1. Photosynthesis: Using Light to Make Food

2. Photosynthesis:
The process that converts solar energy into chemical energy
Producers of the Biosphere:
Plants and other autotrophs
Plants are photoautotrophs:
They use the energy of sunlight
They make organic molecules from water and carbon dioxide

3. Figure 10.1

5. Biology and Society: Plant Power for Power Plants
All food consumed by humans can be traced back to:
Photosynthetic plants.
An “energy plantation”
Is a renewable energy source.
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

6. Figure 7.1

7. Photosynthesis occurs in:
Plants:
Predominant producer of food on land
Algae
Some unicellualr protists, e.g. egulina
Some prokaryotes:
Cynobacteria
Sulfur bacteria

8. (b) Multicellular algae (c) Unicellular protist
(a) Plants
(b) Multicellular algae
(c) Unicellular protist
10 m
40 m
(d) Cyanobacteria
1.5 m
(e) Pruple sulfur
bacteria
Figure 10.2

9. Chloroplasts: Sites of Photosynthesis
Occurs in chloroplasts.
Chloroplasts
Are found in the interior cells of leaves.
Contain stroma, a thick fluid.
Contain thylakoids, membranous sacs.

10. Figure 7.3

11. The Overall Equation for Photosynthesis
The reactants and products of the reaction

12. Photosynthesis as a Redox Process
Photosynthesis is a redox process
Water is oxidized
Carbon dioxide is reduced

13. A Photosynthesis Road Map
Photosynthesis is composed of two processes:
The light reactions:
convert solar energy to chemical energy (ATP & NADPH).
The Calvin cycle:
makes sugar from carbon dioxide.

14. Figure 7.4

15. Split water releasing oxygen
The light reactions
The light reactions
Occur in the grana
Split water releasing oxygen
Convert light energy into chemical energy by:
Producing ATP and
Forming NADPH

16. Forms sugar from carbon dioxide, using:
The Calvin cycle
Occurs in the stroma
Forms sugar from carbon dioxide, using:
ATP for energy, and
NADPH as reducing power

17. An overview of photosynthesis
CO2
Light
LIGHT REACTIONS
CALVIN
CYCLE
Chloroplast
[CH2O]
(sugar)
NADPH
NADP 
ADP
+ P O2
Figure 10.5
ATP

18. Sunlight is a type of energy called:
The Nature of Sunlight
Sunlight is a type of energy called:
Radiation or electromagnetic energy.
The full range of radiation is called:
The electro-magnetic spectrum.
Wavelength:
Is the distance between the crests of waves
Determines the type of electromagnetic energy

19. The visible light spectrum includes:
The colors of light we can see
The wavelengths that drive photosynthesis

20. Figure 7.5

21. Photosynthetic Pigments: The Light Receptors
Are substances that absorb visible light
Reflect light, which include the colors we see
Light
Reflected
Chloroplast
Absorbed
light
Granum
Transmitted

22. The spectrophotometer Is a machine that:
Sends light through pigments
Measures the fraction of light transmitted at each wavelength

23. Chloroplasts contain several pigments:
Chloroplast Pigments
Chloroplasts contain several pigments:
Chlorophyll a: Is the main photosynthetic pigment
Chlorophyll b: Is an accessory pigment
Carotenoids: An accessory pigment (protective)

24. How Photosystems Harvest Light Energy
Light also behaves as photons
A photons is:
A discrete quantity of energy.
The shorter the wavelength the greater the photon energy

25. When chlorophyll molecules absorb photons:
Electrons in the pigment gain energy
Electrons are raised from ground state to excited (unstable) state
Electrons lose excess energy (return to ground state)
The energy is released (light/heat) and used.

26. Figure 7.9

27. Brak Slide 3/22/11

28. Thylakoid-Membrane Photosystems
An organized group (few hundreds) of chlorophyll and other molecules
Composed of a protein complex called a reaction center complex
The reaction ceneter:
Surrounded by a number of light-harvesting complexes
Include a pair of chlorophyll a molecules
Contains a molecule capable of accepting electrons & becoming reduced; it is called “primary electron acceptor”

29. Thylakoid-Membrane Photosystems
Light harvesting complex:
Consists of various pigments molecules (chlorophyll a, b, & carotenoid)
The pigments molecules are bound to proteins
Two photosystems:
Water-splitting photosystem
NADPH-producing photosystem
Both photosystems:
Cooperate in light reaction, and
Produce energy

30. (INTERIOR OF THYLAKOID)
The Photosystem
Primary election
acceptor
Photon
Thylakoid
Light-harvesting
complexes
Reaction
center
Photosystem
STROMA
Thylakoid membrane
Transfer
of energy
Special
chlorophyll a
molecules
Pigment
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
Figure 10.12 e–

31. The light-harvesting complexes
Consist of pigment molecules bound to particular proteins
Funnel the energy of photons of light to the reaction center

32. The thylakoid membrane
When a reaction-center chlorophyll molecule absorbs energy
One of its electrons gets pumped up to a primary electron acceptor
The thylakoid membrane
Is populated by two types of photosystems, I and II

33. Noncyclic Electron Flow
Noncyclic (linear) electron flow
Is the primary pathway of energy transformation in the light reactions

34. Electron transport chain
Produces NADPH, ATP, and oxygen
Figure 10.13
Photosystem II
(PS II)
Photosystem-I
(PS I)
ATP
NADPH
NADP+
ADP
CALVIN
CYCLE
CO2
H2O O2
[CH2O] (sugar)
LIGHT
REACTIONS
Light
Primary
acceptor Pq
Cytochrome
complex PC e
P680 e– +
2 H+ Fd
reductase
Electron
Transport
chain
Electron transport chain
P700
+ 2 H+
+ H+ 7 4 2 8 3 5 1 6

35. Chemiosmosis in Chloroplasts and Mitochondria
Generate ATP by the same basic mechanism, chemiosmosis
But use different sources of energy to accomplish this (electrons from glucose

36. The spatial organization of chemiosmosis
Differs in chloroplasts and mitochondria
Key
Higher [H+]
Lower [H+]
Mitochondrion
Chloroplast
MITOCHONDRION
STRUCTURE
Intermembrance
space
Membrance
Matrix
Electron
transport
chain H+
Diffusion
Thylakoid
Stroma
ATP P
ADP+
Synthase
CHLOROPLAST
Figure 10.16

37. In both organelles
Redox reactions of electron transport chains generate a H+ gradient across a membrane
ATP synthase
Uses this proton-motive force to make ATP

38. The light reactions and chemiosmosis: the organization of the thylakoid membrane
REACTOR
NADP+
ADP
ATP
NADPH
CALVIN
CYCLE
[CH2O] (sugar)
STROMA
(Low H+ concentration)
Photosystem II
H2O
CO2
Cytochrome
complex O2 1
1⁄2 2
Photosystem I
Light
THYLAKOID SPACE
(High H+ concentration)
Thylakoid
membrane
synthase Pq Pc Fd
reductase
+ H+
NADP+ + 2H+ To
Calvin
cycle P 3 H+
2 H+
+2 H+
Figure 10.17

39. The Calvin cycle uses ATP and NADPH to convert CO2 to sugar
Is similar to the citric acid cycle
Occurs in the stroma

40. The Calvin cycle has three phases
Carbon fixation
Reduction
Regeneration of the CO2 acceptor

41. The Calvin cycle Figure 10.18 Input Light 3 CO2 CALVIN CYCLE
(G3P)
Input
(Entering one
at a time)
CO2 3
Rubisco
Short-lived intermediate
3 P P
Ribulose bisphosphate (RuBP)
3-Phosphoglycerate
6 P 6
1,3-Bisphoglycerate
6 NADPH
6 NADPH+
Glyceraldehyde-3-phosphate
6 ATP
ATP
3 ADP
CALVIN
CYCLE 5 1
G3P (a sugar) Output
Light
H2O
LIGHT REACTION
ATP
NADPH
NADP+
ADP
[CH2O] (sugar)
CALVIN CYCLE
Figure 10.18 O2
6 ADP
Glucose and other organic compounds
Phase 1: Carbon fixation
Phase 3: Regeneration of the CO2 acceptor (RuBP)
Phase 2: Reduction

42. Alternative mechanisms of carbon fixation have evolved in hot, arid climates
On hot, dry days, plants close their stomata
Conserving water but limiting access to CO2
Causing oxygen to build up

43. Water-Saving Adaptations of C4 and CAM Plants
C3 plants (Soybean, oat, wheat, rice):
Use CO2 (Calvin cycle) directly from the air.
Are very common and widely distributed.
Low production during hot season
Stomata closed to conserve water
Less CO2 and less photosynthesis

44. C4 plants (Corn, sorghum, sugarcane)
Close their stomata to save water during hot and dry weather.
Can still carry out photosynthesis.
Enzymatic binding of CO2 into 4-C compound
4-C compound donates CO2 to Calvin cycle in a nearby cell

45. C4 leaf anatomy and the C4 pathway
CO2
Mesophyll cell
Bundle-
sheath
cell
Vein
(vascular tissue)
Photosynthetic
cells of C4 plant
leaf
Stoma
Mesophyll
C4 leaf anatomy
PEP carboxylase
Oxaloacetate (4 C)
PEP (3 C)
Malate (4 C)
ADP
ATP
Sheath
Pyruate (3 C)
CALVIN
CYCLE
Sugar
Vascular
tissue
Figure 10.19

46. CAM plants (Pineapple, cacti, succulent plants)
Open stomata only at night to conserve water
Carry photosynthesis during the day
CO2 is incorporated into 4-C compound
4C compound donates CO2 to Calvin cycle during the day

47. The CAM pathway is similar to the C4 pathway
Spatial separation of steps. In C4 plants, carbon fixation and the Calvin cycle occur in different
types of cells.
(a)
Temporal separation of steps. In CAM plants, carbon fixation and the Calvin cycle occur in the same cells at different times.
(b)
Pineapple
Sugarcane
Bundle-
sheath cell
Mesophyll Cell
Organic acid
CALVIN CYCLE
Sugar
CO2 C4
CAM
CO2 incorporated
into four-carbon
organic acids
(carbon fixation)
Night
Day 1 2
Organic acids
release CO2 to
Calvin cycle
Figure 10.20

48. The Importance of Photosynthesis: A Review
A review of photosynthesis
Light reactions:
• Are carried out by molecules in the
thylakoid membranes
• Convert light energy to the chemical
energy of ATP and NADPH
• Split H2O and release O2 to the
atmosphere
Calvin cycle reactions:
• Take place in the stroma
• Use ATP and NADPH to convert
CO2 to the sugar G3P
• Return ADP, inorganic phosphate, and NADP+ to the light reactions O2
CO2
H2O
Light
Light reaction
Calvin cycle
NADP+
ADP
ATP
NADPH
+ P 1
RuBP
3-Phosphoglycerate
Amino acids
Fatty acids
Starch
(storage)
Sucrose (export)
G3P
Photosystem II
Electron transport chain
Photosystem I
Chloroplast
Figure 10.21

49. The Environmental Impact of Photosynthesis

50. Photosynthesis has an enormous impact on the atmosphere.
It swaps O2 for CO2.

51. Organic compounds produced by photosynthesis
Provide the energy and
Building material for ecosystems