transport in cells

• diffusion is the movement of particles from an area of high concentration to an area of low concentration
• substances moved in and out of cells by difusion are oxygen, carbondioxide (during gas exchange), and urea which moves out of cells into the blood for excretion by the kidney
• factors which effect the rate of diffusion- temperature, difference in concentration, surface area of cell membrane
• the effectiveness of an exchange surface is increased by - having a short diffusion path, having a large surface area, (in animals) having a good blood supply
• osmosis- the movement of water molecules from a dilute concentration to a region of high concentration through a partially permeable membrane
• active transport- movement of molecules from a low concentration to a high concentration. Requires energy from respiration