transport across membranes

Question 1

what is a common feature amongst all cell membranes of all organisms?

Answer 1

the cell membrane is the same

- includes membrane surrounding the organelles and the cell surface membrane

Question 2

describe the structure of the cell membrane

Answer 2

1. phospholipid bilayer
   - hydrophilic heads point towards water on either side of the membrane
   - hydrophobic tails so repel water point inwards
2. embedded with protiens
   - channel or carrier (intrinsic or extrinsic)
3. glycolipids, glycoprotiens, and cholesterol

Question 3

describe the fluid mosaic model

Answer 3

1. molecules within membrane move laterallly

2. mixture of phospholipids, glycoprotiens, protiens, and glycolipids

Question 4

use the fluid mosic model to explain how a cell surface membrane is selectively perimable (how molecules can enter and leave the cell)

Answer 4

1. phospholipid bilayer allows movement of small/non-polar/lipid-soluble molecules
   down a concenteration gradient
   restricts the movement of larger, polar molecules
2. channel and carrier protiens
   -allows movement of water soluble/polar/ molecules and ions
   down a concenteration gradient by facilitated diffusion
3. carrier proteins
   - allows movement of molecules against their concenteration gradient using ATP by active transport

Question 5

explain how feature of the cell surface membrane allow it to adapt to its other funtions

Answer 5

1. phospholipid bilayer- acts as a barrier between the internal and external enviroments of a cell
2. bilayer is fluid- can bend to take up different shapes (phagocytosis)
3. extrinsic proteins- cell recognition/ receptors/antigens
4. cholesterol- regulates the stability/fluidity of the membrane

Question 6

explain the role of cholesterol in cell membranes

Answer 6

1. maintains the fluidity of the membranes by restricting lateral movement of the molecules making up the membrane
2. binds fatty acid tails causing them to be closely packed together
3. not present in bacterial cell membranes

Question 7

how do molecules move across a membrane by simple diffusion and what factors affect the rate of simple diffusion?

Answer 7

1. simple diffusion: net movement of small, non-polar molecules across a selectively permiable membrane down the concenteration gradient
2. no ATP
3. affected by:
   - surface area, concenteration gradient, thickness of surface (diffusion pathway)

Question 8

how do molecules move across a membrane by facilitated diffusion and what factors affect the rate of facilitated diffusion?

Answer 8

1. net movement of larger, polar molecules across a selectively perimable membrane, down a concenteration gradient
2. through a channel or carrier protien
3. no ATP
4. affected by:
   - surface area, concenteration gradient, and the number of channel or carrier proteins

Question 9

how do molecules move across a membrane by active transport and what factors affect the rate of active transport?

Answer 9

1. net movement of molecules/ions against the concenteration gradient across a selectively perimable membrane
2. using carrier protiens
3. using energy from the hydrolysis of ATP, to change the shape of the tertiary structure and push the substance through
4. affected by:
   - pH/temperature, speed of carrier protiens, number of carrier protiens, and rate of respiration

Question 10

how do molecules move across a membrane by osmosis transport and what factors affect the rate of osmosis?

Answer 10

1. net movement of water across a selectively permiable membrane down a water potential gradient
2. passive
3. water potential is the likelihood of water molecules diffusing out of or into a solution
4. affected by:
   - surface area, water potential gradient, thickness of exchange surface/diffusion pathway

Question 11

explain how glucose is absorbed by the cells lining the mammalian ileum

Answer 11

1. Na+ actively transported out of epithelial cell into the blood, by Na+/K+ pump
2. creating a concenteration gradient of Na+; higher outside the cell than inside
3. Na+ and glucose move into cell by facilitated diffusion from ileum via a co-transporter protien; Na+ down conc gradient, glucose against conc gradient
4. higher conc of glucose inside cell than in blood
5. glucose moves out of cell by facilitated diffusion into blood through channel protien

Question 12

how might cells be adapted for transport across membranes?

Answer 12

1. increase SA

2. increase no. channel or carrier proteins

Question 13

describe the function of the fatty acid tails in the cell surface membrane

Answer 13

1. form(water) impermeable barrier to water-soluble substances / selectively permeable
2. allows non-polar molecules to pass through;
3. allows cell to maintain different concentrations either side
4. makes membranes self-sealing; able to fuse with other
   membranes
5. able to form vesicles / gives flexibility / fluidity;