1.4 Membrane transport

Question 1

The phospholipid bilayer is

Answer 1

selectively permeable.

Question 2

Some molecules pass through easily (________________), or go through a “tunnel” (_____________-). Others need energy to get through (____________-).

Answer 2

simple diffusion, facilitated diffusion, active transport

Question 3

Large molecules use their own membrane to get through (_______________-).

Answer 3

endocytosis/exocytosis

Question 4

Polar heads:

Answer 4

attracted to other polar (charged) molecules

Question 5

Non-polar tails:

Answer 5

will repel any charged molecule, therefore preventing passage of ions through the membrane.

Question 6

Vesicles

Answer 6

small spheroidal packages that bud off of the rER and the Golgi apparatus

They carry proteins produced by ribosomes on the RER to the Golgi apparatus, where they are prepared for export from the cell via another vesicle

Question 7

Vesicles also allow the plasma membrane to

Answer 7

increase in a growing cell.

Question 8

Phospholipids and membrane proteins are

Answer 8

synthesized and become inserted into the rER membrane.

Question 9

When vesicles bud off the rER and join the plasma membrane,

Answer 9

the plasma membrane increases in area a little bit – this is also used to increase size of organelles.

Question 10

endocytosis

Answer 10

part of plasma pulled inwards

droplet of fluid is enclosed when vesicle pinches off

vesicle can then move through cytoplasm carrying their contents

Question 11

exocytosis

Answer 11

proteins are synthesized by ribsomes and then enter the rough ER

vesicles bud off the rough ER and carry the proteins to the golgi apparatus

golgi apparatus modifies proteins

vesicles bud off the golgi apparatus and carry the modified proteins to the plasma membrane

vesicles fuse with the plasma membrane.

contents of vesicles are expelled

membrane then flattens out again

Question 12

Endocytosis:

Answer 12

The taking in of external substances by an inward pouching of the plasma membrane, forming a vesicle

Question 13

Exocytosis:

Answer 13

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

Question 14

vesicle fuses with membrane during endocytosis and exocytosis by:

Answer 14

approaching the plasma membrane. all membranes are made of the phospholipid bilayer, so share the same properties.

The membranes begin to fuse. Remember the fluidity of the plasma membrane - the phospholipids can flow around each other.

For a moment, there is a single phospholipid bilayer a the point of contact.

The membrane pore opens, allowing the contents to pass through. Notice that throughout the whole process, there is never an unbroken section of the bilayer.

Question 15

Constitutive secretion

Answer 15

occurs continuously in cells, depending on their function

Question 16

Regulated secretion

Answer 16

is in response to a trigger e.g. the release of neurotransmitters

Question 17

types of endocytosis:

Answer 17

phagocytosis
- cell eating
- solids

pinocytosis
- cell drinking
- liquids/fluids

receptor-mediated endocytosis
- receptors involved
- coated vesicle
- coated pit

Question 18

Outline the key ideas of endocytosis

Answer 18

Mechanism whereby cells take in solids and/or solutions

Involve the formation of vesicles

Infolding of the cell membrane to surround the new contents

Called pinocytosis when fluids are taken into the cell

Called phagocytosis when organisms/food particles (solids) are engulfed

May be receptor mediated

Question 19

diffusion

Answer 19

passive net movement of particles from areas of high concentration to low concentration. often through a permeable membrane

Question 20

Solutions consist of a

Answer 20

solute (e.g. salt) dissolved in a solvent (e.g. water)

Question 21

Concentration is the measure of the amount of

Answer 21

solute in the solution.

Question 22

passive

Answer 22

does not require energy

Question 23

net movement

Answer 23

overall movement of particles

Question 24

concentration gradient

Answer 24

the difference of concentrations of a substance in two locations

Question 25

factors affecting rate of diffusion

Answer 25

• SA
• length of diffusion pathway
• concentration gradient

Question 26

maximising surface area for absorption

Answer 26

1. alveoli in lungs
2. membrane folds in mitochondria and in cristae in chloroplasts
3. root hairs for mineral ion uptake
4. villi for absorption of food molecules

Question 27

reducing length of diffusion path

Answer 27

1. membranes are very thin
2. folded membranes increase SA:V ratio
3. more membrane in smaller volume = shorter distances that molecules need to diffuse

Question 28

Osmosis

Answer 28

the passive net movement of water molecules from an area of low [SOLUTE] to high [SOLUTE] through a selectively permeable membrane.

Question 29

Water molecules pass through the cell membrane from an area of

Answer 29

low [solute] to one of high [solute].

Question 30

Water can pass through the cell membrane even though it is hydrophilic because.,…

Answer 30

it is small.

Question 31

Aquaporin

Answer 31

an integral protein that, as its name suggests, acts as a pore in the membrane that speeds the movement of water molecules

Question 32

Osmolarity

Answer 32

the measure of the concentration of a solute inside of a fluid or a cell.

Question 33

Cells can be in three types of osmotic environments (solutions):

Answer 33

hypotonic
- low osmolarity
- net water gain
- solute concentration higher in cell
- water moves into cell

hypertonic
- high osmolarity
- net water loss
- solute concentration higher outside cell
- water moves out of the cell

isotonic
- same osmolarity
- no net gain or loss

Question 34

The importance of osmotic control preventing damage to cells and tissues
Common medical procedures in which an isotonic saline solution is useful:

Answer 34

fluids introduction to a patient’s blood system via an intravenous drip, e.g for rehydration
used to rinse wounds, skin abrasions etc.
keep areas of damaged skin moist before applying skin grafts
eye drops/wash
frozen ice used pack donor organs for transportation

Question 35

Facilitated diffusion

Answer 35

the passive net movement of molecules from an area of high concentration to an area of low concentration through a selectively permeable membrane with the help of protein channels.

Large and polar molecules can’t get across the membrane via simple diffusion.

Question 36

Transmembrane (polytopic) proteins recognise…

Answer 36

a particular molecule and help it to move across the membrane.

Question 37

Cells can control which types of channel proteins are synthesized and placed in the plasma membrane –

Answer 37

this is how they can control which substances diffuse in and out.

Question 38

Active transport

Answer 38

the active net movement of molecules from an area of low concentration to an area of high concentration (against the concentration gradient). This process requires ATP (energy).

Question 39

Integral protein pumps

Answer 39

use the energy from the hydrolysis (splitting) of ATP to move ions or large molecules across the cell membrane.

Question 40

uniport

Answer 40

transport of only one molecule, without coupling to the transport of another molecule or ion.

Question 41

symport

Answer 41

the type of transport in which two different molecules can move through a membrane in same direction by using a common carrier mechanism.

Question 42

antiport

Answer 42

the coupled transportation of two different molecules or ions passing through a membrane in opposite directions

Question 43

Potassium channels in axons are…

Answer 43

voltage gated. They enable the facilitated diffusion of potassium out of the axon

1. At one stage during a nerve impulse there are relatively more positive charges inside.
2. This voltage change causes potassium channels to open, allowing potassium ions to diffuse out of the axon.
3. Once the voltage conditions change the channel rapidly closes again.

Question 44

The sodium–potassium pump

Answer 44

follows a repeating cycle of steps that result in three sodium ions being pumped out of the axon (of neurons) and two potassium ions being pumped in. Each time the pump goes round this cycle it uses one ATP. The cycle consists of these steps:

1. The interior of the pump is open to the inside of the axon; three sodium ions enter the pump and attach to their binding sites.
2. ATP transfers a phosphate group from itself to the pump; this causes the pump to change shape and the interior is then closed.
3. The interior of the pump opens to the outside of the axon and the three sodium ions are released.
4. Two potassium ions from outside can then enter and attach to their binding sites.
5. Binding of potassium causes 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.
6. The interior of the pump opens to the inside of the axon and the two potassium ions are released. Sodium ions can now enter and bind to the pump again (#1).

Question 45

Estimation of osmolarity

Answer 45

a simple lab with many possible variations.

This is an ideal opportunity to practise and improve your understanding of the following IA criteria:
Analysis
Evaluation
Communication
Taking accurate measurements