and their interactions

    ecosystem service

    any of the goods or services that healthy ecosystems provide to ensure the survival of living things on Earth

    ectoderm

    outer germ layer of an embryo that will eventually give rise to skin and nerve cells

    effector

    component of a homeostatic control mechanism, such as a gland or an organ, that acts on a signal from the control center to move the variable back toward the set point

    egg

    gamete produced by a female

    ejaculation

    process in males in which muscle contractions propel sperm from the epididymes and out through the urethra in semen

    ejaculatory duct

    one of two tubes in the male reproductive system that joins the vas deferens with the urethra and carries semen during ejaculation

    electromagnetic force

    atomic force holding together oppositely charged particles (electrons and protons) and repelling particles of the same charge (two electrons or two protons)

    electron transport

    third and final stage of cellular respiration in which electrons from NADH and FADH2 move along an electron-transport chain and protons (H+) are transferred across the membrane of a mitochondrion, thereby driving the synthesis of ATP

    element

    pure substance that cannot be broken down into other types of substances

    elimination

    process in which wastes pass out of the body

    embryo

    stage of growth and development that occurs from implantation in the uterus through the eighth week after fertilization

    embryoblast

    mass of cells inside a blastocyst that will eventually develop into an embryo

    embryonic disc

    two-layered disc of cells that forms by about 12 days after fertilization and is an early stage in embryo formation

    emergency contraception

    any form of birth control that is used after unprotected vaginal intercourse

    emerging infectious disease

    new infectious disease that has no prior history in a human population

    emigration

    movement of individuals out of a population

    empathogen

    type of psychoactive drug that produces feelings of empathy with other people

    emphysema

    lung disease, usually caused by smoking, in which walls of alveoli break down, so less gas can be exchanged in the lungs

    encephalization

    evolutionary enlargement of the brain relative to body size

    encephalization quotient

    measure for comparing brain sizes that corrects for differences in body size

    endemic disease

    disease that is present year-round in a population

    endemic species

    species native to a given region and not found naturally anywhere else on Earth

    endocrine gland

    any gland of the endocrine system, which is the system of glands that release their hormones into the blood

    endocrine hormone

    chemical messenger molecule secreted by a gland of the endocrine system into the blood

    endocrine system

    human body system of glands that release hormones into the blood

    endoderm

    inner germ layer of the embryo that eventually gives rise to cells of organs and glands such as the lungs and thyroid

    endometriosis

    disease in which endometrial tissue grows outside the uterus, typically causing pain and bleeding

    endometrium

    innermost layer of the uterus that builds up during each menstrual cycle and helps nourish the embryo if fertilization occurs or is shed from the uterus as menstrual flow if fertilization does not occur

    endoplasmic reticulum (ER)

    organelle in eukaryotic cells that helps make and transport proteins and lipids

    endosymbiotic theory

    theory that eukaryotic organelles such as mitochondria evolved from ancient, free-living prokaryotes that invaded primitive eukaryotic cells

    endothermic reaction

    chemical reaction that absorbs energy

    energy

    ability to do work

    energy density

    amount of Calories a food provides per unit of mass or volume

    energy homeostasis

    balance between the energy consumed in food and the energy expended in metabolism and physical activity

    enteric division

    division of the autonomic nervous system that controls digestive functions

    enzyme

    protein that speeds up biochemical reactions; biological catalyst

    epidemic

    large-scale disease outbreak in a population

    epidemiology

    study of the patterns, causes, and effects of diseases in human populations

    epidermis

    outer layer of skin that consists mainly of epithelial cells and lacks nerve endings, blood vessels, and other structures

    epididymis (plural, epididymes)

    one of two male reproductive organs where sperm mature and are stored until they leave the body during ejaculation

    epididymitis

    inflammation of the epididymis, which may be acute or chronic

    epistasis

    situation in which a gene affects the expression of another gene or genes

    epithelial tissue

    tissue made up of cells that line inner and outer body surfaces, such as skin and mucous membranes

    erectile dysfunction (ED)

    disorder characterized by the regular and repeated inability of a sexually mature male to obtain or maintain an erection of the penis

    erection

    state in which the penis becomes stiff and erect, usually during sexual arousal, as its columns of spongy tissue become engorged with blood

    esophagus

    long, narrow, tube-like digestive organ through which food passes from the pharynx to the stomach

    essential nutrient

    any nutrient that cannot be synthesized in the human body in adequate amounts for normal functioning so it must be obtained from food

    estrogen

    female sex hormone secreted mainly by the ovaries

    eukaryote

    organism that has cells containing a nucleus and other organelles

    eukaryotic cell

    cell that contains a nucleus and other organelles

    euphoria

    intense feeling of well-being and happiness

    euphoriant

    type of psychoactive drug that brings about a state of euphoria

    evidence

    any type of data that may be used to test a hypothesis

    evolution

    change in the genetic characteristics of living things over time

    exchange pool

    part of a biogeochemical cycle that holds an element or water for a short period of time

    excretion

    process of removing wastes and excess water from the body

    excretory system

    organ system that removes wastes and excess water from the body and includes the kidneys, large intestine, liver, skin, and lungs

    exocrine gland

    gland such as a sweat gland, salivary gland, or mammary gland that secretes a substance into a duct that carries the secretion to the outside of the body

    exon

    region of DNA or RNA that codes for a protein

    exothermic reaction

    chemical reaction that releases energy

    experiment

    type of scientific investigation that is performed under controlled conditions and in which the researcher typically manipulates a variable (independent variable) to see how it affects another variable (dependent variable)

    exponential growth

    pattern of population growth in which a population starts out growing slowly but grows at an increasing rate as population size increases

    extinction

    event in which a species completely dies out and no members of the species remain anywhere on Earth

    eye

    special sensory organ that collects and focuses light to form images and transforms the images into nerve impulses that travel to the brain

    F

    facilitated diffusion

    diffusion with the help of transport proteins

    Fallopian tube

    one of two female reproductive organs that carry eggs from an ovary to the uterus and are the site where fertilization usually takes place

    fast-twitch muscle fiber

    type of skeletal muscle cell that is mainly responsible for anaerobic activities such as weight lifting

    fatty acid

    simple lipid molecule that consists mainly of chains of carbon and hydrogen atoms and that may exist alone or as a monomer of larger lipid molecules

    feces

    solid waste that remains after food is digested and that is eliminated from the body through the anus

    fermentation

    type of anaerobic respiration that includes glycolysis followed by the conversion of pyruvic acid to one or more other compounds and the formation of NAD+

    fertility awareness method

    contraceptive method in which a woman monitors signs of ovulation and avoids unprotected vaginal intercourse around the time of ovulation when fertilization is most likely to occur

    fertility rate

    average number of livebirths per woman by the end of the childbearing years

    fertilization

    union of two haploid gametes (egg and sperm), resulting in a diploid zygote

    fetal viability

    point in fetal development at which a fetus is likely to be able to survive outside the uterus

    fetus

    prenatal human organism between the embryonic stage and birth (weeks 8 through 38 after fertilization)

    fiber

    indigestible carbohydrates such as cellulose that is needed in the human diet for normal bowel movements, among other functions

    fibrous connective tissue

    type of connective tissue that is found in skin, tendons, and ligaments and that is composed of parallel bundles of collagen fibers, making it tough and elastic

    fibrous joint

    immovable joint in which bones are connected by collagen fibers; also called a suture

    fight-or-flight response

    involuntary human body response mediated by the nervous and endocrine systems that prepares the body to fight or flee from perceived danger

    fitness

    in the context of evolution by natural selection, the relative ability of an organism to survive and produce fertile offspring

    flexibility exercise

    any physical activity that stretches and lengthens muscles

    folic acid

    micronutrient needed for good health and reproduction; also called vitamin B9

    follicle

    anatomical structure that consists of a small cluster of cells, surrounding a central cavity

    follicle-stimulating hormone (FSH)

    pituitary gland hormone that stimulates the ovaries to secrete estrogen and mature follicles

    fontanel

    "soft spot" on an infant’s skull that gradually ossifies after birth

    food

    organic molecules that organisms use for energy, building materials, and other purposes

    foodborne disease

    any disease that is transmitted via food; also called food poisoning

    food chain

    diagram that represents a single pathway by which energy flows through organisms an ecosystem

    food web

    diagram that represents multiple interacting pathways by which energy flows through organisms in an ecosystem

    foramen ovale

    temporary opening between the right and left atria of the fetal heart that allows blood to bypass the pulmonary (lung) circulation until the fetus starts breathing air after birth

    force of evolution

    any one of four factors (mutation, gene flow, genetic drift, and natural selection) that changes allele frequencies in a population’s gene pool

    fossil

    preserved remains or traces of an organism that lived in the past

    fossil fuel

    nonrenewable energy resource that forms over millions of years from dead plants and produces pollutants and greenhouse gases when it burns; coal, petroleum, or natural gas

    fossil record

    record of life on Earth as told by the discovery and analysis of fossils

    frameshift mutation

    deletion or insertion of one or more nucleotides that changes the reading frame of the genetic code

    free radical

    highly reactive chemical such as OH- that can damage DNA and contribute to diseases such as cancer

    freshwater biome

    aquatic biome such as a pond, lake, stream, or river in which the water contains little or no salt

    frontal lobe

    part of each hemisphere of the cerebrum that controls executive functions such as reasoning and language

    frontier science

    science undertaken in new areas at the frontier of knowledge in a particular field

    frostbite

    tissue destruction, usually in the extremities, that occurs when tissue freezes

    fungi (singular, fungus)

    organisms in the Fungus Kingdom that includes molds, mushrooms, and yeasts, some of which cause human disease

    G

    Galápagos Islands

    group of 16 small volcanic islands in the Pacific Ocean 966 kilometers (600 miles) off the west coast of South America, where Charles Darwin made some of his most important observations during his voyage on the HMS Beagle

    gallbladder

    sac-like organ that stores bile from the liver and secretes it into the duodenum of the small intestine as needed for digestion

    gamete

    reproductive cell produced during meiosis that has the haploid number of chromosomes; sperm or egg

    gametogenesis

    development of a haploid cell into a gamete (either sperm or egg)

    ganglion (plural, ganglia)

    type of nervous tissue that acts as a relay point for messages transmitted through nerves of the peripheral nervous system

    gas exchange

    biological process through which gases are transferred across cell membranes to either enter or leave the blood

    gastroenteritis

    acute and usually self-limiting infection of the gastrointestinal tract by pathogens; also known as infectious diarrhea

    gastrointestinal (GI) tract

    organs of the digestive system through which food passes during digestion, including the mouth, pharynx, esophagus, stomach, and small and large intestines

    gastrulation

    process in which the two-layer embryonic disc develops a third cell layer (mesoderm) and a primitive gut

    gene

    unit of DNA on a chromosome that may be encoded with the instructions for a protein

    gene cloning

    process of isolating and making copies of a gene

    gene expression

    use of a gene to make a protein

    gene flow

    change in allele frequencies that occurs when individuals move into or out of a population

    gene pool

    all the genes in all of the members of a population

    generalist

    organism that can thrive in a wide variety of environments and make use of a variety of different resources, such as consuming many different types of food

    general sense

    sense of touch, which lacks specialized sensory organs and is monitored instead by sensory receptors all over the body

    gene theory

    theory that many of the characteristics of living things are controlled by genes that are passed from parents to offspring

    gene therapy

    experimental method of curing genetic disorders by inserting normal genes into cells with mutant genes

    genetic code

    universal code of three-base codons that encodes genetic instructions for the amino acid sequences of proteins

    genetic disorder

    disease, syndrome, or other abnormal condition caused by a mutation in one or more genes or by a chromosomal alteration

    genetic drift

    random change in allele frequencies that occurs in a small population

    genetic engineering

    using biotechnology to change the genetic makeup of an organism

    genetics

    science of heredity

    genetic trait

    characteristic that is encoded in DNA

    genital herpes

    sexually transmitted infection caused by herpes simplex virus (usually HSV-2) that is characterized by periodic outbreaks of blisters on the genitals

    genital warts

    small, rough growths on the genitals caused by a sexually transmitted infection with human papillomavirus (HPV)

    genotype

    alleles an individual inherits at a particular genetic locus

    genus

    taxon above the species in the Linnaean classification system; group of closely related species

    geologic time scale

    timeline of Earth based on major events in geology, climate, and the evolution of life

    geothermal energy

    renewable, nonpolluting source of energy that can be obtained from Earth’s naturally occurring internal heat

    germinal stage

    earliest and shortest stage of the human lifespan, lasting about a week from fertilization until the new organism implants in the endometrium of the uterus

    germline mutation

    mutation that occurs in a gamete

    germ theory of disease

    theory that contagious diseases are caused by the transmission of microorganisms that grow and reproduce in their hosts and make them sick

    gestational carrier

    woman who agrees to receive a transplanted embryo from a couple, carry it to term, and then give the infant to the couple after birth

    ghrelin

    hormone produced in the stomach and small intestine that normally stimulates appetite

    giardiasis

    type of gastroenteritis caused by a single-celled protozoan parasite named Giardia lambliathat typically spreads through contaminated food or water via a fecal-oral route

    glial cell

    nervous tissue cell that provides support for neurons and helps them transmit nerve impulses

    global warming

    recent rise in Earth’s average surface temperature generally attributed to an enhanced greenhouse effect caused mainly by human actions

    glomerulus (plural, glomeruli)

    network of capillaries in the nephron of a kidney where substances are filtered out of the blood

    glucagon

    endocrine hormone secreted by alpha cells of the pancreas that signals cells to break down stored glycogen to glucose, thereby increasing the level of blood glucose

    glucose

    simple six-carbon sugar, or monosaccharide, that is the nearly universal food for life

    glucose-6-phosphate dehydrogenase (G6PD)

    red blood cell enzyme involved in metabolizing glucose, deficiency in which is a genetic adaptation to malaria

    glycogen

    complex carbohydrate (polysaccharide) that animals use to store energy

    glycolysis

    first stage of cellular respiration in which glucose is split, in the absence of oxygen, to form two molecules of pyruvate (pyruvic acid) and two (net) molecules of ATP

    goiter

    abnormal enlargement of the thyroid gland

    Golgi apparatus

    organelle in eukaryotic cells that processes proteins and prepares them for use both inside and outside the cell

    gonad

    one of a pair of organs that secrete sex hormones and produce gametes; testis in males and ovary in females

    gonorrhea

    common sexually transmitted infection that is caused by the bacterium Neisseria gonorrhoeae

    gradualism

    model of the timing of evolution in which evolutionary change occurs at a slow and steady pace

    Grave’s disease

    autoimmune disorder in which abnormal antibodies produced by the immune system stimulate the thyroid gland to secrete excessive quantities of its hormones

    gray matter

    type of nervous tissue that is found only in the brain and spinal cord and that is important for information processing

    greenhouse effect

    natural feature of Earth’s atmosphere that occurs when greenhouse gases in the atmosphere absorb and re-radiate heat back down to Earth’s surface, making the surface temperature warmer than it otherwise would be

    greenhouse gas

    naturally occurring or anthropogenic gas such as carbon dioxide that allows the greenhouse effect to warm Earth’s surface

    green revolution

    worldwide advances in agriculture, including increased use of machinery and chemicals, that occurred between 1950 and 1984 and greatly increased global food production

    groundwater

    fresh water that exists in the ground, either in the soil or in rock layers below the surface

    growing season

    period of time each year when it is warm enough and wet enough for plants to grow

    growth hormone

    hormone secreted by the anterior pituitary gland that stimulates growth in cells all over the body

    H

    habitat

    natural environment in which a species lives and to which it is adapted

    habitat loss

    destruction or disruption of a natural habitat, most often due to human actions such agriculture, forestry, mining, or urbanization

    hair

    filament made of tightly packed, keratin-filled keratinocytes that grows out a hair follicle in the dermis of the skin

    hair follicle

    structure in the dermis of skin where a hair originates

    hair root

    part of a hair that is located within the hair follicle and consists of living keratinocytes

    hair shaft

    part of a hair that is visible above the surface of the skin and consists of dead keratinocytes

    hallucinogen

    type of psychoactive drug that causes hallucinations and other perceptual anomalies, as well as subjective changes in thoughts, emotions, and consciousness

    haploid

    having only one chromosome of each type, or half the number of chromosomes of a diploid cell

    Hardy-Weinberg theorem

    founding principle of population genetics that proves allele and genotype frequencies do not change in a population in which the forces of evolution (mutation, natural selection, genetic drift, and migration) are not operating

    Hashimoto’s thyroiditis

    autoimmune disorder in which the immune system destroys the thyroid gland, causing insufficient secretion of thyroid hormones

    hearing

    ability to sense sound waves

    heart

    muscular organ in the chest that pumps blood through blood vessels when it contracts

    heart attack

    blockage of blood flow to heart muscle tissues that may result in the death of cardiac muscle fibers

    heat index (HI)

    number that combines air temperature and relative humidity to indicate how hot the air feels due to the humidity

    helminth

    parasitic worm such as tapeworm, pinworm, or hookworm

    hematopoiesis

    process in which red blood cells, white blood cells, and platelets are produced by red bone marrow

    hemisphere

    one of two halves (left and right) of the cerebrum of the human brain

    hemodialysis

    medical procedure for patients with kidney failure in which wastes and excess water are artificially filtered out of blood by passing it through a machine

    hemoglobin

    oxygen-binding protein containing iron that is the principal component of red blood cells

    hemoglobin C

    abnormal hemoglobin variant found mainly in West and North Africa that is a genetic adaptation to malaria

    hemoglobin E

    abnormal hemoglobin variant found mainly in South and Southeast Asia that is a genetic adaptation to malaria

    hemoglobin S

    abnormal hemoglobin variant found in sub-Saharan Africa, the Middle East, and India that is the single most effective genetic adaptation to malaria

    hemolytic disease of the newborn (HDN)

    type of anemia in which red blood cells in a Rhesus positive fetus are destroyed by antibodies to the Rhesus antigen produced by a Rhesus negative mother

    hemophilia

    any of several genetic disorders that cause dysfunction in the blood-clotting process, leading to uncontrolled bleeding from even minor injuries

    herbivore

    consumer that eats producers such as plants or algae

    herd immunity

    protection from infection of nonvaccinated people in a population because most of the people around them are vaccinated and immune to the infection

    heterotroph

    organism that obtains energy by consuming other organisms

    heterozygote

    organism that inherits two different alleles for a given gene

    high-altitude sickness

    acute illness that results from hypoxia at high altitude and includes symptoms such as fatigue, shortness of breath, headache, and dizziness

    histamine

    chemical released by injured or infected cells or by certain immune system cells that triggers inflammation or an allergic reaction

    homeobox gene

    one of many genes that regulate early development of the organism

    homeostasis

    condition in which a system such as the human body is maintained in a more-or-less steady state

    homeostat

    physiological mechanism that helps maintain homeostasis in an organism; also called homeostatic mechanism

    homeostatic imbalance

    condition in which cells may not get everything they need or toxic wastes may accumulate because of the failure of a homeostatic mechanism

    hominid

    any member of the family of the primate order that includes humans and great apes

    hominin

    any human or human ancestor that evolved after the human lineage diverged from the chimpanzee lineage about 6 million years ago

    Homo

    genus in which the only living species is Homo sapiens

    Homo denisova

    extinct species of archaic humans that lived in Asia beginning about 400,000 years ago and interbred with Neanderthals and early modern Homo sapiens; also called Denisovans

    Homo erectus

    early species in the genus Homo that first evolved about 1.9 million years ago in East Africa, migrated to Eurasia before going extinct about 800,000 years ago, and was probably ancestral to Homo heidelbergensis

    Homo floresiensis

    extinct species of archaic humans that lived on Flores Island in Indonesia from about 100,000 to 60,000 years ago and were very small in size

    Homo habilis

    first known species in the genus Homo that lived from about 2.5 to 1.4 million years ago in East Africa and probably was ancestral to Homo erectus

    Homo heidelbergensis

    transitional species in the genus Homo that probably evolved from Homo erectus about 800,000 years ago and evolved into Homo neanderthalensis and early Homo sapiensaround 200,000 years ago

    homologous chromosomes

    pair of chromosomes that have the same size and shape and contain the same genes

    homologous structure

    structure that is similar in related species because it was inherited from a common ancestor; or structure that develops from the same undifferentiated embryonic tissue in males and females of the same species, such as the testis and ovary in humans

    Homo neanderthalensis

    extinct species of archaic humans that lived in Europe and Asia between about 400,000 and 30,000 years ago; also called Neanderthals

    homozygote

    organism that inherits two alleles of the same type for a given gene

    hormonal contraception

    use of hormones such as estrogen and/or progesterone to prevent pregnancy by interfering with ovulation

    host

    species that is harmed in a parasitic relationship with another species

    human biology

    scientific study of the anatomy, physiology, genetics, evolution, and ecology of the human species

    human genome

    all of the DNA of the human species

    Human Genome Project

    international science project that sequenced all 3.3 billion base pairs of the human genome

    human immunodeficiency virus (HIV)

    virus transmitted through body fluids or mucous membranes that infects and destroys helper T cells and may eventually cause acquired immunodeficiency syndrome (AIDS)

    human papillomavirus (HPV)

    sexually transmitted virus that may cause genital warts and cervical cancer

    hunting and gathering

    type of subsistence strategy that includes hunting wild animals and gathering wild plants and that was utilized by humans from Homo erectus until at least 10,000 years ago

    hunting response

    process of alternating vasoconstriction and vasodilation in extremities that are exposed to cold

    hydrogen bond

    relative weak chemical bond that forms between molecules of the same substance, such as between molecules of water

    hydropower

    renewable, nonpolluting energy that can be obtained from moving water and used to generate electricity

    hyperopia

    vision problem in which close objects are out of focus but distant vision is unaffected; also called farsightedness

    hypersecretion

    secretion of more than the normal amount of a substance, such as secretion of too much hormone by an endocrine gland

    hypertension

    persistently high blood pressure, generally defined as 140/90 mm Hg or higher

    hyperthermia

    dangerous increase in core body temperature above 40.6 degrees C (105 degrees F)

    hyperthyroidism

    disorder in which the thyroid gland produces excessive amounts of hormones

    hypertrophy

    increase in the size of a structure, such as an increase in the size of a muscle through exercise

    hyperventilation

    breathing more quickly and shallowly than normal

    hyposecretion

    secretion of less than the normal amount of a substance, such as an endocrine hormone

    hypothalamus

    part of the brain that secretes hormones and connects the brain with the endocrine system

    hypothermia

    dangerous decrease in core body temperature below 34.4 degrees C (94 degrees F)

    hypothesis

    logical answer to a scientific question that may be tested in a scientific investigation

    hypothyroidism

    disorder in which the thyroid gland produces inadequate amounts of hormones

    hypoxia

    relative lack of oxygen, as, for example, at high altitude

    I

    ileum

    final of three parts of the small intestine where vitamin B12 and bile salts are absorbed

    immigration

    movement of individuals into a population

    immune surveillance

    function of the immune system in which it identifies and eliminates tumor cells

    immune system

    organ system that defends the body form pathogens and cancer

    immunity

    ability to resist a pathogen due to the formation of memory lymphocytes (B or T cells) to that specific pathogen

    immunization

    deliberate exposure of a person to a pathogen in order to provoke an immune response and the formation of memory cells specific to that pathogen

    immunodeficiency

    inability of the immune system to fight off pathogens that a normal, healthy immune system would be able to resist because the immune system is damaged

    immunotherapy

    treatment for an allergy in which a patient is gradually desensitized to an allergen through periodic injections with increasing amounts of the allergen; or treatment for cancer that attempts to stimulate the immune system to destroy cancer cells

    implantation

    process in which a blastocyst embeds in the endometrium lining the uterus

    incisor

    one of eight (four upper and four lower) blade-like teeth at the front of the mouth that are used to slice off pieces of food

    incomplete dominance

    relationship between the alleles for a gene in which one allele is only partly dominant to the other allele, producing an intermediate phenotype

    incubation period

    length of time between infection with a pathogen or other agent of disease and the first appearance of symptoms

    independent variable

    variable in a scientific experiment that is manipulated by the researcher to investigate its effect on another variable, known as the dependent variable; also called the manipulated variable

    infancy

    first year of life after birth in humans

    infant

    human being between birth and the first birthday

    infant mortality rate

    annual number of infant deaths per 1,000 live births in a population, often used as a reliable indicator of the overall level of health of the population

    infection

    invasion of an organism’s tissues by pathogens

    infectious disease

    any disease caused by pathogens; also called communicable or contagious disease

    infectious dose

    amount of a pathogen that must infect an organism to cause disease

    inferential statistics

    statistics such as the t-test that help researchers interpret data to test hypotheses

    infertility

    failure to achieve a successful pregnancy after at least one year of regular, unprotected sexual intercourse

    inflammation

    response of the innate immune system that establishes a physical barrier against the spread of infection and repairs tissue damage while causing redness, swelling, and warmth

    inflammatory bowel disease

    type of disease in which the immune system attacks the intestines, causing diarrhea and abdominal pain; for example, Crohn’s disease or ulcerative colitis

    inheritance of acquired characteristics

    mistaken idea of Jean Baptiste Lamarck that evolution occurs through the inheritance of traits that an organism develops in its own life time

    innate immune system

    subset of the immune system that makes generic attacks such as inflammation against invading pathogens

    insoluble fiber

    nondigestible carbohydrates in food that do not dissolve in water but provide bulk and stimulate peristalsis in the digestive tract

    insulin

    endocrine hormone secreted by beta cells of the pancreas that normally helps cells take up glucose from the blood, thereby decreasing the blood glucose level

    integumentary system

    human body system that includes the skin, nails, and hair

    interneuron

    type of neuron that carries nerve impulses back and forth between sensory and motor neurons

    interphase

    stage of the eukaryotic cell cycle when the cell grows, synthesizes DNA, and prepares to divide

    interspecific competition

    relationship between two species that depend on the same limiting resources in their ecosystem

    intrauterine device (IUD)

    T-shaped contraceptive structure containing copper or a hormone that is inserted into the uterus by a physician and may be left in place for months or years

    intrauterine growth restriction (IUGR)

    abnormally slow growth of a fetus, which may be due to maternal, fetal, or placental factors

    intromission

    process in which a male’s penis deposits sperm in a female’s vagina

    intron

    region of DNA or RNA that does not code for a protein

    invasive species

    species that is introduced (usually by human actions) into a new habitat where it may out-compete native species

    ion

    atom that has gained or lost electrons so it has more or fewer electrons than protons and a negative or positive charge

    isometric

    referring to a muscle contraction in which muscle tension increases but muscle length remains the same

    isotonic

    referring to a muscle contraction in which muscle length decreases but muscle tension remains the same

    isotope

    alternate form of an atom, with the same number of protons but a different number of neutrons

    J

    jejunum

    middle of three parts of the large intestine where most absorption of nutrients occurs

    joint

    structure where two or more bones of the skeleton come together

    K

    keratin

    tough, fibrous protein in skin, hair, and nails

    keratinocyte

    type of epithelial cell found in the skin, hair, and nails that produces keratin

    keystone species

    species that plays an especially important role in its community so that major changes in its numbers affect the populations of many other species

    kidney

    one of a pair of organs of the excretory and urinary systems that filters wastes and excess water out of blood and forms urine

    kidney failure

    loss of the ability of nephrons in the kidney to function fully due to a progressive kidney disease such as diabetic nephropathy or polycystic kidney disease

    kidney stone

    solid crystal that forms in a kidney from minerals such as calcium in urine

    kingdom

    largest and most inclusive taxon in the original Linnaean classification system

    Koch’s postulates

    set of four criteria for identifying the microorganism that causes a particular infectious disease, first proposed by Robert Koch in the 19th century

    Krebs cycle

    second stage of aerobic respiration in which two pyruvate (pyruvic acid) molecules from the first stage react to form ATP, NADH, and FADH2

    kwashiorkor

    severe undernutrition syndrome caused by lack of protein and Calories and characterized by edema of the ankles, feet, and abdomen

    L

    labia (singular, labium)

    "lips" of the vulva, consisting of folds of tissue that protect the urethral and vaginal openings

    labor

    general term for the process of childbirth, which includes three stages: dilation of the cervical canal, birth of the child, and delivery of the placenta (afterbirth)

    lactase

    enzyme needed to digest the milk sugar lactose

    lactase persistence

    ability to produce lactase and digest milk after early childhood

    lactation

    production of breastmilk to feed an infant

    lactic acid fermentation

    type of anaerobic respiration that includes glycolysis followed by the conversion of pyruvic acid to lactic acid and the formation of NAD+

    lactose

    disaccharide sugar that makes up 2-8 percent of milk by weight

    lactose intolerance

    inability to digest the lactose in milk, generally because of lack of the enzyme lactase

    language

    communication of thoughts and feelings through a system of arbitrary symbols called words that are represented by vocal sounds and in many cases also by written marks

    lanugo

    fine, colorless hair that covers a fetus’s face and body until it is shed close to the time of birth

    large intestine

    organ of the digestive system that removes water and salts from food waste and forms solid feces for elimination

    larynx

    organ of the respiratory system between the pharynx and trachea that is also called the voice box because it contains the vocal cords that allow the production of vocal sounds

    last universal common ancestor (LUCA)

    hypothetical early cell (or group of cells) that gave rise to all subsequent life on Earth

    lateralization

    concentration of particular functions in one hemisphere of the cerebrum of the brain

    law of conservation of mass

    law stating that mass is neither created nor destroyed in chemical reactions

    law of independent assortment

    Mendel’s second law stating that factors controlling different characteristics are inherited independently of each other

    law of segregation

    Mendel’s first law stating that the two factors controlling a characteristic separate and go to different gametes

    leptin

    hormone produced mainly by fat cells that normally inhibits appetite by inducing a feeling of satiety

    leukemia

    group of cancers of the blood-forming tissues in bone marrow

    leukocyte

    white blood cell produced by bone marrow to fight infections

    Leydig cell

    type of cell found between seminiferous tubules in the testes that produces and secretes testosterone

    life cycle

    series of stages a sexually reproducing organism goes through from one generation to the next

    life expectancy

    average time an individual is expected to live, or the average age at death

    ligament

    band of fibrous connective tissue that holds bones together

    limiting factor

    any factor that constrains the population size of a species in an ecosystem

    linked genes

    genes that are located on the same chromosome

    Linnaean classification system

    system of classifying organisms based on observable physical traits; consists of a hierarchy of taxa, from the kingdom to the species

    lipid

    class of biochemical compounds that includes fats and oils

    liver

    organ of digestion and excretion that secretes bile for lipid digestion and breaks down excess amino acids and toxins in the blood

    locus

    position of a gene on a chromosome

    logistic growth

    pattern of population growth in which growth slows and population size levels off as the population approaches the carrying capacity

    lower gastrointestinal (GI) tract

    part of the GI tract that includes the small and large intestines

    lung

    one of two paired organs of the respiratory system in which gas exchange takes place between the blood and the atmosphere

    lung cancer

    malignant tumor characterized by uncontrolled cell growth in tissues of the lung

    luteinizing hormone (LH)

    pituitary gland hormone that stimulates the testes to secrete testosterone and the ovaries to secrete estrogen

    lymph

    fluid that leaks out of capillaries into spaces between cells and circulates in the vessels of the lymphatic system

    lymphatic system

    system of the body that produces lymphocytes and filters pathogens from lymph and blood

    lymph node

    one of many small structures located along lymphatic vessels where pathogens are filtered from lymph and destroyed by lymphocytes

    lymphocyte

    type of leukocyte produced by the lymphatic system that is a key cell in the adaptive immune response to a specific pathogen or tumor cell

    M

    macroevolution

    evolutionary change that occurs at or above the level of the species, generally over many generations

    macronutrient

    nutrient such as carbohydrates, proteins, lipids, or water that is needed by the body in relatively large amounts

    major histocompatibility complex (MHC)

    set of molecules normally found on virtually all nucleated human cells that provide a way for the immune system to recognize body cells as self

    malaria

    common parasitic disease caused by Plasmodium protozoa and transmitted by Anophelesmosquitoes in tropical and subtropical regions of the world

    malnutrition

    poor nutritional status due to inadequate or imbalanced nutrient intake; includes unbalanced nutrition, overnutrition, and undernutrition

    mammary gland

    gland in the female breast that produces milk for offspring

    mandible

    lower jaw bone

    marasmus

    severe form of undernutrition characterized by very low weight and caused by extremely low intakes of macronutrients and energy

    marine biome

    aquatic biome in the salt water of the ocean

    mass extinction

    extinction event in which many if not most species disappear from Earth over a relatively short period of time

    maxilla

    one of two fixed bones making up the upper jaw

    mechanical digestion

    physical breakdown of chunks of food into smaller pieces by organs of the digestive system

    mechanoreceptor

    type of sensory receptor that responds to mechanical forces

    meiosis

    type of cell division in which the number of chromosomes is reduced by half and four haploid cells result

    melanin

    brown pigment produced by melanocytes in the skin that gives skin most of its color and prevents UV light from penetrating the skin

    melanocyte

    special skin cell that is responsible for producing melanin

    melanoma

    rare but most serious type of skin cancer that affects melanocytes and usually metastasizes if not treated

    melanosome

    small organelle in a melanocyte that synthesizes, stores, and transports melanin

    memory cell

    lymphocyte (B or T cell) that retains a "memory" of a specific pathogen after an infection is over and thus provides immunity to the pathogen

    menarche

    beginning of menstruation; first monthly period in a female

    Mendelian inheritance

    inheritance of a trait controlled by a single gene with two alleles, one of which may be dominant to the other

    meninges

    three-layered membrane that encloses and protects the brain and spinal cord and contains cerebrospinal fluid

    menopause

    cessation of a woman’s menstrual cycles, usually by age 52

    menstrual cycle

    monthly cycle of processes and events in the ovaries and uterus of a sexually mature human female until menopause

    menstruation

    process in which the endometrium of the uterus is shed from the body during the first several days of the menstrual cycle; also called monthly period or menses

    mesoderm

    middle germ layer of an embryo that will eventually give rise to bone and muscle cells

    Mesozoic Era

    age of dinosaurs that lasted from about 245 to 65 million years ago

    messenger RNA (mRNA)

    type of RNA that copies genetic instructions from DNA in the nucleus and carries them to the cytoplasm

    metabolic syndrome

    condition that includes abdominal obesity, high blood pressure, high blood glucose and triglyceride levels, and low blood HDL levels; major risk factor for cardiovascular diseases and type 2 diabetes

    metabolism

    sum of all the biochemical reactions in an organism

    metaphase

    second phase of mitosis during which chromosomes line up at the equator of the cell

    metastasis (plural, metastases)

    new cancer that forms at a distant site when cancer cells from a primary tumor travel through the bloodstream

    metastasize

    for cancer cells to travel from a primary tumor through the bloodstream and form a new cancer at a distant site

    microevolution

    evolutionary change that occurs over a relatively short period of time within a population

    micronutrient

    nutrient such as a vitamin or mineral that is needed by the body in relatively small amounts

    microvillus (plural, microvilli)

    one of many tiny projections covering each villus in the mucosa lining the small intestine that increases its absorptive surface

    middle adulthood

    second stage of human adulthood that lasts from the mid-30s to the mid-60s

    middle childhood

    stage of a human organism between early childhood and pre-adolescence that covers the ages 6 to 10 years

    mineral

    chemical element such as calcium or potassium that is needed in relatively small amounts for proper body functioning

    mitochondrion (plural, mitochondria)

    organelle in eukaryotic cells that makes energy available to the cell in the form of ATP molecules

    mitosis

    process in which the nucleus of a eukaryotic cell divides

    mixed nerve

    nerve of the peripheral nervous system that contains both sensory and motor neurons so it can transmit signals to and from the central nervous system

    model

    representation of part of the real world

    model organism

    nonhuman species that is extensively studied to understand particular biological phenomena

    molar

    one of twelve teeth with cusps in the back of the mouth behind the premolars that are used for crushing and grinding food

    molecular clock

    use of DNA (or protein) differences to measure how long it has been since related species diverged from a common ancestor

    molecule

    smallest part of a compound that has the properties of that compound

    monoculture

    growing the same crop repeatedly, which depletes soil nutrients and may attract plant pests

    monomer

    small molecule that joins together with many others like it to form a larger molecule called a polymer

    monosaccharide

    simple six-carbon sugar, such as glucose, that exists alone or as a monomer of a complex carbohydrate

    morphology

    form and structure of an organism

    morula

    solid ball of cells that forms during cleavage, when a fertilized egg undergoes its first several mitotic divisions

    motor nerve

    nerve of the peripheral nervous system that transmits information from the central nervous system to muscles, organs, and glands

    motor neuron

    type of neuron that carries nerve impulses from the central nervous system to muscles and glands; also called efferent neuron

    mucous membrane

    epithelial tissue that lines inner body surfaces and body openings and produces mucus

    mucus

    slimy substance produced by mucous membranes that traps pathogens, particles, and debris

    multiple allele trait

    trait controlled by one gene with more than two alleles

    muscle contraction

    increase in the tension or decrease in the length of a muscle that occurs when muscle fibers receive a nervous stimulus

    muscle fiber

    long-thin muscle cell that has the ability to contract, or shorten

    muscle strain

    injury in which muscle fibers tear due to overstretching of a muscle

    muscle tissue

    tissue made up of cells that can contract; smooth, skeletal, or cardiac muscle tissue

    muscular dystrophy

    genetic neuromuscular disorder caused by defective proteins in muscle cells and characterized by death of skeletal muscles and progressive weakness

    muscular system

    human body system that includes all the muscles of the body

    musculoskeletal disorder

    injury to muscles or tendons caused by biomechanical stresses

    mutagen

    environmental factor that causes mutations

    mutation

    change in the sequence of bases in DNA or RNA

    mutualism

    type of symbiotic relationship between two species in which both species benefit

    myasthenia gravis

    genetic neuromuscular disorder caused by the immune system blocking acetylcholine receptors on muscle cells and characterized by progressive muscle weakness and fatigue

    myelin sheath

    lipid layer around the axon of a neuron that allows nerve impulses to travel more rapidly down the axon

    myocardial infarction (MI)

    damage to heart muscle from death of myocardial cells that occurs when blood flow is blocked to part of the heart; also called heart attack

    myocyte

    type of muscle cell that makes up smooth muscle tissue

    myopia

    vision problem in which distant objects are out of focus but close vision is unaffected; also called nearsightedness

    myosin

    thick protein filament in a muscle cell that pulls on a thin actin filament to produce a muscle contraction

    MyPlate

    visual guide for balanced eating that was created in 2011 by the US Department of Agriculture to replace MyPyramid

    N

    nail

    accessory organ of the skin made of sheets of dead keratinocytes at the distal ends of the fingers and toes

    nail bed

    pink skin under the nail plate that is visible through the nail

    nail matrix

    deep layer of epidermal tissue at the proximal end of a nail where nail growth occurs

    nail plate

    visible part of a nail that is external to the skin

    nail root

    portion of a nail that is under the surface of the skin at the proximal end of the nail

    nasal cavity

    large, air-filled space in the skull above and behind the nose that helps conduct air in and out of the body as part of the upper respiratory tract

    natural gas

    naturally occurring nonrenewable gaseous fossil fuel consisting primarily of methane that is less polluting to burn than other fossil fuels

    natural resource

    something supplied by nature that helps support life

    natural selection

    force of evolution in which some living things produce more offspring than others so the characteristics of organisms change over time

    negative feedback loop

    control mechanism that serves to reduce an excessive response and keep a variable within its normal range

    neonate

    newborn infant from birth to the age of four weeks

    nephron

    one of the million tiny structural and functional units of the kidney that filters blood and forms urine

    nerve

    type of nervous tissue that consists of many cable-like bundles of axons and makes up the majority of the peripheral nervous system

    nerve impulse

    electrical signal transmitted by the nervous system

    nervous system

    human organ system that transmits electrical signals throughout the body to coordinate all of the body’s voluntary and involuntary activities

    nervous tissue

    tissue made up of neurons that carry electrical messages and glial cells that support neurons

    neural tube

    structure that forms in an embryo and eventually develops into the brain and spinal cord

    neurogenesis

    formation of new neurons by cell division

    neuroimmune system

    part of the immune system that protects the central nervous system

    neuromuscular disorder

    muscle disorder that occurs due to problems with the nervous control of muscle contractions or with muscle cells themselves

    neuromuscular junction

    chemical synapse where a motor neuron transmits a signal to a muscle fiber to initiate a muscle contraction

    neuron

    functional unit of the nervous system that transmits nerve impulses; also called nerve cell

    neurotransmitter

    type of chemical that carries nerve impulses from the axon of a neuron to another cell across the synapse

    neurulation

    process in which an embryo develops structures that will eventually become the nervous system

    niche

    role of a species in its ecosystem that includes all the ways the species interacts with the biotic and abiotic factors of the ecosystem

    nicotine

    highly addictive psychoactive stimulant drug that is found in tobacco and tobacco smoke

    nitrogen cycle

    biogeochemical cycle through which nitrogen is recycled through the biotic and abiotic components of ecosystems

    nitrogen fixation

    process of changing nitrogen gas to nitrates that is carried out by nitrogen-fixing bacteria in the soil or in the roots of legumes

    nociceptor

    type of sensory receptor that responds to pain

    node of Ranvier

    one of the regularly spaced gaps between myelin sheaths along an axon that allow nerve impulses to travel very rapidly

    nonbiodegradable

    unable to be broken down in the environment by natural processes

    nondisjunction

    failure of replicated chromosomes to separate during meiosis II, resulting in some gametes with a missing chromosome (or part of a chromosome) and some with an extra chromosome (or part of a chromosome)

    non-essential nutrient

    nutrient that can be synthesized by the body in sufficient quantities for normal functioning so it does not need to be obtained from food

    noninfectious disease

    any disease caused by genetic and/or environmental factors other than pathogens; also called noncommunicable disease

    non-Mendelian inheritance

    inheritance of traits that have a more complex genetic basis than one gene with two alleles and complete dominance

    nonpoint-source pollution

    contamination of the environment by a pollutant that enters the environment from multiple sources

    nonrenewable resource

    natural resource that exists in a fixed amount and cannot be replenished at all or cannot be replenished quickly enough to keep pace with human use of the resource

    non-steroid hormone

    type of endocrine hormone that is made of amino acids and binds with a receptor on the plasma membrane of a target cell

    normal range

    spread of values around the set point of a biological variable such as body temperature that is considered insignificant in terms of health

    nuclear energy

    nonrenewable energy resource produced in a nuclear power plant by fission reactions in a radioactive fuel, usually uranium

    nuclear force

    atomic force holding together protons and neutrons in the nucleus of an atom that is stronger than the electromagnetic force repelling positively charged protons from each other

    nucleic acid

    class of biochemical compounds that includes DNA and RNA

    nucleotide

    small molecule containing a sugar, phosphate group, and nitrogen base that is a building block of nucleic acids

    nucleus (plural, nuclei)

    organelle inside eukaryotic cells that contains most of the cell’s DNA and acts as the control center of the cell

    nutrient

    substance the body needs for energy, building materials, or control of body processes

    nutrient density

    how much of a given nutrient is provided by a particular food, relative to the mass of the food or the amount of Calories it provides

    nutrition

    process of taking in nutrients in food and using them for growth, metabolism, and repair

    nutrition facts label

    label on packaged food that lists the nutrient content per serving of the food and also its ingredients

    O

    obesity

    disease in which the body mass index (BMI) is greater than 30.0 kg/m2

    observation

    anything that is detected through human senses or with instruments and measuring devices that enhance human senses

    observational study

    type of nonexperimental scientific investigation in which the researcher measures characteristics in a sample but does not attempt to manipulate or control variables of interest

    occipital lobe

    part of each hemisphere of the cerebrum that is dedicated almost solely to vision

    old age

    last stage of human adulthood that lasts from the mid-60s until death

    olfactory receptor

    chemoreceptor in the nasal passages that detects chemicals in the air

    omnivore

    consumer that eats both plants and animals

    oogenesis

    process of producing eggs in the ovaries of a female fetus

    oogonium (plural, oogonia)

    diploid stem cell in an ovary that undergoes mitosis to begin the process of oogenesis

    opioid

    drug derived from the opium poppy or a synthetic version of such a drug, including heroin and painkillers such as codeine, morphine, or OxyContin

    opportunistic disease

    disease that rarely occurs except in people with a compromised immune system, such as people infected with HIV

    organ

    structure composed of more than one type of tissue that performs a particular function, such as the brain, kidney, or heart

    organelle

    structure within the cytoplasm of a eukaryotic cell that is enclosed within a membrane and performs a specific job

    organic compound

    compound found in or derived from living things that contains mainly carbon

    organism

    individual living thing

    organogenesis

    process in which organs develop in an embryo

    organ system

    group of organs that work together to do a certain job

    osmosis

    diffusion of water molecules across a membrane

    ossification

    process in which cartilage is changed into bone

    osteoarthritis

    joint disorder that results from the breakdown of joint cartilage and bone, most often due to wear and tear on joints

    osteoblast

    type of bone cell that makes and mineralizes bone matrix

    osteocalcin

    endocrine hormone secreted by bone cells that helps to regulate blood glucose and fat deposition

    osteoclast

    type of bone cell that breaks down bone, dissolves its minerals, and releases them into the blood

    osteocyte

    type of bone cell that helps regulate the formation and breakdown of bone tissue

    osteogenic cell

    type of stem cell that can divide and differentiate to form new bone cells

    osteoporosis

    disorder that generally occurs in older adults in which bones lose minerals, become brittle, and break easily

    ovarian cycle

    events of the menstrual cycle that occur in the ovaries, including maturation of a follicle, ovulation, and development of the corpus luteum

    ovarian follicle

    functional unit of an ovary that consists of a nest of epithelial cells surrounding an egg

    ovary

    one of a pair of female reproductive organs that produces eggs and secretes estrogen

    over-harvesting

    use of a natural resource at an unsustainable rate, such as over-fishing or overly intensive use of soils for farming

    overpopulation

    condition in which population size is too large to be supported by available resources without damaging the environment

    ovulation

    release of a secondary oocyte from an ovary about half way through the menstrual cycle

    oxytocin

    endocrine hormone secreted by the pituitary gland that functions during childbirth to stimulate uterine contractions

    P

    pacemaker

    type of cells in the heart that create electrical signals to stimulate heart muscles to contract

    Paleolithic

    "old stone" stage of human technological development that characterized humans starting about 2-5 million years ago with Homo habilis and continued through early modern Homo sapiens

    paleontologist

    scientist who finds and studies fossils to learn about evolution and understand past life

    Paleozoic Era

    age of "old life" from 544-245 million years ago that began with the Cambrian explosion and ended with the Permian extinction

    pancreas

    dual endocrine and exocrine gland near the stomach that secretes insulin and glucagon, which regulate blood glucose, as well as enzymes that aid in digestion

    pancreatic islet

    one of millions of clusters of cells in the pancreas that secrete endocrine hormones such as insulin and glucagon; also called islet of Langerhans

    pancreatitis

    painful inflammation of the pancreas due to gallstones, chronic alcohol use, or other cause

    pandemic

    infectious disease epidemic that spreads across multiple populations or continents or even worldwide

    Pangaea

    supercontinent that formed during the Permian Period and included all of Earth’s major land masses

    papillary layer

    upper layer of the dermis with papillae extending upward into the epidermis

    Pap smear

    medical test in which cells are scraped from the cervix and examined under a microscope in order to detect cancer cells if they are present

    paradigm shift

    radical change in science in which current theories are abandoned and new ideas take their place

    paralysis

    loss of sensation and movement in part of the body, such as may occur with a stroke or spinal cord injury

    parasite

    species that lives in or on another species, called the host, and causes harm to the host while benefitting from the relationship

    parasitism

    symbiotic relationship between two species in which one species (the parasite) benefits while the other species (the host) is harmed

    parasympathetic division

    division of the autonomic nervous system that returns the body to normal after the fight-or-flight response and maintains homeostasis at other times

    parathyroid gland

    one of a pair of small endocrine glands in the neck that secretes hormones that regulate blood calcium

    parietal lobe

    part of each hemisphere of the cerebrum that controls touch, reading, and arithmetic

    Parkinson’s disease

    degenerative brain disorder caused by progressive death of neurons in the midbrain, resulting in muscular symptoms of tremor, rigidity, slowness of movement, and postural instability

    passive immunity

    short-term immunity to a particular pathogen that results when antibodies or activated T cells are transferred to a person who has never been exposed to the pathogen

    passive transport

    movement of substances across a plasma membrane that does not require energy

    pathogen

    disease-causing agent such as a bacterium, virus, fungus, or protozoan

    pectoral girdle

    paired clavicles (collar bones) and scapulas (shoulder blades) that together form the shoulders and attach the arms to the trunk; also called shoulder girdle

    pedigree

    chart showing how a trait is passed from generation to generation within a family

    pelvic girdle

    paired, fused bones (ilium, pubis, and ischium) that form the hips and attach the legs to the trunk

    pelvic inflammatory disease (PID)

    infection that spreads from the vagina to the upper reproductive organs and may lead to ectopic pregnancies or infertility

    penis

    male reproductive organ containing the urethra, through which semen and urine pass out of the body

    peptic ulcer

    sore that develops in the lining of the stomach or duodenum most often caused by infection with the bacterium Helicobacter pylori

    periosteum

    tough, fibrous membrane that covers the outer surface of bones

    peripheral artery disease (PAD)

    narrowing of peripheral arteries, usually in the legs, due to atherosclerosis and generally causing intermittent pain in the legs when walking

    peripheral immune system

    part of the immune system that protects all of the body except for the central nervous system (which is protected by the neuroimmune system)

    peripheral nervous system (PNS)

    one of two major divisions of the nervous system that consists of all the nervous tissue that lies outside the central nervous system

    peristalsis

    rapid, involuntary, wave-like contractions of smooth muscles that push food through the gastrointestinal tract and urine through the urinary tract

    permanent teeth

    second set of 32 teeth that emerge mainly during middle childhood and most of which replace deciduous (baby) teeth after they are lost; consist of 8 incisors, 4 canines, 8 premolars, and 12 molars

    Permian extinction

    extinction event at the end of the Paleozoic Period that was the biggest mass extinction that had occurred on Earth until then

    petroleum

    naturally occurring nonrenewable liquid fossil fuel found in reservoirs and rocks below Earth’s surface that is the world’s primary fuel source for transportation; also called crude oil

    pH

    scale that is used to measure acidity, on which 7 is neutral, less than 7 is acidic, and greater than 7 is basic

    phagocytosis

    process in which certain leukocytes engulf and break down solid particles such as pathogens or debris

    pharmacogenomics

    study of how genetic variation affects individual responses to therapeutic drugs

    pharynx

    tubular organ that connects the mouth and nasal cavity with the larynx and through which air and food pass

    phenotype

    characteristics of an organism that depend on how the organism’s genotype is expressed

    phenotypic plasticity

    ability to change the phenotype in response to changes in the environment

    phenylthiocarbamide (PTC)

    harmless compound that is used to test people for taster status because it tastes bitter to tasters and has no taste to nontasters

    phospholipid

    type of lipid that contains a phosphate group and is the main component of the cell membranes of all living things

    phospholipid bilayer

    double layer of phospholipid molecules that makes up a plasma membrane

    phosphorus cycle

    biogeochemical cycle in which phosphorus is continuously recycled through biotic and abiotic components of ecosystems

    photic zone

    area in an aquatic biome extending to a maximum depth of 200 meters that receives enough sunlight for photosynthesis

    photoautotroph

    producer that uses energy from sunlight to produce organic molecules by photosynthesis

    photoreceptor

    type of sensory receptor that responds to light

    photosynthesis

    process of using light energy to make organic molecules from inorganic substances

    phylogenetic tree

    diagram that shows how species are related to each other through common ancestors

    phylogeny

    evolutionary history of a group of related organisms

    physical exercise

    any bodily activity that enhances or maintains physical fitness and good health

    physiology

    study of the functioning of the human organism

    phytochemical

    any of a large group of plant chemicals that may be needed in small amounts for good health but are not (yet) classified as nutrients

    pineal gland

    endocrine gland that secretes the hormone melanin, which regulates the sleep-wake cycle

    pioneer species

    type of species that first colonizes a disturbed area

    pituitary gland

    master gland of the endocrine system that secretes many hormones, the majority of which regulate other endocrine glands

    placebo

    "fake" treatment that actually has no effect on health and is included in a study to control for the placebo effect

    placebo effect

    psychologically based reaction to a treatment that occurs just because the subject is treated, even if the treatment is a placebo that has no physiological effect on the patient

    placenta

    temporary organ that consists of a large mass of maternal and fetal blood vessels through which the mother’s and embryo’s or fetus’s blood exchange substances

    placental insufficiency

    problem with the placenta that causes inadequate transfer of oxygen and nutrients to the fetus, causing intrauterine growth restriction

    plasma

    straw-yellow fluid part of blood that contains many dissolved substances and blood cells

    plasma membrane

    double layer of phospholipids that surrounds and encloses the contents of a cell; also called cell membrane

    Plasmodium falciparum

    protozoan parasite that causes malaria when it infects a human host

    platelet

    cell fragment in blood that helps blood clot

    pleiotropy

    situation in which a single gene affects more than one trait

    pneumonia

    disease in which the alveoli of the lungs become inflamed and filled with fluid, usually as a result of infection, causing symptoms such as shortness of breath, coughing, chest pain, and fever

    point mutation

    change in a single nucleotide base in a gene

    point-source pollution

    contamination of the environment that occurs when pollutants enter the environment from a single source

    polarity

    difference in electrical charge between different parts of the same molecule

    pollination

    fertilization in plants in which pollen is transferred from one flower to another, often with the help of a pollinator such as a bee

    pollutant

    anything that causes pollution, either a substance or a form of energy

    pollution

    introduction of contaminants into the natural environment, leading to adverse changes in ecosystems and potential damage to human health

    polycystic kidney disease (PKD)

    genetic disorder in which multiple abnormal cysts develop and grow in the kidneys

    polygenic trait

    trait controlled by more than one gene, each of which may have two or more alleles

    polymer

    large molecule that consists of many small repeating units called monomers

    polymerase chain reaction (PCR)

    biotechnology process that makes many copies of a gene or other DNA segment

    polymorphism

    situation in which a gene has two or more alleles in a population at frequencies greater than 1 percent

    polynucleotide

    chain of small molecules called nucleotides that alone or with a complementary chain makes up a nucleic acid (DNA or RNA)

    polypeptide

    chain of amino acids that alone or with other such chains makes up a protein

    polysaccharide

    chain of monosaccharides (simple sugars) that makes up a complex carbohydrate (such as starch or cellulose)

    population

    all the organisms of the same species that live in the same area

    population density

    average number of individuals in a population per unit of area

    population distribution

    how the individuals in a population are arrayed over the area they inhabit

    population genetics

    science focusing on the forces of evolution at the level of allele frequencies in populations

    population growth rate (r)

    net change in population size per year per 100 people already present in the population that occurs because of births, deaths, and migrations

    population projection

    prediction of future population growth or size based on assumptions about future birth and death rates

    population pyramid

    bar graph that represents the age-sex structure of a population

    positive feedback loop

    control mechanism that serves to intensify a response until an endpoint is reached

    posterior pituitary

    back lobe of the pituitary gland that stores and secretes hypothalamic hormones

    pre-adolescence

    stage of the human organism between middle childhood and adolescence that covers the ages 11 to 12 years, during which many children start going through puberty

    precipitation

    water that falls from clouds in the atmosphere to Earth’s surface in the form of rain, snow, sleet, hail, or freezing rain

    predation

    relationship between two species in which members of one species (the predator) consume members of the other species (the prey)

    predator

    species that consumes the other species (the prey) in a predatory relationship

    pregnancy

    carrying of one or more offspring from fertilization until birth

    premolar

    one of eight cusped teeth in the sides of the jaws between the canine teeth and molars that are used for crushing food

    presbyopia

    common vision problem associated with aging in which the eye gradually loses its ability to focus on close objects

    preschool stage

    second part of early childhood that covers the ages 4 to 5 years

    prey

    species that is consumed by the other species (the predator) in a predatory relationship

    primary pollutant

    contaminant that is released directly into the environment from the source(s) of pollution

    primary succession

    change over time in the numbers and types of species that live in an area that was never before colonized by living things

    primate

    any member of the Primate Order of mammals, in which the human species is placed

    prion

    infectious agent composed entirely of proteins that may cause a fatal neurodegenerative disease such as mad cow disease or kuru

    producer

    organism that produces food for itself and other organisms

    product

    substance that forms as the result of a chemical reaction

    progesterone

    female sex hormone secreted mainly by the ovaries that helps maintain a successful pregnancy

    prokaryote

    single-celled organism that lacks a nucleus

    prokaryotic cell

    living cell without a nucleus

    promoter

    region of a gene where RNA polymerase binds to initiate transcription of the gene

    prophase

    first phase of mitosis during which chromatin condenses into chromosomes, the nuclear envelope breaks down, centrioles separate, and a spindle begins to form

    prosimian

    any non-anthropoid primate; lemur, loris, or tarsier

    prostate cancer

    tumor in the prostate gland of the male reproductive system that is the most common type of cancer in men

    prostate gland

    gland in the male reproductive system that secretes fluid into semen and provides nourishing substances to sperm

    protein

    class of biochemical compounds made of amino acids, with complex structures and diverse functions

    protein synthesis

    process in which cells make proteins that includes transcription of DNA and translation of mRNA

    protist

    any member of the Protist Kingdom, the kingdom in the Eukarya Domain that includes all eukaryotes except plants, animals, and fungi

    proto-oncogene

    gene that normally promotes growth and reproduction of cells but may cause cancer if it mutates and becomes an oncogene

    protozoan (plural, protozoa)

    animal-like, single-celled protist such as Giardia or Plasmodium species, both of which are common human parasites

    pseudoscience

    claim, belief, or practice that is presented as scientific but does not adhere to the standards and methods of science

    psychoactive drug

    drug that affects the central nervous system, generally by influencing neurotransmitters in the brain

    puberty

    period during which humans become sexually mature

    pulmonary circulation

    part of the cardiovascular system that carries blood between the heart and lungs

    punctuated equilibrium

    model of the timing of evolution in which long periods of little evolutionary change are interrupted by bursts of rapid evolutionary change

    Punnett square

    chart for determining the expected percentages of different genotypes in the offspring of two parents

    pyruvate kinase (PK)

    enzyme needed for ATP production in red blood cells, deficiency in which is a genetic adaptation to malaria

    Q

    qualitative data

    data that are expressed in words

    quantitative data

    data that are expressed in numbers

    R

    race

    discrete category within the human species that groups together individuals based on a few readily observable traits such as skin color and hair texture

    racism

    association of racial traits such as skin color with unrelated traits such as intelligence, often leading to prejudice and discrimination against people based only on how they look

    radiation therapy

    treatment of cancer using ionizing radiation such as X rays to kill cancerous tissues

    radon

    radioactive gas from underground rocks that may cause lung cancer

    reactant

    starting substance in a chemical reaction

    reading frame

    grouping of nitrogen bases in DNA into three-base codons

    receptor

    protein on a cell membrane that binds with a hormone, neurotransmitter, or other chemical

    recessive

    referring to an allele that is masked by the presence of another allele for the same gene when they occur together in a heterozygote; or referring to a trait controlled by such an allele

    recombinant DNA

    DNA that results when DNA from two organisms is combined

    rectum

    short part of the large intestine between the colon and anus where feces is stored until it is eliminated through the anus

    red blood cell

    type of cell in blood that contains hemoglobin and carries oxygen

    reflex

    rapid motor response to a sensory stimulus in which nerve impulses travel in an arc that includes the spinal cord but not the brain; in infants, may refer to one of several instinctive behaviors, such as crying and sucking, that help an infant survive

    regulatory element

    region of DNA where a regulatory protein binds

    regulatory protein

    protein that regulates gene expression

    relative dating

    method of dating fossils by their location in rock layers that determines which fossils are older or younger but not their age in years

    renal pelvis

    funnel-like end of a ureter where it enters the kidney and where urine collects before it is transported through the ureter

    renal tubule

    tubular structure of a nephron in a kidney through which filtered substances pass and where some filtered substances are reabsorbed by the blood and additional substances are secreted from the blood

    renewable resource

    natural resource that can be replenished by natural processes as quickly as humans use it

    replacement fertility rate

    fertility rate at which women average only enough children by the end of their reproductive years to replace themselves and their partner in the population

    replication

    reproducing a scientific investigation and getting the same result

    reproduction

    process by which living things give rise to offspring

    reproductive system

    organ system responsible for the production and fertilization of gametes and, in females, the carrying of a fetus

    reservoir

    part of a biogeochemical cycle that holds an element or water for a long period of time

    respiration

    exchange of gases between the body and the outside air

    respiratory center

    one of several areas in the medulla and pons of the brain stem that help control unconscious breathing

    respiratory system

    organ system that brings oxygen into the body and releases carbon dioxide and other waste gases into the atmosphere

    respiratory tract

    continuous system of passages through which air flows into and out of the body

    resting potential

    difference in electrical charge across the plasma membrane of a neuron that is not actively transmitting a nerve impulse

    reticular layer

    lower layer of the dermis that gives the dermis strength and elasticity and contains many dermal structures such as glands and hair follicles

    retina

    layer of photoreceptor cells at the back of the eye, including rods that are particularly sensitive to dim light and cones that are sensitive to light of different colors

    Rhesus (Rh) blood group system

    system of blood cell antigens controlled by two genes with many alleles on chromosome 1, producing five common antigens of which the main antigen is the D (Rh+) antigen

    ribcage

    bony "cage" enclosing the thoracic cavity and consisting of the ribs, thoracic vertebrae, and sternum

    ribosomal RNA (rRNA)

    type of RNA that helps form ribosomes and assemble proteins

    ribosome

    organelle inside all cells where proteins are made

    rickets

    disorder in children caused by vitamin D deficiency and characterized by soft, weak bones and skeletal deformities

    ringworm

    skin infection by the fungus Trichophyton that causes a characteristic ring-shaped rash

    RNA (ribonucleic acid)

    single-stranded nucleic acid that helps make proteins

    RNA world hypothesis

    hypothesis that RNA was the first biochemical molecule to evolve and that early life was based on RNA, rather than DNA or proteins

    runoff

    precipitation that falls on land and flows over the surface of the ground

    S

    saliva

    fluid secreted by salivary glands that keeps the mouth moist and contains the digestive enzymes amylase and lipase

    salivary gland

    one of many exocrine glands in the mouth that secrete saliva into the mouth through ducts

    sample

    individuals or events that are actually selected for study in an experiment or other scientific investigation and generally are a subset of all possible cases that could be selected for study

    sarcomere

    basic functional unit of skeletal and cardiac muscles, containing actin and myosin protein filaments that slide over one another to produce a shortening of the sarcomere and a muscle contraction

    sarcopenia

    gradual decrease in the ability to maintain skeletal muscle mass that occurs in later adulthood

    saturated fatty acid

    simple lipid molecule in which a chain of carbon atoms is bonded to as many hydrogen atoms as possible because adjacent carbon atoms in the chain share only single bonds

    savanna hypothesis

    hypothesis that many human traits such as upright bipedalism evolved as adaptations to a savanna habitat

    scavenger

    decomposer that consumes the soft tissues of dead animals such as the remains of a predator’s kill

    science

    distinctive way of gaining knowledge about the natural world that tries to answer questions with evidence and logic

    scientific investigation

    plan for asking questions and testing possible answers to them using evidence and logic

    scientific law

    statement describing what always happens under certain conditions in nature

    scientific method

    process typically followed in a scientific investigation that includes such steps as making observations, asking a question, forming a hypothesis, testing the hypothesis, drawing conclusions, and communicating results

    scientific racism

    ideology popular until the early 20th century that race is a valid biological concept and that human behavior is partly determined by race

    scientific theory

    broad explanation that is widely accepted because it is strongly supported by a great deal of evidence

    scrotum

    pouch-like external structure of the male reproductive system, located behind the penis, that contains the testes, epididymes, and part of the vas deferens

    sebaceous gland

    gland in the dermis of the skin that produces sebum, an oily substance that waterproofs the skin and hair

    secondary pollutant

    contaminant in the environment that forms when primary pollutants react after being released into the environment

    secondary sex characteristic

    trait that is different in males and females but is not directly involved in reproduction, such as male facial hair and female breasts

    secondary succession

    change over time in the numbers and types of species that live in an area that was previously colonized by living things but has been disturbed

    secondhand smoke

    smoke that enters the air from burning cigarettes or from the lungs of smokers

    semen

    fluid containing sperm and glandular secretions, which nourishes sperm and carries them through the urethra and out of the body

    seminal vesicle

    one of a pair of glands of the male reproductive system that secretes fluid into semen

    seminiferous tubule

    one of the many tiny tubes contained within the testes where sperm are produced

    sensor

    component of a homeostatic mechanism that senses the value of a variable and sends data on it to the control center

    sensory nerve

    nerve of the peripheral nervous system that transmits information from sensory receptors in the body to the central nervous system

    sensory neuron

    type of neuron that carries nerve impulses from sensory receptors in tissues and organs to the central nervous system; also called afferent neuron

    sensory receptor

    specialized nerve cell that responds to a particular type of stimulus such as light or chemicals by generating a nerve impulse

    Sertoli cell

    type of cell that lines the seminiferous tubules in the testes and plays several roles in sperm production

    set point

    physiologically optimum value for a given biological variable such as body temperature

    sex chromosome

    X or Y chromosome

    sex hormone

    endocrine hormone secreted mainly by gonads that controls sexual development and reproduction

    sex-linked gene

    gene located on a sex chromosome

    sex-linked trait

    trait controlled by a gene located on a sex chromosome

    sex ratio

    number of males per 100 females in a population

    sexual dimorphism

    differences between the phenotypes of males and females of the same species

    sexually transmitted infection (STI)

    infection caused by a pathogen that spreads mainly through sexual contact; also called sexually transmitted disease (STD)

    sexual reproduction

    type of reproduction that involves the fertilization of gametes produced by two parents and produces genetically variable offspring

    single nucleotide polymorphism (SNP)

    variation in just one nucleotide in alleles that are present in a population at frequencies greater than 1 percent

    sinus rhythm

    normal, rhythmical beating of the heart

    sixth mass extinction

    current mass extinction caused primarily by habitat loss due to human actions

    skeletal muscle

    voluntary, striated muscle that is attached to bones of the skeleton and helps the body move

    skeletal system

    human body system that consists of all the bones of the body as well as cartilage and ligaments and provides an internal framework for the body

    skin

    major organ of the integumentary system that covers and protects the body and helps maintain homeostasis, for example, by regulating body temperature

    skull

    part of the human skeleton that provides a bony framework for the head and includes bones of the cranium and face

    sleep apnea

    disorder characterized by pauses in breathing during sleep, usually because of physical blockage of air flow

    sliding filament theory

    theory that explains muscle contraction by the sliding of myosin filaments over actin filaments within muscle fibers

    slow-twitch muscle fiber

    type of skeletal muscle cell that is mainly responsible for aerobic activities such as long-distance running

    small intestine

    long, narrow, tube-like organ of the digestive system where most chemical digestion of food and virtually all absorption of nutrients take place

    smooth muscle

    involuntary, nonstriated muscle that is found in the walls of internal organs such as the stomach

    sodium-potassium pump

    active transport mechanism in which sodium ions are pumped out of a cell and potassium ions are pumped into the cell with the help of a carrier protein and energy from ATP

    soil

    mixture of eroded rock, minerals, organic matter, and other materials that is essential for plant growth and forms the foundation of terrestrial ecosystems

    soluble fiber

    nondigestible carbohydrates in food that dissolve in water and slow the absorption of nutrients from the GI tract, thereby reducing insulin spikes

    somatic mutation

    mutation that occurs in a cell of the body other than a gamete

    somatic nervous system

    division of the peripheral nervous system that controls voluntary activities

    somatostatin

    endocrine hormone produced by the pancreas that inhibits the production of growth hormone by the pituitary and the secretion of insulin and glucagon by the pancreas

    specialization

    evolution of different adaptations in competing species, which allows them to live in the same area without competing

    special sense

    sense such as vision or hearing that has special sense organs that gather sensory information and change it into nerve impulses

    speciation

    process by which a new species evolves

    species

    group of organisms that are similar enough to mate and produce fertile offspring together

    sperm

    gamete produced by a male organism

    spermatogenesis

    process of producing sperm in the testes

    spermatogonium (plural, spermatogonia)

    diploid stem cell in a testis that undergoes mitosis to begin the process of spermatogenesis

    sphincter

    ring of muscles that can contract to close off an opening between structures, such as between the esophagus and stomach

    spinal cavity

    long, narrow body cavity inside the vertebral column that runs the length of the trunk and contains the spinal cord

    spinal cord

    thin, tubular bundle of nervous tissue that extends from the brainstem down the back to the pelvis and connects the brain with the peripheral nervous system

    spleen

    secondary organ of the lymphatic system where blood and lymph are filtered

    spongy bone

    light-weight, porous inner layer of bone that contains bone marrow

    squamous cell carcinoma

    common type of skin cancer that affects squamous cells in the epidermis and rarely metastasizes

    stabilizing selection

    type of natural selection for a polygenic trait in which phenotypes at both extremes of the phenotypic distribution are selected against, resulting in a narrowing of the range of phenotypic variation

    starch

    type of complex carbohydrate (polysaccharide) that plants use to store energy

    stem cell

    undifferentiated cell that can develop into specialized types of cells

    sterilization

    surgical procedure that is generally irreversible and that makes it impossible for a woman to become pregnant or for a man to ejaculate viable, motile sperm

    steroid

    type of lipid with a ring structure, such as cholesterol or a sex hormone

    steroid hormone

    type of endocrine hormone that is made of lipids and crosses the plasma membrane to bind with a receptor inside a target cell

    stimulant

    type of psychoactive drug that stimulates the brain and increases alertness and wakefulness

    stimulus

    something that triggers a behavior or other response

    stomach

    sac-like organ of the digestive system between the esophagus and small intestine in which both mechanical and chemical digestion take place

    stroke

    cerebrovascular accident in which a broken artery or blood clot results in lack of blood flow to part of the brain, causing death of brain cells

    stunting

    growth deficit diagnosed in children who are at least two standard deviations below the median height for their age in a reference population

    subsistence strategy

    general way in which a group of people obtain food and the types of food they rely on most, such as hunting and gathering, farming, or fishing

    substrate

    specific substance acted upon by a given enzyme

    sugar

    short-chain soluble carbohydrate that is found in many foods, tastes sweet, and provides quick energy

    sunburn

    reddening of the skin that occurs when the outer layer of the skin is damaged by UV light from the sun or tanning lamps

    surrogate mother

    woman who agrees to become pregnant using a man’s sperm and her own egg, carries the fetus to term, and then gives up the baby at birth for adoption by the sperm donor and his partner

    sustainable use

    use of a natural resource in a way that meets the needs of the present and also preserves the resource for use by future generations

    sweat

    salty fluid secreted into ducts by sweat glands in the dermis that excretes wastes and helps cool the body; also called perspiration

    sweat gland

    exocrine gland in the dermis of the skin that produces the salty fluid called sweat through a duct to the skin surface

    symbiosis

    close relationship between organisms in two different species in which at least one of the organisms benefits from the relationship; mutualism, commensalism, or parasitism

    sympathetic division

    division of the autonomic nervous system that controls the fight-or-flight response

    sympatric speciation

    evolution of a new species that occurs without geographic separation first occurring between members of an original species

    synapse

    space between the axon terminal of a neuron and an adjoining cell

    synovial joint

    movable joint in which a fluid-filled synovial cavity separates bones at the joint

    syphilis

    sexually transmitted infection caused by the bacterium Treponema pallidum that may eventually be fatal if untreated

    systemic circulation

    part of the cardiovascular system that carries blood between the heart and body

    systole

    part of a heartbeat in which the atria relax and fill with blood from the lungs and body, while the ventricles contract and pump blood out of the heart

    T

    T3 (triiodothyronine)

    endocrine hormone secreted by the thyroid gland that increases the rate of metabolism in cells throughout the body

    T4 (thyroxine)

    endocrine hormone secreted by the thyroid gland that increases the rate of metabolism in cells throughout the body

    target cell

    type of cell on which a particular hormone has an effect because it has receptor molecules for the hormone

    taste bud

    small structure on the tongue containing chemoreceptor cells that sense chemicals in food

    TATA box

    regulatory element that is part of the promotor of most eukaryotic genes

    taxon (plural, taxa)

    level of organization in a biological classification system such as the Linnaean system; for example, species or genus

    taxonomy

    science of classifying organisms

    T cell

    type of lymphocyte that kills infected or cancerous cells (killer T cell) or helps regulate the immune response (helper T cell)

    teething

    emergence of deciduous (baby) teeth during infancy and early childhood

    telomere

    region of repetitive nucleotide sequences at the end of a chromosome that becomes shorter each time a cell divides

    telophase

    last stage of mitosis during which chromosomes uncoil to form chromatin, the spindle breaks down, and new nuclear membranes form

    temporal lobe

    part of each hemisphere of the cerebrum that controls hearing, memories, and sensations

    tendinitis

    inflammation of a tendon when it is over-extended or worked too hard without rest

    tendon

    tough connective tissue that attaches skeletal muscle to bones

    terrestrial biome

    any land-based biome

    testicular cancer

    cancer of the testes, which is relatively common in young men

    testis (plural, testes)

    one of two male reproductive organs that produce sperm and secrete testosterone; male gonad

    testosterone

    male sex hormone secreted mainly by the testes

    thalamus

    part of the inner brain that is a major hub for nerve impulses traveling back and forth between the cerebrum and spinal cord

    thalassemia

    type of inherited anemia caused by abnormal hemoglobin that is a genetic adaptation to malaria in the Mediterranean region, parts of Africa, and South and Southeast Asia

    thermal pollution

    pollution by heat energy, typically occurring when heated water is discharged into a river or lake

    thermoreceptor

    type of sensory receptor that senses temperature

    thoracic cavity

    body cavity in the chest that holds the lungs and heart

    thrifty gene hypothesis

    idea that "thrifty genes" evolved in some human populations because they allowed people to burn fewer Calories and store the rest as body fat, which would help them survive famines

    thymus

    organ of the lymphatic system where lymphocytes called T cells mature

    thyroid gland

    large endocrine gland in the neck whose hormones control the rate of cellular metabolism and help maintain calcium homeostasis

    tissue

    group of cells, generally of the same kind, that perform a particular function in an organism

    toddlerhood

    first part of early childhood that covers the ages 1 to 3 years

    tonsil

    one of four paired secondary lymphatic organs that encircle the inner throat and filter pathogens out of lymph

    touch

    ability to sense pressure, vibration, temperature, pain, and other tactile stimuli

    toxoplasmosis

    common parasitic disease that may be a selective agent maintaining both Rhesus-positive (Rh+) and Rhesus-negative (Rh-) blood type alleles in human populations

    trachea

    tubular organ of the respiratory system that carries air between the larynx and bronchi; also called windpipe

    transcription

    process in which genetic instructions in DNA are copied to form a complementary strand of mRNA

    trans fat

    type of harmful, artificial fat that is added to some foods to help preserve freshness and improve taste

    transfer RNA (tRNA)

    type of RNA that brings amino acids to ribosomes where they are joined together to form proteins

    transgenic crop

    crop that has been genetically modified with new genes that code for traits useful to humans

    translation

    process in which genetic instructions in mRNA are "read" to synthesize a protein

    transpiration

    process in which plants give off water vapor through tiny pores, called stomata, in their leaves

    transport protein

    protein in a cell membrane that helps other substances cross the membrane to enter or leave the cell

    tribe

    taxon between the subfamily and genus in the Linnaean system of classification

    trichomoniasis

    common, sexually transmitted infection that is caused by the protozoan parasite Trichomonas vaginalis

    triglyceride

    type of lipid that contains glycerol and makes up body fat in animals

    trimester

    one of three, approximately three-month periods into which a pregnancy is divided

    trophic level

    feeding position in a food chain or food web, such as producer, primary consumer, or secondary consumer

    trophoblast

    outer cell layer of a blastocyst that implants in the uterus and eventually develops into the fetal portion of the placenta

    tubal ligation

    surgical sterilization procedure in females in which the Fallopian tubes are blocked so sperm cannot reach and fertilize an egg

    tumor

    abnormal mass of cells that may be cancerous

    tumor-suppressor gene

    gene that normally inhibits division of abnormal cells and may cause cancer if it mutates

    type 1 diabetes

    autoimmune disorder in which the immune system destroys insulin-secreting beta cells in the pancreas, leading to loss of glucose control and high levels of blood glucose

    type 2 diabetes

    multifactorial disorder in which a combination of insulin resistance and impaired insulin production lead to loss of glucose control and high levels of blood glucose

    typology

    system of discrete categories, such as races, that are sometimes used for classifying variation

    U

    ulcerative colitis

    inflammatory bowel disease that causes ulcers (sores) in the colon and rectum

    umbilical cord

    long, narrow conduit containing two arteries and a vein that connects an embryo or fetus to the placenta

    undernutrition

    insufficient intake of nutrients, generally leading to an individual being underweight for height (in adults) or underweight for age (in children)

    universal donor

    individual with type O blood in the ABO blood group system who can donate blood to people of any ABO blood type

    universal recipient

    individual with type AB blood in the ABO blood group system who can receive a blood donation from people of any ABO blood type

    unsaturated fatty acid

    simple lipid molecule in which carbon atoms are not bonded to as many hydrogen atoms as possible because some adjacent carbon atoms in the chain share double or even triple bonds

    upper gastrointestinal (GI) tract

    part of the gastrointestinal tract that includes the mouth, pharynx, esophagus, and stomach

    urbanization

    shift in population from rural to urban areas, which is the process by which cities form and grow

    urea

    waste product of protein catabolism that is mainly filtered from blood in the kidneys and excreted in urine

    ureter

    muscular, tube-like organ of the urinary system that moves urine by peristalsis from a kidney to the bladder

    urethra

    tube-like organ of the urinary system that carries urine out of the body from the bladder and, in males, also carries semen out of the body

    uric acid

    waste product of nucleic acid catabolism that is mainly filtered from blood by the kidneys and excreted in urine

    urinary bladder

    sac-like organ that stores urine until it is excreted from the body

    urinary incontinence

    common chronic problem of uncontrolled leakage of urine

    urinary system

    organ system that includes the kidneys, ureters, urinary bladder, and urethra and that is responsible for filtering waste products and excess water from the blood and excreting them from the body in urine

    urination

    process in which urine leaves the body through the external urethral orifice

    urine

    liquid waste product of the body that is formed by the kidneys and excreted by the other organs of the urinary system

    uterine cycle

    events of the menstrual cycle that occur in the uterus, including menses and the buildup of the endometrium

    uterus (plural, uteri)

    female reproductive organ in which first an embryo and then a fetus grows and develops until birth

    V

    vaccine

    substance containing a modified pathogen that does not cause disease but provokes an adaptive immune response, resulting in immunity to the pathogen

    vacuole

    large sac-like organelle that stores and transports materials inside a cell

    vagina

    female reproductive organ that receives sperm during sexual intercourse and provides a passageway for a baby to leave the mother’s body during birth

    vaginitis

    inflammation of the vagina usually caused by an infection with microbes

    variability-selection hypothesis

    idea that hominins evolved greater adaptability in response to climate change rather than evolving specializations for a particular climate

    vas deferens

    one of a pair of thin tubes that transports sperm from an epididymis to an ejaculatory duct during ejaculation; also called sperm duct

    vasectomy

    surgical sterilization procedure in males in which the vas deferens are blocked so sperm cannot be ejaculated

    vasoconstriction

    narrowing of blood vessels so less blood can flow through them

    vasodilation

    widening of blood vessels so more blood can flow through them

    vector

    organisms such as an insect that spreads pathogens from host to host

    vein

    type of blood vessel that carries blood toward the heart from the lungs or body

    ventilation

    process of moving air into and out of the lungs; also called breathing

    ventral cavity

    major human body cavity at the anterior (front) of the trunk that contains such organs as the lungs, heart, stomach, intestines, and internal reproductive organs

    ventricle

    one of two lower chambers of the heart that pumps blood out of the heart

    vernix

    thick waxy coating that forms on a fetus to protect the skin and that mostly disappears by birth

    vertebra (plural, vertebrae)

    one of 33 small bones that make up the vertebral column

    vertebral column

    flexible column of vertebrae that connects the trunk to the skull and encloses the spinal cord; also called spine or backbone

    vesicle

    small sac-like organelle that stores and transports materials inside a cell

    vesicle transport

    type of active transport in which substances are carried across a cell membrane by vesicles

    vestigial structure

    structure such as the human tailbone or appendix that evolution has reduced in size because it is no longer needed

    villi (singular, villus)

    microscopic, finger-like projections in a mucous membrane that form a large surface area for absorption

    viral load

    amount of virus in a sample of an infected individual’s blood

    virus

    tiny, nonliving particle that contains DNA but lacks other characteristics of living cells and may cause human disease

    vision

    ability to sense light and see; also called sight

    vitamin

    organic compound needed in small amounts for proper body functioning

    vitamin D

    micronutrient synthesized in the skin and needed to absorb calcium for strong bones

    vulva

    external female reproductive structures, including the clitoris, labia, and vaginal and urethral openings

    W

    wasting

    dangerously low levels of body fat and muscle mass, usually due to severe undernutrition

    water cycle

    biogeochemical cycle through which water is recycled on, above, and below Earth’s surface; also called hydrological cycle

    Wernicke’s area

    speech center in the brain that controls the ability to comprehend speech

    wetland

    area that is saturated with water or covered by water for at least one season of the year and has plants that can grow in water-logged soil

    white blood cell

    type of cell in blood that defends the body against invading microorganisms or other threats in blood or extracellular fluid

    white matter

    type of nervous tissue that is found only in the brain and spinal cord and that connects and facilitates communication between gray matter areas

    withdrawal

    contraceptive method with a high failure rate in which a man withdraws his penis from his partner’s vagina before ejaculation occurs; also called coitus interruptus

    X

    X-linked gene

    gene located on the X chromosome

    X-linked trait

    trait controlled by a gene located on the X chromosome

    Y

    yolk sac

    membranous sac attached to an embryo that provides a source of nutrients to the early embryo and becomes part of the primitive gut

    Z

    zero population growth (ZPG)

    equilibrium condition in which the human population is neither increasing nor decreasing in size because the birth rate equals the death rate

    zona pellucida

    protein layer surrounding the cell membrane of a human egg

    zoonosis (plural, zoonoses)

    >infectious disease of nonhuman animals that can be transmitted to humans

    zygote

    diploid cell that forms when two haploid gametes unite during fertilization