Biology – 3.3 Active transport | e-Consult

Both active transport and facilitated diffusion involve the movement of particles across a cell membrane, but they differ significantly in their energy requirements and the mechanisms involved.

Facilitated diffusion is a type of passive transport. It involves the movement of molecules *down* their concentration gradient – from an area of high concentration to an area of low concentration. It does not require energy input. The movement is facilitated by carrier proteins or channel proteins embedded in the cell membrane. These proteins provide a pathway for the molecule to cross the membrane. The molecule simply diffuses through the protein, following the concentration gradient.

Active transport, as previously discussed, requires energy (ATP) to move molecules *against* their concentration gradient. It uses carrier proteins and the energy from respiration to power this movement.

A factor that can affect the rate of facilitated diffusion is the temperature. Increasing the temperature generally increases the rate of diffusion, as the molecules have more kinetic energy and move faster. However, excessively high temperatures can damage the cell membrane and denature the carrier proteins, reducing the efficiency of facilitated diffusion. Also, the concentration gradient itself is a key factor; a steeper gradient will lead to a faster rate of diffusion.