No additional energy is required because every particle has its own energy. This energy produces random movements in particles known as Brownian motion. The plasma membrane is semi-permeable, simple diffusion allows particles that are small enough to fit through the phospholipids and non polar so that they are not repelled by the hydrophobic centre of the membrane.
Uses membrane proteins to facilitate the transport of particles that cannot move by simple diffusion: Large and/or polar These transport proteins span the phospholipid layer but only allow specific molecules through.
Transport proteins called protein pumps use energy (ATP) to move particles against their concentration gradient, from a low concentration gradient to a high concentration. However, they move only specific particles in a specific direction.
Sodium Potassium Pump
Carrier protein that pumps 3 sodium ions outside the cell while pumping 2 potassium ions inside. The pump is called an antiporter because it pumps Na and K ions in opposite directions. Energy required to move the pump is obtained from the hydrolysis of ATP into ADP. The pump is referred to as Na+/K+ATPase because it catalyses the hydrolysis of ATP. One ATP provides energy to move 3Na+ ions and 2K+ ions.