Complete List of Terms and Definitions for Vocabulary # 2

Terms Definitions
lysosome A membrane-enclosed bag of hydrolytic enzymes found in the cytoplasm of eukaryotic cells.
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.
cilium (plural, cilia) 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.
stroma The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.
central vacuole A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development.
plastid One of a family of closely related plant organelles, including chloroplasts, chromoplasts, and amyloplasts (leucoplasts).
thylakoid A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy.
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.
transport vesicle A tiny membranous sac in a cell's cytoplasm carrying molecules produced by the cell.
granum (plural, grana) A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis.
nucleolus (plural, nucleoli) A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes.
chromosome A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins. See chromatin
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.
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.
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.
ultracentrifuge A machine that spins test tubes at the fastest speeds to separate liquids and particles of different densities.
centrosome Material present in the cytoplasm of all eukaryotic cells, important during cell division; the microtubule-organizing center.
organelle One of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells.
cell fractionation The disruption of a cell and separation of its organelles by centrifugation.
glycoprotein A protein covalently attached to a carbohydrate.
mitochondrion (plural, mitochondria) An organelle in eukaryotic cells that serves as the site of cellular respiration.
collagen 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.
rough ER That portion of the endoplasmic reticulum studded with ribosomes.
peroxisome A microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide.
actin 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.
flagellum plural, flagella) 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.
cell wall 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.
contractile vacuole A membranous sac that helps move excess water out of the cell.
cytoplasm The entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane.
nucleoid A dense region of DNA in a prokaryotic cell.
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.
prokaryotic cell A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea.
cytosol The semifluid portion of the cytoplasm.
tonoplast A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the cell sap.
food vacuole A membranous sac formed by phagocytosis.
nuclear lamina A netlike array of protein filaments that maintains the shape of the nucleus
cytoskeleton A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions.
nuclease A team of enzymes that hydrolyze DNA and RNA into their component nucleotides
extracellular matrix (ECM) The substance in which animal tissue cells are embedded consisting of protein and polysaccharides.
smooth ER That portion of the endoplasmic reticulum that is free of ribosomes.
phagocytosis A type of endocytosis involving large, particulate substances.
plasma membrane The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell's chemical composition.