(15 points! ) 1.)how does passive transport occur if the cell doesn’t expend any energy? 2.) how do transport proteins move molecules against a concentration gradiant in active transport? 3.) how do endocytosis and exocytosis utilize the plasma membrane of a cell?

1. Some substances passes through small holes in the surface cell membrane. This is called diffusion and does not require cell to expend energy.In this way the passive transport occur if the cell doo not expend any energy. 2.In active transport,the particles move across the cell membrane from slower concentration to higher concentration . Active transport is the energy requiring process of pumping molecules and ions across membranes uphill against a gradient.This process uses the energy of ATP. 3. Endocytosis and Exocytosis are important mechanisms for bringing substances into and out of a cell.The vesicles fuse with the plasma membrane ,causing the contents of the vesicles to spill outside the cell.