AP Bio - Chapter 4

plasma membrane

plasma membrane

Membrane that encloses a cell and separates it from the external environment.

cytosol

Jellylike mixture of water and solutes that is enclosed by a cell’s plasma membrane.

Organelles

Structure that carries out a specialized metabolic function inside a cell.

nucleus

Of an atom, core area occupied by protons and neutrons. Of a eukaryotic cell, double-membraned organelle that holds the DNA.

cytoplasm

In a prokaryote, collective term for everything enclosed by the plasma membrane. In a eukaryote, everything between the plasma membrane and the nucleus.

surface-to-volume ratio

Relationship in which the volume of an object increases with the cube of the diameter, and the surface area increases with the square.

cell theory

Set of principles that constitute the foundation of modern biology: every living organism consists of one or more cells; the cell is the basic structural and functional unit of life; all cells come from division of preexisting cells; and all cells pass hereditary material (DNA) to offspring.

ribosomes

Organelle of protein synthesis.

plasmids

In some prokaryotes, small extrachomosomal circle of DNA that carries a few genes.

nucleoid

Of a bacterium or archaeon, region of cytoplasm where the DNA is concentrated.

cell wall

Rigid but permeable structure that surrounds the plasma membrane of some cells.

pili

Protein filament that projects from the surface of some prokaryotic cells.

flagella

Long, slender cellular structure used for motility.

biofilm

Community of microorganisms living within a shared mass of secreted slime

chromatin

Collective term for all of the DNA and associated proteins in a cell nucleus.

nucleoplasm

Viscous fluid inside the nucleus.

nucleolus

In a cell nucleus, a dense, irregularly shaped region where ribosome subunits are assembled.

nuclear envelope

Double membrane that constitutes the outer boundary of the nucleus. Pores in the membrane control which molecules can cross it.

endomembrane system

Multifunctional network of membrane-enclosed organelles (endoplasmic reticulum, Golgi bodies, and vesicles).

Vesicles

Saclike, membrane-enclosed organelle; different kinds store, transport, or break down their contents.

lysosomes

Enzyme-filled vesicle that breaks down cellular wastes and debris.

peroxisomes

Enzyme-filled vesicle that breaks down molecules and has other specialized functions in animal organs.

vacuoles

Large, fluid-filled vesicle that isolates or breaks down waste, debris, toxins, or food.

central vacuole

Very large fluid-filled vesicle of plant cells.

endoplasmic reticulum (ER)

System of sacs and tubes that is a continuous extension of the nuclear envelope. Comprises smooth ER, rough ER.

Golgi body

Membrane-enclosed organelle that modifies proteins and lipids, then packages the finished products into vesicles.

mitochondria

Double-membraned organelle that produces ATP by aerobic respiration in eukaryotes.

Plastids

One of several types of double-membraned organelles that functions in photosynthesis, pigmentation, or storage in plants and algal cells; for example, a chloroplast or amyloplast.

chloroplasts

Organelle of photosynthesis in the cells of plants and photosynthetic protists.

cytoskeleton

Network of protein filaments that support, organize, and move eukaryotic cells and their internal structures.

microtubules

Cytoskeletal element that participates in cellular movement. Hollow filament of tubulin subunits.

microfilaments

Reinforcing cytoskeletal element involved in cell movement; fiber of actin subunits.

Intermediate filaments

Stable cytoskeletal element of animals and some protists; different types are assembled from different fibrous proteins.

Motor proteins

Type of energy-using protein that interacts with cytoskeletal elements to move a cell’s parts or the whole cell.

Cilia

Short, hairlike structures on the plasma membrane of some eukaryotic cells. Often occur in clumps that beat in unison.

centriole

Barrel-shaped organelle from which microtubules lengthen.

basal body

Organelle that develops from a centriole.

pseudopods

A temporary protrusion that helps some eukaryotic cells move and engulf prey.

extracellular matrix

Complex mixture of substances secreted by a cell onto its surface; composition and function vary by cell type.

primary wall

The first cell wall of young plant cells.

secondary wall

Lignin-reinforced wall that forms inside the primary wall of a mature plant cell.

lignin

Material that strengthens cell walls of vascular plants.

basement membrane

Extracellular matrix that attaches epithelium to underlying tissue.

cuticle

Secreted covering at a body surface.

Cell junctions

Structure that connects a cell to another cell or to extracellular matrix.

tight junctions

Cell junction that fastens together the plasma membrane of adjacent animal cells. Collectively prevent fluids from leaking between the cells.

adhering junctions

Cell junction that fastens an animal cell to another cell, or to basement membrane.

Gap junctions

Cell junction that forms a closable channel across the plasma membranes of adjoining animal cells; allows ions that serve as signals to move between cells.

plasmodesmata

Singular, plasmodesma. Cell junction that forms an open channel between the cytoplasm of adjacent plant cells.