Photosynthesis

1. en.wikipedia.org Photosynthesis LECTURE #9

2. The basics • Primary producers convert atmospheric carbon into sugar. • The energy comes from sunlight • Oxygen is produced as a byproduct CO2 + H2O + energy C6H12O6 + O2

3. Primary producer diversity SINGLE-CELL PROTIST EUGLENA webnt.calhoun.edu VASCULAR PLANT CELERY Wikipedia.org COLONIAL ALGAE VOLVOX Duke.edu MACROALGAE SEAWEED Krogh PHYTOPLANKTON DIATOMS scienceblogs.com VASCULAR PLANT REDWOOD flowersociety.org CYANOBACTERIA ANABAENAWikipedia.org

4. Chlorophyll • Chlorophyll = green pigment involved in photosynthesis. cbu.edu cleantechnica.com

6. A little anatomy…

7. Leaf anatomy • Epidermis = “skin” of the plant. Has waxy covering. • Stomata = “pores” in the epidermis. • Mesophyll cells = 100+ chloroplasts per cell. emc.maricopa.edu

9. Chloroplast structure • Stroma= liquid inside inner membrane. • Thylakoids= network of membranes containing pigments. • Grana = stacks of thylakoid “pancakes.”

10. 2 parts to photosynthesis • The “Light” Reactions • Light is absorbed • Water is split • Oxygen is released • The “Dark” Reactions (Calvin Cycle) • Electrons are added to CO2 to make sugar

11. The Light Reactions

12. The Light Reactions • Photosystems II and I • Working units of the light reactions • Located in the thylakoids

13. The Light Reactions • Antennae complex • Pigment molecules • Absorb light energy, transfer it to reaction center • Reaction center • Contains a pair of chlorophyll  molecules • Receives solar energy • Transforms solar energy into chemical energy

14. Photosystem II When light energy is delivered to the reaction center in Photosystem II, an electron in the chlorophyll  molecule gets excited, moving up its energy hill. This electron can then be captured by the primary electron acceptor.

15. Filling the electron “gap” • That chlorophyll is now missing electrons… • Electrons are removed from H2O to replace chlorophyll’s electrons. • “Splitting of water” • O2 is a byproduct

16. The Electron Transport Chain (ETC) • High-energy electrons from Photosystem II are passed through the ETC… • ETC molecules reduced/oxidizedas they gain/lose electrons • Electrons fall back down the energy hill, releasing energy • ATP is synthesized • Upon reaching ground state, electrons go to Photosystem I ***

17. The Light Reactions The low-energy electron now moves into Photosystem I where it is hit by another photon of sunlight and is excited (moved up the energy hill) once again.

18. The Light Reactions • Photosystem I absorbs energy and promotes electrons to a higher energy state. • Electrons grabbed by primary electron acceptor • Transferred down a short energy hill (ETC) • Electrons deposited on NADP+ • NADP+ is reduced to form NADPH, a high energy molecule.

19. NADP+  NADPH Low energy High energy (Oxidized form) (Reduced form) NADP+ and NAD+ are electron carriers When they are “full,” they are carrying 2 electrons and 1 hydrogen atom and become NADPH or NADH.

20. The Light Reactions

21. Summary of Light Reactions • Photosystem II electrons “excited” • As they fall down energy hill, ATP produced • Water split to replace electrons lost • H20  2H+ + ½ O2 + 2 e- • Photosystem I electrons “excited” • As they fall down energy hill, they reduceNADP+ to form NADPH (used in “dark” reactions) • Products of light reactions: NADPH, ATP, O2

23. The Light Reactions 21% of Earth’s current atmosphere is O2 • This “waste product” of photosynthesis is critically important to all aerobic species.

24. The Calvin Cycle(The Dark Reactions)

25. The Calvin Cycle • Here, the high energy molecules formed in the light reactions (ATP and NADPH) are used. • Occurs in the stroma • Carbon dioxide is reduced into sugar

26. The Calvin Cycle • Four phases • Carbon fixation • Energizing the sugar • Production of sugar • Regeneration of starting materials

27. The Calvin Cycle #1. Carbon fixation • CO2 is attached to a five-carbon sugar (RuBP) • Accomplished by the enzyme Rubisco • 3 CO2 + 3 RuBP 3 six-carbon sugars • Immediately breaks into 6 three-carbon sugars (PGA) • 3 CO2 + 3RuBP  6 PGA

28. Carbon fixation

29. The Calvin Cycle #2. Energizing the sugar • 6 ATP and 6 NADPH are “spent” to reduce (energize) these three-carbon PGA sugars • Products are 6 high-energy sugars called G3P 6 ATP 6 NADPH

30. The Calvin Cycle

31. The Calvin Cycle #3. Production of sugar • One G3P molecule exits the Calvin cycle • This is the product of the Calvin cycle • The exiting G3P molecule is readily converted to glucose in reactions outside of the Calvin cycle • The other 5 G3P molecules remain in cycle

32. The Calvin Cycle

33. The Calvin Cycle #4. Regeneration of RuBP • The 5 G3P molecules remaining are used to regenerate RuBP • 5 G3P  3 RuBP • This conversion requires 3 ATP

34. The Calvin Cycle

36. Summary of Calvin Cycle • 3 CO2 + 3RuBP   6 PGA • 6 PGA 6 G3P • 6 ATP and 6 NADPH spent • One G3P removed as product • 5 G3P  3 RuBP • 3 ATP are spent • Overall accomplishment: 3 CO2 1 G3P* *Two G3P = 1 glucose

37. Summary of Photosynthesis In the Light Reactions, solar energy is converted to chemical energy that is stored in the form of ATP and NADPH. Water is required; oxygen is a byproduct. In the Calvin Cycle, this energy is used to make a high-energy sugar (G3P) from carbon dioxide and the sugar RuBP. Requires Rubisco bonding CO2 to the RuBP sugar and 6 ATP and 6 NADPH from the Light Reactions.

38. The product of photosynthesis 155 billion tons of material per year! alaska-in-pictures.com

39. daviddarling.info