Transport across membranes

Question 1

Simple vs Facilitated Diffusion?

Answer 1

 Simple = molecules move directly through the phospholipid bilayer
 Facilitated = molecules pass through transport proteins (large use carrier, charged use channel)

Question 2

Factors that affect rate of diffusion?

Answer 2

 surface area (increase = increase rate of diffusion)
 concentration gradient (increase = increase rate of diffusion)
 thickness (decrease = decrease diffusion distance = increase rate of diffusion)
 temperature (increase = increase kinetic energy = molecules move faster = increase rate of diffusion)
 size of molecules (smaller molecules = increase rate of diffusion)

Question 3

What is Fick’s Law?

Answer 3

(Surface Area x Concentration Gradient)/Thickness

Question 4

Define Osmosis?

Answer 4

The net movement of water molecules from an area of higher water potential to an area of lower water potential through a partially permeable membrane

Question 5

Which liquid has the highest water potential?

Answer 5

 distilled/pure water
 has a value of 0kPa
 lower water potential by adding solutes (makes water potential negative)
 water moves from less negative water potential (e.g. -35 kPa) to more negative water potential (e.g. -75 kPa)

Question 6

Surround animal cell with pure water?

Answer 6

swells and burst (water enters by osmosis)

Question 7

Surround plant cell with pure water?

Answer 7

 swells but does not burst
 cell wall prevents it from bursting
 made of cellulose – strong material
 the cell is Turgid

Question 8

Surround animal cell with concentrated sugar/salt solution?

Answer 8

shrinks (water leaves by osmosis)

Question 9

Surround plant cell with concentrated sugar/salt solution?

Answer 9

 water leaves by osmosis
 cell wall prevents cell from shrinking, keeps it rigid
 the protoplast (cell membrane plus contents) shrink
 the cell is Plasmolysed

Question 10

Define Active Transport?

Answer 10

The movement of particles from an area of low concentration to an area of high concentration against the concentration. gradient using ATP and carrier proteins

Question 11

Describe the process of active transport?

Answer 11

 molecules (in area of low concentration) bind to carrier protein
 ATP breaks down to ADP, Pi and Energy
 the Pi and Energy cause the carrier protein to change shape
 carrier protein releases molecules on opposite side (in area of high concentration)
 the carrier protein releases the attached Pi to return to its original shape

Question 12

Adaptations of small intestine?

Answer 12

 folded to form Villus (large surface area)
 cells lining SI have Microvilli (large surface area)
 wall of SI is thin (short diffusion distance)
 rich blood supply (maintains concentration gradient)
 cells lining SI have transport proteins and mitochondria

Question 13

Active Transport of Glucose in SI?

Answer 13

 sodium ions are actively transported from the cells lining the SI into the blood
 lowers the sodium ion concentration in the cell
 therefore sodium ions move from the lumen of the SI into the cell
 this pulls in glucose via a cotransport protein
 therefore glucose builds up in the cell and moves into the blood by diffusion