Unleashing the Power of Sunlight: Photosynthesis in Detail

1. Where It Starts – Photosynthesis Lecture 8 - Autumn 2007

2. Sunlight as an Energy Source • Photosynthesis runs on a fraction of the electromagnetic spectrum, or the full range of energy radiating from the sun

3. Visible Light • Wavelengths humans perceive as different colors • Violet (380 nm) to red (750 nm) • Longer wavelengths, lower energy

4. Electromagnetic Spectrum Shortest Gamma rays wavelength X-rays UV radiation Visible light Infrared radiation Microwaves Longest Radio waves wavelength

5. Photons • Packets of light energy • Each type of photon has fixed amount of energy • Photons having most energy travel as shortest wavelength (deep blue sea - blue light travels the deepest because it has the most energy)

6. Pigments • Light-absorbing molecules • Absorb some wavelengths and transmit others • Color you see are the wavelengths not absorbed

7. Variety of Pigments Chlorophylls a and b Carotenoids Etc.

8. Chlorophylls Main pigments in most photoautotrophs - Organisms which make their own food chlorophyll a Wavelength absorption (%) chlorophyll b Wavelength (nanometers)

9. Carotenoids • Found in all photoautotrophs • Absorb blue-violet and blue-green that chlorophylls miss • Reflect red, yellow, orange wavelengths • Two types • Carotenes - pure hydrocarbons • Xanthophylls - contain oxygen

10. Yellow, brown, purple, or blue accessory pigments Xanthophylls

11. Phycobilins & Anthocyanins Red to purple pigments • Phycobilins • Found in red algae and cyanobacteria • Anthocyanins • Give many flowers their colors

12. T.E. Englemann’s Experiment -simple elegance - illuminate a long strand of photosynthetic algae with a spectrum of light, and watch were the mobile bacteria accumulate!

13. Light-Dependent Reactions • Pigments absorb light energy, give up e- which enter electron transfer chains • Water molecules are split, ATP and NADH are formed, and oxygen is released (waste product - lucky for us!) • Pigments that gave up electrons get replacements

14. Light-Independent Reactions • Synthesis part of photosynthesis • Can proceed in the dark • Take place in the stroma (special structures inside the chloroplast) • Calvin-Benson cycle

15. Photosynthesis Equation- remember forever

16. Chloroplasts Organelles of photosynthesis

17. Inside the Chloroplast • Two outer membranes enclose a semifluid interior, the stroma • Thylakoid membrane inside the stroma

18. Inside the Chloroplast • Photosystems are embedded in thylakoids, containing 200 to 300 pigments and other molecules that trap sun’s energy • Two types of photosystems: I and II

19. Carbon and Energy Sources • Photoautotrophs • Carbon source is carbon dioxide • Energy source is sunlight (mostly) • Heterotrophs • Get carbon and energy by eating autotrophs (plants) and/or one another (cannibalism too)

20. Photoautotrophs • Capture sunlight energy and use it to carry out photosynthesis • Plants • Some bacteria • Many protistans

21. Photosynthesis Energy-storing pathway Releases oxygen Requires carbon dioxide Aerobic Respiration Energy-releasing pathway Requires oxygen Releases carbon dioxide Linked Processes

22. Photosystem Function: Harvester Pigments • Most pigments in photosystem are harvester pigments • When excited by light energy, these pigments transfer energy to adjacent pigment molecules • Each transfer involves some energy loss - heat and atomic motion

23. ATP and NADPH Formation

24. Using the Products of Photosynthesis • Phosphorylated glucose is the building block for: • Sucrose • The most easily transported plant carbohydrate • Starch • The most common storage form

25. Summary of Photosynthesis