1 / 26

Photosynthesis

Photosynthesis. Autotrophs/ producers. Why?. Energy = the ability to do work Energy cannot be created nor destroyed, only transformed Electromagnetic energy (sun)  chemical bond energy + heat energy Increase in order within the cell is coupled

isabelle-hopper
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 Autotrophs/ producers

  2. Why? • Energy = the ability to do work • Energy cannot be created nor destroyed, only transformed • Electromagnetic energy (sun)  chemical bond energy + heat energy • Increase in order within the cell is coupled with a decrease in order outside the cell

  3. Who? • Bacteria • Cyanobacteria • Plants • Aquatic • Photo-zone • Terrestrial • Temperate • Desert

  4. Where ? • Plant cells: Organelle = Chloroplast • Chloroplast contains 3 distinct membranes • Outer membrane • Inner membrane • Thylakoid membrane *** energy site *** • Interconnected • Form stacks called grana • Surrounded by the stroma • Chlorophyll located within thylakoids

  5. Where Else? • Cyanobacteria use electrons from water & solar energy to convert atmospheric CO2 into organic compounds. nH2O + nCO2 (CH2O)n+ nO2 • No chloroplasts are needed.

  6. When? • Light-dependent reactions • Daylight hours • Daylight hours with suspended processes • C4 & CAM • Light-independent reactions • Day or night • Calvin cycle • Carbon-fixation reactions

  7. Absorption Ranges • Chlorophyll a – indigo/purple (~425nm) • Chlorophyll a - orange/red (~ 665 nm) • Chlorophyll b – indigo/ blue (~450 nm) • Carotenoids – green (~480 nm) • Not as plentiful as chlorophyll pigments • Responsible for Fall leaves, blossom & fruit colors • Only chlorophyll a is directly involved in photosynthesis; the others are accessory pigments

  8. How? • Sunlight hits chlorophyll & carotenoid pigments • Excites pigments’ electrons • Electrons move down thylakoid membrane • Electron-transport proteins pump protons (H+) across thylakoid membrane • H+-pump drives ATP synthesis in the stroma • Electron transport also drives NADP+NADPH

  9. Light Reaction Details(within thylakoid membranes) • Photosystem II: light energy excites electrons • Electrons (e-) are passed to primary e- acceptor • Primary electron acceptor passes electrons to electron transport chain • Photosystem I: light excites chlorophyll a’s e- • e- are passed to different primary e- acceptor • This passes e- to a different transport chain • Energy e- lose being passed is used to move H+ in

  10. Replenishing electrons • Reduction = gaining electrons • Oxidation = losing electrons • Reduction reactions couple to oxidation rxns • Photosystem II gives e- to photosystem I • NADP+ accepts e-; is reduced to NADPH • Replacement e- for photosystem II is from H2O • 2 H2O  4 H+ + 4 e- + O2 (via water-splitting enzyme nearby on thylakoid membrane)

  11. Making ATP • Chemiosmosis = ATP-making process • Relies on H+ concentration gradient across the thylakoid membranes • ATP synthase in the thylakoids harnesses the potential energy of the H+ gradient into chemical energy of ATP • The movement of e- drives these reactions

  12. Calvin Cycle {“Carbon fixation”} • Occurs within the stroma of chloroplast • ATP & NADPH’s energy used to make 3-C sugar • Atmospheric CO2 is source of carbons • Cycle of enzymes accept C from CO2 (x 3) • 5-C ribulose bisphosphate (RuBP) accepts 1 C • RuBP+C into two 3-phosphoglycerates (3-PGA) • ATP/NADPH drives formation of glyceraldehyde 3-phosphate (G3P) & reformation of RuBP.

  13. Alternative Pathways • Hot, dry climates • Would lose water through stomata which is port of entry for CO2 • High O2 & low CO2 levels inhibit photosynthesis • C4 plants (corn, sugar cane, crab grass) • Tropical climates • Make a 4-C compound & transport to other cells • CAM (cactus, pineapple, et al.) • Open stomata at night & close during day

  14. Factors affecting photosynthesis • Light intensity • Directly correlated until it reaches a plateau • CO2 levels • Directly correlated until it plateaus. • Temperature • Has a peak optimal range • Enzyme-specific • Water & carbon dioxide loss with closing stomata

More Related