Chapter 5 Biological Membranes

Question 1

plasma membrane

Answer 1

The selectively permeable surface membrane

that encloses the cell contents and through which all materials entering or leaving the cell must pass.

Question 2

fluid mosaic model

Answer 2

The currently accepted model of the plasma

membrane and other cell membranes, in which protein molcules “float” in a fluid phospholipid bilayer.

Question 3

amphipathic

Answer 3

A molecule containing both hydrophobic and hydrophilic regions.

Question 4

Integral membrane proteins

Answer 4

A protein that is tightly associated with
the lipid bilayer of a biological membrane; a transmembrane integral protein spans the bilayer. Compare with peripheral membrane protein.

Question 5

Transmembrane proteins

Answer 5

An integral membrane protein that spans the lipid bilayer.

Question 6

Peripheral membrane proteins

Answer 6

A protein associated with one of the surfaces of a biological membrane. Compare with integral membrane protein.

Question 7

selectively permeable membranes

Answer 7

A membrane that allows some substances to cross it more easily than others. Biological membranes are generally permeable to water but restrict the passage of many solutes.

Question 8

transport proteins

Answer 8

facilitate the passage of certain ions and molecules through biological membranes.

Question 9

Carrier proteins

Answer 9

transport proteins that undergo a series of conformational changes as they bind and transport a specific solute

Question 10

ABC transporters

Answer 10

ATP-binding cassette transporters

Question 11

Channel proteins

Answer 11

transport proteins that form passageways through which water and certain ions travel through the membrane.

Question 12

Porins

Answer 12

transport proteins that form passageways through which water and certain ions travel through the membrane.

Question 13

Diffusion

Answer 13

The net movement of particles (atoms, molecules, or ions)
from a region of higher concentration to a region of lower concentration (i.e., down a concentration gradient), resulting from random motion

Question 14

concentration

gradient

Answer 14

A difference in the concentration of a substance from one point to another, as for example, across a cell membrane.

Question 15

simple diffusion

Answer 15

solute molecules or ions move directly through the membrane down their concentration gradient.

Question 16

Facilitated diffusion

Answer 16

The passive transport of ions or molecules by a specific carrier protein in a membrane. As in simple diffusion, net transport is down a concentration gradient, and no additional energy has to be supplied

Question 17

Osmosis

Answer 17

The net movement of water (the principal solvent in biological systems) by diffusion through a selectively
permeable membrane from a region of higher concentration of water (a hypotonic solution) to a region of lower concentration of water (a hypertonic solution).

Question 18

osmotic pressure

Answer 18

The pressure that must be exerted on the hypertonic
side of a selectively permeable membrane to prevent
diffusion of water (by osmosis) from the side containing pure water.

Question 19

isotonic

Answer 19

A term applied to solutions that have identical concentrations of solute molecules and hence the same
osmotic pressure. Compare with hypertonic and hypotonic.

Question 20

hypertonic

Answer 20

osmotic pressure (or solute concentration) greater than that of the solution with which it is compared.

Question 21

plasmolysis

Answer 21

The shrinkage of cytoplasm and the pulling away of the plasma membrane from the cell wall when a plant cell (or other walled cell) loses water, usually in a hypertonic
environment.

Question 22

hypotonic

Answer 22

osmotic pressure (or solute concentration) less than that of the solution with which it is compared.

Question 23

cotransport

Answer 23

The active transport of a substance from a region of low
concentration to a region of high concentration by coupling its transport to the transport of a substance down its concentration gradient.

Question 24

exocytosis

Answer 24

The active transport of materials out of the cell by fusion of cytoplasmic vesicles with the plasma membrane.

Question 25

endocytosis

Answer 25

The active transport of substances
into the cell by the formation of invaginated regions of the plasma membrane that pinch off and become cytoplasmic vesicles.

Question 26

phagocytosis

Answer 26

Literally, “cell eating”; a type of

endocytosis by which certain cells engulf food particles, microorganisms, foreign matt er, or other cells.

Question 27

pinocytosis,

Answer 27

Cell drinking; a type of endocytosis by which cells engulf and absorb droplets of liquids.

Question 28

receptor-mediated endocytosis

Answer 28

A type of endocytosis in which extracellular molecules become bound to specific receptors on the cell surface and then enter the cytoplasm enclosed in vesicles.

Question 29

ligand molecules

Answer 29

A molecule that binds to a specifi c site in a receptor or other protein.

Question 30

Anchoring junctions

Answer 30

include desmosomes and adhering junctions; they are found between cells that form a sheet of tissue.

Question 31

Desmosomes

Answer 31

Buttonlike plaques, present on two opposing cell surfaces, that hold the cells together by means of protein filaments that span the intercellular space.

Question 32

Adhering

junctions

Answer 32

A type of anchoring junction between cells; connects

epithelial cells.

Question 33

Tight junctions

Answer 33

Specialized structures that form between some animal cells, producing a tight seal that prevents materials from passing through the spaces between the cells.

Question 34

Gap junctions

Answer 34

Structure consisting of specialized regions of the plasma membrane of two adjacent cells; contains numerous pores that allow the passage of certain small molecules and ions between them.

Question 35

Plasmodesmata

Answer 35

Cytoplasmic channels connecting adjacent plant cells and allowing for the movement of molecules and ions between cells.

Question 36

turgor pressure

Answer 36

Hydrostatic pressure that develops within a walled cell and presses outward against the plasma membrane.

Question 37

active transport

Answer 37

Transport of a substance across a membrane that does not rely on the potential energy of a concentration gradient for the substance being transported and therefore requires an additional energy source (oft en ATP); includes carrier-mediated active transport, endocytosis, and exocytosis

Question 38

sodium–potassium pump

Answer 38

Active transport system that transports sodium ions out of, and potassium ions into, cells.