Modes of transport across the plasma membrane

Question 1

Define: active transport

Answer 1

the uptake of a substance across the phospholipid bilayer (through pump proteins) against its concentration gradient, requiring ATP.

Question 2

HOw many moelcules per pump?

Answer 2

1-2

Question 3

How do pumps undergo a shape change?

Answer 3

MOlecule binds to it, shape change, pushes to other side.

Question 4

Enzyme function of pumps?

Answer 4

catalyse the breakdown reaction of ATP -> ADP + Pi + energy

Question 5

Define: bulk transport

Answer 5

the movement of very large substances onto or out of the cell, requiring ATP.

Question 6

Define: endocytosis

Answer 6

the process of bulk transport of material into a cell.

Question 7

How does endocytosis work

Answer 7

The cell membrane flexes to entrap the particle, then engulfs/closes the particles within a vesicle.

Question 8

Define: phagocytosis

Answer 8

when a solid food particle is transported into the cell (most cells cannot do)

Question 9

Define: pinocytosis

Answer 9

when material in solution is transported into the cell

Question 10

Define: exocytosis

Answer 10

the process of bulk transport of material outside of a cell.

Question 11

how does exocytosis ork?

Answer 11

Vesicles fuse with the plasma membrane and contents are secreted (if valuable) or voided (if not) from the cell.

Question 12

Define: osmosis

Answer 12

the net movement of water molecules through a selectively permeable membrane from a region of lower solute concentration to one of higher concentration.

Question 13

Describe how water passes through the plasma membrane.

Answer 13

Though it is hydrophilic, it still can pass through the hydrophobic fatty acid tails but does so in limited amounts.
In larger amounts, it passes through proteins in the plb called aquaporins.

Question 14

Define: hypotonic solution

Answer 14

when a solution has a lower solute concentration than the (cytosol of the) cell placed within it.

Question 15

Animal cell and hypotonic solution.

Answer 15

Water molecules will move from hypotonic solution into the cell, causing it to lyse or burst (distilled water)

Question 16

plant cell in hypotonic solution?

Answer 16

Water molecules will move from hypotonic solution into the cell, causing it to become turgid but soon the cell will stop water coming in (fully turgid)

Question 17

Define: isotonic solution

Answer 17

when the solvent concentration of a solution is the same as the solute concentration of the cell (cytosol) placed in it.

Question 18

what will happen to cell in isotonic solution?

Answer 18

The same number of water molecules will diffuse into and out of the cell, and its shape will remain the same.

Question 19

Define: hypertonic solution

Answer 19

when a solution has a higher solute concentration than the cell (cytosol) placed in it.

Question 20

Describe animal cell in hypertonic solution.

Answer 20

From cytosol to hypertonic solution. Cell will crenate (shrink), and might see spikes from the cytoskeleton

Question 21

Describe plant cell in hypertonic solution

Answer 21

Cell will become plasmolysed (cell walls will cave in, membrane will shrink from wall, forming pockets.)

Question 22

Define: diffusion

Answer 22

the net movement of a substance, from a region of higher concentration to one of lower concentration.

Question 23

What does net mean?

Answer 23

Overall, as the particles are moving randomly.

Question 24

Is diffusion passive?

Answer 24

Yes

Question 25

When is the endpoint?

Answer 25

Equilibrium (equal conc on both sides however rare in bio as the products are usually being used up_

Question 26

Factors affecting rate of diffusion?

Answer 26

Temp (molecules move quicker so rod will be quicker)
Concentration (stepper the conc gradient, the faster)
Size and type (polar/non polar)
Surface area to volume ratio: lower size, higher sa:v and quicker rate of diffusion
permeability of membrane

Question 27

2 types of diffusion?

Answer 27

simple diffusion and faciliated diffusion

Question 28

Define: simple diffusion

Answer 28

movement of substances directly across the phospholipid bilayer from a region of higher concentration to one of lower concentration.

Question 29

Define: facilitated diffusion

Answer 29

the movement of substances through transporter proteins (channel/carrier) in the plasma membrane from a region of higher concentration to one of lower concentration

Question 30

2 types of transporter proteins?

Answer 30

Channel proteins and carrier proteins

Question 31

Define: channel protein

Answer 31

A transmembrane protein that contains an always open, water-filled pore. Bc water is hydrophilic other hydrophilic substances can pass through it.

Question 32

Are there separate channel proteins for charged and polar molecules?

Answer 32

Yes

Question 33

Define: carrier protein

Answer 33

a transmembrane protein to which a molecule binds to, and then it changes shape, enabling the molecule to pass through it.

Question 34

Are carrier proteins specific to one type of molecule?

Answer 34

Yes

Question 35

Describe rate of diffusion for simple diffusion

Answer 35

LInear. as concentration gradient increases, rate of diffusion increases

Question 36

Describe rate of diffusion for facilitated diffusion.

Answer 36

Non linear. As concentration gradient increases, rate of diffusion increases to a point but then goes steady as there are limited transporter proteins.

Question 37

movement of non polar molecules across the plb?

Answer 37

They can pass through the plb through simple diffusion, as they can dissolve in/aren’t repelled by the fatty acid tails.

Small molecules (Co2, O2, urea) can pass through pores in the plb. Large molecules still can.

Question 38

movement of polar/charged molecules across plb?

Answer 38

Note: small polar molecules (water, urea, ethanol) can pass, despite being polar, as they can fit through pores.

Large polar/charged particles can’t cross as they will be repelled by the hydrophobic fatty acid tails.

Ions pass through channel proteins.
Large charged molecules (amino acids and ATP?) pass through carrier proteins
Large polar molecules don’t move (glucose goes through carrier protein

Question 39

Describe how active transport maintains concentration gradients using an example.

Answer 39

Water needs to flow inside of a cactus. Salt is actively transported into the cactus, so that water flows from low concentration (outside of cactus cells) to high concentration (inside)