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anchoring junctions Adhesive junctions that link cells together into tissues basal body 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 capsule A sticky layer that surrounds the cell walls of some bacteria, protecting the cell surface and sometimes helping to glue the cell to surfaces cell junctions A structure that connects cells within a tissue to one another cell theory The theory that all living things are composed of cells and all cells come from other cells cellular metabolism The sum of endergonic and exergonic reactions in a working cell central vacuole A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development centriole 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 chloroplast 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 chromatin 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 chromosome A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins. See chromatin communicating junctions A channel between adjacent tissue cells through which water and other small molecules pass freely crista (plural, cristae) An infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzyme catalyzing the synthesis of ATP cytoplasm The entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane cytoskeleton A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions dynein arms A protein extension from a microtubule doublet in a cilium or flagellum; involved in energy conversions that drive the bending of cilia and flagella electron microscope (EM) 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 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 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 extracellular matrix (ECM) The substance in which animal tissue cells are embedded consisting of protein and polysaccharides flagellum 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 glycoprotein A protein covalently attached to a carbohydrate An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum golgi apparatus granum A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis intermediate filament A component of the cytoskeleton that includes all filaments intermediate in size between microtubules and microfilaments intermembrane space One of the fluid-filled compartments in the mitchondrion light microscope An optical instrument with lenses that refract (bend) visible light to magnify images of specimens lysosomal storage disease A hereditary disorder associated with abnormal lysosomes, where the sufferer is missing one of the lysosomal digestive enzymes lysosome A membrane-enclosed bag of hydrolytic enzymes found in the cytoplasm of eukaryotic cells magnification An increase in the apparent size of an object microfilament 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 micrograph A photograph taken through a microscope microtubule A hollow rod of tubulin protein in the cytoplasm of all eukaryotic cells and in cilia, flagella, and the cytoskeleton mitochondrial matrix The compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the Krebs cycle mitochondrion An organelle in eukaryotic cells that serves as the site of cellular respiration nuclear envelope The membrane in eukaryotes that encloses the nucleus, separating it from the cytoplasm nucleoid region The region in a prokaryotic cell consisting of a concentrated mass of DNA nucleolus A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes nucleus An atom's central core, containing protons and neutrons. (2) The chromosome-containing organelle of a eukaryotic cell. (3) A cluster of neurons organelle One of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells pili A surface appendage in certain bacteria that functions in adherence and the transfer of DNA during conjugation plasma membrane The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell's chemical composition plasmodesma An open channel in the cell wall of plants through which strands of cytosol connect from adjacent cells prokaryotic cell wall A fairly rigid, chemically complex structure that exists outside the plasma membrane of most prokaryotes prokaryotic flagella A long surface projection that propels a prokaryotic cell through its liquid environment; totally different from the flagella of a eukaryotic cell prokaryotic flagella A long surface projection that propels a prokaryotic cell through its liquid environment; totally different from the flagella of a eukaryotic cell resolving power A measure of the clarity of an image; the minimum distance that two points can be separated and still be distinguished as two separate points ribosome 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 rough ER That portion of the endoplasmic reticulum studded with ribosomes scanning electron microscope A microscope that uses an electron beam to scan the surface of a sample to study details of its topography secretory protein Proteins that are secreted by the cell via the endoplasmic reticulum smooth ER That portion of the endoplasmic reticulum that is free of ribosomes stroma The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water tight junction A type of intercellular junction in animal cells that prevents the leakage of material between cells transmission electron microscope A microscope that passes an electron beam through very thin sections, 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-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