The document discusses gas exchange and respiration. It explains that respiration is a series of oxidation reactions that take place in cells to release energy from organic compounds like glucose. Gas exchange is the process by which oxygen enters cells and carbon dioxide is removed, which is driven by the constant demand for oxygen and release of carbon dioxide from respiration. Special surfaces in animals and plants, like lungs, gills and leaves, have evolved to promote the diffusion of gases and act as gas exchange surfaces. These surfaces have a large area, are thin, and are moist to aid diffusion of gases in and out.

1. AS Level Biology Lesson 2

2. Gas exchange and respiration If cells are to stay active, grow and divide they need energy . This energy comes from the oxidation of organic molecules such as glucose in respiration . All respiration involves oxidation reactions, all cells must have a constant supply of oxygen.

3. Respiration A series of oxidation reactions taking place in all living cells. It results in the release of energy from organic compounds such as glucose.

4. Gas exchange … ..is not the same as respiration! Process by which oxygen gets into cells and carbon dioxide is removed. Respiration creates the constant demand for oxygen and a constant release of carbon dioxide.

5. Gas exchange surfaces Special surfaces the animals and plants have evolved to promote the exchange of gases. allow the diffusion of gas into and out of cells These surfaces include mesophyll layers in leaves, skin in earthworms, gills in fish and lungs in mammals.)

6. Features of gas exchange surfaces Have a large surface area relative to the volume of the organism. They are thin, so have a short diffusion pathway. They have a moist surface where gases can dissolve first before they diffuse in our out. They are able to maintain the diffusion gradient down which the gases can diffuse.

7. Gas exchange in humans Humans have a high metabolic rate so require a fast rate of gas exchange. To help with this there are two key feature that have evolved in the human system: A blood transport system with red cells containing haemoglobin A means of ventilation to get the gases to and from the gas exchange surface.