← Chapter 6 AP Biology Campbell 8 Edition Export Options Alphabetize Word-Def Delimiter Tab Comma Custom Def-Word Delimiter New Line Semicolon Custom Data Copy and paste the text below. It is read-only. Select All actin A globular protein that links into chains, two of which twist helically about each other, forming microfilaments (actin filaments) in muscle and other kinds of cells. basal body A eukaryotic cell structure consisting of a 9 + 0 arrangement of microtubule triplets. The basal body may organize the microtubule assembly of a cilium or flagellum and is structurally very similar to a centriole. capsule (1) A sticky layer that surrounds the cell wall of some prokaryotes, protecting the cell surface and sometimes helping to glue the cell to surfaces. (2) The sporangium of a bryophyte (moss, liverwort, or hornwort). cell fractionation The disruption of a cell and separation of its parts by centrifugation. central vacuole A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development. centriole A structure in the centrosome of an animal cell composed of a cylinder of microtubule triplets arranged in a 9 + 0 pattern. A centrosome has a pair of centrioles. centrosome Structure present in the cytoplasm of animal cells, important during cell division; functions as a microtubule-organizing center. A centrosome has two centrioles. chloroplast An organelle found in plants and phot osynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water. chromatin The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope. chromosome A cellular structure carrying genetic material, found in the nucleus of eukaryotic cells. Each chromosome consists of one very long DNA molecule and associated proteins. (A bacterial chromosome usually consists of a single circular DNA molecule and associated proteins. It is found in the nucleoid region, which is not membrane bounded.) See also chromatin. cilium A short cellular appendage containing microtubules. A motile cilium is specialized for locomotion and is formed from a core of nine outer doublet microtubules and two inner single microtubules (the "9 + 2" arrangement) ensheathed in an extension of the plasma membrane. A primary cilium is usually nonmotile and plays a sensory and signaling role; it lacks the two inner microtubules (the "9 + 0" arrangement). collagen A glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom. contractile vacuole A membranous sac that helps move excess water out of certain freshwater protists. crista An infolding of the inner membrane of a mitochondrion that houses electron transport chains and molecules of the enzyme catalyzing the synthesis of ATP (ATP synthase). cytoplasm The contents of the cell, exclusive of the nucleus and bounded by the plasma membrane. cytoplasmic streaming A circular flow of cytoplasm, involving myosin and actin filaments, that speeds the distribution of materials within cells. cytoskeleton A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical, transport, and signaling functions. cytosol The semifluid portion of the cytoplasm. desmosome A type of intercellular junction in animal cells that functions as a rivet. dynein In cilia and flagella, a large contractile protein extending from one microtubule doublet to the adjacent doublet. ATP hydrolysis drives changes in dynein shape that lead to bending of cilia and flagella. electron microscope (EM) A microscope that uses magnets to focus an electron beam on or through a specimen, resulting in resolving power a thousandfold greater than that of a light microscope. A transmission electron microscope (TEM) is used to study the internal structure of thin sections of cells. A scanning electron microscope (SEM) is used to study the fine details of cell surfaces. endomembrane system The collection of membranes inside and around a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles; includes the smooth and rough endoplasmic reticulum, the Golgi apparatus, lysosomes, and vacuoles. endoplasmic reticulum (ER) An extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions. eukaryotic cell A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles. Organisms with eukaryotic cells (protists, plants, fungi, and animals) are called eukaryotes. extracellular matrix (ECM) The substance in which animal cells are embedded, consisting of protein and polysaccharides synthesized and secreted by cells. fibronectin A glycoprotein that helps animal cells attach to the extracellular matrix. flagellum A long cellular appendage specialized for locomotion. Like motile cilia, eukaryotic flagella have a core with nine outer doublet microtubules and two inner single microtubules ensheathed in an extension of the plasma membrane. Prokaryotic flagella have a different structure. food vacuole A membranous sac formed by phagocytosis of microorganisms or particles to be used as food by the cell. gap junction A type of intercellular junction in animals that allows the passage of materials between cells. glycoprotein A protein with one or more carbohydrates covalently attached to it. Golgi apparatus An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum and synthesize some products, notably noncellulose carbohydrates. granum A stack of membrane-bounded thylakoids in the chloroplast. Grana function in the light reactions of photosynthesis. integrin in animal cells, a transmembrane receptor protein that interconnects the extracellular matrix and the cytoskeleton. intermediate filament A component of the cytoskeleton that includes filaments intermediate in size between microtubules and microfilaments. light microscope (LM) An optical instrument with lenses that refract (bend) visible light to magnify images of specimens. lysosome A membrane-enclosed sac of hydrolytic enzymes found in the cytoplasm of animal cells and some protists. microfilament A cable composed of actin proteins in the cytoplasm of almost every eukaryotic cell, making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction; also known as an actin filament. microtubule A hollow rod composed of tubulin proteins that make up part of the cytoskeleton in all eukaryotic cells and is found in cilia and flagella. middle lamella In plants, a thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young cells. mitochondrial matrix The compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the citric acid cycle. mitochondrion An organelle in eukaryotic cells that serves as the site of cellular respiration. motor protein A protein that interacts with cytoskeletal elements and other cell components, producing movement of the whole cell or parts of the cell. nuclear envelope The double membrane in a eukaryotic cell that encloses the nucleus, separating it from the cytoplasm. nuclear lamina A netlike array of protein filaments lining the inner surface of the nuclear envelope; it helps maintain the shape of the nucleus. nucleoid A dense region of DNA in a prokaryotic cell. nucleolus A specialized structure in the nucleus, consisting of chromatin regions containing ribosomal RNA genes along with ribosomal proteins imported from the cytoplasmic site of rRNA synthesis and ribosomal subunit assembly. See also ribosome. nucleus (1) An atom's central core, containing protons and neutrons. (2) The chromosome-containing organelle of a eukaryotic cell. (3) A cluster of neurons. organelle of several membrane-enclosed structures with specialized functions, suspended in the cytosol of eukaryotic cells. peroxisome An organelle containing enzymes that transfer hydrogen (H2) from various substrates to oxygen (O2), producing and then degrading hydrogen peroxide (H2O2). phagocytosis A type of endocytosis in which large particulate substances are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells). plasma membrane The membrane at the boundary of every cell that acts as a selective barrier, regulating the cell's chemical composition. plasmodesma An open channel in the cell wall of a plant through which strands of cytosol connect from an adjacent cell. plastid One of a family of closely related organelles that includes chloroplasts, chromoplasts, and amyloplasts (leucoplasts). Plastids are found in cells of photosynthetic organisms. primary cell wall In plants, a relatively thin and flexible layer first secreted by a young cell. prokaryotic cell A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles. proteoglycan A glycoprotein consisting of a small core protein with many carbohydrate chains attached, found in the extracellular matrix of animal cells. A  may consist of up to 95% carbohydrate. pseudopodium A cellular extension of amoeboid cells used in moving and feeding. ribosomal RNA (rRNA) The most abundant type of RNA, which together with proteins makes up ribosomes. ribosome A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus. See also nucleolus. rough ER That portion of the endoplasmic reticulum studded with ribosomes. scanning electron microscope (SEM) A microscope that uses an electron beam to scan the surface of a sample to study details of its topography. secondary cell wall In plants, a strong and durable matrix often deposited in several laminated layers for cell protection and support. smooth ER That portion of the endoplasmic reticulum that is free of ribosomes. stroma Within the chloroplast, the dense fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water. thylakoid A flattened membranous sac inside a chloroplast. Thylakoids exist in an interconnected system in the chloroplast and contain the molecular "machinery" used to convert light energy to chemical energy. tight junction A type of intercellular junction in animal cells that prevents the leakage of material between cells. transmission electron microscope (TEM) A microscope that passes an electron beam through very thin sections and is primarily used to study the internal ultrastructure of cells. transport vesicle A tiny membranous sac in a cell's cytoplasm carrying molecules produced by the cell. vacuole A membrane-bounded vesicle whose function varies in different kinds of cells. vesicle A sac made of membrane in the cytoplasm.