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| 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. |
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| 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. |
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| 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. |
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| A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development. |
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| 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. |
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| Material present in the cytoplasm of all eukaryotic cells, important during cell division; the microtubule-organizing center. |
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| 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. |
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| The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope. |
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| A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins. See chromatin. |
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| 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. |
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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 membranous sac that helps move excess water out of the cell. |
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| An infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzyme catalyzing the synthesis of ATP. |
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| The entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane. |
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| A circular flow of cytoplasm, involving myosin and actin filaments, that speeds the distribution of materials within cells. |
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| A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions. |
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| The semifluid portion of the cytoplasm. |
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| A type of intercellular junction in animal cells that functions as an anchor. |
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| A large contractile protein forming the side-arms of microtubule doublets in cilia and flagella. |
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| endoplasmic reticulum (ER) |
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Definition
| An 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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| extracellular matrix (ECM) |
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Definition
| The substance in which animal tissue cells are embedded, consisting of protein and polysaccharides. |
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| A glycoprotein that helps cells attach to the extracellular matrix. |
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| A long cellular appendage specialized for locomotion. The flagella of prokaryotes and eukaryotes differ in both structure and function. |
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| A membranous sac formed by phagocytosis. |
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| A type of intercellular junction in animal cells that allows the passage of material or current between cells. |
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| A protein covalently attached to a carbohydrate. |
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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. |
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| A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis. |
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| A receptor protein built into the plasma membrane that interconnects the extracellular matrix and the cytoskeleton. |
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| A component of the cytoskeleton that includes all filaments intermediate in size between microtubules and microfilaments. |
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| A membrane-enclosed sac of hydrolytic enzymes found in the cytoplasm of eukaryotic cells. |
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| 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. |
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| A hollow rod of tubulin protein in the cytoplasm of all eukaryotic cells and in cilia, flagella, and the cytoskeleton. |
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| A thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young plant cells. |
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| The compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the Krebs cycle. |
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| An organelle in eukaryotic cells that serves as the site of cellular respiration. |
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| A type of protein filament that interacts with actin filaments to cause cell contraction. |
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| A netlike array of protein filaments that maintains the shape of the nucleus. |
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| A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes. |
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| The chromosome-containing organelle of a eukaryotic cell. |
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| One of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells. |
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| A microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide. |
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| The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell’s chemical composition. |
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| An open channel in the cell wall of plant through which strands of cytosol connect from an adjacent cell. |
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| One of a family of closely related plant organelles that includes chloroplasts, chromoplasts, and amyloplasts (leucoplasts). |
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Definition
| A relatively thin and flexible layer first secreted by a young plant cell. |
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| A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea. |
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Definition
| A glycoprotein in the extracellular matrix of animal cells, rich in carbohydrate. |
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| A cellular extension of amoeboid cells used in moving and feeding. |
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| 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. |
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| A strong and durable matrix often deposited in several laminated layers for plant cell protection and support. |
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Definition
| The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water. |
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Definition
| A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy. |
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Definition
| A type of intercellular junction in animal cells that prevents the leakage of material between cells. |
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| A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the vacuolar contents, called cell sap; also known as the vacuolar membrane. |
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| A sac made of membrane inside of cells. |
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