Date: Monday, June 29 th 2015 Topic: Oxygen in Nature / Oxygen Cycle Objective: To fathom the importance of Oxygen and to identify the five stages of the Oxygen Cycle. CLASS # 5 – U2 OXYGEN IN NATURE / OXYGEN CYCLE Oxygen in Nature Oxygen occupies, approximately, the 21% of the atmosphere. It is the most important gas from the biological point of view, since it is used by living things to breathe. It may be found in its free form (O2) or form by other compounds, like Water (H2O) This gas comes from the Photosynthesis made by algae in the Hydrosphere and by green plants in the Lithosphere.

Oxygen Cycle The Oxygen Cycle is a chain of reaction that describe the circulation of the oxygen in the atmosphere, the hydrosphere, the lithosphere, and the biosphere, as shown below: photosynthesis breathing CO2 organic compounds in decomposition 1. It begins when plants absorb H2O and CO2 and make the Photosynthesis 2. Oxygen is released and goes back to Air and Water. 3. The O2 circulates among the living things. 4. The O2 is used to breathe (Respiration Process). 5. The terrestrial organisms release water vapor and CO2 that goes into the Carbon Cycle

Practice # 3 Answer the following questions: 1. Explain the importance of the Oxygen in Nature? 2. How many stages does the Oxygen Cycle have? Explain what happens in the third stage. 3. After what you have learned, how are Oxygen and Carbon connected?