1 / 39

Chapter 7

Chapter 7. Photosynthesis: Using Light to Make Food. Sustain Life. Energy classification Autotrophs—self nourishing Obtain carbon from CO 2 Obtain energy from light (photosynthesis) or chemical reactions (chemosynthesis) Heterotrophs—use others for energy source

kerry
Download Presentation

Chapter 7

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 7 Photosynthesis: Using Light to Make Food

  2. Sustain Life • Energy classification • Autotrophs—self nourishing • Obtain carbon from CO2 • Obtain energy from light (photosynthesis) or chemical reactions (chemosynthesis) • Heterotrophs—use others for energy source • Obtain carbon from autotrophs • Obtain energy from autotrophs • Even if ingest other heterotrophs, at some point the original carbon & energy came from an autotroph • Carbon & Energy • Enter life through photosynthesis (autotrophs) • Released through glycolysis & cellular respiration (heterotrophs)

  3. Photosynthesis • Chlorophyll • Plants • Algae • Some bacteria • Transfer sun’s energy into chemical bonds • Converts energy of photons to energy stored in ATP • Oxygen production is a byproduct

  4. Photosynthesis • Three stages • Light-capturing • Light-dependent • Convert light energy into chemical energy • Light-independent • Form organic compounds (glucose) • CO2 + H2O => C6H12O6 (glucose) + O2 • Remember that this is the opposite direction but the same basic reaction as cellular respiration.

  5. Properties of light • Wavelength • Spectrum

  6. Properties of light • Photons • Packets of particle-like light • Fixed energy (each photon a specific energy wavelength) • Think of them as bundles of energy, like an electrified rubber ball • Energy level • Low energy = long wavelength • Microwaves, radio waves • High energy = short wavelength • Gamma rays, x-rays • Only a small part of spectrum (400-750 nm) is used for vision & photosynthesis

  7. 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; it absorbs all parts of the spectrum except green.

  8. 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

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

  10. 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

  11. 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)

  12. 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

  13. chloroplasts

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

  15. Light-Dependent reactions • Photosystems—Clusters of chlorophyll, pigments, proteins • Light-gathering “antennae” • Photosystem I (P680)—absorbs red light at 680nm • Photosystem II (P700)—absorbs far-red light at 700nm

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

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

  18. Light-Dependent reactions • Electrons continue until bonding NADP+ to form NADPH • NADPH used in next part of cycle • Process is very similar to cellular respiration!!!! • Oxidative phosphorylation

  19. Light-dependent reaction

  20. Light-dependent reaction

  21. Light-dependent reaction

  22. Light-independent reactions

  23. Light-independent reactions • ATP provides energy for bond formation • NADPH provides hydrogen & electrons • CO2 provides carbon & oxygen

  24. Light-independent reactions • CO2 in air diffuses into stroma • CO2 attaches to rubisco (RuBP) • Enters Calvin cycle (also called Calvin-Benson) • 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

  25. 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

  26. *(G3P = PGAL)

  27. Photosynthesis summary

  28. stomata • Microscopic openings in leaves • Close when hot & dry • Keeps water inside • Prevents CO2 & O2 exchange

  29. C3 Plants • Basswood, beans, peas, evergreens • 3-Carbon PGA is first stable intermediate in Calvincycle • 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

  30. C4 Plants • Corn, sugar cane, tropical plants • Adapted to hot, dry climates • Close stomata to conserve water • This limits CO2 entry and allows O2 to accumulate • This allows CO2 to remain high for Calvin cycle • Carbon stored in special cells, can be donated to Calvin cycle later • Requires 1 more ATP than C3, but less water lost & more sugar produced

  31. C4 Plants

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

More Related