What is the difference between passive and active transport across cell membranes?

Passive transport occurs without the use of energy, while active transport requires energy.

Passive transport is the movement of molecules across a cell membrane from an area of high concentration to an area of low concentration. This process occurs naturally and does not require the cell to use energy. There are three types of passive transport: diffusion, osmosis, and facilitated diffusion. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. Osmosis is the diffusion of water across a selectively permeable membrane. Facilitated diffusion is the movement of molecules across a membrane with the help of a protein channel.

Active transport, on the other hand, requires energy to move molecules across a cell membrane. This process occurs against the concentration gradient, meaning that molecules are moved from an area of low concentration to an area of high concentration. There are two types of active transport: primary active transport and secondary active transport. Primary active transport uses energy from ATP to move molecules across the membrane. Secondary active transport uses the energy from the movement of one molecule to move another molecule against its concentration gradient.

In summary, passive transport occurs naturally and does not require energy, while active transport requires energy to move molecules against their concentration gradient.