transport across the cell membrane

Question 1

how are cell membranes described as being?

Answer 1

differentially permeable, semipermeable or selectively permeable: meaning that they allow certain ions and molecules to pass through but restrict others

Question 2

passive processes

Answer 2

no energy is used to transport materials in, out or around cell

Question 3

active processes

Answer 3

uses cells energy in the form of ATP (adenine triphosphate)

Question 4

3 basic processes to transport materials in/out/around cell

Answer 4

simple diffusion, facilitated transport, vesicular transport

Question 5

diffusion

Answer 5

the spreading out of particles so that they are evenly distributed over the available space. occurs in gases and liquids because both mols are constantly moving

Question 6

concentration/diffusion gradient

Answer 6

the difference in concentration that brings about diffusion - the greater the difference in concentrations, the ‘steeper’ the diffusion gradient and the faster the rate of diffusion

Question 7

net diffusion

Answer 7

the movement of liquid/gas molecules from places of higher concentration to places of lower concentration along a concentration gradient

Question 8

simple diffusion:

Answer 8

a passive process resulting from the random movement of ions and molecules
osmosis - where water passes across the membrane

Question 9

facilitated transport

Answer 9

porteins in the cell membrane allow molecules to be transported across the membrane, the proteins are channel proteins - which form proteins channels and carrier proteins - which allow carrier-mediated transport

Question 10

protein channels

Answer 10

to diffcue across a cell, water-soluble molecules must pass through protein channels allowing facilitated diffusion
- channels provide a pathway for hydrophilic particles to travel through cell membrane
- small in diameter, so water and ions can pass, but not larger mols

Question 11

carrier-mediated transport

Answer 11

only open on one side of the membrane at a time, when a specific substance binds to a binding site within the protein, the protein changes cshape and opens on the other side, then the substance can be released on the side opposite to where it entered

Question 12

important characteristics of carrier mediated transport

Answer 12

• CP are specific, only bind to a particular molecule eg a carrier that only transports glucose cannot transport anything else
• carriers can become saturated, once all available carriers are occupied, any increase in the concentration of molecules to be transported cannot increase rate of movement
• carrier activity is regulated by things like hormones

Question 13

two types of carrier mediated transport:

Answer 13

1. facilitated diffusion
2. active transport

Question 14

carrier mediated transport: facilitated diffusion

Answer 14

occurs when substances are transported through a protein along the concentration gradient from a higher conc to lower conc.
passive process - doesn’t require energy, but molecule has to attach to binding site of specific carrier protein, then be released one site has changed

Question 15

carrier mediated transport: active transport

Answer 15

requires energy as substances are being transported across the membrane AGAINST the concentration gradient (low-high)
- advantage as substance can pass regardless of concentration

Question 16

vesicular transport

Answer 16

movement of substances across the cell membrane in vesicles - active process, as energy is needed to form vesicles

Question 17

VT: endoctyosis

Answer 17

taking liquids or solid into the cell
the cell membrane folds around a droplet of liquid or solid particle until its completely closed, the vesicle is then formed and pinches off and is suspended in cells cytoplasm

Question 18

phagocytosis and pinocytosis

Answer 18

phago: vesicles containing solid particles
pino: vesicles containing liquid particles

Question 19

VT: exocytosis

Answer 19

contents of vesicle are passed outside
- vesicle migrates to cell membrane and fuses with membrane then contents are pushed out of cell