What term describes the diffusion of a substance across a biological membrane without the use of energy?

The term that describes the diffusion of a substance across a biological membrane without the use of energy is passive transport. This process relies on the concentration gradient, meaning substances move from areas of higher concentration to areas of lower concentration until equilibrium is reached. Since this movement occurs naturally and does not require cellular energy in the form of ATP, it falls under the umbrella of passive mechanisms.

In biological systems, passive transport is essential for maintaining cellular homeostasis. For example, oxygen and carbon dioxide often pass through cell membranes via passive transport, allowing cells to uptake essential gases and expel waste efficiently.

Other processes mentioned do involve energy or additional mechanisms. Active transport, for instance, requires energy to move substances against their concentration gradient. Facilitated diffusion utilizes specific transport proteins to help substances cross the membrane but still operates under the principles of passive movement. Endocytosis is an entirely different process where the cell engulfs substances, which also demands energy.

Understanding passive transport and its role in cellular function is crucial for grasping how cells interact with their environment and maintain internal balance.