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Chapter 7

Chapter 7. Where it Starts--Photosynthesis. Sustain Life. Obtain energy Autotrophs Heterotrophs Metabolism—biochemical processes release energy Photosynthesis Cellular Respiration. Sustain Life. Food energy stored in chemical bonds Exergonic (cellular respiration)

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Chapter 7

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  1. Chapter 7 Where it Starts--Photosynthesis

  2. Sustain Life • Obtain energy • Autotrophs • Heterotrophs • Metabolism—biochemical processes release energy • Photosynthesis • Cellular Respiration

  3. Sustain Life • Food energy stored in chemical bonds • Exergonic (cellular respiration) • Endergonic (photosynthesis) • Energy transfers from endergonic to exergonic through ATP

  4. Photosynthesis • Chlorophyll • Plants • Algae • Some bacteria • Transfer sun’s energy into chemical bonds

  5. Photosynthesis • Three stages • Light-capturing • Light-dependent • Light-independent • CO2 + H2O => C6H12O6 (glucose) + O2

  6. Properties of light • Wavelength • Spectrum

  7. Properties of light • Photons • Packets of particle-like light • Fixed energy • Energy level • Low energy = long wavelength • Microwaves, radio waves • High energy = short wavelength • Gamma rays, x-rays

  8. Properties of light • The light that you see is REFLECTED, not absorbed. • Therefore, a green plant is reflecting the green part of the spectrum (and photons of that energy), not absorbing them.

  9. pigments • Molecules that absorb photons of only a particular wavelength • Chlorophyll a • Absorbs red, blue, violet light • Reflects green, yellow light • Major pigment in almost all photoautotrophs • Chlorophyll b • Absorbs red-orange, some blue • Reflects green, some blue

  10. Pigments • Carotenoids • Absorb blue-violet, blue-green light • Reflect red, orange, yellow light • Give color to many flowers, fruits, vegetables • Color leaves in Autumn

  11. Pigments • Anthocyanins • Absorb green, yellow, some orange light • Reflect red, purple light • Cherries, many flowers • Color leaves in Autumn • Phycobilins • Absorb green, yellow, orange light • Reflect red, blue-green light • Some algae & bacteria

  12. Electron energy • Pigment absorbs light of specific wavelentgh • Corresponds to energy of photon • Electron absorbs energy from photon • Energy boosts electron to higher level • Electron then returns to original level • When it returns, emits some energy (heat or photon)

  13. overview • Stage 1 (Light-Dependent) • Light energy converted to bond energy of ATP • Water molecules split, helping to form NADPH • Oxygen atoms escape • Stage 2 (Light-Independent) • ATP energy used to synthesize glucose & other carbohydrates

  14. chloroplasts

  15. Light-Dependent reactions • Occurs in thylakoids • Electrons transfer light energy in electron transport chain

  16. Light-Dependent reactions • Electron transfers pump H+ into inner thylakoid compartment • Repeats, building up concentration and electric gradients

  17. Light-Dependent reactions • H+ can only pass through channels inside ATP Synthase • Ion flow through channel makes protein turn, forcing Phosphate onto ADP

  18. Light-Dependent reactions • Electrons continue until bonding NADP+ to form NADPH • NADPH used in next part of cycle

  19. Light-independent reactions

  20. Light-independent reactions • CO2 in air attaches to rubisco (RuBP) • Splits to form PGA • PGA gets phosphate from ATP, then H+ and electrons from NADPH • Forms PGAL • Two PGAL combine to form glucose plus phosphate group

  21. Light-independent reactions • Some PGAL recycles to form more RuBP • Takes 6 “turns” of cycle to form one glucose molecule • 6 CO2 must be fixed and 12 PGAL must form to produce one glucose molecule and keep the cycle running

  22. *(G3P = PGAL)

  23. Stomata • Close when hot & dry • Keeps water inside • Prevents CO2 & O2 exchange

  24. C3 Plants • Basswood, beans, peas, evergreens • 3-Carbon PGA is first stable intermediate in Calvin-Benson cycle • Stomata close, O2 builds up • Increased O2 levels compete w/ CO2 in cycle • Rubisco attaches oxygen, NOT carbon to RuBP • This yields 1 PGA rather than 2 • Lowers sugar production & growth of plant • 12 “turns” rather than 6 to make sugars • Better adapted to cold & wet

  25. C4 Plants • Corn, tropical plants • Also close stomata on hot, dry days • Pumps carbon through cycles in 2 cells • Mesophyll cells: create 4-carbon molecule (oxaloacetate) • Bundle-sheath cells: take 4-carbon molecule (malate), releases CO2 to Calvin-Benson cycle • This allows CO2 to remain high for C-B cycle • Requires 1 more ATP than C3, but less water lost & more sugar produced • Adapted to higher light & temp, lower water

  26. C4 Plants

  27. CAM Plants • Desert plants (cactus) • Crassulcean Acid Metabolism • Opens stomata at night, uses C4 cycle • Cells store malate & organic acids • During day when stomata close, malate releases CO2 for C-B cycle

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