© 2010 Pearson Education, Inc.
THE BASICS OF PHOTOSYNTHESIS
• Photosynthesis:
– Is used by plants, some protists, and some...
© 2010 Pearson Education, Inc.
Chloroplasts: Sites of Photosynthesis
• Chloroplasts are:
– The site of photosynthesis
– Fo...
© 2010 Pearson Education, Inc.
• Inside chloroplasts are membranous sacs called
thylakoids, which are suspended in a thick...
© 2010 Pearson Education, Inc.
• Stomata are tiny pores in leaves where carbon dioxide enters and
oxygen exits.
Leaf cross section
Stomata
Vein
CO2 O2
Figure 7.2-1
Leaf cross section
Stomata
Vein
CO2 O2
Interior cell LM
StromaGranum Thylakoid
Chloroplast
Outer
membrane
Inner
membrane
T...
Leaf cross section
Stomata
Vein
CO2 O2
Figure 7.2a
StromaGranum Thylakoid
Chloroplast Outer
membrane
Inner
membrane
TEM
Figure 7.2b
© 2010 Pearson Education, Inc.
The Overall Equation for Photosynthesis
• In the overall equation for photosynthesis, notic...
Carbon
dioxide
6 O26 CO2
6 H2O C6H12O6
Water Glucose
Photo-
synthesis Oxygen gas
Light
energy
Figure 7.UN1
© 2010 Pearson Education, Inc.
• In photosynthesis:
– Sunlight provides the energy
– Electrons are boosted “uphill” and ad...
© 2010 Pearson Education, Inc.
• During photosynthesis, water is split into:
– Hydrogen
– Oxygen
• Hydrogen is transferred...
© 2010 Pearson Education, Inc.
A Photosynthesis Road Map
• Photosynthesis occurs in two stages:
– The light reactions conv...
Light
H2O
O2
Chloroplast
Light
reactions
NADPH
ATP
Figure 7.3-1
Light
H2O
O2
Chloroplast
Light
reactions
NADPH
ATP
Calvin
cycle
CO2
NADP+
ADP
P
Sugar
(C6H12O6)
Figure 7.3-2
© 2010 Pearson Education, Inc.
How Photosystems Harvest Light Energy
• Light behaves as photons, discrete packets of energ...
© 2010 Pearson Education, Inc.
• Chlorophyll molecules absorb photons.
– Electrons in the pigment gain energy.
– As the el...
Light
Photon
Heat
Light (fluorescence)
Ground state
Chlorophyll
molecule
Excited state
e–
(a) Absorption of a photon
Figur...
© 2010 Pearson Education, Inc.
• A photosystem is a group of chlorophyll and other molecules that
function as a light-gath...
Chloroplast
Figure 7.9-1
Chloroplast
Thylakoid
membrane
Pigment molecules
Figure 7.9-2
Chloroplast
Thylakoid
membrane
Pigment molecules
Antenna pigment
molecules
Primary
electron
acceptor
Reaction-
center
chlo...
© 2010 Pearson Education, Inc.
How the Light Reactions Generate ATP and
NADPH
• Two types of photosystems cooperate in the...
Primary
electron
acceptor
Water-splitting
photosystem
Light
H2O
2 H
Reaction-
center
chlorophyll
2e–
2e–
O2++ 1
2
Figure 7...
Primary
electron
acceptor
Water-splitting
photosystem
Light
H2O
2 H
Reaction-
center
chlorophyll
2e–
2e–
O2++
Energy
to ma...
Primary
electron
acceptor
Water-splitting
photosystem
Light
H2O
2 H
Reaction-
center
chlorophyll
2e–
2e–
O2++
Energy
to ma...
© 2010 Pearson Education, Inc.
• The light reactions are located in the thylakoid membrane.
© 2010 Pearson Education, Inc.
• An electron transport chain:
– Connects the two photosystems
– Releases energy that the c...
Light
H2O
Thylakoid
membrane
2e–
O2
ATP
NADP
Light
Stroma
Inside thylakoid
Photosystem Photosystem
Electron transport cha...
Light
H2O
Thylakoid
membrane
2e–
O2
ATP
NADP
Light
Stroma
Inside thylakoid
Photosystem Photosystem
Electron transport cha...
Water-splitting
photosystem
e–
ATP
NADPH
e–
e–
e–
e–
e–
e–
NADPH-producing
photosystem
Figure 7.12
THE CALVIN CYCLE: MAKING SUGAR
FROM CARBON DIOXIDE
• The Calvin cycle:
– Functions like a sugar factory within the stroma ...
Calvin
cycle
P
P
P
Three-carbon moleculeRuBP sugar
CO2 (from air)
Figure 7.13-1
ATP
NADPH
Calvin
cycle
ADP  P
NADP
P
P
P
P
G3P sugar
Three-carbon moleculeRuBP sugar
CO2 (from air)
Figure 7.13-2
ATP
NADPH
ADP  P
NADP
P
P
P
P
P
P
G3P sugar
Three-carbon molecule
G3P sugar
G3P sugar
RuBP sugar
CO2 (from air)
Calvin
c...
ATP
NADPH
Calvin
cycle
ADP  P
NADP
P
P
P
P
P
P
ADP  P
ATP
G3P sugar
Three-carbon molecule
G3P sugar
G3P sugar
RuBP suga...
Evolution Connection:
Solar-Driven Evolution
• C3 plants:
– Use CO2 directly from the air
– Are very common and widely dis...
© 2010 Pearson Education, Inc.
• C4 plants:
– Close their stomata to save water during hot and dry weather
– Can still car...
Sugar
C4 Pathway
(example: sugarcane)
C4 plant
Calvin
cycle
Cell
type 1
Four-carbon
compound
Cell
type 2
CO2
CO2
Figure 7....
CAM plant
Sugar
Calvin
cycle
Day
Four-carbon
compound
Night
CAM Pathway
(example: pineapple)
CO2
CO2
Figure 7.14b
Carbon
dioxide
6 O26 CO2
6 H2O C6H12O6
Water Glucose
Photo-
synthesis Oxygen gas
Light
energy
Figure 7.UN1
Light
reactions
CO2
O2
H2O
(C6H12O6)
NADPH
Light
Sugar
ATP
ADP
P
NADP
Calvin
cycle
Figure 7.UN2
Light
reactions
CO2
O2
H2O
(C6H12O6)
NADPH
Light
Sugar
ATP
ADP
P
NADP
Calvin
cycle
Figure 7.UN3
Carbon
dioxide
6 O26 CO2
6 H2O C6H12O6
Water Glucose
Photosynthesis
Oxygen
gas
Light energy
Figure 7.UN4
Light H2O
O2
Chloroplast
Light
reactions
NADPH
ATP
Calvin
cycle
CO2
NADP+
ADP
P
Sugar
(C6H12O6)
Stack of
thylakoids Stroma...
acceptor
Water-splitting
photosystem
Photon
H2O
2 H
Chlorophyll
2e–
O2++
ATP
NADPH-producing
photosystem
Chlorophyll
NADPH...
NADPH
Calvin
cycle
ADP P
NADP
P
ATP
G3P
CO2
Glucose and
other compounds
Figure 7.UN7
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  1. 1. © 2010 Pearson Education, Inc. THE BASICS OF PHOTOSYNTHESIS • Photosynthesis: – Is used by plants, some protists, and some bacteria – Transforms light energy into chemical energy – Uses carbon dioxide and water as starting materials • The chemical energy produced via photosynthesis is stored in the bonds of sugar molecules.
  2. 2. © 2010 Pearson Education, Inc. Chloroplasts: Sites of Photosynthesis • Chloroplasts are: – The site of photosynthesis – Found mostly in the interior cells of leaves
  3. 3. © 2010 Pearson Education, Inc. • Inside chloroplasts are membranous sacs called thylakoids, which are suspended in a thick fluid, called stroma. • Thylakoids are concentrated in stacks called grana. • The green color of chloroplasts is from chlorophyll, a light- absorbing pigment.
  4. 4. © 2010 Pearson Education, Inc. • Stomata are tiny pores in leaves where carbon dioxide enters and oxygen exits.
  5. 5. Leaf cross section Stomata Vein CO2 O2 Figure 7.2-1
  6. 6. Leaf cross section Stomata Vein CO2 O2 Interior cell LM StromaGranum Thylakoid Chloroplast Outer membrane Inner membrane TEM Figure 7.2-2
  7. 7. Leaf cross section Stomata Vein CO2 O2 Figure 7.2a
  8. 8. StromaGranum Thylakoid Chloroplast Outer membrane Inner membrane TEM Figure 7.2b
  9. 9. © 2010 Pearson Education, Inc. The Overall Equation for Photosynthesis • In the overall equation for photosynthesis, notice that: – The reactants of photosynthesis are the waste products of cellular respiration.
  10. 10. Carbon dioxide 6 O26 CO2 6 H2O C6H12O6 Water Glucose Photo- synthesis Oxygen gas Light energy Figure 7.UN1
  11. 11. © 2010 Pearson Education, Inc. • In photosynthesis: – Sunlight provides the energy – Electrons are boosted “uphill” and added to carbon dioxide – Sugar is produced
  12. 12. © 2010 Pearson Education, Inc. • During photosynthesis, water is split into: – Hydrogen – Oxygen • Hydrogen is transferred along with electrons and added to carbon dioxide to produce sugar. • Oxygen escapes through stomata into the atmosphere.
  13. 13. © 2010 Pearson Education, Inc. A Photosynthesis Road Map • Photosynthesis occurs in two stages: – The light reactions convert solar energy to chemical energy – The Calvin cycle uses the products of the light reactions to make sugar from carbon dioxide Blast Animation: Photosynthesis: Light-Independent Reaction
  14. 14. Light H2O O2 Chloroplast Light reactions NADPH ATP Figure 7.3-1
  15. 15. Light H2O O2 Chloroplast Light reactions NADPH ATP Calvin cycle CO2 NADP+ ADP P Sugar (C6H12O6) Figure 7.3-2
  16. 16. © 2010 Pearson Education, Inc. How Photosystems Harvest Light Energy • Light behaves as photons, discrete packets of energy.
  17. 17. © 2010 Pearson Education, Inc. • Chlorophyll molecules absorb photons. – Electrons in the pigment gain energy. – As the electrons fall back to their ground state, energy is released as heat or light.
  18. 18. Light Photon Heat Light (fluorescence) Ground state Chlorophyll molecule Excited state e– (a) Absorption of a photon Figure 7.8a
  19. 19. © 2010 Pearson Education, Inc. • A photosystem is a group of chlorophyll and other molecules that function as a light-gathering antenna.
  20. 20. Chloroplast Figure 7.9-1
  21. 21. Chloroplast Thylakoid membrane Pigment molecules Figure 7.9-2
  22. 22. Chloroplast Thylakoid membrane Pigment molecules Antenna pigment molecules Primary electron acceptor Reaction- center chlorophyll a Photon Electron transfer Reaction center Photosystem Transfer of energy Figure 7.9-3
  23. 23. © 2010 Pearson Education, Inc. How the Light Reactions Generate ATP and NADPH • Two types of photosystems cooperate in the light reactions: – The water-splitting photosystem – The NADPH-producing photosystem
  24. 24. Primary electron acceptor Water-splitting photosystem Light H2O 2 H Reaction- center chlorophyll 2e– 2e– O2++ 1 2 Figure 7.10-1
  25. 25. Primary electron acceptor Water-splitting photosystem Light H2O 2 H Reaction- center chlorophyll 2e– 2e– O2++ Energy to make ATP 1 2 Figure 7.10-2
  26. 26. Primary electron acceptor Water-splitting photosystem Light H2O 2 H Reaction- center chlorophyll 2e– 2e– O2++ Energy to make ATP Primary electron acceptor 2e– Light NADPH-producing photosystem Reaction- center chlorophyll 2e– NADPH NADP 1 2 Figure 7.10-3
  27. 27. © 2010 Pearson Education, Inc. • The light reactions are located in the thylakoid membrane.
  28. 28. © 2010 Pearson Education, Inc. • An electron transport chain: – Connects the two photosystems – Releases energy that the chloroplast uses to make ATP
  29. 29. Light H2O Thylakoid membrane 2e– O2 ATP NADP Light Stroma Inside thylakoid Photosystem Photosystem Electron transport chain NADPH ADP P H+ ATP synthase To Calvin cycle H Electron flow H+ H H H H 1 2 Figure 7.11
  30. 30. Light H2O Thylakoid membrane 2e– O2 ATP NADP Light Stroma Inside thylakoid Photosystem Photosystem Electron transport chain NADPH ADP P ATP synthase To Calvin cycle Electron flow H 1 2 H H H H H H Figure 7.11a
  31. 31. Water-splitting photosystem e– ATP NADPH e– e– e– e– e– e– NADPH-producing photosystem Figure 7.12
  32. 32. THE CALVIN CYCLE: MAKING SUGAR FROM CARBON DIOXIDE • The Calvin cycle: – Functions like a sugar factory within the stroma of a chloroplast – Regenerates the starting material with each turn © 2010 Pearson Education, Inc.
  33. 33. Calvin cycle P P P Three-carbon moleculeRuBP sugar CO2 (from air) Figure 7.13-1
  34. 34. ATP NADPH Calvin cycle ADP  P NADP P P P P G3P sugar Three-carbon moleculeRuBP sugar CO2 (from air) Figure 7.13-2
  35. 35. ATP NADPH ADP  P NADP P P P P P P G3P sugar Three-carbon molecule G3P sugar G3P sugar RuBP sugar CO2 (from air) Calvin cycle Glucose (and other organic compounds) Figure 7.13-3
  36. 36. ATP NADPH Calvin cycle ADP  P NADP P P P P P P ADP  P ATP G3P sugar Three-carbon molecule G3P sugar G3P sugar RuBP sugar CO2 (from air) Glucose (and other organic compounds) Figure 7.13-4
  37. 37. Evolution Connection: Solar-Driven Evolution • C3 plants: – Use CO2 directly from the air – Are very common and widely distributed © 2010 Pearson Education, Inc.
  38. 38. © 2010 Pearson Education, Inc. • C4 plants: – Close their stomata to save water during hot and dry weather – Can still carry out photosynthesis • CAM plants: – Are adapted to very dry climates – Open their stomata only at night to conserve water
  39. 39. Sugar C4 Pathway (example: sugarcane) C4 plant Calvin cycle Cell type 1 Four-carbon compound Cell type 2 CO2 CO2 Figure 7.14a
  40. 40. CAM plant Sugar Calvin cycle Day Four-carbon compound Night CAM Pathway (example: pineapple) CO2 CO2 Figure 7.14b
  41. 41. Carbon dioxide 6 O26 CO2 6 H2O C6H12O6 Water Glucose Photo- synthesis Oxygen gas Light energy Figure 7.UN1
  42. 42. Light reactions CO2 O2 H2O (C6H12O6) NADPH Light Sugar ATP ADP P NADP Calvin cycle Figure 7.UN2
  43. 43. Light reactions CO2 O2 H2O (C6H12O6) NADPH Light Sugar ATP ADP P NADP Calvin cycle Figure 7.UN3
  44. 44. Carbon dioxide 6 O26 CO2 6 H2O C6H12O6 Water Glucose Photosynthesis Oxygen gas Light energy Figure 7.UN4
  45. 45. Light H2O O2 Chloroplast Light reactions NADPH ATP Calvin cycle CO2 NADP+ ADP P Sugar (C6H12O6) Stack of thylakoids Stroma Figure 7.UN5
  46. 46. acceptor Water-splitting photosystem Photon H2O 2 H Chlorophyll 2e– O2++ ATP NADPH-producing photosystem Chlorophyll NADPH NADP+ e– 2e– 2e– 2e– e– acceptorADP Photon 2 1 Figure 7.UN6
  47. 47. NADPH Calvin cycle ADP P NADP P ATP G3P CO2 Glucose and other compounds Figure 7.UN7

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