transport across cell membranes

Question 1

name and describe five ways substances can move across the cell-surface membrane into a cell

Answer 1

1.simple diffusion of small non polar molecules down a concentration gradient
2. facilitated diffusion down a concentration gradient via protein carrier
3.osmosis of water down a water potential gradient
4. active transport against a concentration gradient via protein carrier using ATP
5. co transport of 2 different substances using carrier protein

Question 2

how is ATP hydrolase involved in co transport

Answer 2

ATP to ADP and Pi releases energy
which allows ions to be moved against a concentration gradient

Question 3

explain how the movement of Na+ out of the cell allows the absorption of glucose into the cell lining in the ileum

Answer 3

maintains a concentration gradient for Na+
Na+ moving in by co transport brings glucose with it

Question 4

describe and explain two features you would expect to find in a cell specialised for absorption

Answer 4

1. large number of mitochondria so make ATP by respiration
2. folded membrane so large surface area

Question 5

describe how the movement of substances across cell membranes in affected by the membrane structure

Answer 5

1. phospholipid bilayer allows movement of non polar and lipid soluble substances
2. phospholipid bilayer prevents movement of charged substances
   3.carrier proteins allow active transport
3. channel and carrier proteins allow co transport
4. cholesterol affects fluidity

Question 6

two similarities in the movement of substances by diffusion and osmosis

Answer 6

1. movement down a concentration gradient
2. passive process

Question 7

explain how carrier proteins work in active transport

Answer 7

1.uses hydrolysis of ATP
2. sodium ion and portion bind to protein
3. protein changes shape and moves sodium across membrane

Question 8

explain how a high salt diet can result in a build up of tissue fluid

Answer 8

1. high salt lowers water potential of tissue fluid
2. so less water returns to capillaries by osmosis

Question 9

compare and contrast the processes by which water and inorganic ions move in and out of cells

Answer 9

1. both move down conc gradient
2. both move out through protein channels in membrane
3. but ions can move against a conc gradient by active transport where as a water can not

Question 10

contrast the processes of facilitated diffusion and active transport

Answer 10

1. facilitated diffusion involves channel or carrier proteins where as active transport only involves carrier proteins
2. facilitated doesn’t use ATP where as active does
3. facilitated goes down the conc gradient where as active goes up

Question 11

describe the fluid mosaic model of membranes

Answer 11

fluid: phospholipid bilayer which can move
mosaic: extrinsic and intrinsic proteins are embedded on the membrane and the pattern resembles a mosaic

Question 12

explain the role of cholesterol

Answer 12

reduces fluidity to make bilayer more stable

Question 13

explain the role of glycolipids

Answer 13

cell signalling and recognition

Question 14

explain the functions extrinsic proteins

Answer 14

receptors
antigens
bind cells together

Question 15

explain the functions of intrinsic proteins

Answer 15

channel used in facilitated diffusion
carrier involved in facilitated and active transport

Question 16

explain the functions of membranes

Answer 16

selectively permeable to regulate passage of molecules
isolate organelles from cytoplasm

Question 17

3 factors effecting permeability and how

Answer 17

temp- can denature proteins
pH- change tertiary structure
solvent - may dissolve membrane

Question 18

define osmosis

Answer 18

water diffused across semi permeable membranes from an area of higher water potential to an area of lower water potential until a dynamic equilibrium is established

Question 19

what is water potential?

Answer 19

pressure created by water molecules (kPa)
pure water has a water potential of 0

Question 20

how does osmosis affect plant cells?

Answer 20

too much water in cells = turgid
to little = shrink (flaccid)

Question 21

how does osmosis affect animal cells?

Answer 21

too much water = bursts(lysis)
too little = crenation

Question 22

define simple diffusion

Answer 22

passive process
net movement of small lipid soluble molecules directly through the bilayer from an area of high concentration to an area of lower concentration

Question 23

define facilitated diffusion

Answer 23

passive process
specific channel or carrier proteins with complementary binding sites transport large and polar molecules down a conc gradient

Question 24

state ficks law

Answer 24

rate of diffusion = surface area x difference in conc/ diffusion distance

Question 25

define active transport

Answer 25

active process involving ATP specific carrier protein transport molecules against a conc gradient

Question 26

define co transport

Answer 26

movement of a substance against its conc gradient is coupled with the movement of another substance along its conc gradient

Question 27

explain how co transport is involved in the absorption of glucose/ amino acids in the small intestine

Answer 27

1.Na+ actively transported out of epithelial cells into bloodstream 2. Na+ conc lower in cells than lumen of gut 3. transport of glucose/ amino acids from lumen to to epithelial cells is coupled to facilitated diffusion of Na+ down electrochemical gradient

Question 28

describe how it is called passive movement

Answer 28

when in high conc the solute molecules posses potential energy which moves them

Question 29

describe the process of active transport

Answer 29

1. special carrier proteins span membranes 2. specific substance bonds to receptor 3. causes ATP inside cell to attach to protein 4.ATP hydrolase hydrolyses ATP into ADP and Pi 5. this energy changes the shape of the protein channel so it can pass through 6. ADP detaches and channel closes up to be used again

Question 30

describe the process of co transport in the small intestine for absorption of glucose into the blood

Answer 30

1. sodium potassium pump uses ATP to actively move Na+ from epithelium so small intestine 2. this creates a Na+ conc gradient from lumen into epithelial cells 3. Na+ move into cells through co transporter proteins 4. proteins use this energy to move glucose molecules from lumen into cells 5. glucose molecules move into capillaries by facilitated diffusion

Question 31

what is exocytosis?

Answer 31

substances are excreted by vesicles

Question 32

what is endocytosis?

Answer 32

membrane invaginates and forms vesicle which travels to where it is needed