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Photosynthesis Chapter 8 Where does all of our energy come from? How do plants get food? Photosynthesis- Process by which green plants or organism with chlorophyll convert light energy into chemical energy in the bonds of carbohydrates Autotrophic – Can transfer energy to produce food – can synthesize food Heterotrophic – Must obtain energy from preformed food – gotta eat food! What is needed for autotrophs to photosynthesize? Carbon dioxide (atmospheric) Water (in the soil or air) Sunlight (or artificial light source) Chlorophyll (present in leaves and sometimes stems) Enzymes (to regulate the rate of the reaction) Who helped us figure this out? Van Helmont (1600s)—experiment with potted plant to determine what a plant uses to grow. Conclusion: mass of tree comes from water He got it only half right: there is also CO2! Who helped us figure this out? Joseph Priestly (1770s) experiment with candle, sprig of mint and a jar Who helped us figure this out? Ingen-Housz—repeated Priestley’s experiment but put the sprig of mint in the dark Candle would not burn for as long in the dark, so LIGHT is important for plants Putting it all together The experiments performed by van Helmont, Priestley, and Ingenhousz led to work by other scientists who finally discovered that in the presence of light, plants transform carbon dioxide and water into carbohydrates, and they also release oxygen THE FORMULA CO2 + 6H20 + light Seems chlorophyll enzymes C6H12O6 simple, huh? Takes EIGHTY different chemical reactions from start to finish Where does Photosynthesis happen? In the chloroplasts! Chloroplasts are oval structure consisting of stacks called grana (photosynthetic membranes) and a liquid called stroma. Chlorophyll is found in the stacked grana What are the pigments Two main ones Chlorophyll a and Chlorophyll b Other accessory pigments Absorb other wavelengths of light Carotenoids, xylophylls, anthocyanin Light White light is a mixture of all the wavelengths of visible light Color is all about the reflection of light Absorption and Reflection Chlorophyll absorbs red/blue light the best It mostly reflects green light THIS IS WHY PLANTS ARE GREEN! Why do the leaves change? When [water] is low, plant pigments break down Mostly green pigment, that goes away first ATP When chlorophyll absorbs light, it is absorbing energy It stores it in the bonds of Adenosine Triphosphate (ATP) ATP Made of Adenine (nitrogenous base) Ribose (5 carbon sugar) 3 phosphate groups ATP ADP This is temporary storage AMP ATP Is constantly made and broken down Think of ATP like cash in your pocket Glucose like an ATM card Glycogen like your savings account Lipids like a Savings Bond ATP v ADP 2 Main steps of PS 1. Light reactions—occurs only in the presence of light Occurs in the grana (thylakoids) of the chloroplasts Also known as Photolysis because light is used to split water molecules into hydrogen and oxygen 2 Main steps of PS 1. Dark Reactions—can occur in light or darkness. Follows light reactions Occurs in the stroma of the chloroplasts Also known as Carbon fixation because CO2 will get “fixed up” with the hydrogens and energy from the light reaction Photosynthesis Overview Light Reactions 1. 2. 3. 4. The light energy strikes the leaf, passes into the leaf and hits a chloroplast inside an individual cell. The light energy, upon entering the chloroplasts, is captured by the chlorophyll inside a granum. Inside the grana some of the energy is used to split water into hydrogen and oxygen. The oxygen is released into the air. The Dark Reactions 5. 6. 7. 8. 9. The hydrogen is taken to the stroma along with the grana's remaining light energy. Carbon dioxide enters the leaf and passes into the chloroplast. In the stroma the remaining light energy is used to combine hydrogen and carbon dioxide to make carbohydrates. This occurs during the Calvin Cycle The energy-rich carbohydrates are carried to the plant's cells. The energy-rich carbohydrates are used by the cells to drive the plant's life processes.
