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Light Energy & Photosynthetic Pigments

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  1. Light Energy & Photosynthetic Pigments Chapter 3.2

  2. Chloroplasts double membrane stroma fluid-filled interior thylakoid sacs grana stacks Thylakoid membrane contains chlorophyll molecules electron transport chain ATP synthase H+ gradient built up within thylakoid sac Review: Plant structure H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+

  3. Photosynthesis • All photosynthesis reactions occur within the chloroplasts • Partly within the stroma and partly within thylakoid membranes • Chloroplasts contain their own DNA and ribosomes and are able to replicate by fission

  4. The stages • Stage 1: Capturing light energy • Stage 2: Using captured light energy to make ATP and reduce NADP+ to NADPH • Stage 3: Using the free energy of ATP and the reducing power of NADPH to make glucose and oxygen

  5. Stages cont’d • Photosystems absorb particular wavelengths and transfer their energy to ADP, Pi and NADP+ forming ATP and NADPH • 2 types of reactions occur in photosynthesis; the light reactions and carbon fixation • Light reactions: only take place when light available , not affected by changes in temperature, use light and water, produce NADPH and ATP • Carbon fixation: dependent on NADPH and ATP, (therefore on light reactions too), varies with temperature not intensity of light

  6. Photosynthesis • Light reactions • light-dependent reactions • energy production reactions • convert solar energy to chemical energy • ATP & NADPH • Calvin cycle • light-independent reactions • sugar production reactions • uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6

  7. light energy  H2O + + + O2 ATP NADPH sunlight Stage 1 & 2 = Light Reactions H2O • produces ATP • produces NADPH • releases O2 as a waste product Energy Building Reactions NADPH ATP O2

  8. CO2 + + + + ATP NADPH C6H12O6 ADP NADP Stage 3: Calvin Cycle • builds sugars • uses ATP & NADPH • recycles ADP & NADP back to make more ATP & NADPH CO2 ADP NADP SugarBuilding Reactions NADPH ATP sugars C6H12O6

  9. light energy  CO2 + H2O + + O2 C6H12O6 sunlight Putting it all together Plants make both: • energy • ATP & NADPH • sugars H2O CO2 ADP NADP SugarBuilding Reactions Energy Building Reactions NADPH ATP sugars C6H12O6 O2

  10. H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Light reactions • Electron Transport Chain • like in cellular respiration • membrane-bound proteins in organelle • electron acceptors • NADPH • proton (H+) gradient across inner membrane • ATP synthase enzyme

  11. How does this occur? • Various forms of radiation surround us, from the sun and other sources. • Some are visible and some are invisible.

  12. A Look at Light • The spectrum of color V I B G Y O R

  13. Wave model of light • Electromagnetic radiation travels at 300000000m/s • Frequencies of visible radiation (light) are perceived as different colours We can remember the visible spectrum with ROY G BIV!

  14. Frequencies of visible radiation (light) are perceived as different colours. • Highest frequency, smallest wavelength = violet • Lowest frequency, largest wavelength = red • All frequencies and wavelengths = white

  15. Light • Electromagnetic radiation, travelling at 3x108 m/s • Exhibits properties of waves and photons (particles) • Wavelength is inversely proportional to its energy • Visible light ranges from 400 to 700 nm

  16. How Does a Plant Capture Light? Light can be • transmitted (light passes through an object. • Reflected (light bounces off object) • Absorbed (light goes into object)

  17. How Does a Plant Capture Light? • Plants have chlorophyll PIGMENTS (molecules that can absorb specific wavelengths of light) Plant leaves appear green. Therefore, what colours must the chlorophyll pigments absorb? reflect? Everything but Green GREEN

  18. Absorption spectrum Graph that illustrates the wavelengths of light absorbed by a pigment

  19. Chlorophyll and Accessory Pigments • Chlorophyll a is the only pigment that can transfer light energy to the carbon fixation reactions of photosynthesis • Chlorophyll b and carotenoids acts as accessory pigments, absorbing wavelengths that chlorophyll a cannot • Carotenoids: (ex β- carotene) possess 2 hydrocarbon rings connected by hydrocarbon chain

  20. Accessory pigments cont’d • Xantophylls – produce yellow color • Carotenoids – produce yellow-orange colour • Interspersed within thylakoid membrane • Anthocyanins – produce red, violet, blue colour • Located in plant cell vacuoles – Photosynthetically active radiation (PAR) – wavelengths between 400 nm – 700nm support photosynthesis