1.4: Membrane Transport

Question 1

1.4.U1 Describe simple diffusion

Answer 1

Diffusion: net movement of molecules from areas of higher concentration to areas of lower concentration without the input of energy (passive).

Question 2

1.4.U1 Describe two examples of simple diffusion of molecules into/out of cells

Answer 2

• Gas exchange by diffusion in lung alveoli cells
• Gas exchange by diffusion through eye cornea cells

Question 3

1.4.U1 Outline factors that regulate the rate of diffusion

Answer 3

• concentration of the diffusing molecule… increase concentration, increase diffusion rate
• temperature… increase temperature, increase diffusion rate
• pressure… increase pressure, increase diffusion rate

Question 4

1.4.U1 Describe facilitated diffusion

Answer 4

Movement of molecules from higher to lower concentration through a channel protein without input of energy.

Question 5

1.4.U1 Describe one example of facilitated diffusion through a protein channel

Answer 5

The CFTR channel moves chloride ions from higher concentration inside the cell to areas of lower concentration outside the cell.

Question 6

1.4.U1 Define osmosis

Answer 6

The movement of water by diffusion across a membrane. Water moves from areas of high water potential, to areas of low water potential.

Question 7

1.4.U1 Predict the direction of water movement based upon differences in solute concentration

Answer 7

Water moves from hypotonic solutions (dilute, high water potential) into hypertonic solutions (concentrated, low water potential).

Question 8

1.4.U1 Compare active transport and passive transport

Answer 8

Active__Passive

Requires energy input Does not require energy

Against the concentration gradient with the concentration from [low] to [high] gradient from [high] to [low]

Question 9

1.4.U1 Describe one example of active transport of molecules into and out of cells through protein pumps

Answer 9

Pumps are proteins that actively transport other molecules using ATP as an energy source. Example: proton pump, NA⁺/K⁺ pump

Question 10

1.4.U2 Describe the fuid properties of the cell membrane and vesicles

Answer 10

Fluidity refers to the viscous flow of phospholipids in the cell membrane and organelles of the endomembrane system (including vesicles). Fluidity is affected by:

• fatty acid length
• fatty acid saturation
• presence of cholesterol

Question 11

1.4.U2 Explain vesicle formation via endocytosis

Answer 11

In endocytosis, the cell actively transports molecules into the cell by engulfing them into vesicles fromed through cell membrane capture and fusion

Question 12

1.4.U2 Outline two examples of materials brought into the cell via endocytosis

Answer 12

• White blood cells can engulf bacteria when fighting infection
• Single-celled organisms like Amoeba can engulf bacteria as food source

Question 13

1.4.U2 Describe release of materials from cells via exocytosis

Answer 13

A secretory vesicle moves towards the cell membrane, fuses with the membrane and releases the contents into the extracellular space.

Question 14

1.4.U2 Outline two examples of materials released from a cell via exocytosis

Answer 14

• secretion of neurotransmitter at synaptic terminus
• secretion of digestive juices from exocrine glands

Question 15

1.4.U3 List two reasons for vesicle movement

Answer 15

Transport vesicles can move molecules between locations inside the cell (e.g. proteins from the ER to the Golgi)

Secretory vesicles can move molecules inside the cell to the outside of the cell (e.g. to dispose of waste or secrete a protein)

Question 16

1.4.U3 Describe how organelles of the endomembrane system function together to produce and secrete proteins

Answer 16

1. ​Transcription of DNA, creating mRNA - in nucleus
2. Translation of mRNA at the ribosome on the rough ER, creating a protein
3. Packaging of the protein into a transport vesicle
4. Transportof the protein inside the vesicle to the Golgi
5. Modify the protein within the Golgi
6. Secrete the protein when the vesicle fuses with the cell membrane during exocytosis

Question 17

1.4.U3 Outline how phospholipids and membrane bound proteins are synthesised and transported to the cell membrane

Answer 17

Phospholipid molecules are synthesised at the endoplasmic reticulum. The phospholipids become part of the ER…remember the ER is part of the ENDOMEMBRANE system, so it too is made of phospholipids. When a transport vesicle buds off the ER, the newly made phospholipids can be part of the vesicle. There might also be proteins (made at a bound ribosome on the rough ER) that embed in the vesicle. As the vesicle moves through the cell towards the Golgi, the new phospholipids and embedded protein are also transported. They will fuse with the Golgi, bud off as a secretory vesicle and move towards the cell membrane. When the secretory vesicle fuses with the cell membrane, the new phospholipids and embedded proteins become part of the cell membrane.

Question 18

1.4.A1 Describe the structure of the sodium-potassium pump.

Answer 18

The sodium-potassium pump is an integral transmembrane protein found along the axons of neurons.

Question 19

1.4.A1 Describe the role of the sodium-potassium pump in maintaining neuronal resting potential.

Answer 19

The nerve impulse involves the rapid diffusion of sodium and potassium through ion specific channels. In order for this to occur, a concentration gradient across the membrane must be established and maintained. This is done through active transport of both sodium and potassium. The sodium-potassium pump is responsible for this process.

Question 20

1.4.A1 Outline the six steps of sodium-potassium pump action

Answer 20

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 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.
6. The interior of the pump opens to the

Question 21

1.4.A2 Explain what happens to cells when placed in different solutions with different osmolarities

Answer 21

• In an isotonic solution an equal amount of water enters and leaves the cell via osmosis.
• In a hypertonic solution there is a net movement of water out of the cell. Animal cells shrivel and plant cells become plasmolysed.
• In a hypotonic solution there is a net movement of water into the cell. Animal calls will swell and may lyse (burst). Plant cells will become turgid with the vacuole full of water and pressure on the cell walls.

Question 22

1.4.A2 Outline the use of normal saline in medical procedures

Answer 22

Normal saline is a solution of water and salt ions that is isotonic to human blood. It is used as an eye wash, to flush wounds and via I.V. (intravenous) to rehydrate patients. During organ transplant, the organs are bathed in normal saline. Because the solution is isotonic to body cells, the cells will not shrink or swell when exposed to the saline solution.

Question 23

1.4.S1 Define osmolarity

Answer 23

the concentration of solutes in a solution

Question 24

1.4.S1 Define isotonic, hypotonic and hypertonic

Answer 24

Isotonic - the osmolarity of two solutions is the same

Hypotonic - a solution with a lower osmolarity (less solutes) compared to another solution

Hypertonic - a solution with a higher osmolarity (more solutes) compared to another solution

Question 25

1.4.S1 Calculate the percent change between measurement values

Answer 25

Percent change = (final - initial)/initial x 100

Question 26

1.4.S1 Calculate the standard deviation of a data set

Answer 26

Question 27

1.4.S1 State that the term standard deviation is used to summarise the spread of values around the mean and that 68% of the values fall within one SD of the mean.