Lewis/Life - Glossary

M

macroevolution MAK-ro-ev-eh-LU-shun Large-scale evolutionary changes, such as speciation and extinction. 375

macromolecule MAK-ro-MOL-e-kuel A very large molecule. 35

macronucleus MAK-ro-NEW-klee-us A large nucleus in a protozoan cell. 459

macronutrients MAK-ro-NU-tree-entz Carbohydrates, fats, and proteins obtained from food in large amounts. 755

macrophage MAK-ro-FAYge Very large, wandering phagocyte. 790

malignant tumor mal-IG-nant TOO-mer A cancerous tumor. 180

malleus MAL-e-us A small bone in the middle ear. 653

Malpighian tubule mal-PIG-he-in TOOB-yul An insect excretory structure. 778

mammary gland MAM-a-ree gland Milk-producing sweat gland derivative in mammals. 603

mangrove swamp MAN-growv SWAMP Tropical area that connects the sea and forests. 881

mantle A dorsal fold of tissue that secretes a shell in mollusks. 519

marsupial mar-SOOP-e-al A pouched mammal. 366

mast cell Immune system cell that releases allergy mediators when stimulated. 791, 800

matrix MAY-trix The inner compartment of a mitochondrion. The nonliving part of connective tissue. 128, 594

mechanoreception mek-AN-o-ree-SEP-shun Detecting touch. 644

medulla oblongata mah-DULE-ah ob-long-AH-tah The part of the brain stem nearest the spinal cord; regulates breathing, heartbeat, blood pressure, and reflexes. 627

medusa med-EW-sa The free-swimming form of a cnidarian. 517

megagametophyte MEG-ah-gah-MEE-toe-fight Large, egg-producing structure in a plant. 557

megakaryocyte MEG-ah-KAR-ee-o-site A huge bone marrow cell that breaks apart to yield platelets. 717

megasporangia MEG-ah-spor-AN-gee-ah Structures in which megaspores form. 557

megaspore MEG-ah-spor Structure in plants that yields female gametophyte. 557

megaspore mother cell MEG-ah-spor MOTH-er SEL A cell within an ovule in plants that divides meiotically to produce four haploid cells, three of which degenerate and one of which becomes the egg. 563

meiosis mi-O-sis Cell division that halves the genetic material. 192

melanocyte mel-AN-o-site Cell that produces melanin pigment. 598

melanocyte-stimulating hormone mel-AN-o-site STIM-u-lat-ing HOR-moan (MSH) A hormone produced between the anterior and posterior pituitary in some vertebrate species that controls skin pigmentation. 669

melatonin mel-ah-TOE-nin A hormone produced in the pineal gland that may control other hormones by sensing light and dark cycles. 675

memory cell Mature B cell, specific to an antigen already met, that responds quickly by secreting antibodies when that antigen is encountered again. 795

mesoderm MEZ-o-derm The middle embryonic germ layer, whose cells become bone, muscle, blood, dermis, and reproductive organs. 220

mesoglia mez-o-GLEE-a A jellylike substance in the middle of a cnidarian body. 517

mesohyl MEZ-o-hile A part of a sponge that contains amoebocytes. 515

mesophyll cell MEZ-o-fill SEL Thin-walled plant cell that takes part in C4 photosynthesis. 160

messenger RNA MESS-en-ger RNA (mRNA) A molecule of ribonucleic acid that is complementary in sequence to the sense strand of a gene. 329

meta-analysis ME-tah a-NAL-i-sis A study that combines results of several studies. 27

metabolic pathway met-a-BOL-ik PATH-way A series of connected, enzymatically catalyzed reactions in a cell. 114

metabolism meh-TAB-o-liz-um The biochemical reactions that acquire and use energy. 8, 114

metacentric met-a-SEN-trik A chromosome whose centromere divides it into two similarly sized arms. 296

metamerism MET-a-mer-izm A body consisting of repeating segments. 521

metamorphosis met-a-MORE-foe-sis A developmental process in which an animal changes drastically in body form between the juvenile and the adult. 512

metaphase MET-ah-faze The second stage of cell division, when chromosomes align down the center of a cell. In mitosis, the chromosomes form a single line. 171

metaphase I MET-ah-faze I In meiosis I, when homologs align. 200

metaphase II MET-a-faze II When replicated chromosomes align down the center of the cell in meiosis II. 201

metapopulation met-a-pop-eu-LAY-shun Local populations that frequently exchange members. 838

metastasis meh-TAH-stah-sis Spreading of cancer. 181

methanogen meth-AN-o-gen Archaean that produces methane as a by-product of its metabolism. 451

microevolution MIKE-ro-ev-eh-LU-shun Subtle, incremental single-trait changes that underlie speciation. 375

microfilaments MI-kro-FILL-ah-ments Tiny actin rods in cells, especially contractile cells. 97

microgametophyte MIK-ro-gah-MEE-toe-fight Small sperm-producing structure in a plant. 557

micronucleus mi-kro-NUKE-lee-us A small nucleus in a protozoan cell. 459

micronutrients MIKE-ro-NU-tree-entz Vitamins and minerals, which are required in small amounts. 755

microsporangia MIKE-ro-spor-AN-gee-ah Structures in which microspores form. 557

microspore MIKE-ro-spor Structure in plants that gives rise to male gametophyte. 557

microspore mother cell MIKE-ro-spor MOTH-er SEL Cell in pollen sacs that divides meiotically to produce four haploid microspores. 563

microtubules MI-kro-TU-bules Long, hollow tubules of tubulin protein that move cells. 74, 97

microvilli MIKE-ro-VIL-i Tiny projections on the surfaces of epithelial cells that comprise intestinal villi. 762

midbrain MID-brane Part of the brain stem above the pons where white matter connects with higher brain structures and gray matter contributes to sight and hearing. 620

mineralocorticoids MIN-er-ral-o-KOR-tah-KOIDZ Hormones produced in the adrenal cortex that maintain blood volume and electrolyte balance by stimulating the kidneys to return sodium ions and water to the blood and to excrete potassium ions. 670

missense mutation MISS-sentz mu-TAY-shun A mutation that changes a codon specifying a certain amino acid into a codon specifying a different amino acid. 341

mitochondria MI-toe-KON-dree-ah Organelles within which the reactions of cellular metabolism occur. 71

mitosis mi-TOE-sis A form of cell division in which two genetically identical cells form from one. 168

mitotic spindle mi-TOT-ik SPIN-del A structure of microtubules that aligns and separates chromosomes in mitosis. 170

mixotroph MIX-o-trof A bacterium that uses inorganic molecules for energy and organic molecules for carbon. 445

mode of inheritance Whether a trait is autosomal or sex-linked, and dominant or recessive. 267

molecular evolution Estimating degrees of evolutionary relatedness by comparing informational polymer sequences among species. 395

molecular tree diagram A depiction of hypothesized relationships between species based on molecular sequence data. 397

molecular weight The sum of the weights of the atoms that make up a molecule. 35

molecule MOL-eh-kuel Combined atoms. 34

mollusk MOLL-usk Animal with a soft body, hard shell, three body regions, muscular feet, and circulatory, excretory, and nervous systems. 512

molting hormone An insect hormone produced in the late larva that triggers metamorphosis. 665

Monera mone-AIR-ah The kingdom that includes bacteria and cyanobacteria. 14, 430

monoclonal antibodies MON-o-KLON-al AN-tee-bod-eez Identical antibodies provided by a single B cell. 804

monocots MON-o-kotz Flowering plants that have one seed leaf. 541

monogamy mono-OG-a-mee Formation of a permanent male-female pair. 830

monohybrid cross MON-o-HI-brid CROSS Mating of individuals for a particular gene. 266

monomer MON-o-mer A single link in a polymeric molecule. 43

monosaccharide MON-o-SAK-eh-ride A sugar that is one five- or six-carbon unit. 43

monosomy MON-o-SOAM-ee Absence of one chromosome. 298

monotreme MON-o-treem An egg-laying mammal. 366, 527

monounsaturated (fat) MON-o-un-SAT-yer-a-tid A fatty acid with one double bond. 45

monozygotic twins mon-o-zi-GOT-ik TWINZ Identical twins resulting from the splitting of a fertilized ovum. 279

morphogens MORF-o-genz Proteins that form gradients that influence development. 215

morula MORE-u-lah The preembryonic stage of a solid ball of cells. 218

mosaic catastrophism mo-ZAY-ik cat-ASS-trof-izm The idea that a series of great floods molded the earth's features and caused extinctions and speciations. 376

moss The most common type of bryophyte. 493

motif moe-teef A common part of a transcription factor. 327

motor neuron MO-ter NEUR-on A neuron that transmits a message from the central nervous system toward a muscle or gland, with a long axon and short dendrites. 611

motor unit A neuron and all the muscle fibers it contacts. 699

mucigel MYUS-eh-gel A slimy substance that root cap cells produce. 546

multicellular mull-tee-SEL-u-lar Consisting of many cells. 10, 60

multifactorial mull-tee-fac-TORE-e-al Traits molded by one or more genes and the environment. 276

multiple fission MULL-ti-pull FISH-in A form of asexual reproduction in protozoa in which a parent cell undergoes several nuclear divisions and then partitions off several progeny at one time. 459

muscle fasciculi MUS-sel fah-SIK-u-li Bundles of muscle fibers. 694

muscle fiber Skeletal muscle cell. 694

muscle spindles Receptors in skeletal muscle that monitor the degree of muscle tone or how many fibers contract at a time. 701

muscular tissue Tissue consisting of contractile cells that provide motion. 594

mutagen MUTE-a-jen An agent that causes a mutation. 339

mutant MU-tent A phenotype or allele that is not the most common for a certain gene in a population or that has been altered from the "normal" condition. 265

mutation mu-TAY-shun A change in a gene or chromosome. 265

mutualism MU-chu-a-lism Symbiosis that benefits both partners. 434

mycelium mi-SELL-ee-um An assemblage of hyphae that forms an individual fungus. 477

mycology mi-KOL-o-gee The study of fungi. 476

mycorrhizae mi-kor-IZ-ee Parts of a fungus that wrap around plant roots. 485

myelin sheath MI-eh-lin SHEATH A fatty material that insulates some nerve fibers in vertebrates, allowing rapid nerve impulse transmission. 614

myoepithelial cell mi-o-ep-ee-THEEL-ee-al SEL Cell that can contract and be part of a layer. 598

myofibrils mi-o-FI-brilz Cylindrical subunits of a muscle fiber. 694

myofilaments mi-o-FILL-eh-mentz Acin or myosin "strings" that make up myofibrils. 695

myosin MI-o-sin The protein that forms thick filaments in muscle tissue. 100, 597

myriapods mi-REE-a-podz Centipedes and millipedes. 522

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