1. PHOTOSYNTHESIS

2. Energy can be transformed from one form to another
FREE ENERGY
(available for work)
vs.
HEAT
(not available for work)

3. THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON EARTH

4. THE BASICS OF PHOTOSYNTHESIS
Almost all plants are photosynthetic autotrophs, as are some bacteria and protists
Phototrophs generate their own organic matter through photosynthesis
Sunlight energy is transformed to energy stored in the form of chemical bonds
(c) Euglena
(d) Cyanobacteria
(b) Kelp
(a) Mosses, ferns, and
flowering plants

5. Food Chain

6. THE FOOD WEB

7. WHY ARE PLANTS GREEN?
It's not that easy bein' green Having to spend each day the color of the leaves When I think it could be nicer being red or yellow or gold Or something much more colorful like that…
Kermit the Frog

8. Electromagnetic Spectrum and Visible Light
Gamma rays
Infrared & Microwaves
X-rays UV
Radio waves
Visible light
Wavelength (nm)

9. WHY ARE PLANTS GREEN?
Different wavelengths of visible light are seen by the human eye as different colors.
Gamma rays
Micro- waves
Radio
waves
X-rays UV
Infrared
Visible light
Wavelength (nm)

10. The feathers of male cardinals are loaded with carotenoid pigments
The feathers of male cardinals are loaded with carotenoid pigments. These pigments absorb some wavelengths of light and reflect others.
Reflected light
Sunlight minus absorbed wavelengths or colors equals the apparent color of an object.

11. Why are plants green?
Reflected light
Transmitted light

12. WHY ARE PLANTS GREEN? Plant Cells have Green Chloroplasts
The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).

13. THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED
Chloroplasts absorb light energy and convert it to chemical energy
Reflected
light
Light
Absorbed
light
Transmitted
light
Chloroplast

14. AN OVERVIEW OF PHOTOSYNTHESIS
Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
Carbon dioxide
Water
Glucose
Oxygen gas
PHOTOSYNTHESIS

15. AN OVERVIEW OF PHOTOSYNTHESIS
The light reactions convert solar energy to chemical energy
Produce ATP & NADPH
Light
Chloroplast
NADP
ADP
+ P
Calvin
cycle
Light
reactions

16. AN OVERVIEW OF PHOTOSYNTHESIS
The Calvin cycle or the dark reactions make sugar from carbon dioxide
ATP generated by the light reactions provides the energy for sugar synthesis
The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose
Light
Chloroplast
NADP
ADP
+ P
Calvin
cycle
Light
reactions

17. Photosynthesis occurs in chloroplasts
In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts
Leaves generally have the most chloroplasts
A chloroplast contains:
stroma, a fluid
grana, stacks of thylakoids
The thylakoids contain chlorophyll
Chlorophyll is the green pigment that captures light for photosynthesis

18. The location and structure of chloroplasts
LEAF CROSS SECTION
MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST
Intermembrane space
Outer
membrane
Granum
Inner membrane
Grana
Stroma
Thylakoid compartment
Stroma
Thylakoid

19. Chloroplast Pigments Chloroplasts contain several pigments
Chlorophyll a
Chlorophyll b
Carotenoids
Figure 7.7

20. Chlorophyll a and b: primary pigment

21. Phytoerythrobilin: xanthophyll for bacteria

22. Β-carotene and lutein: accessory plant pigments

23. Different pigments absorb light differently

24. A light harvesting complex: LHCII

25. Chlorophyll and other pigments: antenna molecules:

26. The light-absorbing pigments of thylakoid or bacterial membranes are arranged in functional arrays called photosystems.

27. All the pigment molecules in a photosystem can absorb photons, but only a few chlorophyll molecules associated with the photochemical reaction center are specialized to transduce light into chemical energy.

28. The other pigment molecules in a photosystem are called light-harvesting or antenna molecules. They absorb light energy and transmit it rapidly and efficiently to the reaction center

31. Excitation of chlorophyll in a chloroplast
Loss of energy due to heat causes the photons of light to be less energetic.
But in nature, the structure of the light harvesting centers prevent the loss of energy as heat or even light.
The proteins and other molecules allow the photochemical reactions to take place in a solid state manner e e
Excited
state 2
Heat
Light
Light
(fluorescence)
Photon
Ground
state
Chlorophyll
molecule
(a) Absorption of a photon
(b) fluorescence of isolated chlorophyll in solution

32. In plants, two photosynthetic reaction centers work in tandem
Photosystem II and photosystem I work together to catalyze the light-driven movement of electrons from H2O to NADP+, essentially producing NADPH and ATP in the process
The excited electrons are passed from the primary electron acceptor to electron transport chains
Their energy ends up in ATP and NADPH

33. Two types of photosystems cooperate in the light reactions
Photon
ATP
mill
Photon
Water-splitting
photosystem
NADPH-producing
photosystem

34. Noncyclic Photophosphorylation
Photosystem II regains electrons by splitting water, leaving O2 gas as a by-product
Primary electron acceptor
Electron transport chain
Electron transport
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy for synthesis of
by chemiosmosis

35. Sample photosystem II: Synochoccus elongates cyanobacterium

36. Plants produce O2 gas by splitting H2O
The O2 liberated by photosynthesis is made from the oxygen in water (H+ and e-)

37. The water-splitting complex (aka oxygen-evolving complex)

38. Plastocyanin and the cytochrome b6f complex connect the two photosystems

39. Plastocyanin and the cytochrome b6f complex connect the two photosystems

41. Chemiosmosis powers ATP synthesis in the light reactions
The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H+ through that membrane
The flow of H+ back through the membrane is harnessed by ATP synthase to make ATP
In the stroma, the H+ ions combine with NADP+ to form NADPH

42. ELECTRON TRANSPORT CHAIN
The production of ATP by chemiosmosis in photosynthesis
Thylakoid compartment (high H+)
Light
Light
Thylakoid membrane
Antenna molecules
Stroma (low H+)
ELECTRON TRANSPORT CHAIN
PHOTOSYSTEM II
PHOTOSYSTEM I
ATP SYNTHASE

44. Bacteria: Cyclic Photophosphorylkation
Process for ATP generation associated with some photosynthetic pacteria
Reaction Center => 700 nm

45. Cyanobacteria utilize some electron carriers in both photophosphorylation and oxidative phosphorylation

47. How the Light Reactions Generate ATP and NADPH
Primary
electron
acceptor
NADP
Energy
to make
Primary
electron
acceptor 3 2
Light
Electron transport chain
Light
Primary
electron
acceptor
Reaction-
center
chlorophyll 1
NADPH-producing
photosystem
Water-splitting
photosystem
2 H + 1/2

48. Photosystem I: light to NADPH

49. Photosystem I: light to NADPH

51. NADPH and ATP produced by the light reactions is used to synthesize glucose

52. The 1st stage of CO2 assimilation in photosynthetic organisms: FIXATION

53. Rubisco: A photosynthetic VIP
Rubisco, more properly known as ribulose 1,5-bisphosphate carboxylase, is the enzyme responsible for catalyzing the incorporation of 3 CO2 molecules into a single 3-phosphoglycerate molecule.

54. 2nd stage of CO2 assimilation
Conversion of 3-phosphoglycerate to glyceraldehyde 3-phosphate
Essentially the reverse of the similar reaction in glycolysis, but NADPH is used instead of NADH.

56. 3rd stage of CO2 assimilation
Regeneration of ribulose 1,5-bisphosphate from triose phosphates

59. Overall: Photosynthesis uses light energy to make food molecules
Chloroplast
Photosystem II Electron transport chains Photosystem I
CALVIN CYCLE
Stroma
Electrons
Cellular respiration
Cellulose
Starch
Other organic compounds
LIGHT REACTIONS
CALVIN CYCLE