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Photosynthesis

Photosynthesis. Unit 6 continued. We need energy. Energy is the ability to do work Most energy on earth comes from the sun Heterotrophs get energy by eating other organisms

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Photosynthesis

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  1. Photosynthesis Unit 6 continued

  2. We need energy • Energy is the ability to do work • Most energy on earth comes from the sun • Heterotrophs get energy by eating other organisms • Autotrophs make their own food and energy  photosynthesis = when they use the sun (light energy) as their energy source

  3. How do we store energy? • Chemical bonds are formed = energy is stored • Chemical bonds are broken = energy is released • Adenosine triphosphate (ATP) = main source of energy for cells, provides power for almost all functions • Contains adenine, ribose (5-carbon sugar), and 3 phosphate groups

  4. How do we store energy? • ATP = “charged” battery, stores energy • Energy is released by breaking off the last phosphate group  Adenosine diphosphate (ADP) • ADP = “dead” battery, energy has been released

  5. How does photosynthesis work? • Plants use the energy from the sun to convert water and carbon dioxide into oxygen and glucose (sugar) • Joseph Priestly – discovered that plants make oxygen. He placed a lit candle under a jar and waited until it had consumed all the oxygen. He discovered that if he placed a sprig of mint in the jar and waited a few days, the candle could be lit again, indicating that the plant produced oxygen.

  6. Photosynthesis equation • 6CO2 + 6H2O light> C6H12O6 + 6O2 • Carbon dioxide + water light> glucose + oxygen • Carbon dioxide, water, and light must be present for photosynthesis to occur

  7. What kind of light does photosynthesis need to occur? • Sunlight is “white” light  a mixture of different wavelengths of light • Pigment = light-absorbing molecule • Chlorophyll = main pigment of plants, does not absorb green light very well  gets reflected back to our eyes

  8. Inside a Chloroplast • Thylakoids = small disc-shaped saclike photosynthetic membranes • Grana = stacks of thylakoids • Stroma = region outside thylakoid membranes

  9. Electron Carriers • Electrons gain a great deal of energy when they are excited by the sun  require special carriers • NADP+ (nicotinamide adenine dinucleotide phosphate) = main electron carrier • NADP+ holds 2 high energy electrons and additional hydrogen ion  becomes NADPH • NADPH carries electrons to chemical reactions elsewhere in the cell

  10. Two Parts of Photosynthesis • 1. Light-dependent reaction = produces energy from solar power (photons) in the form of ATP and NADPH • 2. Calvin Cycle or Light Independent Reaction • Also called “carbon fixation” or “C3 Fixation” • Uses energy (ATP and NADPH) from light reaction to make glucose

  11. Light Reaction (Electron Flow) • Occurs in thylakoid membranes • During the light reaction, there are 2 possible routes for electron flow: • Cyclic electron flow • Noncyclic electron flow

  12. Cyclic Electron Flow • Occurs in the thylakoid membrane. • Uses Photosystem I only • P700 reaction center- chlorophyll a • Uses Electron Transport Chain (ETC) • Generates ATP only

  13. e- Primary Electron Acceptor SUN e- ATP produced by ETC e- Photons e- P700 Accessory Pigments Photosystem I Cyclic Electron Flow

  14. Noncyclic Electron Flow • Occurs in the thylakoid membrane • Uses Photosystem II and Photosystem I • P680 reaction center (PSII) - chlorophyll a • P700 reaction center (PS I) - chlorophyll a • Uses Electron Transport Chain (ETC) • Generates O2, ATP and NADPH

  15. Primary Electron Acceptor 2e- Enzyme Reaction Primary Electron Acceptor 2e- 2e- ETC 2e- SUN 2e- NADPH P700 Photon ATP P680 Photon H2O 1/2O2+ 2H+ Photosystem I Photosystem II Noncyclic Electron Flow

  16. Noncyclic Electron Flow • ADP + P ATP • NADP+ + H  NADPH • Oxygen comes from the splitting of H2O, not CO2 H2O  1/2 O2 + 2H+

  17. Calvin Cycle • Carbon Fixation (light independent reaction) • C3 plants (80% of plants on earth) • Occurs in the stroma • Uses ATP and NADPH from light reaction as energy • Uses CO2 • To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.

  18. (36C) (6C) 6C-C-C-C-C-C (unstable) 6CO2 6C-C-C 6C-C-C 12PGA (36C) 6ATP 6ATP (30C) 6C-C-C-C-C 6NADPH 6NADPH RuBP (36C) 6C-C-C 6C-C-C 6ATP 12G3P (30C) (6C) C-C-C-C-C-C Glucose Calvin Cycle – Carbon Fixation

  19. Factors affecting photosynthesis • Temperature • Availability of water • Light intensity • These factors are different in different areas of the world  plants develop special adaptations

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