1 / 24

Photosynthesis

Photosynthesis. Two-stage process Light-dependent reaction Occurs only during daylight Light-independent reaction May continue in the dark. Evidence for two stages. Temperature has a clear effect on the rate of photosynthesis

alyson
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 Two-stage process Light-dependent reaction Occurs only during daylight Light-independent reaction May continue in the dark

  2. Evidence for two stages Temperature has a clear effect on the rate of photosynthesis This suggests that although light levels initially limit the rate, there is a second stage controlled by temperature-sensitive enzymes A plant given alternating periods of dark and light forms more carbohydrate than one in continuous light Period of darkness ensures that all the product from first stage is converted into carbohydrate before it builds up

  3. Excitation of electrons Photon of light hits chlorophyll molecule Energy transferred to the electrons in the molecule Electrons raised to higher energy levels If they are raised to a high enough level they will dissociate Electrons picked up by an electron acceptor ATP formed as the electron is passed along an electron transport chain

  4. Electron transport chain electron acceptor ATP ADP + Pi final electron acceptor

  5. Light-dependent stage Occurs in the thylakoids Involves splitting of water by light – photolysis ADP is converted to ATP by light – photophosphorylation Cyclic photophosphorylation uses only PSI Non-cyclic photophosphorylation uses both PSI and PSII

  6. Cyclic photophosphorylation e- electron acceptor ATP ADP + Pi Chlorophyll e- light

  7. Non-cyclic photophosphorylation electron acceptor e- 2H ATP electron acceptor e- ADP + Pi 2H+ e- Photosystem I Photosystem II H2O e- light light ½O2

  8. NADP NADP+ e- NADPH + H+ 2H To the light independent reaction 2H+

  9. Photolysis of water 4 H2O → 4 H+ + 4 OH- 4 OH- - 4 e- → O2 + 2 H2O Splitting of water is catalysed by an enzyme – perhaps PSII! NADP+ Photosystem II

  10. Light-dependent stage Water is converted to protons, electrons and oxygen Reduced NADP is generated Occurs in the thylakoid membrane

  11. Non-cyclic photophosphorylation electron acceptor e- 2H ATP electron acceptor e- ADP + Pi 2H+ e- Photosystem I Photosystem II H2O e- light light ½O2

  12. NADP NADP+ e- NADPH + H+ 2H To the light independent reaction 2H+

  13. Melvin Calvin Member of the Radiation Laboratory at Berkeley, University of California Studied using radioactively labelled carbon dioxide 14CO2 fed to Chlorella algae and its path tracked

  14. Light-independent stage Carbon dioxide is converted to carbohydrate Occurs in the stroma of the chloroplast

  15. Match structure and function

  16. Three phases Carboxylation Carbon dioxide fixation with ribulose bisphosphate (RuBP) Reduction Reduction of glycerate 3-phosphate (GP) to glyceraldehyde 3-phosphate (GALP) Regeneration Re-formation of the CO2 acceptor molecules

  17. Chemicals

  18. Phase 1: Carboxylation Rubisco CO2 GP 6C molecule RuBP GP

  19. RUBISCO

  20. Phase 2: Reduction 2ATP 2ADP + 2Pi GP GALP GALP GP 2NADPH + H+ 2NADP+

  21. Phase 3: Regeneration ATP ADP + Pi GALP RuBP GALP

  22. Synthesis of Organic Substances GALP GP GALP GALP GALP fatty acids glycerol amino acids hexose lipids

  23. The Maths 2 molecules of GALP are made each turn 5 out of 6 molecules of GALP are used to regenerate RuBP 2 molecules of GALP are needed to make a hexose sugar How many turns are needed to make 1 molecule of hexose sugar? How many molecules of ATP and reduced NADP are needed?

More Related