AP Bio Unit 2

action potential

An electrical signal that propagates (travels) along the membrane of a neuron or other excitable cell as a nongraded (all-or-none) depolarization.

active transport

The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy.

amphipathic

Having both a hydrophilic region and a hydrophobic region.

aquaporins

A channel protein in a cellular membrane that specifically facilitates osmosis, the diffusion of free water across the membrane.

axon

A typically long extension, or process, of a neuron that carries nerve impulses away from the cell body toward target cells.

cell wall

A protective layer external to the plasma membrane in the cells of plants, prokaryotes, fungi, and some protists. Polysaccharides such as cellulose (in plants and some protists), chitin (in fungi), and peptidoglycan (in bacteria) are important structural components

centrioles

A structure in the centrosome of an animal cell composed of a cylinder of microtubule triplets arranged in a “9 plus 0” pattern; centrosome has a pair of them

chloroplast

An organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.

cholesterol

A steroid that forms an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other biologically important steroids, such as many hormones.

concentration gradient

A region along which the density of a chemical substance increases or decreases.

cotransport

The coupling of the “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient.

cytoskeleton

A network of microtubules, microfilaments, and intermediate filaments that extend throughout the cytoplasm and serve a variety of mechanical, transport, and signaling functions.

dendrite

One of usually numerous, short, highly branched extensions of a neuron that receive signals from other neurons.

diffusion

The random thermal motion of particles of liquids, gases, or solids. In the presence of a concentration or electrochemical gradient, results in the net movement of a substance from a region where it is more concentrated to a region where it is less concentrated.

electrochemical gradient

The diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (a chemical force) and the ion’s tendency to move relative to the membrane potential (an electrical force).

electrogenic pump

An active transport protein that generates voltage across a membrane while pumping ions.

endocytosis

Cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane.

endoplasmic reticulum

An extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions.

eukaryote

Organisms with eukaryotic cells (protists, plants, fungi, and animals)

exocytosis

The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane.

extracellular matrix

The meshwork surrounding animal cells, consisting of glycoproteins, polysaccharides, and proteoglycans synthesized and secreted by cells.

facilitated diffusion

The passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins, requiring no energy expenditure.

flaccid

Limp. Lacking turgor (stiffness or firmness), as in a plant cell in surroundings where there is a tendency for water to leave the cell. (A walled cell becomes this if it has a higher water potential than its surroundings, resulting in the loss of water.)

flagella

A long cellular appendage specialized for locomotion. Like motile cilia, eukaryotic ones have a core with nine outer doublet microtubules and two inner single microtubules (the “9 plus 2” arrangement) ensheathed in an extension of the plasma membrane. Prokaryotic ones have a different structure.

fluid mosaic model

The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids.

gated channels

A transmembrane protein channel that opens or closes in response to a particular stimulus.

glycolipid

A lipid with one or more covalently attached carbohydrates.

glycoprotein

A protein with one or more covalently attached carbohydrates

Golgi apparatus

An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum and synthesize some products, notably noncellulose carbohydrates.

homeostasis

The steady-state physiological condition of the body.

hypertonic

Referring to a solution that, when surrounding a cell, will cause the cell to lose water.

hypotonic

Referring to a solution that, when surrounding a cell, will cause the cell to take up water.

integral proteins

A transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane (or lining the channel in the case of a channel protein).

ion channels

A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient

isotonic

Referring to a solution that, when surrounding a cell, causes no net movement of water into or out of the cell.

ligand

A molecule that binds specifically to another molecule, usually a larger one.

lysosome

A membrane-enclosed sac of hydrolytic enzymes found in the cytoplasm of animal cells and some protists.

membrane potential

The difference in electrical charge (voltage) across a cell’s plasma membrane due to the differential distribution of ions; affects the activity of excitable cells and the transmembrane movement of all charged substances.

microfilaments

A cable composed of actin proteins in the cytoplasm of almost every eukaryotic cell, making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction; also called an actin filament.

microtubules

A hollow rod composed of tubulin proteins that makes up part of the cytoskeleton in all eukaryotic cells and is found in cilia and flagella.

mitochondria

An organelle in eukaryotic cells that serves as the site of cellular respiration; uses oxygen to break down organic molecules and synthesize ATP.

myelin

Wrapped around the axon of a neuron, an insulating coat of cell membranes from Schwann cells or oligodendrocytes. It is interrupted by nodes of Ranvier, where action potentials are generated.

nuclear envelope

In a eukaryotic cell, the double membrane that surrounds the nucleus, perforated with pores that regulate traffic with the cytoplasm. The outer membrane is continuous with the endoplasmic reticulum.

nucleus

An atom’s central core, containing protons and neutrons. (2) The organelle of a eukaryotic cell that contains the genetic material in the form of chromosomes, made up of chromatin. (3) A cluster of neurons.

organelle

Any of several membrane-enclosed structures with specialized functions, suspended in the cytosol of eukaryotic cells.

osmolarity

Solute concentration expressed as molarity.

osmoregulation

Regulation of solute concentrations and water balance by a cell or organism.

osmosis

The diffusion of free water across a selectively permeable membrane.

passive transport

The diffusion of a substance across a biological membrane with no expenditure of energy.

peripheral proteins

A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer.

phagocytosis

A type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells).

pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

plasma membrane

The membrane at the boundary of every cell that acts as a selective barrier, regulating the cell’s chemical composition.

plasmolysis

A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment.

prokaryote

A single-celled organism of the domain Bacteria or Archaea.

proton pump

An active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient, generating a membrane potential in the process.

receptor-mediated endocytosis

The movement of specific molecules into a cell by the infolding of vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.

ribosome

A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus; A specialized structure in the nucleus, consisting of chromosomal regions containing ribosomal RNA (rRNA) genes along with ribosomal proteins imported from the cytoplasm; site of rRNA synthesis and ribosomal subunit assembly.

rough ER

That portion of the endoplasmic reticulum with ribosomes attached.

saturated fatty acid

A fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds, thus maximizing the number of hydrogen atoms that are attached to the carbon skeleton.

selective permeability

A property of biological membranes that allows them to regulate the passage of substances across them.

smooth ER

That portion of the endoplasmic reticulum that is free of ribosomes.

sodium potassium pump

A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell.

sucrose-H+ cotransporter

an active transport protein that moves sucrose into a plant cell against its concentration gradient by coupling it with the downhill movement of hydrogen ions

surface area to volume ratio

a mathematical comparison of the amount of cell membrane available for exchanging materials versus the total internal volume that requires those supplies

synapse

The junction where a neuron communicates with another cell across a narrow gap via a neurotransmitter or an electrical coupling.

transport proteins

A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.

turgid

Swollen or distended, as in plant cells. (A walled cell becomes it if it has a lower water potential than its surroundings, resulting in entry of water.)

turgor pressure

The force directed against a plant cell wall after the influx of water and swelling of the cell due to osmosis.

unsaturated fatty acid

A fatty acid that has one or more double bonds between carbons in the hydrocarbon tail. Such bonding reduces the number of hydrogen atoms attached to the carbon skeleton.

vacuole

A membrane-bounded vesicle whose specialized function varies in different kinds of cells.

vesicle

A membrane-bound sac in or outside a cell.

vesicle creation

the process where a portion of a cellular membrane pinches off to form a small, membrane-bound sac that transports materials inside or outside the cell

water potential

The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure.