1. 1 Photosynthesis Chapter 10

2. 2 Outline Chloroplasts Light-Independent Reactions Absorption Spectra – Pigments Light-Dependent Reactions Photosystems C 3 Photosynthesis C 4 Photosynthesis CAM Photosynthesis

3. 3 Photosynthesis The energy used by most living cells ultimately comes from the sun, and is captured by plants, algae, or bacteria via photosynthesis. – light dependent reactions  capture energy from sunlight  use energy to produce ATP and NADPH – Calvin cycle  formation of organic molecules

4. 4 Leaf Structure

5. 5 Chloroplasts Internal membranes, thylakoids, are organized into grana. – Thylakoid membranes house pigments for capturing light and the machinery to produce ATP.  clustered together to form a photosystem  acts as an antenna, gathering light energy harvested by multiple pigment molecules

6. 6 Chloroplasts

7. 7 Light and Reducing Power Light-dependent reactions of photosynthesis use the energy of light to reduce NADP to NADPH and to manufacture ATP. – Reducing power generated by splitting water is used to convert CO 2 into organic matter during carbon fixation.

8. 8 Light-Independent Reactions

9. 9 Energy in Photons Energy content of a photon is inversely proportional to the wavelength of light. – Highest intensity photons, at the short- wavelength end of the electromagnetic spectrum, are gamma rays. – Ultraviolet light possesses considerably more energy than visible light.  potent force in disrupting DNA

10. 10 Electromagnetic Spectrum

11. 11 Absorption Spectra Photon absorption depends on its wavelength, and the chemical nature of the molecule it hits. – Each molecule has a characteristic absorption spectrum.  range and efficiency of photons the molecule is capable of absorbing

12. 12 Pigments Pigments are molecules that absorb light in the visible range. – green plant photosynthesis  carotenoids  chlorophyll  chlorophyll a - main pigment  chlorophyll b - accessory pigment

13. 13 Absorption Spectra

14. 14 Chlorophyll Chlorophylls absorb photons by means of an excitation process. – Photons excite electrons in the pigment’s ring structure, and are channeled away through alternating carbon-bond system.  Wavelengths absorbed depend on the available energy levels to which excited electrons can be boosted.

15. 15 Chlorophyll

16. 16 Light-Dependent Reaction Stages Primary photoevent Charge separation Electron transport Chemiosmosis

17. 17 Photosystems Photosynthesis output increases linearly at low light intensities but lessens at higher intensities. – saturation point Photosystem - network of pigments that channels excitation energy gathered by any of the molecules to the reaction center – reaction center allows photon excitation to move away from chlorophylls and is the key conversion of light to chemical energy

18. 18 Light to Chemical Energy

19. 19 Photosystem Function Bacteria use a single photosystem. – electron is joined with a proton to make hydrogen – electron is recycled to chlorophyll

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21. 21 Photosystem Function Plants use two photosystems – photosystem I and II  generate power to reduce NADP + to NADPH with enough left over to make ATP  two stage process: photosystem II – I.  noncyclic photophosphorylation  ejected electrons end up in NADPH

22. 22 Photosystems I and II

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24. 24 Calvin Cycle Also referred to as C 3 photosynthesis – C 3 plants - ribulose 1,5-bisphosphate is carboxylated to form a three-carbon compound via rubisco activity

25. 25 Calvin Cycle

26. 26 Photorespiration In photorespiration, O 2 is incorporated into RuBP, which undergoes additional reactions that release CO 2. – decreased yields of photosynthesis

27. 27 C 4 Pathway Plants adapted to warmer environments deal with the loss of CO 2 in two ways: – C 4 conducted in mesophyll cells, Calvin cycle in bundle sheath cells  creates high local levels of CO 2 to favor carboxylation reaction of rubisco  isolates CO 2 production spatially

28. 28 Crassulacean Acid Metabolism CAM plants open stomata during the night, and close them during the day to cut-down the loss of water vapor. – isolates CO 2 production temporally

29. 29 Carbon Fixation

30. 30 Summary Chloroplasts Light-Independent Reactions Absorption Spectra – Pigments Light-Dependent Reactions Photosystems C 3 Photosynthesis C 4 Photosynthesis CAM Photosynthesis

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