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cells

Cytoplasm

The contents of the cell, excluding the nucleus

cytoskelton

The network of microtubules and microfilaments that gives a eukaryotic cell its shape and its capacity to arrange its organelles and to move.

cytosol

The fluid portion of the cytoplasm, excluding organelles and other solids

dynamic instability

A property of actin filaments in the cytoskeleton, characterized by rapid shortening or lengthening of individual filaments

endomembrane system

A system of intracellular membranes that exchange material with one another, consisting of the Golgi apparatus, endoplasmic reticulum, and lysosomes when present

endoplasmic reticulum (ER)

A system of membranous tubes and flattened sacs found in the cytoplasm of eukaryotes. Exists in two forms: rough ER, studded with ribosomes}; and smooth ER, lacking ribosomes.

eukaryotes

Organisms whose cells contain their genetic material inside a nucleus. Includes all life other than the viruses, archaea, and bacteria

extracellular matrix

A material of heterogeneous composition surrounding cells and performing many functions including adhesion of cells.

flagellum

Long, whiplike appendage that propels cells

glyoxysome

An organelle found in plants, in which stored lipids are converted to carbohydrates

Golgi apparatus

A system of membranes that modifies and packages proteins for export by the cell

intermediate filaments

Components of the cytoskeleton whose diameters fall between those of the larger microtubules and those of the smaller microfilaments.

lysosome

A membrane-enclosed organelle originating from the Golgi apparatus and containing hydrolytic enzymes

microfilament

In eukaryotic cells, a fibrous structure made up of actin monomers. Microfilaments play roles in the cytoskeleton, in cell movement, and in muscle contraction

microtubules

Tubular structures found in centrioles, spindle apparatus, cilia, flagella, and cytoskeleton of eukaryotic cells. These tubules play roles in the motion and maintenance of shape of eukaryotic cells.

mitochondrion

An organelle in eukaryotic cells that contains the enzymes of the citric acid cycle, the respiratory chain, and oxidative phosphorylation.

in eukaryotic cells, the cell organelle that is surrounded by two membranes and that is the site of cellular respiration, which produces ATP

nucleoid

The region that harbors the chromosomes of a prokaryotic cell. Unlike the eukaryotic nucleus, it is not bounded by a membrane.

nucleolus

A small, generally spherical body found within the nucleus of eukaryotic cells. The site of synthesis of ribosomal RNA.

nucleus

In cells, the centrally located compartment of eukaryotic cells that is bounded by a double membrane and contains the chromosomes. (2) In the brain, an identifiable group of neurons that share common characteristics or functions.

organelle

Any of the membrane-enclosed structures within a eukaryotic cell. Examples include the nucleus, endoplasmic reticulum, and mitochondria

peroxisome

An organelle that houses reactions in which toxic peroxides are formed and then converted to water

plasma membrane

The membrane that surrounds the cell, regulating the entry and exit of molecules and ions. Every cell has a plasma membrane

plasmodesma

A cytoplasmic strand connecting two adjacent plant cells

prokaryotes

Unicellular organisms that do not have nuclei

proteoglycan

A glycoprotein containing a protein core with attached long, linear carbohydrate chains

ribosome

A small particle in the cell that is the site of protein synthesis

Rough ER

The portion of the endoplasmic reticulum whose outer surface has attached ribosomes

secondary lysosome

Membrane-enclosed organelle formed by the fusion of a primary lysosome with a phagosome, in which macromolecules taken up by phagocytosis are hydrolyzed into their monomers

smooth ER

Portion of the endoplasmic reticulum that lacks ribosomes and has a tubular appearance

surface area-to-volume ratio

For any cell, organism, or geometrical solid, the ratio of surface area to volume; this is an important factor in setting an upper limit on the size a cell or organism can attain

vacuole

Membrane-enclosed organelle in plant cells that can function for storage, water concentration for turgor, or hydrolysis of stored macromolecules

vesicle

Within the cytoplasm, a membrane-enclosed compartment that is associated with other organelles; the Golgi complex is one example

cell junctions

Specialized structures associated with the plasma membranes of epithelial cells. Some contribute to cell adhesion, others to intercellular communication

cell theory

States that cells are the basic structural and physiological units of all living organisms, and that all cells come from preexisting cells

cell wall

A relatively rigid structure that encloses cells of plants, fungi, many protists, and most prokaryotes, and which gives these cells their shape and limits their expansion in hypotonic media

chloroplast

An organelle bounded by a double membrane containing the enzymes and pigments that perform photosynthesis. Chloroplasts occur only in eukaryotes

cilium

Hairlike organelle used for locomotion by many unicellular organisms and for moving water and mucus by many multicellular organisms. Generally shorter than a flagellum

collagen

A fibrous protein found extensively in bone and connective tissue

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