What are the different ways in which substances can move across cell membranes?

Passive transport Diffusion = occurs in gases or aqueous solutions whereby particles are free to move and spread from a higher concentration to a lower concentration. An example is air freshener being sprayed in one part of a room (high concentration) and the scent spreading to other parts of the room (low concentration). Osmosis = occurs with molecules of water which also move from an area of a high concentration to that of a lower one, through a partially permeable membrane (only let SOME substances pass through). Active transport Movement of particles from a region of lower concentration to a region of higher concentration, using energy released from during respiration (ATP). Carrier proteins help with this. An example is the movement of glucose into the epithelial cells of the villi of the small intestine.