2.1.8: Key Terms

cell theory

see unified cell theory

cell wall

rigid cell covering comprised of various molecules that protects the cell, provides structural support, and gives shape to the cell

central vacuole

large plant cell organelle that regulates the cell’s storage compartment, holds water, and plays a significant role in cell growth as the site of macromolecule degradation

centrosome

region in animal cells made of two centrioles that serves as an organizing center for microtubules

chlorophyll

green pigment that captures the light energy that drives the light reactions of photosynthesis

chloroplast

plant cell organelle that carries out photosynthesis

chromatin

protein-DNA complex that serves as the chromosomes' building material

chromosome

structure within the nucleus that comprises chromatin that contains DNA, the hereditary material

cilium

(plural = cilia) short, hair-like structure that extends from the plasma membrane in large numbers and functions to move an entire cell or move substances along the cell's outer surface

cytoplasm

entire region between the plasma membrane and the nuclear envelope, consisting of organelles suspended in the gel-like cytosol, the cytoskeleton, and various chemicals

cytoskeleton

protein fiber network that collectively maintains the cell's shape, secures some organelles in specific positions, allows cytoplasm and vesicles to move within the cell, and enables unicellular organisms to move independently

cytosol

the cytoplasm's gel-like material in which cell structures are suspended

desmosome

linkages between adjacent epithelial cells that form when cadherins in the plasma membrane attach to intermediate filaments

electron microscope

an instrument that magnifies an object using an electron beam that passes and bends through a lens system to visualize a specimen

endomembrane system

group of organelles and membranes in eukaryotic cells that work together modifying, packaging, and transporting lipids and proteins

endoplasmic reticulum (ER)

series of interconnected membranous structures within eukaryotic cells that collectively modify proteins and synthesize lipids

eukaryotic cell

cell that has a membrane-bound nucleus and several other membrane-bound compartments or sacs

extracellular matrix

material secreted from animal or fungal cells that provides mechanical protection and anchoring for the cells in the tissue

flagellum

(plural = flagella) long, hair-like structure that extends from the plasma membrane and moves the cell

gap junction

channel between two adjacent animal cells that allows ions, nutrients, and low molecular weight substances to pass between cells, enabling the cells to communicate

Golgi apparatus

eukaryotic organelle comprised of a series of stacked membranes that sorts, tags, and packages lipids and proteins for distribution

intermediate filament

cytoskeletal component, comprised of several fibrous protein intertwined strands, that bears tension, supports cell-cell junctions, and anchors cells to extracellular structures

light microscope

an instrument that magnifies an object using a beam of visible light that passes and bends through a lens system to visualize a specimen

lysosome

organelle in an animal cell that functions as the cell’s digestive component; it breaks down proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles

microfilament

the cytoskeleton system's narrowest element; it provides rigidity and shape to the cell and enables cellular movements

microscope

an instrument that magnifies an object

microtubule

the cytoskeleton system's widest element; it helps the cell resist compression, provides a track along which vesicles move through the cell, pulls replicated chromosomes to opposite ends of a dividing cell, and is the structural element of centrioles, flagella, and cilia

mitochondria

(singular = mitochondrion) cellular organelles responsible for carrying out cellular respiration, resulting in producing ATP, the cell’s main energy-carrying molecule

nuclear envelope

double-membrane structure that constitutes the nucleus' outermost portion

nucleoid

central part of a prokaryotic cell's central part where the chromosome is located

nucleolus

darkly staining body within the nucleus that is responsible for assembling ribosome subunits

nucleoplasm

semi-solid fluid inside the nucleus that contains the chromatin and nucleolus

nucleus

cell organelle that houses the cell’s DNA and directs ribosome and protein synthesis

organelle

compartment or sac within a cell

peroxisome

small, round organelle that contains hydrogen peroxide, oxidizes fatty acids and amino acids, and detoxifies many poisons

plasma membrane

phospholipid bilayer with embedded (integral) or attached (peripheral) proteins, and separates the cell's internal content from its surrounding environment

plasmodesma

(plural = plasmodesmata) channel that passes between adjacent plant cells' cell walls, connects their cytoplasm, and allows transporting of materials from cell to cell

prokaryote

unicellular organism that lacks a nucleus or any other membrane-bound organelle

ribosome

cellular structure that carries out protein synthesis

rough endoplasmic reticulum (RER)

region of the endoplasmic reticulum that is studded with ribosomes and engages in protein modification and phospholipid synthesis

smooth endoplasmic reticulum (SER)

region of the endoplasmic reticulum that has few or no ribosomes on its cytoplasmic surface and synthesizes carbohydrates, lipids, and steroid hormones; detoxifies certain chemicals (like pesticides, preservatives, medications, and environmental pollutants), and stores calcium ions

tight junction

protein adherence that creates a firm seal between two adjacent animal cells

unified cell theory

a biological concept that states that one or more cells comprise all organisms; the cell is the basic unit of life; and new cells arise from existing cells

vacuole

membrane-bound sac, somewhat larger than a vesicle, which functions in cellular storage and transport

vesicle

small, membrane-bound sac that functions in cellular storage and transport; its membrane is capable of fusing with the plasma membrane and the membranes of the endoplasmic reticulum and Golgi apparatus