What type of protein can create a channel that does not require ATP for function?

The type of protein that creates a channel allowing substances to pass through a membrane without needing ATP for energy is best represented by channel proteins. These proteins facilitate the passive transport of molecules such as ions or water across the cell membrane, utilizing concentration gradients rather than energy input.

Channel proteins are specifically designed to form pores in the membrane, permitting the free flow of specific ions or molecules when conditions are favorable. This process is a key part of cellular function, aiding in the maintenance of homeostasis without the expenditure of energy.

While beta barrel proteins can indeed function as channels, they are a specific type of channel protein found in the outer membranes of certain bacteria and organelles. The broader definition and function of channel proteins encompass several forms, including those that may not exactly fit the beta barrel structure but still operate without ATP, making 'channel protein' the more encompassing and correct choice in this context.

In contrast, active transport proteins require ATP because they move substances against their concentration gradient, and single-pass trans-membrane proteins typically do not form channels necessary for this passive function.