1.4 MEMBRANE TRANSPORT

Question 1

Potassium channel overview

Answer 1

Potassium channels in axons are voltage gated.

They enable the facilitate diffusion of potassium out of the axon

Question 2

Potassium channels
Facilitated diffusion
Step 1

Answer 2

At one stage during a nerve impulse there are relatively more positive charges inside

Question 3

Potassium channels
Facilitated diffusion
Step 2

Answer 3

This voltage change causes potassium channels to open.

Allowing potassium to diffuse out of the axon.

Question 4

Potassium
Channels
Facilitated diffusion
Step 3

Answer 4

Once the voltage conditions change the then the channel rapidly closes again

Question 5

Sodium-potassium pump overview

Answer 5

Na-K pump follows a repeating cycle of steps that result in 3 Na ions being pumped out of the axon (of the neutron) and 2 K ions being pumped in

Each time the pump goes round this cycle it uses one ATP–> active transport

Question 6

Na-K pump
Active transport
Step 1

Answer 6

The interior of the pimp is open to the inside of the axon

3 Na enter the pump and attach to their binding site

Question 7

Na-K pump
Active transport
Step 2

Answer 7

ATP transfers a phosphate group from itself to the pump

This causes the pump to change shape and the interior is then closed

Question 8

Na-K pump
Active transport
Step 3

Answer 8

The interior of the pump opens to the outside of the axon

3 Na ions are released

Question 9

Na-K pump
Active transport
Step 4

Answer 9

2 K ions from outside enter and attach to their binding site

Question 10

Na-K pump
Active transport
Step 5

Answer 10

Binding of K causes the release of the phosphate group
This causes the pump to change shape again
So that it is again only open to the inside of the axon

Question 11

Na-K pump
Active transport
Step 6

Answer 11

The interior of the pump opens to the inside of the axon and the two K ions are release

Question 12

Na-K pump
Active transport
Final step

Answer 12

Sodium ions can now enter and bind to the pump again

Step 1

Question 13

Factors affecting rate of diffusion through a partially permeable membrane

Answer 13

High conc gradient = high rate
Short diffusion path = high
High/large SA =faster rate

Question 14

Adaptations in biology in maintaining concentration gradient

Answer 14

REDUCING LENGTH OF DIFFUSION PATH
membranes are of thin (7-10 nm)
Folded membranes increase SA:VOL
More membranes in a smaller volume = shorter distance

MAXIMISING S.A for absorption 
Alveoli in lungs 
Membrane folds in mitochondria
Root hair for water: mineral ions uptake 
Villi for absorption

Question 15

Vesicle movement in cells

Answer 15

Vesicles are small spheroidal packages that bud off the RER and Golgi apparatus

Carry proteins produced by ribosomes on RER to Golgi apparatus
–> prepared for export from cell via another vesicle

Question 16

EXOCYTOSIS

Answer 16

The fluidity of membranes allow materials to be released
“Release of substances from a cell (secretion) where a vesicle fuses with the cell plasma membrane”

Used to remove waste products

Question 17

ENDOCYTOSIS

Answer 17

The fluidity of membranes allows materials to be taken into cells

“Taking in of external substances by an inward pouching of the plasma membrane, forming a vesicle”

To form a vesicle a small region of plasma membrane is pulled from the rest and pinched off

Placenta: protein/ antibodies from mother’s blood absorbed into foetus by endocytosis

Question 18

VESICLE

Answer 18

Small sac of membrane with droplet of fluid inside

Question 19

Preventing osmosis in excised tissue and organs

Answer 19

Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis

Isotonic saline solution useful for preventing damage to cells and tissues + donor organ transportation

Question 20

Different osmosis states

Answer 20

Hypertonic sol - plasmolysed cell: more water leaving

Isotonic sol - flaccid cell equilibrium

Hypotonic sol- turgid cell more in