Which of the following is NOT a factor affecting facilitated diffusion?

Facilitated diffusion is a process that allows substances to cross membranes with the assistance of special proteins, typically in response to a concentration gradient. Several factors influence this type of diffusion, including the concentration gradient, the availability of transporters, and regulatory signals that may modulate the activity of these transport proteins.

The concentration gradient is a fundamental factor; facilitated diffusion occurs down this gradient, meaning that it relies on differences in concentration between the inside and outside of the cell to drive the movement of molecules. Transporter availability is equally crucial since facilitated diffusion requires specific transport proteins to assist in the movement of substances; if these transporters are not present in sufficient quantities, diffusion cannot occur effectively. Signal regulation involves various cellular mechanisms that may enhance or inhibit the activity of transporters, adjusting how substances move based on the cell's needs.

In contrast, temperature, while it does influence molecular movement and rates of diffusion in general, does not directly affect facilitated diffusion itself. This is because the process relies on specific transporter mechanisms that function based on the existing concentration gradient and regulatory mechanisms rather than purely on general conditions like temperature. Hence, it is the least relevant factor when specifically discussing facilitated diffusion.