Cells (Holt Biology - Honors) Tools A B cell a membrane-bound structure that is the basic Unit of life cell membrane the lipid bilayer that forms the outer boundary of the cell cell theory the theory that all living things are made up of cells, that cells arethe basic units of organisms, and that cells come only from existing cells cell wall a rigid structure that surrounds the cells of plants, fungi, manyprotists, and most bacteria chloroplast a plastid containing chlorophyll; the site of photosynthesis chromatin the DNA and proteins in the nucleus of a nondividing cell chromosome DNA and protein in a coiled, rod-shaped form that occurs during cell division cilia short, hair-like organelles that extend from a cell and functions in locomotion or in the movement of substances across the cell surface crista a fold of the inner membrane of mitochondria cytoplasm the region of a cell between the cell membrane and the nucleus cytoskeleton a network of long protein strands in the cytosol that helpsmaintain the shape and size of a eukaryotic cell cytosol the gelatin-like aqueous fluid that bathes the organelles on the inside ofthe cell membrane endoplasmic reticulum a system of membranous tubules and sacs ineukaryotic cells that functions as a path along which molecules move from one part of the cell to another eukaryote a cell that contains a nucleus and membrane-bound organelles flagellum a hairlike structure made up of microtubules that function in locomotion Golgi apparatus a system of membranes in eukaryotic cells that modifiesproteins for export by the cell microfilament a polymer chain of the protein actin; the smallest strand in the cytoskeleton microtubule a hollow tube of protein that constitutes the largest strand in the cytoskeleton mitochondrion the organelle that is the site of aerobic respiration in eukaryoticcells nuclear envelope a double membrane that surrounds the nucleus of aeukaryotic cell nuclear matrix the nuclear skeleton, a shape-maintaining protein nuclear pore a small hole in the nuclear envelope through which substances pass between the nucleus and the cytoplasm nucleolus the structure in which ribosomes are synthesized and partiallyassembled; found in most nuclei nucleus in a eukaryotic cell, the organelle that contains most of the DNA anddirects the cell's activities organelle one of several formed bodies with a specialized function that issuspended in the cytoplasm and found in eukaryotic cells peripheral protein a protein attached to the interior or exterior surface of the cell membrane prokaryote a unicellular organism that lacks a nucleus and membrane-boundorganelles protozoan a single-celled, eukaryotic protist that is able to moveindependently ribosome an organelle that functions in the synthesis of proteins rough endoplasmic reticulum the portion of the endoplasmic reticulum thatcontains attached ribosomes selectively permeable membrane a membrane that keeps out some moleculesbut allows others to pass through smooth endoplasmic reticulum the portion of the endoplasmic reticulum thatlacks attached ribosomes vacuole a fluid-filled organelle that stores enzymes or metabolic wastes in a plant cell