Cell Transport

Question 1

State Fick’s law [1 mark]

Answer 1

Rate of reaction = (surface area x difference in concentration) / diffusion distance

Difference in concentration = concentration gradient

Question 2

What’s the difference between carrier and channel proteins? [2 marks]

Answer 2

Carrier proteins…
change tertiary structure in order to transport substances.

Channel proteins…
do not change tertiary structure in order to transport substances.

Question 3

What are the similarities between carrier and channel proteins? [3 marks]

Answer 3

> Transports SPECIFIC substances across membrane.
Made of polypeptides.
Found in cell membrane.
Can be used for facilitated diffusion.
Can allow transport down the concentration gradient - high to low.

Question 4

Name and explain 3 factors that affect membrane permeability?

Answer 4

> Temperature =
high temperature denatures membrane proteins - phospholipid molecules have more kinetic energy & move further apart.

> pH =
changes tertiary structure of membrane proteins.

> Use of a solvent =
may dissolve membrane.

Question 5

What are intrinsic proteins? Give examples.

Answer 5

Connects/spans from 1 side of phospholipid bilayer to the other.

E.G.
Channel proteins
Carrier proteins

Question 6

What are extrinsic proteins? Give examples.

Answer 6

Occur/embedded in the surface of phospholipid bilayer.

E.G.
Receptors

Question 7

Are small molecules polar or non-polar in terms of cell transport?

Answer 7

Non-polar

(think about it - a small molecule will barely have any charge)

Question 8

Are large molecules polar or non-polar in terms of cell transport?

Answer 8

Polar

(think about it - a large molecule will have a large difference in charge)

Question 9

State how small non-polar molecules and large polar molecules are transported [2 marks]

Answer 9

Small and non-polar —> via simple diffusion

Large and polar —> via facilitated diffusion

Question 10

What is meant by simple diffusion?

Answer 10

The NET movement of small/non-polar molecules through a membrane from a high to low concentration down the concentration gradient, until evenly distributed.

Question 11

What are examples of small, non-polar molecules?

Answer 11

Oxygen

Carbon dioxide

Question 12

What are examples of large, polar molecules?

Answer 12

Water

Ammonia

Question 13

What is meant by osmosis?

Answer 13

The movement of water through an area of high water potential to an area of low water potential down the concentration gradient through a partially permeable membrane.

Question 14

What is active transport?

Answer 14

The movement of substances across a membrane via a CARRIER PROTEIN from an area of low concentration to a high concentration against the concentration gradient.

Uses ENERGY from RESPIRATION / Hydrolysis of ATP.

Question 15

What is co-transport?

Answer 15

Movement of a substance against its concentration gradient coupled with the movement of another substance down its concentration gradient, across a cell membrane via a CARRIER PROTEIN

Question 16

What kind of process is simple diffusion?

Answer 16

A passive process

meaning it does not require energy from ATP hydrolysis

Question 17

What is facilitated diffusion?

Answer 17

The NET movement of large/polar substances through specific CHANNEL or CARRIER down the concentration gradient.

Question 18

What kind of process is facilitated diffusion?

Answer 18

A passive process

meaning it does not require energy from ATP hydrolysis

Question 19

Explain how channel proteins and carrier proteins work

Answer 19

Channel =
Hydrophilic channels bind to specific ions - 1 side of the protein closes & the other opens.

Carrier =
Binds to the complementary molecule - releases the molecule on the other side of membrane.

Question 20

What kind of process is active transport?

Answer 20

Active process

ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape.

Question 21

Compare and contrast active transport and facilitated diffusion.

Answer 21

BOTH =
> May involve carrier proteins.’

Active transport =
> Active process - requires energy from ATP hydrolysis
> Against conc gradient

Facilitated diffusion =
> Passive process
> May also involve channel proteins.
> Down conc gradient

Question 22

Explain how co-transport is involved in the absorption of glucose/ amino acids in the small intestine.

Ileum / Lumen (inside of intestine) —– Epithelial cells (villi) —— capillary (bloodstream)

Answer 22

1) Na+ actively transported out of epithelial cells & into bloodstream.

2) Na+ concentration lower in epithelial cells than lumen of gut.

3) Transport of glucose/ amino acids from lumen to epithelial cells is ‘coupled’ to facilitated diffusion of Na+ down concentration gradient.

Question 23

Explain how co-transport is involved in the absorption of glucose/ amino acids in the small intestine. (long answer)

https://www.youtube.com/watch?v=zn9ypKnhQZA

Ileum / Lumen (inside of intestine) —– Epithelial cells (villi) —— capillary (bloodstream)

Answer 23

Na+ actively transported out of epithelial cells into bloodstream.

This reduces Na+ concentration in epithelial cells.

Na+ ions can facilitated diffuse from lumen down conc. gradient into epithelial cells.

Na+ diffuses through a co-transported protein, so glucose/amino acids attach and are transported to the epithelial cells against their conc. gradient.

Glucose/amino acids then move by facilitated diffusion from the epithelial cell to the blood.

Question 24

What does the sodium-potassium pump do in active transport?

Answer 24

A carrier protein that transports sodium out of and potassium into the cell as it repeatedly changes shape

Question 25

When preparing the cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm.

This did not cause the cells to burst but moved the chromosomes further apart in order to reduce the overlapping of the chromosomes when observed with an optical microscope.

Suggest how this procedure moved the chromosomes apart. [2 marks]

Answer 25

Water moves into the cells/cytoplasm by osmosis; [1]

Cell/cytoplasm gets bigger; [1]

Question 26

Students investigated the uptake of chloride ions in barley plants.

They divided the plants into two groups and placed their roots in solutions containing radioactive chloride ions.

Group A plants had a substance that inhibited respiration added to the solution.
Group B plants did not have the substance added to the solution.

The students calculated the total amount of chloride ions absorbed by the plants every 15 minutes.

Their results are shown in the figure below.

https://www.thestudentroom.co.uk/showthread.php?t=5985898

Explain the results shown in the figure above [4 marks]

Answer 26

Group A ― initial uptake slower because by diffusion (only);

Group A ― levels off because same concentrations inside cells and outside cells / reached equilibrium;

Group B ― uptake is faster because by diffusion AND active transport;

Group B ― fails to level off because uptake against gradient / no equilibrium to be reached;

Group B ― rate slows because fewer chloride ions in external solution / respiratory substrate used up.

(Group A only undergoes diffusion because limited respiration means less energy for AT)

Question 27

Students investigated the uptake of chloride ions in barley plants.

They divided the plants into two groups and placed their roots in solutions containing radioactive chloride ions.

Group A plants had a substance that inhibited respiration added to the solution.
Group B plants did not have the substance added to the solution.

The students calculated the total amount of chloride ions absorbed by the plants every 15 minutes.

Their results are shown in the figure below.

https://www.thestudentroom.co.uk/showthread.php?t=5985898

Calculate the ratio of the mean rate of uptake of chloride ions in the first hour to the rate of uptake of chloride ions in the second hour for group B plants. [2 marks]

Answer 27

First hour : Second hour

______________ : 1

(470–360) / 60 for rate in second hour [1] - change in y / change in x

= 3.3 [1]

RATIO

3.3:1

OR

1st hour:
Rate of uptake = 360 chloride ions per 60 minutes = 6 ions per minute

2nd hour:
Rate of uptake = (470 - 360) chloride ions per (120 - 60) minutes = 110 ions per 60 minutes = 1.833… ions per minute

Ratio of first hourly rate to second hourly rate:
6 : 1.833… = 6/1.833… : 1.833…/1.833… = 3.2727… : 1.000 ≈ 3.3 : 1

Question 28

Putting bee honey on a cut kills bacteria. Honey contains a high concentration of sugar.

Use your knowledge of water potential to suggest how putting honey on a cut kills bacteria. [3 marks]

Answer 28

Water potential in (bacterial) cells higher(than in honey) / water potential in honey lower(than in bacterial cells); [1]

Water leaves bacteria / cells by osmosis; [1]

(Loss of water) stops (metabolic) reactions [1]

Question 29

Give two ways in which active transport differs from diffusion [2 marks]

Answer 29

1)
> Diffusion is down the conc. gradient
> AT is against the conc. gradient

2)
> AT requires energy from ATP hydrolysis (active process)
> Diffusion does not require energy from ATP hydrolysis (passive process)

Question 30

Contrast the processes of facilitated diffusion and active transport [3 marks]

Answer 30

1)
> FD uses both carrier and channel proteins
> AT uses ONLY carrier proteins

2)
> AT requires energy from ATP hydrolysis (active process)
> FD does not require energy from ATP hydrolysis (passive process)

3)
> FD is can go in any direction of the conc. gradient
> AT is against the conc. gradient