Passive Transport of Water and Solutes

Question 1

Plasma membrane

Answer 1

permeability barrier that covers entire cell surface

Question 2

Intra cellular Fluid

Answer 2

cytosol + fluids inside all organelles + nucleus

Question 3

Functions of cell membrane

Answer 3

• selective physical barrier
• for exchanges between cells and environment
• involved in communication between cells and environments
• structural supports

Question 4

Membrane structures

Answer 4

• phospholipid bilayer : amphipathic molecules
• in aqueous environment : bimolecular layer with nonpolar fatty acid chains in middle
• polar regions interact with ECF and cytosol

Question 5

Fluid mosaic model

Answer 5

• no chemical bonds linking them
• each molecule free to move independently

Question 6

Cholesterol

Answer 6

involved in formation of vesicles via “pinching off” parts of membrane

Question 7

Integral membrane protein

Answer 7

• tightly bound into membrane (amphipathic molecules)
• most span entire membrane : transmembrane protein
• some have channel through them

Question 8

Peripheral proteins

Answer 8

• loosely attached to membrane-spanning proteins / polar regions of phospholipids
• not amphipathic (cytosolic surface of membrane)

Question 9

Concept of diffusion

Answer 9

molecules move from area of higher concentration to lower concentration of molecules

Question 10

Brownian motion

Answer 10

heat that increases speed of motion of molecules

Question 11

Flux

Answer 11

amount of material crossing a surface in a unit of time

Question 12

Net flux

Answer 12

difference between two one-way fluxes

Question 13

Diffusion equilibrium

Answer 13

two one-way fluxes equal in magnitude but opposite in directions

Question 14

Factors affecting diffusion rate of substances across membrane

Answer 14

1. steepness of concentration gradient
2. directly related to temperature
3. inversely related to molecular size
4. directly related to surface area
5. inversely related to distance of travel

Question 15

Diffusion through phospholipid bilayer

Answer 15

• very small or nonpolar molecules can cross directly
• large or polar molecules cross at slow rate

Question 16

Exchanges of ions & small polar molecules between blood and interstitial fluid

Answer 16

pass through water-filled channels

Question 17

Exchanges of protein between blood and interstitial fluid

Answer 17

only small amount passes through water-filled channels

Question 18

Variation in size of water-filled channel

Answer 18

brain capillaries : tight junctions between epithelial cells
liver capillaries : large gaps in membrane

Question 19

Flow of oxygen and nutrients

Answer 19

capillary plasma > capillary wall > interstitial fluid > entry into cells

Question 20

Flow of carbon dioxide

Answer 20

muscle cells > interstitial fluids > capillary wall > capillary plasma

Question 21

Simple diffusion

Answer 21

• small nonpolar, hydrophobic molecules
• two polar molecules (water & urea)

Question 22

Importance of simple diffusion

Answer 22

• transfer of O2 and CO2 between blood and body cells
• absorption of some nutrients
• excretion of some wastes by body cells

Question 23

Diffusion of ions through membrane channel

Answer 23

• gated membrane channel
• small and inorganic ions
  limited numbers of channel and each is specific

Question 24

Facilitated diffusion

Answer 24

• polar or highly charged molecules
• transporter molecules is present to transport molecules

Question 25

Carrier-mediated transport

Answer 25

- specificity : move only one type of molecule - competition : able to move several members of related groups of substrates but they must compete for binding sites - saturation : limited numbers of transporters in plasma membrane (transport maximum)