Final answer:
Facilitated diffusion is a passive process using carrier proteins to move substances down a concentration gradient without ATP, whereas active transport requires ATP to move substances against the gradient. The correct answer is option 1) Facilitated diffusion.
Step-by-step explanation:
The primary modes of substance transport across cell membranes are facilitated diffusion and active transport. Facilitated diffusion is a type of passive transport in which substances move through the membrane from an area of higher concentration to an area of lower concentration using carrier proteins, without the need for cellular energy (ATP).
On the other hand, active transport involves moving substances against their concentration gradient, from lower to higher concentration, which requires energy in the form of ATP.
c. The statement that facilitated diffusion works in the same direction as active transport is not accurate. Facilitated diffusion works down the concentration gradient, while active transport works against it.
d. The statement "Not all membranes are amphiphilic" is not directly applicable to either facilitated diffusion or active transport. Amphiphilic refers to the chemical property of a molecule that has both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts. Cell membranes are typically amphiphilic, which is crucial for their function, but this property does not determine the mode of transport.
To summarize, facilitated diffusion is associated with passive movement down a concentration gradient without energy, while active transport requires energy to move substances against the gradient.