A eukaryotic cell organelle consisting of microtubule triplets; may organize the microtubule assembly of a cilium or flagellum; structurally identical to a centriole.
The theory that all living things are composed of cells and that all cells come from other cells.
A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists; protects the cell and helps maintain its shape.
A membrane-enclosed sac occupying most of the interior of a mature plant cell, having diverse roles in reproduction, growth, and development.
A structure in an animal cell composed of cylinders of microtubule triplets arranged in a 9 and 0 pattern; involved in animal cell division.
An organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic molecules (sugars) from carbon dioxide and water.
A threadlike, gene-carrying structure found in the nucleus of a eukaryotic cell and most visible during mitosis and meiosis; also, the main gene-carrying structure of a prokaryotic cell.
A short cellular appendage specialized for locomotion formed from a core of nine outer doublet microtubules and two single microtubules covered by the cell's plasma membrane.
Infolding of the inner membrane of a mitochondrion in which is embedded the electron transport chain and the enzyme catalyzing the synthesis of ATP.
Everything inside a cell between the plasma membrane and the nucleus; consists of a semifluid medium and organelles.
A network of protein fibers in the cytoplasm of a eukaryotic cell; includes microfilaments, intermediate filaments, and microtubules.
An instrument that focuses an electron beam through, or onto the surface of, a specimen; achieves a hundredfold greater resolution than a light microscope.
A network of membranes inside and around a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles.
An extensive membranous network in a eukaryotic cell, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions.
A process by which the mitochondria and chloroplasts of eukaryotic cells probably evolved from symbiotic associations between small prokaryotic cells living inside larger cells.
A type of cell that has a membrane-enclosed nucleus and other membrane-enclosed organelles. All organisms except bacteria and archaea are composed of these types of cells.
A substance in which the cells of an animal tissue are embedded; consists of protein and polysaccharides.
A long cellular appendage specialized for locomotion. The appendages of prokaryotes and eukaryotes differ in both structure and function. In eukaryotes, they have a 9 + 2 arrangement of microtubules covered by the cell's plasma membrane.
A macromolecule consisting of one or more polypeptides linked to short chains of sugars (carbohydrates).
An organelle in eukaryotic cells consisting of stacks of membranous sacs that modify, store, and ship products of the endoplasmic reticulum.
A stack of hollow disks formed of thylakoid membrane in a chloroplast; sites where light energy is trapped by chlorophyll and converted to chemical energy during the light reactions of photosynthesis.
An intermediate-sized protein fiber that is one of the three main kinds of fibers making up the cytoskeleton of eukaryotic cells; ropelike, made of fibrous proteins.
One of the two fluid-filled internal compartments of the mitochondrion. The intermembrane space is the narrow region between the inner and outer membranes.
An optical instrument with lenses that refract (bend) visible light to magnify images and project them into a viewer's eye or onto photographic film.
A digestive organelle in eukaryotic cells; contains hydrolytic enzymes that digest the cell's food and wastes.
The thinnest of the three main kinds of protein fibers making up the cytoskeleton of a eukaryotic cell; a solid, helical rod composed of the globular protein actin.
The thickest of the three main kinds of fibers making up the cytoskeleton of a eukaryotic cell; a straight, hollow tube made of globular proteins called tubulins; form the basis of the structure and movement of cilia and flagella.
An organelle in eukaryotic cells where cellular respiration occurs. Enclosed by two concentric membranes, it is where most of the cell's ATP is made.
A double membrane, perforated with pores, which encloses the nucleus and separates it from the rest of the eukaryotic cell.
A structure within the nucleus of a eukaryotic cell where ribosomal RNA is made and assembled with proteins imported from the cytoplasm to make ribosomal subunits.
An organelle containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide.
The membrane that sets a cell off from its surroundings and acts as a selective barrier to the passage of ions and molecules into and out of the cell; consists of a phospholipid bilayer in which are embedded molecules of protein and cholesterol.
An open channel in a plant cell wall through which strands of cytoplasm connect from adjacent cells.
A type of cell lacking a membrane-enclosed nucleus and other membrane-enclosed organelles; found only in the domains Bacteria and Archaea.
A cell structure consisting of RNA and protein organized into two subunits and functioning as the site of protein synthesis in the cytoplasm. The subunits are constructed in the nucleolus.
A network of interconnected membranous sacs in a eukaryotic cell's cytoplasm; covered with ribosomes that make membrane proteins and secretory proteins.
scanning electron microscope
A microscope that uses an electron beam to study the surface architecture of a cell or other specimen.
A network of interconnected membranous tubules in a eukaryotic cell's cytoplasm; lacks ribosomes.
The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water; Sugars are made in this area by the enzymes of the Calvin cycle.
One of a number of disk-shaped membranous sacs inside a chloroplast; contain chlorophyll and the enzymes of the light reactions of photosynthesis; A stack of these sacs are called a granum.
transmission electron microscope
A microscope that uses an electron beam to study the internal structure of thinly sectioned specimens.
A tiny membranous sac in a cell's cytoplasm carrying molecules produced by the cell; buds from the endoplasmic reticulum or Golgi and eventually fuses with another membranous organelle or the plasma membrane, releasing its contents.
A membrane-enclosed sac that is part of the endomembrane system of a eukaryotic cell, having diverse functions (such as food storage).
The movement of a substance across a biological membrane against its concentration gradient, aided by specific transport proteins and requiring input of energy (often as ATP).
A transport protein in the plasma membrane of some plant or animal cells that facilitates the diffusion of water across the membrane (through osmosis).
An increase or decrease in the density of a chemical substance in an area; substances tend to move from where they are more concentrated to where they are less concentrated.
The spontaneous tendency of a substance to move down its concentration gradient from where it is more concentrated to where it is less concentrated.
Cellular uptake of molecules or particles via formation of new vesicles from the plasma membrane.
The movement of materials out of the cytoplasm of a cell by the fusion of vesicles with the plasma membrane.
The passage of a substance through a specific transport protein across a biological membrane down its concentration gradient.
A description of membrane structure, depicting a cellular membrane as a mosaic of diverse protein molecules embedded in a fluid bilayer made of phospholipid molecules.
In comparing two solutions, the one with the greater concentration of solutes; cells in such a solution will lose water to their surroundings.
In comparing two solutions, the one with the lower concentration of solutes; cells in such a solution will take up water from their surroundings.
A solution having the same solute concentration as another solution, thus having no effect on passage of water in or out of the cell.
Method by which organisms regulate solute concentrations and balance the gain and loss of water.
The diffusion of a substance across a biological membrane, without any input of energy.
Cellular "eating"; a type of endocytosis whereby a cell engulfs macromolecules, other cells, or particles into its cytoplasm.
Cellular "drinking"; a type of endocytosis in which the cell takes fluid and dissolved solutes into small membranous vesicles.
The movement of specific molecules into a cell by the inward budding of membranous vesicles. The vesicles contain proteins with receptor sites specific to the molecules being taken in.
A property of biological membranes that allows some substances to cross more easily than others and blocks the passage of other substances altogether.