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Biology LibreTexts

25.5: Glossary: E

  • Page ID
  • 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


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


    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


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


    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


    gamete produced by a female


    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


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


    process in which wastes pass out of the body


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


    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


    movement of individuals out of a population


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


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


    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


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


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


    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


    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


    protein that speeds up biochemical reactions; biological catalyst


    large-scale disease outbreak in a population


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


    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


    inflammation of the epididymis, which may be acute or chronic


    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


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


    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


    female sex hormone secreted mainly by the ovaries


    organism that has cells containing a nucleus and other organelles

    eukaryotic cell

    cell that contains a nucleus and other organelles


    intense feeling of well-being and happiness


    type of psychoactive drug that brings about a state of euphoria


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


    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


    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


    region of DNA or RNA that codes for a protein

    exothermic reaction

    chemical reaction that releases energy


    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


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


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