1. Solar Power
Photosynthesis

2. Photoautotrophs
Photosynthetic organisms (plants, algae and some bacteria) make their own food from light and CO2
Mostly occurs in chloroplasts of the leaf cells (spongy mesophyll)

4. Chloroplasts Found in all green parts Most abundant in mesophyll cells
Chlorophyll is a green pigment which give plants their color

5. Chloroplast Structure
Thylakoids are membrane-bound discs in the chloroplast
Outside fluid is called the stroma
Contained in a double membrane

6. Chloroplast x5,755

7. Basic Chemical Equation
6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O Or
CO2 + H2O → CH2O + O2
Carbon Dioxide + Water + Light  Carbohydrates + Oxygen

8. Water is Split and Reformed
Page 171 of your book describes the discovery process (interesting read)
The water in the products is not the same water!
6 C O H2 O ↓
C6H12O6 + 6 H2O + 6 O2

9. Oxidation/Reduction
An oxidation reaction removes electrons from an atom H |
HO-C-OH → O=C=O
A reduction reaction adds electrons to an atom H |
O=C=O → HO-C-OH
(20 electrons)
(16 electrons)

10. OIL RIG Oxidation is Loss (of electrons)
Reduction is Gain (of electrons) (reducing the charge)

11. Reduction Process
Splitting of water releases electrons and hydrogen ions
These bond to the carbon, reducing it to a sugar
Electrons increase the potential energy of the molecule
∆G is + (endergonic)
Light provides the extra free energy

12. Steps of Photosynthesis
Light Reactions
Sunlight harvested to create ATP and NADPH
Calvin Cycle
ATP and NADPH turn CO2 into sugar

13. The Basics of Light Light = electromagnetic energy
Shorter the wavelength, the higher the energy
Chlorophyll absorbs the energy contained in light

15. Part 1: The Light Reactions

16. Phase 1: Excitation of Electrons

17. How Chlorophyll Absorbs Light
The electron in chlorophyll gets excited and jumps to a higher orbital
When it falls back into its normal orbital, it releases light energy
This can then energize the molecule next to it
Light
light
Step 1

18. Light and heat!
High free energy = unstable
Energy is spontaneously given off as heat and light

20. These electrons can be excited by energy from the sun

21. Photosystems Chlorophyll is arranged in photosystems
Hundreds of chlorophyll molecules and proteins
All molecules “pass their energy” to one particular chlorophyll
Called the reaction center
Step 1

22. The Primary Electron Acceptor
When the reaction center chlorophyll molecule's electron is excited it passes to the primary electron acceptor
Does not fall back down
Step 1

23. Photsystem e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e-
To Primary Electron Acceptor
Photsystem
Energy! e- e- e- e- e-
Energy! e- e- e- e- e-
Energy! e- e- e- e- e-
Energy! e- e- e- e- e- e- e- e- e- e-

25. Located in the thylakoid membrane
Photosystem I and II
Have slightly different reaction centers and absorb slightly different wavelengths of light
Located in the thylakoid membrane
Chlorophyll is the same! Protein arrangement around the chlorophyll is different

27. Phase 2: Electron Flow generates ATP and NADPH 2A Noncyclic Electron Flow 2B Cyclic Electron Flow

28. 2A Non-cyclic electron flow
The predominate route
Electron from photosystem II transferred to photosystem I
ATP is made during this process
Electron ends up on NADP+ molecule, forming NADPH
Water is split, replacing the electron of the Reaction center

29. Step 1 Photosystem II absorbs light Energy passed to reaction center
Electron is excited
Electron is passed to primary electron receptor
Reaction center has an electron hole

30. Step 2 Enzyme splits water
2H2O → 4H+ + O2 + 4e-
Electrons replace the reaction center electron
Forms O2

31. Splitting of Water H H e e e e e e e e O O H H e e e e e e H H e e H

32. Step 3
Each electron is passed down an Electron Transport Chain to Photosystem I
ATP made via chemiosmosis!

33. Step 4
Electrons “falling” down the chain allow proteins to pump H+ ions into thylakoid space
Buildup of H+ in thylakoid space
H+ ions diffuse through ATP synthase

34. Chemiosmosis
Electrons falling down the chain is coupled with pumping H+ into the thylakoid space (innermost part of thylakoids)
This causes the concentration of H+ in the thylakoid to be much higher than in the stroma
H+ ions cannot simply pass through the membrane
Instead they diffuse through ATP Synthase which uses the energy of the concentration gradient to produce ATP

36. Step 5 Electron ends up in the reaction center of Photosystem I
Replaces an electron that is passed to the primary electron acceptor

37. Step 6
The primary electron acceptor of photosystem I passes electrons to NADP+ forming NADPH
No ATP is made

38. Note this diagram uses a different set of numbers

40. H+ H+ H+
Light
Light H+
NADPH e- H+
H2O O2 e-

41. Noncyclic Electron Flow Review
Sunlight energizes electrons, which drive the synthesis of ATP as they are passed from photosystem II to photosystem I
They are again excited in photosystem I and transferred to NADP+ to form NADPH
NADPH and ATP are used in the Calvin cycle to make sugar

42. Review of Light Reactions
2TY&feature=video_response

43. 2B Cyclic Electron Flow
Non-cyclic electron flow creates equal amounts of ATP and NADPH but the Calvin cycle requires more ATP than NADPH
So electrons are sometimes rerouted back to the ETC from photosystem I to produce more ATP
No NADPH is produced, nor is water split

44. No water split! e-
No O2 made
No NADPH made

45. Review of Light Reactions
Light is harnessed by chlorophyll pigments in chloroplast's thylakoid membranes
This energy is used to create NADPH and ATP via Non Cyclic Electron Flow
Water is split and O2 is released as a byproduct
Extra ATP is made via Cyclic Electron Flow
The ATP and NADPH is used in the Calvin Cycle

46. DNA
Make a list of everything needed in the light reactions of photosynthesis

47. Light Reaction Requirements
Chloroplast/ thylakoid membrane
Chlorophyll / photosystems
H2O – provides electrons
Light – provides energy
ETC / NADP+ reductase
NADP+ / ADP + Pi
ATP Synthase H+

48. The Two Steps

49. Part II: The Calvin Cycle

50. Overview Takes place in stroma of chloroplast
Uses CO2 and energy from NADPH and ATP to make sugar
Actual product is glyceraldehyde 3- phosphate (G3P)
G3P can then form glucose and other sugars
3CO2 + 9ATP + 6NADPH → 1 G3P + 9 ADP + 9Pi + 6NADP+

53. Review of Calvin Cycle
logy/Bio231/calvin.html
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