Which of the following describes the movement of substances across a cell membrane without using energy?

The movement of substances across a cell membrane without using energy is characterized as passive transport. This process occurs naturally as molecules move from areas of higher concentration to areas of lower concentration, following the concentration gradient. This movement does not require the input of metabolic energy, as it relies solely on the kinetic energy of the molecules themselves.

Passive transport encompasses several mechanisms, including simple diffusion, facilitated diffusion, and osmosis. While facilitated diffusion is a specific form of passive transport that involves the assistance of transport proteins in moving molecules across the membrane, the broader term 'passive transport' correctly encompasses all types of movement that occur without energy expenditure.

Active transport and exocytosis, on the other hand, involve the use of energy. Active transport requires ATP to move substances against their concentration gradient, and exocytosis utilizes energy for the process of vesicle fusion with the cell membrane to expel substances from the cell. Thus, the emphasis on a lack of energy usage firmly aligns with passive transport as the correct answer.