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Photosynthesis

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

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Photosynthesis

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  1. Photosynthesis Chapter 8

  2. Where does all of our energy come from?

  3. 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!

  4. 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)

  5. Who helped us figure this out? • Van Helmont (1600s)—experiment with potted plant to determine what a plant uses to grow.

  6. Conclusion: mass of tree comes from water He got it only half right: there is also CO2!

  7. Who helped us figure this out? • Joseph Priestly (1770s) experiment with candle, sprig of mint and a jar

  8. 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

  9. 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

  10. THE FORMULA • CO2 + 6H20 + light C6H12O6 chlorophyll enzymes • Seems simple, huh? • Takes EIGHTY different chemical reactions from start to finish

  11. 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

  12. What are the pigments • Two main ones • Chlorophyll a and Chlorophyll b • Other accessory pigments • Absorb other wavelengths of light • Carotenoids, xylophylls, anthocyanin

  13. Light • White light is a mixture of all the wavelengths of visible light • Color is all about the reflection of light

  14. Absorption and Reflection • Chlorophyll absorbs red/blue light the best • It mostly reflects green light • THIS IS WHY PLANTS ARE GREEN!

  15. Why do the leaves change? • When [water] is low, plant pigments break down • Mostly green pigment, that goes away first

  16. ATP • When chlorophyll absorbs light, it is absorbing energy • It stores it in the bonds of Adenosine Triphosphate (ATP)

  17. ATP ATP • Made of • Adenine (nitrogenous base) • Ribose (5 carbon sugar) • 3 phosphate groups • This is temporary storage ADP AMP

  18. ATP • Is constantly made and broken down • Think of ATP like cash in your pocket • Glucoselike an ATM card • Glycogenlike your savings account • Lipidslike a Savings Bond

  19. ATP v ADP

  20. 2 Main steps of PS • Light reactions—occurs only in the presence of light • Occurs in the grana (thylakoids) of the chloroplasts • Also known as Photolysisbecause light is used to split water molecules into hydrogen and oxygen

  21. 2 Main steps of PS • Dark Reactions—can occur in light or darkness. Follows light reactions • Occurs in the stroma of the chloroplasts • Also known as Carbon fixationbecause CO2 will get “fixed up” with the hydrogens and energy from the light reaction

  22. Photosynthesis Overview

  23. Light Reactions • The light energy strikes the leaf, passes into the leaf and hits a chloroplastinside 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.

  24. The Dark Reactions • The hydrogen is taken to the stroma along with the grana'sremaining 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.

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