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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 centrifugation 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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| The organelle of a eukaryotic cell that contains the genetic material in the form of chromosomes, made up of chromatin. |
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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 the 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 circular DNA molecule and associated proteins.) It is found in the nucleoid region, which is not membrane-bounded. |
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| The complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope. |
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| A specialized structure in the nucleus, consisting of chromosomal regions containing ribosomal RNA (rRNA) genes along with ribosomal proteins imported from the cytoplasm; site of rRNA synthesis and ribosomal subunit assembly. |
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| A complex of rRNA and protein 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 contact or by the transfer of membraneous 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 membraneous sac in the cytoplasm of a eukaryotic cell. |
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| Endoplasmic Reticulum (ER) |
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| An extensive membraneous 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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| Smooth Endoplasmic Reticulum |
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| That portion of the endoplasmic reticulum that is free of ribosomes. |
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| Rough Endoplasmic Reticulum |
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| That 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 membraneous 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 membraneous 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 microphages, 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 membraneous sac formed by phagocytosis of microorganisms or particles to be used as food by the cell. |
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| A membraneous sac that helps move excess water out of certain freshwater protists. |
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| In a mature plant cell, a large membraneous sac with diverse roles in growth, storage, and sequestration of toxic substances. |
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| An organelle in eukaryotic cells that serves as the site of cellular respiration; uses oxygen to break down organic molecules and synthesizes 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, membraneous sac inside a chloroplast. Thykaloids 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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| The dense fluid within the chloroplast surrounding the thylakoid membrane and containing ribosomes and DNA; involved in the synthesis of organic molecules from carbon dioxide and water. |
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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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| 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 cytoskeletal 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 they 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 has a pair of centrioles. |
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| A long cellular appendage specialized for locomotion. Like mobile 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 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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| A cable composed of actin proteins in the cytoplasm of almost every eukaryotic cell, making up part of the cytoplasm 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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| 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. |
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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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| A cellular extension of ameboid cells used in moving and feeding. |
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| A circular flow of cytoplasm, involving interactions of myosin and actin filaments, that 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 plans 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 relatively 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 plant cells, a strong and durable matrix that is often deposited in several laminated layers around the plamsa membrane and provides protection and support. |
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| Extracellular Matrix (ECM) |
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| 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 of 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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| An open channel through the cell wall that connects the cytoplasm of adjacent plant cells, allowing water, small solutes, and some larger molecules to pass between the cells. |
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