When does facilitated diffusion occur? -When one liquid has a higher osmotic pressure than the other.
-When certain large molecules are unable to move through the membrane
without the help of channel proteins.
-When ATP is available to assist in moving molecules.
-When there's a strong membrane potential present, with the inside of the cell
being more negative than the outside of the cell.

When certain large molecules are unable to move through the membrane without the help of channel proteins

Explanation:

Facilitated diffusion occurs when large molecules that are unable to pass through a membrane on their own make use of channel proteins to move from one side of the membrane to the other. Facilitated diffusion can occur when a liquid on one side of a membrane has a higher osmotic pressure than a liquid on the other side of the membrane, but it isn’t a required feature of facilitated diffusion. Similarly, facilitated diffusion can occur when there’s a large membrane potential present, but it isn’t a required feature of facilitated diffusion. Facilitated diffusion doesn’t require the use of energy, so the presence of ATP is irrelevant to facilitated diffusion occurring.

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