1 / 118

Photosynthesis

Photosynthesis. Campbell and Reece Chapter 10. Autotrophs. “self-feeders” s ustain themselves w/out eating a nything derived from other living things are the biosphere’s producers p hotoautotrophs : plants, algae, some protists , & some prokaryotes. Heterotrophs.

armine
Download Presentation

Photosynthesis

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. Photosynthesis Campbell and Reece Chapter 10

  2. Autotrophs • “self-feeders” • sustain themselves w/out eating anything derived from other living things • are the biosphere’s producers • photoautotrophs: plants, algae, some protists, & some prokaryotes

  3. Heterotrophs • live on cpds produced by other organisms • are the biosphere’s consumers • Includes: carnivores, omnivores, decomposers

  4. Origin of Photosynthesis • Photosynthesis most likely originated in prokaryotes that had infolded regions of plasma membrane containing clusters of that included photosystems and photosynthetic enzymes

  5. Chloroplasts • All green parts of plants have chloroplasts but leaves are major sites of photosynthesis in most plants • 1 mm² of top of a leaf contains .5 million chloroplasts!

  6. Parts of a Leaf

  7. Parts of a Leaf • Mesophyll:leaf cells specialized for photosynthesis • Stomata:microscopic pore surrounded by guard cells in epidermis of leaf & stems, allows gas exchange • Veins: vascular bundle in a leaf

  8. Chloroplast Structure • ~2-4 μm by 4-7 μm • dbl membrane surrounding dense fluid called the stroma • membrane w/in stroma made of sacs called thylakoids • inside thylakoid: thylakoid space • Chlorophyll & photosystems reside in thylakoid membrane

  9. Chloroplast Structure

  10. Photosynthesis Equation • equation worked out in 19th century • use glucose as product to simplify relationship with respiration but what actually happens….

  11. Photosynthesis Equation • direct product is 3-C sugar that can be used to make glucose • light • CO2 + H2O  [CH2O] + O2

  12. Photosynthesis Equation • [CH2O] brackets mean what is inside is not actual sugar but represents general formula for carbohydrate (building a carbohydrate 1 carbon at a time)

  13. Photosynthesis Equation • originally, it was thought the O2 released came from CO2 • assumption challenged in 1930’s (van Niel, Stanford University) • Studied bacteria that use CO2 to make carbohydrates but do not release O2 • Concluded that at least in the bacteria he studied CO2 was not split

  14. Photosynthesis Equation • Another group bacteria use H2S (hydrogen sulfide) instead of water releasing S: • CO2 + 2H2S  [CH2O] + H2O + 2S • vanNiel concluded the H2S split & H was used with C to build sugars & inferred water must split in photosynthesis with H to sugars & O released

  15. Photosynthesis Equation • Van Niel’s hypothesis confirmed in 1950’s when O-18 used in water and traced thru photosynthesis

  16. Photosynthesis as Redox Reactions • photosynthesis equation: C becomes reduced & O oxidized

  17. Summary of Photosynthesis

  18. Photosynthesis Vocabulary • Photophosphorylation: process of generating ATP from ADP + P by means of chemiosmosis using a proton-motive force generated across the thylakoid membrane • Carbon Fixation: incorporation of C from CO2 into an organic cpd by an autotroph

  19. Light Reactions

  20. Light • Form of electromagnetic energy or radiation • 380 nm – 750 nm = visible light • Photon: discrete particle of energy • Amt nrg inversely proportional to wavelength

  21. Electromagnetic Spectrum

  22. Photosynthesis Pigments • pigment substance that absorbs light • different pigments absorb different wavelengths • we see color that is reflected (not absorbed) • Chlorophyll absorbs violet-blue & red

  23. Spectrophotometer • Measures the proportion of light of different wavelengths absorbed & transmitted by a pigment solution

  24. Absorption Spectrum • graph plotting a pigment’s light absorption versus wavelength

  25. Chlorophyll’s Absorption Spectrum • gives clues to relative effectiveness of different wavelengths for driving photosynthesis (light can perform work in chloroplasts only if it is absorbed)

  26. Pigments in Photosynthesis • chlorophyll a • Violet-blue & red light works best • appear blue green • chlorophyll b • violet blue • appear olive green • carotenoids • violet & blue-green • appear various shades yellow & orange

  27. Chlorophyll a/b

  28. Rate of Photosynthesis vs. Wavelength of Light

  29. Carotenoids • absorb wavelengths that chlorophylls do not • more importantly they function as photoprotection: they absorb & dissipate light nrg that would otherwise damage chlorophyll or would interact with O2 yielding reactive oxidative products that would damage cell (act as antioxidants)

  30. Phytochemicals • carotenoids in health food products • promoted as antioxidants

  31. What Happens When Chlorophyll Absorbs Light ? • colors from corresponding wavelengths that are absorbed disappear from the spectrum of transmitted & reflected light • butnrg cannot disappear

  32. What Happens When Chlorophyll Absorbs Light? • nrg from photon absorbed by e- in pigment (more nrg .. e- moves to orbital further out from nucleus where it has more PE & less stability) • ground state: when e- in normal orbital • excited state: e- in orbital of higher nrg

  33. Which Photons are Absorbed? • only those photons whose wavelength’s nrg is exactly = to the nrg difference between the ground & excited states • explains why each pigment has unique absorption spectrum

  34. Electrons in the Excited State • unstable when excited • if isolated: chlorophyll molecules absorb photons the e- immediately drop back to ground state releasing nrg as heat or light (fluorescence) & heat

  35. Excitation of Isolated Chlorophyll Molecule

  36. Photosystems • chlorophyll molecules in native state found in thylakoid membrane organized into complexes called photosystems

  37. Photosystem • composed of: • Reaction-Center Complex surrounded by: • Light-Harvesting Complex • consists of various pigments bound to proteins: • chlorophyll a • chlorophyll b • carotenoids

  38. Photosystems • Light-Harvesting Complex acts like “antennae” for the Reaction-Center Complex

  39. Reaction-Center Complex • contains molecule (the primary e- acceptor) capable of accepting e- & becoming reduced

  40. 1st Step of Light Reactions • solar-powered transfer of e- from reaction-center chlorophyll a  primary e- acceptor • redox reaction

  41. 2 Types of Photosystems • PS II • It’s reaction-center complex known as P680 • 680 wavelength in red part of spectrum • PS I • It’s reaction-center complex known as P700 • 700 wavelength far red part of spectrum

  42. P680 & P700 both Chlorophyll a

  43. Linear Electron Flow

  44. Linear e- Flow Figure 10.14 • 1. photon strikes PS II chlorophyll a & 1 e- jumps to higher nrg level -> this e- falls back to its ground state transferring its nrg to nearby chlorophyll molecule so 1 of its e- jump to excited state …..continues like this until it reaches P680 pair of chlorophyll a molecules in reaction-center & a pair of e- jumps to excited state

  45. Linear Electron Flow: Figure 10.14

  46. Linear Electron Flow:Figure 10.14 Step 2: e- transferred from excited P680  primary e- acceptor making P680  P680+

  47. Linear Electron Flow: Figure 10.14

  48. Linear Electron Flow:Figure 10.14 Step 3: enzyme splits 2water  4 e- + 4 H+ + O2 2 e- replace those that left P680 so P680+ returns to P680 one of strongest biological oxidizing agents H+ released into thylakoid space O2 diffuses out of chloroplast  out of cell

  49. Linear Electron Flow: Figure 10.14

More Related