Cell Membranes

Question 1

Selective Permeability

Answer 1

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

Question 2

Amphipathic

Answer 2

Having both a hydrophilic region and a hydrophobic region

Question 3

Fluid Mosaic Model

Answer 3

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

Question 4

Integral Proteins

Answer 4

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)

Question 5

Peripheral Proteins

Answer 5

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

Question 6

Glycolipids

Answer 6

A lipid with one or more covalently attached carbohydrates

Question 7

Glycoproteins

Answer 7

A protein with one or more covalently attached carbohydrates

Question 8

Transport Proteins

Answer 8

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

Question 9

Aquaporins

Answer 9

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

Question 10

Diffusion

Answer 10

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

Question 11

Concentration Gradient

Answer 11

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

Question 12

Passive Transport

Answer 12

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

Question 13

Osmosis

Answer 13

The diffusion of free water across a selectively permeable membrane

Question 14

Tonicity

Answer 14

The ability of a solution surrounding a cell to cause that cell to gain or lose water

Question 15

Isotonic

Answer 15

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

Question 16

Hypertonic

Answer 16

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

Question 17

Hypotonic

Answer 17

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

Question 18

Osmoregulation

Answer 18

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

Question 19

Turgid

Answer 19

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

Question 20

Flaccid

Answer 20

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)

Question 21

Plasmolysis

Answer 21

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

Question 22

Facilitated Diffusion

Answer 22

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

Question 23

Ion Channels

Answer 23

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

Question 24

Gated Channels

Answer 24

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

Question 25

Active Transport

Answer 25

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

Question 26

Sodium-Potassium Pump

Answer 26

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

Question 27

Membrane Potential

Answer 27

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

Question 28

Electrochemical Gradient

Answer 28

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)

Question 29

Electrogenic Pump

Answer 29

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

Question 30

Proton Pump

Answer 30

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

Question 31

Cotransport

Answer 31

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

Question 32

Exocytosis

Answer 32

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

Question 33

Endocytosis

Answer 33

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

Question 34

Ligand

Answer 34

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

Question 35

Phagocytosis

Answer 35

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)

Question 36

Pinocytosis

Answer 36

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

Question 37

Receptor-Mediated Endocytosis

Answer 37

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