Passive transport is a fundamental biological process that allows substances to move across cell membranes without the need for energy input. This is primarily due to the natural concentration gradient that exists in the environment. Substances tend to move from areas of higher concentration to areas of lower concentration, a process known as diffusion.
In passive transport, molecules such as oxygen, carbon dioxide, and certain ions can easily pass through the phospholipid bilayer of cell membranes. This movement occurs spontaneously, as the system seeks to achieve equilibrium. Since the energy from the environment (in the form of kinetic energy) is already present, no additional energy is required from the cell to facilitate this process.
Additionally, passive transport includes methods like facilitated diffusion, where specific proteins in the membrane help transport molecules across, still without requiring energy. In essence, passive transport relies on the natural inclination of molecules to move toward balance, making it an energy-efficient way for cells to manage their internal environment.