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| An optical instrument with lenses that refract (bend) visible light to magnify images of specimens. |
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| Any of several membrane-enclosed structures with specialized functions, suspended in the cytosol of eukaryotic cells. |
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| A microscope that uses magnets to focus an electron beam on or through a specimen, resulting in a practical resolution of a hundredfold greater than that of a light microscope using standard techniques. |
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| scanning electron microscope (SEM) |
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| A microscope that uses an electron beam to scan the surface of a sample, coated with metal atoms, to study details of its topography. |
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| transmission electron microscope (TEM) |
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| A microscope that passes an electron beam through very thin sections stained with metal atoms and is primarily used to study the internal ultrastructure of cells. |
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| The disruption of a cell and separation of its parts by centrifuge at successively higher speeds. |
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| The semifluid portion of the cytoplasm. |
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| 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. |
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| A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles. Organisms with prokaryotic cells (bacteria and archaea) are called prokaryotes. |
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| A non-membrane-bounded region in a prokaryotic cell where the DNA is concentrated. |
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| The contents of the cell bounded by the plasma membrane; in eukaryotes, the portion exclusive of the nucleus. |
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| The membrane at the boundary of every cell that acts as a selective barrier, regulating the cell’s chemical composition. |
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| (1) An atom’s central core, containing protons and neutrons. (2) The organelle of a eukaryotic cell that contains the genetic material in the form of chromosomes, made up of chromatin. (3) A cluster of neutrons. |
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| In a eukaryotic cell, the double membrane that surrounds the nucleus, perforated with pores that regulate traffic with the cytoplasm. The outer membrane is continuous with the endoplasmic reticulum. |
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| A netlike array of protein filaments that lines the inner surface of the nuclear envelope and helps maintain the shape of the nucleus. |
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| 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.) |
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| A special structure in the nucleus, consisting of chromosomal regions containing ribosomal RNA genes along with ribosomal proteins imported from the cytoplasm; site of RNA synthesis and ribosomal subunit assembly. (plural: nucleoli) |
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| A complex of RNA and proteins molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus. |
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| The collection of membranes inside and surrounding a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles; includes the plasma membrane, the nuclear envelope, the smooth and rough endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles and vacuoles. |
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| A membranous sac in the cytoplasm of a eukaryotic cell. |
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| endoplasmic reticulum (ER) |
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| extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions. |
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| The portion of the endoplasmic reticulum that is free of ribosomes. |
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| The portion of the endoplasmic reticulum with ribosomes attached. |
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| A protein with one or more covalently attached carbohydrates. |
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| A small membranous sac in a eukaryotic cell’s cytoplasm carrying molecules produced by the cell. |
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| 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. |
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| A membrane-enclosed sac of hydrolytic enzymes found in the cytoplasm of animal cells and some protists. |
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| A type of endocytosis in which large particulate substances or small organisms 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). |
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| A membrane-bounded vesicle whose specialized function varies in different kinds of cells. |
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| A membranous sac formed by phagocytosis of microorganisms or particles to be used as food by the cell. |
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| A membranous sac that helps move excess water out of certain freshwater protists. |
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| In a mature plant cell, a large membranous sac with diverse roles in growth, storage and sequestration of toxic substances. |
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| mitochondria(mitochondrion) |
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Definition
| An organelle in eukaryotic cells that serves as the site of cellular respiration; uses oxygen to break down organic molecules and synthesize ATP. |
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| An organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water. |
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| The theory that mitochondria and plastids, including chloroplasts, originated as prokaryotic cells engulfed by an ancestral eukaryotic cell. The engulfed cell and its host cell then evolved into a single organism. |
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| An infolding of the inner membrane of a mitochondrion. The inner membrane houses electron transport chains and molecules of the enzyme catalyzing the synthesis of ATP (ATP synthase). |
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| The compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the citric acid cycle, as well as ribosomes and DNA. |
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| A flattened, membranous sac inside a chloroplast. Thylakoids often exist in stacks called grana that are interconnected; their membranes contain molecular “machinery” used to convert light energy to chemical energy. |
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| A stack of membrane-bounded thylakoids in the chloroplast. Grana function in the light reactions of photosynthesis. |
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| A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior in the plant. |
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| One of a family of closely related organelles that includes chloroplasts, chromoplasts and amyloplasts. Plastids are found in cells of photosynthetic eukaryotes. |
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| An organelle containing enzymes that transfer hydrogen atoms from various substrates to oxygen (O2), producing and then degrading hydrogen peroxide (H2O2). |
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| A network of microtubules, microfilaments and intermediate filaments that extend throughout the cytoplasm and serve a variety of mechanical, transport and signaling functions. |
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| A protein that interacts with cytoskeleton elements and other cell components, producing movement of the whole cell or parts of the cell. |
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| A hollow rod composed of tubulin proteins that makes up part of the cytoskeleton in all eukaryotic cells and is found in cilia and flagella. |
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| A structure present in the cytoplasm of animal cells that functions as a microtubule-organizing center and is important during cell division. A centrosome has two centrioles. |
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| A structure in the centrosome of an animal cell composed of a cylinder of microtubule triplets arranged in a 9 + 0 pattern. A centrosome as a pair of centrioles. |
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| 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 (the “9 + 2” arrangement) ensheathed in an extension of the plasma membrane. Prokaryotic flagella have a different structure. |
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| A short appendage containing microtubules in eukaryotic cells. A motile cilium is specialized for locomotion or moving fluid past the cell; it 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). |
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Definition
| 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. |
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| In cilia and flagella, a large motor 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. |
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| 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. |
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| 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. |
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| (1) The outer region of cytoplasm in a eukaryotic cell, lying just under the plasma membrane, that has a more gel-like consistency than the inner regions due to the presence of multiple microfilaments. (2) In plants, ground tissue that is between the vascular tissue and dermal tissue in a root or eudicot stem. |
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| A type of motor protein that associates into filaments that interact with actin filaments to cause cell contraction. |
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| pseudopodia (pseudopodium) |
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| A cellular extension of amoeboid cells used in moving and feeding. |
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| A circular flow of cytoplasm, involving interaction of myosin and actin filaments, which speeds the distribution of materials within cells. |
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| A component of the cytoskeleton that includes filaments intermediate in size between microtubules and microfilaments. |
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| A protective layer external to the plasma membrane in the cells of plants, prokaryotes, fungi and some protists. Polysaccharides such as cellulose (in plants and some protists), chitin (in fungi) and peptidoglycan (in bacteria) are important structural components of cell walls. |
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| In plants, a relatively thin and flexible layer that surrounds the plasma membrane of a young cell. |
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| In plants, a thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young cells. |
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| In plants cells, a strong and durable matrix that is often deposited in several laminated layers around the plasma membrane and provides protection and support. |
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| extracellular matrix (ECM) |
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Definition
| The meshwork surrounding animal cells, consisting of glycoproteins, polysaccharides and proteoglycans synthesized and secreted by the cells. |
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| 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. |
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| A large molecule consisting of a small core protein with many carbohydrate chains attached, found in the extracellular matrix or animal cells. A proteoglycan may consist of up to 95% carbohydrate. |
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| An extracellular glycoprotein secreted by animal cells that helps them attach to the extracellular matrix. |
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| In animal cells, a transmembrane receptor protein with two subunits that interconnects the extracellular matrix and the cytoskeleton. |
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| plasmodesmata (plasmodesma) |
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Definition
| An open channel through the cell wall that connects the cytoplasm of adjacent plants cells, allowing water, small solutes and some larger molecules to pass between the cells. |
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| A type of intercellular junction between animal cells that prevents the leakage of material through the space between cells. |
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| A type of intercellular junction in animal cells that functions as a rivet, fastening cells together. |
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| In animal cells, a kind of intercellular junction consisting of proteins surrounding a pore that allows the passage of materials between cells. |
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