Which process is specifically described as requiring no energy for movement across membranes?

The process that is specifically characterized by the movement of molecules across membranes without the need for energy is diffusion. This includes both simple diffusion and osmosis, which is a specific type of diffusion involving water molecules.

Osmosis refers to the movement of water across a selectively permeable membrane, from an area of lower solute concentration to an area of higher solute concentration, also occurring without the input of energy.

Diffusion is the broader term that describes the natural movement of molecules from an area of higher concentration to an area of lower concentration, also facilitated by concentration gradients and not requiring energy.

Facilitated diffusion, while also a passive transport mechanism, does involve the assistance of protein channels or carriers to help large or polar molecules cross the membrane. However, it remains a form of passive transport since it still does not require energy (ATP).

Thus, it is accurate to encompass all these processes under passive transport mechanisms that do not require energy, leading to the assertion that all these processes are included in the correct answer.