Cell Vocabulary

light microscope
(LM)An optical instrument with lenses that refract (bend) visible light to magnify images of specimens
magnification
An increase in the apparent size of an object.
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.
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.

cell theory
The theory that all living things are composed of cells and all cells come from other cells.
prokaryotic cell
A type of cell lacking a membrane-enclosed nucleus and other membrane-enclosed organelles; found only in the domains Bacteria and Archaea.
eukaryotic cell
A type of cell that has a membrane-enclosed nucleus and other membrane-enclosed organelles. All organisms except bacteria and archaea are composed of eukaryotic cells.
plasma membrane
The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell’s chemical composition
organelle
One of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells.
nucleus
The chromosome-containing organelle of a eukaryotic cell.
cytoplasm
The entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane.

phospholipids
A molecule that is a constituent of the inner bilayer of biological membranes, having a polar, hydrophilic head and a nonpolar, hydrophobic tail.
phospholipid bilayer
fluid mosaic
The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids.
transport proteins
A membrane protein that helps move substances across a cell membrane.

nuclear envelope
The membrane in eukaryotes that encloses the nucleus, separating it from the cytoplasm.
nucleolus
(plural, nucleoli) A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes
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.
gene
A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).

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.
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.
rough ER
That portion of the endoplasmic reticulum studded with ribosomes.
smooth ER
That portion of the endoplasmic reticulum that is free of ribosomes.

golgi apparatus
An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum.
transport vesicle
A tiny membranous sac in a cell's cytoplasm carrying molecules produced by the cell.
lysosome
A membrane-enclosed bag of hydrolytic enzymes found in the cytoplasm of eukaryotic cells.
food vacuoles
The simplest type of digestive cavity, found in single-celled organisms.
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.
central vacuole
A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development.

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.
mitochondrion
(plural, mitochondria) An organelle in eukaryotic cells that serves as the site of cellular respiration.
cytoskeleton
A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions.
microtubule
A hollow rod of tubulin protein in the cytoplasm of all eukaryotic cells and in cilia, flagella, and the cytoskeleton.
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.
cilium
(plural, cilia) A short appendage that propels some protists through water and moves fluids across the surface of many tissue cells in animals. In common with eukaryotic flagella, cilia have a 9 + 2 arrangement of microtubules covered by the cell’s plasma membrane.
cell wall
A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists; protects the cell and helps maintain its shape
cell junctions
A structure that connects cells within a tissue to one another.