Unit 1

Diffusion

 Diffusion is important to all living organisms as it allows important substance to pass into and out cells. In unicellular organisms oxygen is constantly diffusing into the cell as it uses it up, and carbon dioxide is constantly diffusing out. Diffusion is also important to multicellular organisms. Blood is used to carry gases around the body. This blood picks up and loses the gases in the lungs of mammals. In the lungs oxygen diffuses into the blood. When this blood reaches the tissues, the oxygen diffuses into the tissue cells from the blood. In the tissues the oxygen is used up in respiration and carbon dioxide is produced. In the tissues carbon dioxide diffuses from the tissue cells into the blood. When this blood reaches the lungs, the carbon dioxide diffuses into the air sacs and this air is then breathed out. Osmosis Osmosis is a special type of diffusion.  If we always think of the water concentration, we can easily explain what happens in terms of osmosis. A hypotonic solution will…