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Biology LibreTexts

25.13: Glossary: M

  • Page ID
    17837
  • 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