1.4 Membrane Transport

Question 1

Describe the structure of the phospholipid bilayer.

Answer 1

Phospholipid bilayer has a polar head (phosphate group) which is hydrophilic and a non-polar hydrocarbon tail which is hydrophobic. This prevents the passage of ions without the help of membrane proteins

Question 2

What is diffusion

Answer 2

passive net movement of particles from an area of high concentration to an area of low concentration.

Question 3

Factors affecting the rate of diffusion

Answer 3

Concentration gradient: higher concentration gradient = higher rate of diffusion
Length of Diffusion path:
shorter diffusion path = higher rate of diffusion
Surface area = larger surface area = higher rate of diffusion

Question 4

Adaptations

Answer 4

1. membranes are thin (shorter diffusion path)
2. folded membranes to increase SA:VOL ratio
3. more membrane in a smaller volume = shorter distances across which molecules diffuse
   e.g. alveoli in lungs, cristae in mitochondria, villi for absorption of digested food molecules

Question 5

What is osmosis

Answer 5

passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration (aquaporin)

Question 6

osmotic control types

Answer 6

plasmolyzed, flaccid, turgid/ crenated, in equilibrium, lysed

Question 7

Facilitated diffusion

Answer 7

protein facilitates in the movement of material from high to low concentration e.g. (ion channels)

Question 8

How is ATP utilized in active transport

Answer 8

Integral protein pumps use energy from the hydrolysis of ATP to move ions or large molecules against their concentration gradients

Question 9

Uniport, Symport, Antiport

Answer 9

uniport (one molecule one direction), symport (two molecules one direction), antiport (two molecules two directions)

Question 10

Describe the sodium- potassium pump

Answer 10

The interior of the sodium potassium pump is originally open to the inside of the axon and 3 Na+ attach to their binding sites in the pump. The hydrolysis of ATP produces an ADP and a phosphate group, and the phosphate group attaches to the protein, resulting in a change in the shape. The interior of the pump is then open to the outside of the cell, and the 3 Na+ are released as 2 K+ ions attach to their binding sites on the protein, which results in the release of the phosphate group, changing the shape of the pump, which causes the pump’s interior to be open again to the inside of the axon. The K+ ions are then released into the cell.

Question 11

Endocytosis

Answer 11

taking in of external substances by inward pouching of the plasma membrane, which forms a vesicle

Question 12

Exocytosis

Answer 12

release of substances (secretion) from a cell when a vesicle joins with the plasma membrane

Question 13

Outline the process of exocytosis

Answer 13

The vesicle containing the material approaches the cell membrane, and the membranes begin to fuse (possible because of the fluidity of membranes). For a small amount of time, there is a singular phospholipid bilayer at the point of contact. The membrane pore then opens, allowing the substances to exit the cell, and there is never an unbroken section of the bilayer.

Question 14

Three factors affecting the permeability of a cell membrane

Answer 14

1. temperature
2. pH
3. ethanol - the interior of the phospholipid bilayer is nonpolar, and ethanol is also nonpolar and the membrane will begin to dissolve in ethanol, making it more permeable as it starts to break down