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Photosynthesis 7th grade science All cells need energy to carry out their functions, such as making proteins and transporting substances into and out of the cell www.kidslu.com/science/mitoch ondria.php Plants and other organisms such as algae and some bacteria, use energy in sunlight to make their own food Photosynthesis – the process by which a cell captures energy in sunlight and uses it to make food Nearly all living things obtain energy either directly or indirectly from the energy of sunlight captured during photosynthesis http://citruscollege.com/apps/pub.asp?Q=847 Grass obtains energy directly from the sunlight because it makes its own food through photosynthesis. Then the zebra eats the grass; it gets energy that has been stored in the grass. Lastly, the lion gets energy that has been stored in the zebra – the zebra and lion obtain the sun’s energy indirectly An organism that can make its own food is called an autotroph and an organism that cannot manufacture its own food is called a heterotroph http://creationwiki.org/File:Chemosynthesis.jpg The Two Stages of Photosynthesis! During photosynthesis, plants and some other organisms use energy from the sun to convert carbon dioxide and water into oxygen and sugars http://www.emaki.net/blog/2007/03/photosynthesis.html Stage 1: Capturing the Sun’s Energy This process occurs mostly in the leaves – the green color comes from the pigments, which are colored chemical compounds that absorb light (chloroplasts are the green organelle inside plant cells) The main photosynthetic pigment in chloroplasts is chlorophyll! Stage 2: Using Energy to Make Food Next, the cell uses the captured energy to produce sugars - the cell needs two raw materials for this stage – Water (H2O) & Carbon Dioxide (CO2) 1. The root absorbs water from the soil 2. Then the water moves up through the plant’s stem to the leaves 3. Carbon Dioxide enters the plant through the small openings on the underside of the leaves called the stomata 4. Once in the leaves, the water and carbon dioxide move into the chloroplasts www.windowtothe garden.com/thepla nt.html Inside the chloroplasts, the H2O and CO2 undergo a complex series of chemical reactions – the rxns are powered by the energy captured in the first stage!! H2O + CO2 ………………. sunlight …… O2 + C6H12O6 Oxygen (O2) and Six-carbon sugars (C6H12O6) are produced! Almost ALL of the oxygen in the Earth’s air was produced by living things through the process of photosynthesis! 6 CO2 + Carbon Dioxide Reactants Light Energy 6 H2O ---> C6H12O6 + Water A Sugar products 6 O2 Oxygen Six molecules of carbon dioxide and six molecules of water, when “powered by sunlight” yield a molecule of sugar (sometimes called starch or glucose) and six molecules of the element oxygen. A look at things to come…….