front 1 actin | back 1 A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells. |
front 2 basal body | back 2 A eukaryotic cell organelle consisting of a 9 + 0 arrangement of microtubule triplets; may organize the microtubule assembly of a cilium or flagellum; structurally identical to a centriole. |
front 3 cell fractionation | back 3 The disruption of a cell and separation of its organelles by centrifugation. |
front 4 cell wall | back 4 A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists. In plant cells, the wall is formed of cellulose fibers embedded in a polysaccharide-protein matrix. The primary cell wall is thin and flexible, whereas the secondary cell wall is stronger and more rigid and is the primary constituent of wood. |
front 5 central vacuole | back 5 A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development. |
front 6 centriole | back 6 A structure in an animal cell composed of cylinders of microtubule triplets arranged in a 9 + 0 pattern. An animal cell usually has a pair of centrioles involved in cell division. |
front 7 centrosome | back 7 Material present in the cytoplasm of all eukaryotic cells, important during cell division; the microtubule-organizing center. |
front 8 chloroplast | back 8 An organelle found only in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water. |
front 9 chromosome | back 9 A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins. See chromatin. |
front 10 cilium | back 10 A short cellular appendage specialized for locomotion, formed from a core of nine outer doublet microtubules and two inner single microtubules ensheathed in an extension of plasma membrane. |
front 11 collagen | back 11 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. |
front 12 contractile vacuole | back 12 A membranous sac that helps move excess water out of the cell. |
front 13 cortex | back 13 The region of the root between the stele and epidermis filled with ground tissue. |
front 14 crista | back 14 An infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzyme catalyzing the synthesis of ATP. |
front 15 cytoplasmic streaming | back 15 A circular flow of cytoplasm, involving myosin and actin filaments, that speeds the distribution of materials within cells. |
front 16 cytoskeleton | back 16 A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions. |
front 17 cytosol | back 17 The semifluid portion of the cytoplasm. |
front 18 dynein | back 18 A large contractile protein forming the side-arms of microtubule doublets in cilia and flagella. |
front 19 electron microscope (EM) | back 19 A microscope that focuses an electron beam 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. |
front 20 endomembrane system | back 20 The collection of membranes inside and around a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles. |
front 21 endoplasmic reticulum (ER) | back 21 An extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions. |
front 22 endosymbiotic theory | back 22 A hypothesis about the origin of the eukaryotic cell, maintaining that the forerunners of eukaryotic cells were symbiotic associations of prokaryotic cells living inside larger prokaryotes. |
front 23 eukaryotic cell | back 23 A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles, present in protists, plants, fungi, and animals; also called eukaryote. |
front 24 extracellular matrix (ECM) | back 24 The substance in which animal tissue cells are embedded consisting of protein and polysaccharides. |
front 25 fibronectin | back 25 A glycoprotein that helps cells attach to the extracellular matrix. |
front 26 flagellum | back 26 A long cellular appendage specialized for locomotion, formed from a core of nine outer doublet microtubules and two inner single microtubules, ensheathed in an extension of plasma membrane. |
front 27 food vacuole | back 27 A membranous sac formed by phagocytosis. |
front 28 Golgi apparatus | back 28 An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum. |
front 29 granum | back 29 A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis. |
front 30 integrin | back 30 Receptor proteins built into the plasma membrane that interconnect the extracellular matrix and the cytoskeleton. |
front 31 intermediate filament | back 31 A component of the cytoskeleton that includes all filaments intermediate in size between microtubules and microfilaments. |
front 32 lysosome | back 32 A membrane-enclosed bag of hydrolytic enzymes found in the cytoplasm of eukaryotic cells. |
front 33 microfilament | back 33 A solid rod of actin protein in the cytoplasm of almost all eukaryotic cells, making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction. |
front 34 microtubule | back 34 A hollow rod of tubulin protein in the cytoplasm of all eukaryotic cells and in cilia, flagella, and the cytoskeleton. |
front 35 middle lamella | back 35 A thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young plant cells. |
front 36 mitochondrial matrix | back 36 The compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the Krebs cycle. |
front 37 mitochondrion | back 37 An organelle in eukaryotic cells that serves as the site of cellular respiration. |
front 38 myosin | back 38 A type of protein filament that interacts with actin filaments to cause cell contraction. |
front 39 nuclear envelope | back 39 The membrane in eukaryotes that encloses the nucleus, separating it from the cytoplasm. |
front 40 nuclear lamina | back 40 A netlike array of protein filaments that maintains the shape of the nucleus. |
front 41 nucleoid | back 41 A dense region of DNA in a prokaryotic cell. |
front 42 nucleolus | back 42 A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes. |
front 43 nucleus | back 43 (1) An atom's central core, containing protons and neutrons. (2) The chromosome-containing organelle of a eukaryotic cell. (3) A cluster of neurons. |
front 44 organelle | back 44 One of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells. |
front 45 peroxisome | back 45 A microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide. |
front 46 phagocytosis | back 46 A type of endocytosis involving large, particulate substances. |
front 47 plasma membrane | back 47 The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell's chemical composition. |
front 48 plasmodesmata | back 48 An open channel in the cell wall of plants through which strands of cytosol connect from adjacent cells. |
front 49 plastid | back 49 One of a family of closely related plant organelles, including chloroplasts, chromoplasts, and amyloplasts (leucoplasts). |
front 50 primary cell wall | back 50 A relatively thin and flexible layer first secreted by a young plant cell. |
front 51 proteoglycan | back 51 A glycoprotein in the extracellular matrix of animal cells, rich in carbohydrate. |
front 52 pseudopodium | back 52 A cellular extension of amoeboid cells used in moving and feeding. |
front 53 ribosome | back 53 A cell organelle constructed in the nucleolus and functioning as the site of protein synthesis in the cytoplasm; consists of rRNA and protein molecules, which make up two subunits. |
front 54 rough ER | back 54 That portion of the endoplasmic reticulum studded with ribosomes. |
front 55 scanning electron microscope (SEM) | back 55 A microscope that uses an electron beam to scan the surface of a sample to study details of its topography. |
front 56 secondary cell wall | back 56 A strong and durable matrix often deposited in several laminated layers for plant cell protection and support. |
front 57 smooth ER | back 57 That portion of the endoplasmic reticulum that is free of ribosomes. |
front 58 stroma | back 58 The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water. |
front 59 thylakoid | back 59 A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy. |
front 60 transmission electron microscope (TEM) | back 60 A microscope that passes an electron beam through very thin sections, primarily used to study the internal ultrastructure of cells. |
front 61 transport vesicle | back 61 A tiny membranous sac in a cell's cytoplasm carrying molecules produced by the cell. |
front 62 vacuole | back 62 A membrane-enclosed sac taking up most of the interior of a mature plant cell and containing a variety of substances important in plant reproduction, growth, and development. |
front 63 vesicle | back 63 A sac made of membrane inside of cells. |