1. Chapter 10
Photosynthesis

2. Objectives Describe the structure and function of a chloroplast.
Describe methods of solar capture and ATP production.
Describe how carbohydrates are synthesized.
Compare and contrast the 3 modes of photosynthesis.

3. Key Terms ATP Synthase Chloroplast Chlorophyll Stroma Thylakoid
light reactions
Calvin cycle
Antenna complex
Ribulose biphosphate
PGAL
Photosystem
Photorespiration
CAM photosynthesis
C3 Photosynthesis
C4 Photosynthesis
Chemiosmosis

4. Do you know this reaction?12
+ 6 H2O

5. Photosynthesis occurs in 2 stages.

6. Solar Energy Capture

7. Solar energy

8. Most available energy is not used
42% of solar energy reaches Earth’s surface
2% of the 42% utilized by plants, remainder becomes heat
Only 0.1% - 1.6% is incorporated into plant material.
Photosynthesis uses the portion of the electromagnetic spectrum known as visible light.

9. Photosynthetic Pigments

10. Electromagnetic Spectrum

11. Absorption Spectra

12. Photosynthetic Pigments Animation: Light and Pigments
Chlorophyll a and b
Absorbs violet, blue and red better than other colors.
Green NOT absorbed!
Animation: Light and Pigments

13. Photosynthetic Pigments
Chlorophyll a - main photosynthetic pigment
chlorophyll b - accessory pigments; broadens the spectrum used for photosynthesis
carotenoids - accessory pigments that absorb excessive light that would damage chlorophyll

15. Leaf Structure

16. Chlorophyll (Terpene)

18. Structure & Function of Chloroplasts

19. Chloroplasts Internal membranes, thylakoids, are organized into grana.
Thylakoid membranes house pigments for capturing light and the machinery to produce ATP.
clustered together to form a photosystem
acts as an antenna, gathering light energy harvested by multiple pigment molecules

20. Chloroplasts

21. Interaction of Light with Chloroplasts

23. Stage 1 Light-dependent Reactions

24. (Solar Energy Capture)
The Light Reactions
(Solar Energy Capture)
In membranes of thylakoids
Involves two light-gathering units
Photosystem I
Photosystem II
Converts sunlight to chemical energy (ATP).
O2 is a "waste product"

25. Photosynthesis Output
Increases linearly at low light intensities but lessens at higher intensities.
Reaches a saturation point

26. Electron Pathways
Cyclic – electrons originate & return to PSI reaction center
ATP is produced
Noncyclic – electrons leave PSII and go to PSI
H2O is oxidized yielding H+, e- and O2
NADP+ becomes NADPH

27. Photosystem
Network of pigments that channels excitation energy gathered by any of the molecules to the reaction center.
reaction center allows photon excitation to move away from chlorophylls and is the key conversion of light to chemical energy

28. Photosystem II complex (PSII) (P680 - Oxygen evolving apparatus)
                                                                                                               
Membrane protein complex found in photosynthetic organisms (higher plants, green algae and cyanobacteria)
Harnesses light energy to split H2O into O2, protons and electrons.
Responsible for the production of atmospheric oxygen
Also involved in the production of a substantial proportion of the global biomass.

29. Reaction Center
Allows photon excitation to move away from chlorophylls and is the key conversion of light to chemical energy

30. Photosystem Function electron is joined with a proton to make hydrogen
Bacteria use a single photosystem, Photosystem I (P700)
electron is joined with a proton to make hydrogen
electron is recycled to chlorophyll

31. Photosystem Function Plants use two photosystems
photosystem I (P700) and II (P680)
generate power to reduce NADP+ to NADPH with enough left over to make ATP
two stage process: photosystem II – I.
noncyclic photophosphorylation
ejected electrons end up in NADPH

32. Cyclic Electron Pathway

33. Linear Electron Pathway

35. Chlorophylls a & b and accessory pigments
(Chlorophyll a)
Chlorophylls a & b and accessory pigments

36. ATP production tied to an electro- chemical gradient.
Chemiosmosis
ATP production tied to an electro- chemical gradient.

39. Stage 2 Light-independent Reactions

40. Carbohydrate Synthesis

41. Sometimes called light-independent reactions.
Calvin Cycle
Sometimes called light-independent reactions.
Essential Question
Does the Calvin cycle continue running in a plant kept in the dark?

42. Calvin Cycle Takes place in the stroma
Makes sugar from CO2 (CO2 becomes CH2O)
Energy supplied by ATP made by light reaction
Electrons supplied by NADPH
G3P (glyceraldehyde-3-phosphate = PGAL)

43. Light-Independent Reactions

44. P3G (glyceraldehyde-3-phosphate = PGAL)
Product of Calvin cycle
Important biochemical reactant

46. Modes of PhotosynthesisC3 C4
CAM

47. C3 Photosynthesis Most plants are C3. (Kentucky Bluegrass)
Stomata open during the day
Photosynthesis throughout the leaf. CO2 enters Calvin Cycle directly - fixed using RuBP carbolylase
More efficient than C4 and CAM under cool and moist conditions and under normal light (fewer enzymes and no specialized anatomy).

48. C4 Pathway
Plants adapted to warmer environments deal with the loss of CO2 in two ways:
C4 conducted in mesophyll cells, Calvin cycle in bundle sheath cells
creates high local levels of CO2 to favor carboxylation reaction of rubisco
isolates CO2 production spatially

49. C4 Photosynthesis
CO2 undergoes “preliminary fixation into malate (a C4 molecule) before entering Calvin cycle.
Malate stored in large vacuoles in mesophyll cells (CO2 fixation is partitioned by space)
Hot, dry climates
Photosynthesis takes place in inner cells
Include several thousand species in at least 19 families. (crabgrass, corn, and many summer annuals)

50. C4 Photosynthesis (Cont’d)
Adaptive Value:
Photosynthesizes faster than C3 plants under high light intensity and high temperatures
Better water use efficiency because PEP Carboxylase brings in CO2 faster and does not need to keep stomata open as much (less water lost by transpiration)

51. C4 Photosynthesis

52. Leaf Structure

53. Comparison of C3 and C4 Leaf Anatomy

54. CAM Photosynthesis (Crassulacean Acid Metabolism )
The CO2 converted to an acid and stored during night as an acid.
Stomata open at night, usually closed during the day. (Reduces loss of water vapor)
Daytime - acid broken down and the CO2 is released to RUBISCO for photosynthesis
Include many succulents, also some orchids and bromeliads.

55. CAM Photosynthesis Adaptive Value
Better Water Use Efficiency than C3 under arid conditions (transpiration rates are lower, no sunlight, lower temperatures, lower wind speeds, etc.)

56. CAM Photosynthesis Adaptive Value
CAM-idle under extreme conditions.
Stomata closed night and day.
O2 from photosynthesis is used for respiration, CO2 from respiration used for photosynthesis.
Cannot CAM-idle forever.
Survival of dry spells and rapid recovery when water is available again. (No dormancy)

57. Carbon Fixation

58. Photorespiration
O2 is incorporated into RuBP, which undergoes additional reactions that release CO2.
decreased yields of photosynthesis

59. THAT’S ALL FOLKS