Photosynthesis: Light into Energy, Chlorophyll, and Calvin Cycle Overview

1. Topics 2.9 and 8.3 • Photosynthesis • Great Intro video (Show at end too) C:\Documents and Settings\BBAUGHMAN\Desktop\Desktop\Cool Videos\Cells\MH_Photosynthesis

2. Photosynthesis • The conversion of light energy into chemical energy • The production of carbon compounds in cells using light energy. 

3. Light • Visible light has a range of wavelengths (colors) with violet the shortest wavelength and red the longest. • Visible light wavelengths are between 400 and 700 nm (know this!) • Chlorophyll = the main photosynthetic pigment • absorbs red and blue wavelengths best • Reflects green

4. Absorption of light by photosystems generates excited electrons. • Absorption spectrum= the range of a pigment’s ability to absorb various wavelengths (colors) of light Blue and red light work best! Green= worst!

5. Explain the relationship between the action spectrum and the absorption spectrum of photosynthetic pigments in green plants. • Skill: Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis. Absorption spectrum Action spectrum

6. The chloroplast • Sites of photosynthesis • Pigment: chlorophyll • Mesophyll: tissue in interior of leaf where chloroplasts are found. • Double membrane • Thylakoids, grana, stroma

7. The chloroplast: draw and label

8. Photosynthesis: an overview • Redox process • H2O is split, • electrons and hydrogens ultimately are used to REDUCE CO2 to make sugar. • 2 major steps: • light dependent reactions (“photo”) • Main Products: √ NADPH √ATP ( through a process called photophosphorylation) • light independent reactions/Calvin cycle (“synthesis”) Carbon fixation: carbon into organics (i.e. glucose etc.) Overall net equation: 6CO2 + 6H2O + light energy ---> C6H12O6 + 6O2

10. Light-Dependent Reactions • Light-dependent reactions take place in the thylakoid membranes and the space inside them.

11. The Light-Dependent Reactions: • Photosystem II (P680): • photons excite chlorophyll e- to a primary electron acceptor • PHOTOLYSIS= e- are replaced by splitting of H2O (this produces O2) • e-’s travel to Photosystem I down an electron transport chain in thylakoid membrane (Pq~cytochromes~Pc) • as e- move down the ETC, protons are pumped into thylakoid space. • used for chemiosmosis • ADP ---> ATP (noncyclic photophosphorylation)

13. Explain photophosphorylation in terms of chemiosmosis.

14. The Light Reactions: (Continued) • Photosystem I (P700): √ P700 accepts Electron from ETC of Photosystem II. • This electron gets excited by light and goes to the primary electron acceptor, then to… √ 2nd ETC • Fd (ferredoxin)NADP+reductase transfers e- to NADP+. • This makes NADPH ( which goes to Calvin cycle…) • Noncyclic electron flow produces equal amounts of ATP and NADPH

15. Light reactions • McGraw Hill animation • Another noncyclic animation • C:\Documents and Settings\BBAUGHMAN\Desktop\bio powerpoints\Chapter 09 BDOL IC • http://vcell.ndsu.nodak.edu/animations/photosynthesis/movie.htm

16. Light-Independent Reactions • Light-independent reactions take place in the stroma.

17. The light-independent reactions/Calvin cycle • Overall: 3 molecules of CO2 are ‘fixed’ into glyceraldehyde 3-phosphate (G3P) • Note: ATP and NADPH from the light-dependent reactions are used to fix carbon dioxide to make organic molecules now. • 3 Phases: • 1- Carbon fixation~ • 2- Reduction~ • 3- Regeneration~

18. Rubisco is short for Ribulose Bisphosphate Carboxylase Calvin cycle (Phase 1) • 1- Carbon fixation~ catalyzed by enzyme Rubisco (a carboxylase) • each CO2 is attached to RuBP (ribulose bisphosphate) • IB calls this the carboxylation of RuBP • This makes Glycerate 3-Phosphate (3-Phosphoglycerate)

19. Calvin Cycle (Phase 2) • 2- Reduction~ • ATP used to make an intermediate compound. • Then electrons and hydrogens from NADPH are used to reduce the intermediate compound to Glyceraldehyde-3 Phosphate (G3P); • Note: G3P is also called a triose phosphate by IB! • G3P is used to make Glucose!!

20. Calvin Cycle (Phase 3) 3- Regeneration~ • 1G3P exits cycle; • 5 G3P rearranged to make 3 RuBP; • 3 ATP used; cycle continues • http://highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter5/animation_quiz_1.html • good calvin cycle animation • http://www.sinauer.com/cooper/4e/animations0305.html • calvin cycle animation

21. Calvin Cycle, net synthesis • Reactants used = • 9 ATP (from light reactions) • 6 NADPH (from light reactions) • 3 CO2 • Product = one G3P • G3P can then be used by the plant to make glucose and other organic compounds

22. Chloroplast Structure and function

23. Skill: • Annotation of a diagram to indicate the adaptations of a chloroplast to its function.

24. Think: How can the rate of photosynthesis be measured? • Directly by: • Production of oxygen • Uptake of carbon dioxide • Indirectly by: • Increase in biomass

25. Factors affecting Photosynthesis Rate • The following are Limiting factors that limit the rate of photosynthesis. • Temperature • Light intensity • Carbon Dioxide Concentration • Draw a graph for each of the above. What is the expected shape for each?

26. Skill: Design of experiments to investigate the effect of limiting factors on photosynthesis. Read p. 136-138 for ideas • Follow the link below to do the assignment on page 138 • https://docs.google.com/forms/d/1on1qUOd_m1eIniL-I2GEGWXJUw8H-roWe-eCLf44yp4/viewform?usp=send_form • Water free of dissolved carbon dioxide for photosynthesis experiments can be produced by boiling and cooling water.

27. A review of photosynthesis • overview animation

28. • Skill: Separation of photosynthetic pigments by chromatograph. (Practical 4)

29. Application: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis. • Read p. 134-135 and take notes on most important impacts.

30. Nature of science: • Developments in scientific research follow improvements in apparatus—sources of 14C and autoradiography enabled Calvin to elucidate the pathways of carbon fixation. Calvin’s Lollipop Apparatus

31. Application: Calvin’s experiment to elucidate the carboxylation of RuBP.

32. Theory of knowledge • The lollipop experiment used to work out the biochemical details of the Calvin cycle shows considerable creativity. To what extent is the creation of an elegant protocol similar to the creation of a work of art? Calvin’s Lollipop Apparatus

33. Utilization: • The Global Artificial Photosynthesis (GAP) project aims to create an artificial “leaf” within the next decade. An electronic version of the leaf that creates oxygen and hydrogen from water and sunlight has already been invented and will be developed for use in the next decade. • See Printed Article

34. END of IB

35. The Light Reactions: Cyclic Electron Flow • Purpose: Make more ATP b/c Calvin Cycle needs more ATP than NADPH. • Electrons from Photosystem I are excited go to primary electron acceptor • Electron passed on to Fd (ferredoxin) (normal) • Instead of continuing to make NADPH, the electron goes back through ETC to generate proton gradient for chemiosmosis that makes ATP • Electron completes cycle by ending at photosystem I again. • animation

36. Cyclic electron flow (review) • Alternative cycle when ATP is deficient • Photosystem I used but not II; produces ATP but no NADPH • Why? The Calvin cycle consumes more ATP than NADPH……. • Cyclic photophosphorylation • animation

37. How did Calvin figure out the order of these reactions? • http://wiki.answers.com/Q/Determining_the_order_of_reactions_in_Calvin_cycle

38. Carbon Fixation: C3 plants • Most plants are C3 plants • Carbon fixation occurs by enzyme Rubisco • Makes a 3 Carbon (C3) compound (3-phosphoglycerate) • Problem= Rubisco is also able to accept O2 • When stomata are closed on hot dry days, O2 accumulates in leaf, CO2 concentration goes down. • Why do STOMATA close??

39. Alternative carbon fixation methods, I • In hot, dry environments, we have a problem!! • Photorespiration: hot/dry days; stomata close; CO2 decreases, O2 increases in leaves; O2 added to rubisco; no ATP or food generated • Two Solutions….. • 1- C4 plants (ex. grasses): Have 2 types of photosynthetic cells: • mesophyll; PEP carboxylase (instead of rubisco) fixes CO2 and makes a 4-C organic acid • bundle-sheath: 4-C organic acid releases CO2 which goes into the CALVIN CYCLE

40. Alternative carbon fixation methods, II • 2- CAM plants: • open stomata during night, close during day; • cacti, pineapples, etc. • Crassulacean Acid Metabolism-- CO2 is stored in organic acids at night • During daylight CO2 is released for use in photosynthesis • Why?

41. The Light-Dependent Reactions: Photosystems • Light harvesting units of the thylakoid membrane • Composed mainly of protein and pigment antenna complexes (chlorophyll a, b and carotenoid molecules) • Antenna pigment molecules are struck by photons (light particles) • Absorption spectrum= the range of a pigment’s ability to absorb various wavelengths (colors) of light • Energy is passed to reaction centers (redox location) • Consist of a specific “chlorophyll a” molecule and the Primary Electron Acceptor. • Excited e- from chlorophyll is trapped by a primary e- acceptor Blue and red light work best! Green= worst!