3.2.3 Transport Across Membranes

Question 1

Function of Cell Surface Membrane

Answer 1

• barrier between cell and surroundings
• control the passage of substance (intrinsic protein)
• cell recognition (antigen, extrinsic protein)
• receptor site for hormones (extrinsic protein)
• insulates nerves, allows transmission of nerve impulses
• cell adhesion (glycoprotein)

Question 2

Function of Intercellular Membrane

Answer 2

• intracellular transport system
• reaction surface
• providing compartments for isolating chemical reactions

Question 3

Simple Diffusion

Answer 3

• for small, uncharged, LIPID SOLUBLE molecules
• net movement of particles down a conc gradient, from region of high conc to region of low conc
• plasma membrane is SELECTIVELY PERMEABLE

Question 4

Cholesterol in Plasma Membrane

Answer 4

• provides membrane strength (makes it less fluid)

- reduces the loss of water and ions

Question 5

Cell adaptations for diffusion

Answer 5

-large s.a.
steep conc gradient
-high temp
-short distance

Question 6

Ficks Law

Answer 6

rate of diffusion=s.a * conc difference / thickness

Question 7

Facilitated Diffusion- Carrier Proteins

Answer 7

allow lipidphobic molecules to pass through

• by binding to complementary shape of carrier protein (like induced fit model)
• No input of metabolic energy required

Question 8

Facilitated Diffusion- Ion Channels

Answer 8

• allow diffusion of charged particles
• most are gated to control movement
• different in conc of ions create +ve and -ve charge on sides of cell membrane, ELECTROCHEMICAL GRADIENT causes nerve impulse

Question 9

Osmosis

Answer 9

net movement of water molecules from area of higher water potential to an area of lower water potential through a semipermeable membrane

Question 10

water potential

Answer 10

unit; kPa

water has water potential of 0, every thing else is negative

Question 11

3 solution states (water potential)

Answer 11

Hypertonic (burst/lysis or turgid)
isotonic (normal)
Hypertonic (crenated or plasmolysed)

Question 12

co-transport

Answer 12

movement of 2 or more molecules using the same protien carrier
(only need 1 to go down conc gradient for no need of ATP)

Question 13

cotransport of glucose

Answer 13

1. Sodium Potasium Pump (active transport)
   causes low conc of sodium in cell
2. Co-transport of glucose and sodium from the intestine (glucose against conc gradient)
   3.Facilitated diffusion of Glucose

Question 14

active transport

Answer 14

movement of molecules/ion against the conc gradient, with the use of ATP, carrier protein/pump
THROUGH SEMI PERMEABLE MEMBRANE

Question 15

processes needing active transport

Answer 15

• urea from liver
• minerals to root hair cell
• glucose into phloem
• amino acid from gut
• SODIUM POTASSIUM PUMP for nervous impulse

Question 16

steps in active transport

Answer 16

1. ion binds to SPECIFIC carrier protien
2. ATP binds to protein (phosphate stays on protein, ADP goes)
3. carrier protein changes shape so molecule transported across
4. phosphate group binds to ADP, protein returns to original position