Topic 1.4 Membrane Transport

Question 1

Factors affecting rate of diffusion

Answer 1

Concentration gradient
Surface area
Length of diffusion path

Question 2

Osmosis

Answer 2

Osmosis may occur when there is a partially permeable membrane, such as acell membrane.
When a cell is submerged inwater, the water molecules pass through the cell membrane from an area of low solute concentration (outside the cell) to one of high solute concentration (inside the cell)

Question 3

Importance of osmotic control

Answer 3

Hypertonic: lacking water/ plasmolyzed/ threat of plasmolysis
Isotonic: neutral/ flaccid
Hypotonic: too much water/ turgid/ threat of cytolysis

Question 4

Types of diffusion

Answer 4

Simple diffusion
Facilitated diffusion
Osmosis
Active transport

Question 5

Facilitated Diffusion

Answer 5

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

Transmembrane (polytopic) proteins recognise a particular molecule and help it to move across the membrane. The direction it moves is dependent on the concentration gradient.

Question 6

Active Transport

Answer 6

• REQUIRES ATP
• Integral protein pumps use the energy from the hydrolysis of ATP to move ions or large molecules across the cell membrane.
• AGAINST CONCENTRATION GRADIENT

Question 7

Hydrolysis

Answer 7

The bond releases one phosphate and a lot of energy

Question 8

Function of sodium-potassium pumps

Answer 8

The sodium-potassium pump uses one ATP to transport 3 sodium ions out and two potassium ions in. ATP also transfers a phosphate group from itself to the pump which alters the shape of the pump closing the inside and releasing the sodium ions. The potassium ions then cause the pumps to release the phosphate group allowing the potassium ions in.

Question 9

Endocytosis and Exocytosis

Answer 9

Endocytosis: the taking in of external substances
Exocytosis: the release of substances