Question

Consider the following statements with reference to facilitated diffusion:
(a) Requires ATP energy
(b) Transport saturates
(c) Highly selective
(d) Requires special membrane protein
(e) Uphill transport
Out of the above statements:

• A. a, b and c are relevant but d and e are irrelevant
• B. b, c and e are relevant but a and d are irrelevant
• C. c, d and e are relevant but a and b are irrelevant
• D. b, c and d are relevant but a and e are irrelevant

Answer 1

The correct option is D b, c and d are relevant but a and e are irrelevant

Facilitated diffusion is a type of passive transport (no energy required) which requires special type of membrane proteins to carry different molecules or ions accross the membrane along from high concentration to low concentration. These proteins tend to be selective and associate with a few select molecules or ions. Since, there is a limited quantity of such transport proteins, the degree to which they can be occupied is also limited. This can lead to saturation (full occupancy) if the concentration of the molecules or ions to be transported is extremely high.
Thus, facilitated diffusion is highly selective, does not require energy and a type of downhill transport (movement of molecules or ions occur from high concentration to low concentration). It also requires special membrane proteins and saturation can occur during transportation in this process.
Uphill transport is the movement of molecules or ions from low concentration to high concentration.
Accordingly, option b, c and d are relevant but a and e are irrelevant.