Passive Membrane Transport

Question 1

Solvent

Answer 1

is what dissolves

Question 2

Solute

Answer 2

is what gets dissolved

Question 3

Concentration

Answer 3

amount of solute per volume of solvent

Question 4

Concentration gradient

Answer 4

Difference in concentration of a chemical from one area to another

Question 5

concentration gradient info

Answer 5

– More Na+ and O2 in interstitial fluid than cytosol
– More K+ and CO2 in cytosol than interstitial fluid

Question 6

electrical gradient

Answer 6

Difference in electrical charge from one area to another

Question 7

electrical gradient info

Answer 7

– Inner surface of plasma membrane is more negatively charged
– Outer surface of plasma membrane is more positively charged
– Charge difference across plasma membrane termed membrane potential

Question 8

electrochemical gradient

Answer 8

Combined influence of concentration and electrical gradients on a
particular ion

Question 9

electrochemical gradient directions

Answer 9

– Substances tend to move down concentration gradient to reach equilibrium
– Positively charged substances tend to move to negatively charged areas
– Negatively charged substances tend to move to positively charged areas

Question 10

passive transport

Answer 10

– Do not require energy (ATP)
– Substances move DOWN/ALONG concentration gradient (high to low)
– Naturally move from where there is more of a substance to where there is less

Question 11

active transport

Answer 11

– Require energy (ATP)
– Substances move UP/AGAINST concentration gradient (low to high)
– Move from where there is less of a substance to where there is more

Question 12

Diffusion

Answer 12

Movement of substances from
regions of higher concentration to
regions of lower concentration
(down their concentration gradient)
* Particles continue to move until
equilibrium is reached

Question 13

Factors influencing diffusion rate

Answer 13

– Steepness of concentration gradient
▪ The greater the difference in concentration between the two sides, the
higher the rate of diffusion
– Temperature
▪ The higher the temperature, the faster the rate of diffusion
– Mass of diffusing substance
▪ The larger the mass of the diffusing particle, the slower its diffusion rate
– Surface area
▪ The larger the membrane surface area for diffusion, the faster the
diffusion rate
– Diffusion distance
▪ The greater the distance over which diffusion must occur, the longer it
takes

Question 14

simple diffusion

Answer 14

*Movement of solutes from regions of
higher concentration to regions of
lower concentration without a
protein transporter
* Small, non-polar solutes
– Includes: oxygen, carbon dioxide,
nitrogen, fatty-acids, steroids, fat-soluble
vitamins (A,D,E,K), water, ethanol, urea
*Movement dependent on
concentration gradient alone
– Continues to move as long as
gradient exists

Question 15

facilitated diffusion

Answer 15

• Movement of solutes from regions of higher concentration to
  regions of lower concentration with a protein transporter
• Two types:
  – Channel-Mediated diffusion
  – Carriers-Mediated diffusion

Question 16

Channel-Mediated Diffusion

Answer 16

– Channels specific for one ion type
– Most numerous: K+ or Cl–
– Fewer channels: Na+ or Ca+

Question 17

Leak channel

Answer 17

continuously open

Question 18

gated channel

Answer 18

– Usually closed
– Open in response to a stimulus for
fraction of second

Question 19

types of gated channel

Answer 19

▪ Ligand-gated: open in response to a ligand binding to the receptor
▪ Voltage-gated: open in response to a change in the electrical gradient
▪ Mechanically-gated: open in response to mechanical stimulation (vibration, touch, pressure, tissue stretch)

Question 20

Carrier-Mediated Diffusion

Answer 20

Movement of small, polar
molecules through a carrier protein

• Binding of substance causes change in carrier protein shape
• Releases substance on other side of membrane

Question 21

Osmosis

Answer 21

Osmosis is diffusion of a solvent
– In living systems, the solvent is water
– Osmosis is movement of water from an area of higher water concentration toan area of lower water concentration

Question 22

How osmosis works

Answer 22

Plasma membrane is selectively permeable, and allows water to pass through, but prevents some solutes
– Osmosis moves WATER from an area of lower solute concentration to an area of higher solute concentration

Question 23

Methods of osmosis

Answer 23

Water passes through plasma membrane in two ways
– By moving between neighboring phospholipid molecules via simple diffusion
– By moving through aquaporins- integral proteins that function as water channels

Question 24

Hydrostatic pressure

Answer 24

force exerted by water onto the surface of its container
– The higher the water concentration, the greater the hydrostaticpressure
– Produces water movement

Question 25

Osmotic pressure

Answer 25

force of exerted by solution with impermeable solutes
– Proportional to the concentration of the solute particles that cannot cross the membrane
– The higher the solute concentration, the higher the solution’s
osmotic pressure
– Prevents/Opposes water movement

Question 26

isotonic

Answer 26

-membrane permeable to water
-solute and water concentration equal on both sides of the membrane
-no net movement of water
-cell stays the same

Question 26

tonicity

Answer 26

Ability of a solution to change the volume or pressure of a cell by osmosis

Question 27

hypotonic

Answer 27

-membrane permeable to water
-solute concentration lower outside the cell
-water goes inside
-cell may burst open

Question 28

hypertonic

Answer 28

-membrane permeable to water
-solute concentration higher outside the cell
-water goes outside
-cell will shrivel