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.
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.
The disruption of a cell and separation of its organelles by centrifugation.
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.
A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development.
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.
Material present in the cytoplasm of all eukaryotic cells, important during cell division; the microtubule-organizing center.
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.
A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins. See chromatin.
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.
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.
A membranous sac that helps move excess water out of the cell.
The region of the root between the stele and epidermis filled with ground tissue.
An infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzyme catalyzing the synthesis of ATP.
A circular flow of cytoplasm, involving myosin and actin filaments, that speeds the distribution of materials within cells.
A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions.
The semifluid portion of the cytoplasm.
A large contractile protein forming the side-arms of microtubule doublets in 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.
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.
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.
A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles, present in protists, plants, fungi, and animals; also called eukaryote.
extracellular matrix (ECM)
The substance in which animal tissue cells are embedded consisting of protein and polysaccharides.
A glycoprotein that helps cells attach to the extracellular matrix.
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.
A membranous sac formed by phagocytosis.
An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum.
A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis.
Receptor proteins built into the plasma membrane that interconnect the extracellular matrix and the cytoskeleton.
A component of the cytoskeleton that includes all filaments intermediate in size between microtubules and microfilaments.
A membrane-enclosed bag of hydrolytic enzymes found in the cytoplasm of eukaryotic cells.
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.
A hollow rod of tubulin protein in the cytoplasm of all eukaryotic cells and in cilia, flagella, and the cytoskeleton.
A thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young plant cells.
The compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the Krebs cycle.
An organelle in eukaryotic cells that serves as the site of cellular respiration.
A type of protein filament that interacts with actin filaments to cause cell contraction.
The membrane in eukaryotes that encloses the nucleus, separating it from the cytoplasm.
A netlike array of protein filaments that maintains the shape of the nucleus.
A dense region of DNA in a prokaryotic cell.
A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes.
(1) An atom's central core, containing protons and neutrons. (2) The chromosome-containing organelle of a eukaryotic cell. (3) A cluster of neurons.
One of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells.
A microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide.
A type of endocytosis involving large, particulate substances.
The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell's chemical composition.
An open channel in the cell wall of plants through which strands of cytosol connect from adjacent cells.
One of a family of closely related plant organelles, including chloroplasts, chromoplasts, and amyloplasts (leucoplasts).
primary cell wall
A relatively thin and flexible layer first secreted by a young plant cell.
A glycoprotein in the extracellular matrix of animal cells, rich in carbohydrate.
A cellular extension of amoeboid cells used in moving and feeding.
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.
That portion of the endoplasmic reticulum studded with ribosomes.
scanning electron microscope (SEM)
A microscope that uses an electron beam to scan the surface of a sample to study details of its topography.
secondary cell wall
A strong and durable matrix often deposited in several laminated layers for plant cell protection and support.
That portion of the endoplasmic reticulum that is free of ribosomes.
The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.
A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy.
transmission electron microscope (TEM)
A microscope that passes an electron beam through very thin sections, primarily used to study the internal ultrastructure of cells.
A tiny membranous sac in a cell's cytoplasm carrying molecules produced by the cell.
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.
A sac made of membrane inside of cells.