Question

which mechanism requires energy?
osmosis
diffusion of ions through a potassium channel
diffusion of oxygen into a red blood cell
exocytosis

Explanation:

• Osmosis is the passive movement of water across a semi - permeable membrane.
• Diffusion of ions through a potassium channel and diffusion of oxygen into a red blood cell are passive transport processes (facilitated diffusion and simple diffusion respectively), which do not require energy as they move substances down their concentration gradients.
• Exocytosis is an active process. In exocytosis, vesicles fuse with the plasma membrane to release their contents (such as neurotransmitters, hormones etc.) outside the cell. This process requires energy (usually in the form of ATP) to form vesicles, move them to the membrane and fuse them.

Answer:

exocytosis