1. The Energy Conversion Process of Photosynthesis

2. Chloroplasts: The Sites of Photosynthesis in Plants
Leaves are the major locations of photosynthesis
Their green color is from chlorophyll, the green pigment within chloroplasts
Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast
CO2 enters and O2 exits the leaf through microscopic pores called stomata
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3. A typical mesophyll cell has 30–40 chloroplasts
Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf
A typical mesophyll cell has 30–40 chloroplasts
The chlorophyll is in the membranes of thylakoids (connected sacs in the chloroplast); thylakoids may be stacked in columns called grana
Chloroplasts also contain stroma, a dense fluid
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4. Fig. 10-3
Leaf cross section
Vein
Mesophyll
Stomata
CO2 O2
Chloroplast
Mesophyll cell
Outer
membrane
Figure 10.3 Zooming in on the location of photosynthesis in a plant
Thylakoid
Intermembrane
space
5 µm
Stroma
Granum
Thylakoid
space
Inner
membrane
1 µm

5. Fig. 10-3a Leaf cross section Vein Mesophyll Stomata CO2 O2
Chloroplast
Mesophyll cell
Figure 10.3 Zooming in on the location of photosynthesis in a plant
5 µm

6. Fig. 10-3b Chloroplast Outer membrane Thylakoid Intermembrane space
Stroma
Granum
Thylakoid
space
Inner
membrane
Figure 10.3 Zooming in on the location of photosynthesis in a plant
1 µm

7. Photosynthesis Photosynthesis-
Converting solar energy into the usable energy of carbohydrates.
Photosynthesis requires:
Light Energy
Carbon Dioxide
Water
Chlorophyll
Putting together with light

8. The light reactions (in the thylakoids):
Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules.
Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)
The light reactions (in the thylakoids):
Split H2O
Release O2
Reduce NADP+ to NADPH
Generate ATP from ADP by photophosphorylation

9. Light Energy Photon- packets of Energy
Light travels in waves and is a type of radiation
Short wave length radiation has high energy photons
Long wave length radiation has lower energy photons

10. Light Energy
Photons of visible light have enough energy to raise electrons to higher levels of energy which is needed for photosynthesis.
Visible light energy is absorbed by plants to produce sugar. (C6H12O6)
Chlorophyll is the substance that absorbs light energy.

11. Pop Quiz 1. In your own words, define photosynthesis
2. In your own words, define cellular respiration.
3. What is ATP
4. How is ATP generated or made?
5. Which bond in ATP is loaded with energy?

12. Chlorophyll (borophyll)
Two Types of Chlorophyll
Chlorophyll A
Chlorophyll B
Carotenoids
Other pigments that are yellow-orange in plants which absorb violets, blues, and greens.
As chlorophyll A and B breakdown they become more noticeable, especially during the fall.
Both absorb violet, blue, and red light. Because green is only minimally absorbed, the leaf appears green. The green light is reflected off of the leaf. }

13. Photosynthesis- the formula
6 CO2 + 6 H2O  C6H12O6 + 6 O2
LIGHT
CHLOROPHYLL

14. i Light NADP+ ADP Light Reactions Chloroplast H2O + P Fig. 10-5-1
Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
Chloroplast

15. i Light NADP+ ADP Light Reactions ATP NADPH Chloroplast O2 H2O + P
Fig
H2O
Light
NADP+
ADP + P i
Light
Reactions
ATP
Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
NADPH
Chloroplast O2

16. i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH
Fig
H2O
CO2
Light
NADP+
ADP + P i
Calvin
Cycle
Light
Reactions
ATP
Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
NADPH
Chloroplast O2

17. Chloroplasts – contain chlorophyll
Chloroplasts are double membrane organelles. (See figure in book)
Note the granum, stroma, thylakoid, and thylakoid space
Chlorophyll is found within the membranes of the thylakoids

18. Photosynthesis has two reactions
Light dependent Reactions (light RXN)
Light capturing reaction
absorbs solar energy
Occurs in the thylakoid membrane
Light independent Reactions (dark RXN) Now called the Calvin Cycle
Synthesis reaction
Produces glucose
Occurs in the stroma

19. Light Dependent Reactions
Takes place in the thylakoid membrane
Requires two light gathering systems
Photosystems- systems used to gather solar energy which contain chlorophyll A,B, and carotenoids.
The photosystems were named in the order that they were discovered, not the order in which they occur.
Photosystem I (PSI) The molecules of Chlorophyll a & b which make up the photosystems Photosystem II (PSII) act like antennas gathering solar energy and focus it to a particular spot. }

20. i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH
Fig
H2O
CO2
Light
NADP+
ADP + P i
Calvin
Cycle
Light
Reactions
ATP
Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
NADPH
Chloroplast
[CH2O]
(sugar) O2

21. PSI and PSII
Basically, the function of the photosystems is to convert energy so that glucose can be produced. This is accomplished by generating electron flow.
Sometimes PSI occurs exclusively called the cyclic electron pathway.
When both PSI and PSII occur PSII occurs first and then PSI. This process is the non-cyclic electron pathway.

22. Generating electron flow
Energy is directed onto a particular molecule of chlorophyll A . The electrons of this molecule are so excited that they escape their orbitals and move through a series of electron acceptors.
Reaction center- The molecule of chlorophyll A that loses an electron.

23. (INTERIOR OF THYLAKOID)
Fig
Photosystem
STROMA
Photon
Primary
electron
acceptor
Light-harvesting
complexes
Reaction-center
complex e–
Thylakoid membrane
Figure How a photosystem harvests light
Pigment
molecules
Transfer
of energy
Special pair of
chlorophyll a
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)

24. Cyclic Electron Pathway (PS1) (not play station 1)
An electron leaves the RXN center but eventually returns to it.
As the electron is passed from acceptor to acceptor Energy for ATP is released.
Occurs when:
CO2 levels are extremely low
by photosynthetic bacteria

25. Cyclic pathway – PS1 (cont.)
Does not produce NADPH
Produces ONLY ATP
Probably first to evolve,
Because CO2 levels are low no glucose is produced and the organism must survive on the small amount of ATP that is generated

26. Non-cyclic Pathway (PS 2) (not play station 2)
Water is split and an electron enters PSII
Causes the reaction center to lose an electron and travel through a series of electron acceptors.
As the electron is passed along ATP is generated. This ATP will be used in the Light independent reactions
The electron then enters PSI which during the non-cyclic pathway produces the molecule NADPH instead of ATP.

27. Non-cyclic (cont.)
The products of the non-cyclic pathway, NADPH and ATP, enter the Stroma
NADP is one of several biological molecules that act as an electron carrier.
In the stroma, the light independent reactions occur.
The splitting of water results in a H ion (which is basically an electron) and O which is released from the leaf as a waste product.

28. Electron transport chain
Fig
Electron
transport
chain
Primary
acceptor
Primary
acceptor 4 7
Electron transport chain Fd Pq e– 2 e– 8 e–
H2O e–
NADP+
+ H+
Cytochrome
complex
2 H+
NADP+
reductase + 3
1/2 O2
NADPH Pc e– e–
P700 5
P680
Light 1
Light 6 6
ATP
Figure How linear electron flow during the light reactions generates ATP and NADPH
Pigment
molecules
Photosystem I
(PS I)
Photosystem II
(PS II)

29. Electron transport chain
Fig
H2O
CO2
Light
NADP+
ADP + P i
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
RuBP
3-Phosphoglycerate
Calvin
Cycle
ATP
G3P
Figure A review of photosynthesis
Starch
(storage)
NADPH
Chloroplast O2
Sucrose (export)

30. Photophosphorylation
Occurs when ATP is generated using photosynthesis.
Photophosphorylation occurs because of severe differences in the concentration of H+ ions inside the thylakoid space compared to the stroma.
The movement of ions allows for a phosphate to be added to ADP.

31. Diagram of the Light Dependent Reactions and ATP Synthase

32. Quiz
1. How is the cyclic pathway different than the non-cyclic pathway?
2. In the non-cyclic pathway, what produces ATP?
3. In the non-cyclic pathway, what produces NADPH?
4. What is the role of NADPH?

33. Light Independent Reactions AKA- Calvin Cycle (The Dark RXN)
The products of the light dependent reactions are NADPH and ATP.
Both are used in the light independent reactions.
The actual process of producing glucose during the light independent RXN is called the Calvin Cycle.

34. A Comparison of Chemiosmosis in Chloroplasts and Mitochondria
Chloroplasts and mitochondria generate ATP by chemiosmosis, but use different sources of energy
Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP
Spatial organization of chemiosmosis differs between chloroplasts and mitochondria but also shows similarities

35. In mitochondria, protons are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix
In chloroplasts, protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma

36. H+ Diffusion Electron transport chain ADP + P
Fig
Mitochondrion
Chloroplast
MITOCHONDRION
STRUCTURE
CHLOROPLAST
STRUCTURE H+
Diffusion
Intermembrane
space
Thylakoid
space
Electron
transport
chain
Inner
membrane
Thylakoid
membrane
Figure Comparison of chemiosmosis in mitochondria and chloroplasts
ATP
synthase
Matrix
Stroma
Key
ADP + P i
ATP
Higher [H+] H+
Lower [H+]

37. In summary, light reactions generate ATP and increase the potential energy of electrons by moving them from H2O to NADPH
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

38. The Calvin Cycle (light independent reactions)
Has three steps/parts (see fig)
1. CO2 fixation
2. CO2 reduction
3. Regeneration of RuBP
RuBP is a 5 carbon compound that will combine with CO2 to form a 6 Carbon Compound.
Remember, glucose is a 6 C compound

39. Step 1- CO2 Fixation
Refers to the attachment of CO2 to an organic compound.
3 CO2 bind with 3 RuBP molecules.
Results in 3 six Carbon compounds
which change to 6 three carbon compounds
The three Carbon compound is called PGA
The Calvin Cycle is sometimes called the C-3 cycle because of PGA.

40. Phase 1: Carbon fixation Ribulose bisphosphate
Fig
Input 3
(Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco 3 P P
Short-lived
intermediate 3 P P 6 P
Ribulose bisphosphate
(RuBP)
3-Phosphoglycerate
Figure The Calvin cycle

41. Step 2 - CO2 Reduction Requires ATP and NADPH (from light RXN)
PGA gets converted to G3P (PGAL) using ATP and NADPH.
ATP  ADP + P
NADPH  NADP
PGA  G3P (PGAL)
The reduction of CO2 to CH2O results in 6 total PGAL molecules.
5 molecules of G3P (PGAL) will be used to regenerate RuBP.
It takes 3 turns of the Calvin Cycle to have a net gain of 1 G3P (PGAL)

42. Fig. 10-18-2 Figure 10.18 The Calvin cycle Input 3 (Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco 3 P P
Short-lived
intermediate 3 P P 6 P
Ribulose bisphosphate
(RuBP)
3-Phosphoglycerate 6
ATP
6 ADP
Calvin
Cycle 6 P P
1,3-Bisphosphoglycerate 6
NADPH
6 NADP+ 6 P i
Figure The Calvin cycle 6 P
Glyceraldehyde-3-phosphate
(G3P)
Phase 2:
Reduction 1 P
Glucose and
other organic
compounds
Output
G3P
(a sugar)

43. G3P (PGAL) Glucose Glucose is used to produce ATP
Plants need several other organic compounds.
G3P (PGAL) can be converted to many other compounds such as: fatty acids, Amino Acids, and of course Glucose.
Technically, the Calvin cycle ends with the production of G3P (PGAL)

44. Step 3 - RuBP Regeneration
5 (PGAL) G3P 3 RuBP
3 ATP  3 ADP + P
ATP comes from the light dependent reactions

45. Fig. 10-18-3 Figure 10.18 The Calvin cycle Input 3 (Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco 3 P P
Short-lived
intermediate 3 P P 6 P
Ribulose bisphosphate
(RuBP)
3-Phosphoglycerate 6
ATP
6 ADP
3 ADP
Calvin
Cycle 6 3 P P
ATP
1,3-Bisphosphoglycerate 6
NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+ 6 P i
Figure The Calvin cycle 5 P
G3P 6 P
Glyceraldehyde-3-phosphate
(G3P)
Phase 2:
Reduction 1 P
Glucose and
other organic
compounds
Output
G3P
(a sugar)

46. Electron transport chain
Fig
H2O
CO2
Light
NADP+
ADP + P i
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
RuBP
3-Phosphoglycerate
Calvin
Cycle
ATP
G3P
Figure A review of photosynthesis
Starch
(storage)
NADPH
Chloroplast O2
Sucrose (export)

47. Variations in Photosynthesis
The C-3 Pathway –
CO2 is fixed during the Calvin cycle, and the first detectable molecule is a 3 Carbon compound (PGA).
The C-4 Pathway –
CO2 is fixed to a 3 C compound (forming a 4 C compound) prior to the Calvin Cycle.
CAM Plant Pathway –
Similar to the C- 4 Pathway, but at a slightly different time.

48. C-3 Pathway Occurs in the mesophyll of the leaf RuBP  PGA P3G (PGAL)
See Figure

49. C-4 Pathway
CO2 is attached to a 3 C compound called PEP with an enzyme called PEP-carboxylase.
This process forms oxaloacetate and occurs in the mesophyll.
Oxaloacetate enters the bundle sheath cells where the Calvin Cycle takes place
Occurs in warm dry climates
Partition PSS in space
See Figure 10.14

50. The C4 pathway Mesophyll cell CO2 PEP carboxylase Oxaloacetate (4C)
Fig b
The C4
pathway
Mesophyll
cell
CO2
PEP carboxylase
Oxaloacetate (4C)
PEP (3C)
ADP
Malate (4C)
ATP
Pyruvate (3C)
Bundle-
sheath
cell
CO2
Calvin
Cycle
Figure C4 leaf anatomy and the C4 pathway
Sugar
Vascular
tissue

51. CAM plant Pathway
A C4 compound is produced similar to the C-4 pathway.
That compound is produced during the night, and stored in the vacuole until day.
Occurs in the mesophyll
Occurs in hot, dry and stressful environments
Allows Stomates to open at night when it is cooler and less water is lost to evaporation.

52. (a) Spatial separation of steps (b) Temporal separation of steps
Fig
Sugarcane
Pineapple C4
CAM
CO2
CO2
Mesophyll
cell 1
CO2 incorporated
into four-carbon
organic acids
(carbon fixation)
Night
Organic acid
Organic acid
Figure C4 and CAM photosynthesis compared
Bundle-
sheath
cell
CO2
CO2
Day 2
Organic acids
release CO2 to
Calvin cycle
Calvin
Cycle
Calvin
Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps

53. The Importance of Photosynthesis: A Review
The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds
Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells
Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits
In addition to food production, photosynthesis produces the O2 in our atmosphere