Ch 7: Membrane Structure and Function

Question 1

What is passive transport?

Answer 1

Passive transport is diffusion of a substance across a membrane with no energy investment

Question 2

What is diffusion?

Answer 2

diffusion is the movement of particles of any substnace so that they spread out evenly into the available space

Question 3

What is a concentration gradient?

Answer 3

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

Question 4

What does concentration gradient represent?

Answer 4

it represents potential energy that drives diffusion

Question 5

What does rate of diffusion depend on?

Answer 5

it depends on membrane permeability to the specific substance

Question 6

What is osmosis?

Answer 6

it is the diffusion of free water (water molecules not clustered around another substance) across a selectively permeable membrane, free water molecules diffuse across a membrane from the region of lower solute concentration to the region of higher solute concentration

Question 7

What is tonicity?

Answer 7

the ability of a surroudning solution to cause a cell to gain or lose water

Question 8

What does tonicity depend on?

Answer 8

tonicity depends on the concentration of these solutes in the solution that cannot cross the membran, relative to that inside the cell, if the solution has a higher concentration of these solutes than the inside of the cell, water will tend to leave the cell, and vice versa.

Question 9

What does it mean for a solution to be isotonic?

Answer 9

the solute concentration is the same as that inside the cell, meaning water diffuses across the membrane at the same rate in both directions

Question 10

How is the cell wall in an isotonic solution?

Answer 10

the volume of a cell without a cell wall is stable in an isotonic solution

Question 11

What does hypertonic mean?

Answer 11

a solution is hypertonic is the solute concentration is greater than that inside the cell

Question 12

What is plasmolysis?

Answer 12

a phenomenon where the cell shrivels and the membrane pulls away from the cell wall in multiple locations

Question 13

What is hypotonic?

Answer 13

when the solute concentration is less than that inside the cell

Question 14

What does a plant cell do in a hypotonic solution?

Answer 14

a plant cell will take up water and swell until the inelastic wall exerts back a pressure on the cell, called turgor pressure

Question 15

What is osmoregulation?

Answer 15

when cells without walls cant tolerate excessive water loss or uptake so they have to have a control of solute concentration and water balance

Question 16

What is facilitated diffusion?

Answer 16

when transport proteins speed the passive movement of molecules across the plasma membrane, ex. aquaporins facilitate the diffusion of water

Question 17

What is the function of a channel protein?

Answer 17

a channel protein provides corridors that allow a specific molecule or ion to cross the membrane

Question 18

Ion Channels

Answer 18

facilitate the transport of ions

Question 19

What is a gated channel?

Answer 19

some ion channels open or close in response to a stimulus (chemical or electrical)

Question 20

Why is facilitated diffusion passive?

Answer 20

the solute moves down its concentration gradient and the transport requires no energy

Question 21

What is active transport?

Answer 21

requires energy, usually in the form of ATP hydrolysis, to move substances against their concentration gradients, all proteins involved in active transport are carrier proteins

Question 22

Active transport enables

Answer 22

cells to maintain solute concentrations that differ from the environment, ex. sodium-potassium pump

Question 23

What is membrane potential?

Answer 23

the voltage (electrical potential energy) across a membrane

Question 24

How is voltage created?

Answer 24

by differences in the distribution of positive and negative ions across a membrane

Question 25

What is a electrochemical gradient?

Answer 25

Two combined forces, a chemical and electrical force, drive the diffusions of ions across a membrane

Question 26

What is an electrogenic pump?

Answer 26

a transport protein that generates voltage across a membrane, storing energy that can be used for cellular work

Question 27

Main electrogenic pump for plants

Answer 27

in plants, fungi, and bacteria is the proton pump, which actively transports hydrogen ions out of the cell

Question 28

Main electrogenic pump for animals

Answer 28

in animals it is the sodium-potassium pump

Question 29

What is cotransport?

Answer 29

when active transport of a solute indirectly drives transport of other substances, the “downhill” diffusion of solute is coupled to the “uphill” transport of a second substance against its own concentration gradient

Question 30

What is exocytosis?

Answer 30

transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cell

Question 31

What is endocytosis?

Answer 31

macromolecules are taken into the cell in vesicles, the membrane forms a pocket that deepens and pinches off forming a vesicle around the material for transport

Question 32

What are the three types of endocytosis?

Answer 32

phagocytosis, pinocytosis, and receptor-mediated endocytosis

Question 33

What is phagocytosis?

Answer 33

a cell engulfs a particle by extending pseudopodia around it and packing it in a membranous sac called a food vacuole

Question 34

What is pinocytosis?

Answer 34

molecules are taken up when extracellular fluid is “gulped” into tiny vesicles, any and all solutes are taken into the cell

Question 35

What is receptor-mediated endocytosis?

Answer 35

vesicle formation is triggered by solute binding to receptors