1. Chapter 8: Photosynthesis
Mr. Wilmot

2. Part I- Photosynthetic structures And Overview
Where it takes place
What structures are involved and what are the raw material and products

3. Photosynthesis takes place in the mesophyll cells of the leaf

4. Each Mesophyll Cell contains many Chloroplasts
Also, CO2 comes into, and O2 Leaves the cell through the stoma. Water gets to, and Glucose leaves through the Xylem and Phloem
Water
Glucose
CO2 O2

5. The Chloroplast- Contains Chlorophyll- a light absorbing pigment
Chlorophyll is actually located on the membrane of the thylakoid
Granum
Thylakoid
Stroma
___________
(Stack of Thylakoid)
_________
___________
Aqueous Place Inside
Chloroplast

6. Chlorophyll and Chloroplasts
Light- energy from the sun that travels to earth comes in different wavelengths
a. The visible part of this spectrum appears as different colors

7. Pigments- light absorbing molecules that captures energy from the sun
Chlorophyll- the plants principle pigment
Include Chlorophyll A and Chlorophyll B
There are other accessory pigment that augment the primary pigment allowing for more energy to be absorbed
Include carotenoids and xanthophylls

8. Chlorophyll absorbs light very well in the blue-violet and red wavelengths
It does not absorb green wavelengths, instead it reflects these wavelengths

9. Chloroplast Anatomy Chloroplasts- site of photosynthesis
Thylakoids- sac-like photosynthetic membranes
Arranged in stacks called Grana
Contain pigments- chlorophyll
b. Stroma- the fluid inside the chloroplast

10. Energy Collection Light is energy Pigments absorb light and energy
Light energy is transferred directly to electrons in the chlorophyll molecule
The raising of energy levels of electrons is the driving force of photosynthesis

11. High Energy Electrons
Chemically, the high energy electrons produced by chlorophyll require a special carrier
Analogy: Hot potato, oven mitt = special carrier
Electron carriers are the so called oven mitt, transferring these electrons from the chlorophyll to other molecules

12. NADP+: is an electron carrier
Function- accepts and holds two high energy electrons along with a hydrogen ion (H+).
This converts NADP+ to NADPH
Used to help build carbohydrates

13. An Overview of Photosynthesis

14. Light-Dependent Reactions
Equation is a simplified form of photosynthesis; actually requires many steps to get from light to carbohydrates
Actually involves 2 sets of reactions
Light depedendent
Light independent

15. Require light and light absorbing pigments
Light dependent- set of reactions in photosynthesis that use energy from light to produce ATP and NADPH
Require light and light absorbing pigments
These reactions take place within the thylakoids of chloroplasts
Water is need for these reactions as a source of electrons and H+
Oxygen is released as a bi-product
Confused?
Check this out…..
Light phase reactions animation

16. Light Independent Reactions – a.k.a. “The Dark Side”, er Phase
a. Plants absorb CO2 from the atmosphere and complete the process of photosynthesis
b. ATP and NADPH produced in the “light phase” reactions are used to produce high energy sugars…. with the addition of CO2.
Dark Phase Animation

17. c. No light is required d. Reactions occur in the stroma (liquid outside of thylakoid) e. Reliant on the light phase for materials f. Both light and dark phases work together to create energy-rich carbohydrates

18. End of Part 1

19. The Process of Photosynthesis
Light-Dependent Reactions: Generating ATP and NADPH
Summary: The light dependent reactions use energy from sunlight to produce oxygen and convert ADP and NADP+ into the energy carriers ATP and NADPH
These carriers provide energy needed to build high-energy sugars from low-energy carbon dioxide

20. The Light-Dependent Reaction Takes Place on the membrane of the Thylakoid

21. Light-Dependent Reactions
It happens in two parts called photosystems:
1- Photosystem 2
2- Photosystem 1
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. 21

22. Light-Dependent Reactions
a. Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level.
Photosystem II
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. 22

23. Light-Dependent Reactions
These high-energy electrons are passed on to the electron transport chain.
Photosystem II
Electron carriers
High-energy electron 23

24. Light-Dependent Reactions
b. Enzymes on the thylakoid membrane break water molecules into:
Photosystem II
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
Electron carriers
High-energy electron
Copyright Pearson Prentice Hall 24

25. Light-Dependent Reactions
hydrogen ions
oxygen atoms
energized electrons
Photosystem II
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
Electron carriers
High-energy electron 25

26. Light-Dependent Reactions
c. The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain.
Photosystem II
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
High-energy electron 26

27. Light-Dependent Reactions
d. As plants remove electrons from water, oxygen is left behind and is released into the air.
Photosystem II
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts.
High-energy electron 27

28. Light-Dependent Reactions
e. The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane.
Photosystem II
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
High-energy electron 28

29. Light-Dependent Reactions
f. Energy from the electrons is used to transport H+ ions from the stroma into the inner thylakoid space.
Photosystem II
Inside Thylakoid
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
Outside Thylakoid 29

30. Light-Dependent Reactions
g. High-energy electrons move through the electron transport chain from photosystem II to photosystem I.
Photosystem II
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
Photosystem I 30

31. Light-Dependent Reactions
h. Pigments in photosystem I use energy from light to re-energize the electrons.
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
Photosystem I 31

32. Light-Dependent Reactions
i. NADP+ then picks up these high-energy electrons, along with H+ ions, and becomes NADPH.
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
2 NADP+ 2 2
NADPH 32

33. Light-Dependent Reactions
j. As electrons are passed from chlorophyll to NADP+, more H+ ions are pumped across the membrane.
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
2 NADP+ 2 2
NADPH 33

34. Light-Dependent Reactions
k. Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged.
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
2 NADP+ 2 2
NADPH 34

35. Light-Dependent Reactions
The difference in charges across the membrane provides the energy to make ATP.
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
2 NADP+ 2 2
NADPH 35

36. Light-Dependent Reactions
H+ ions cannot cross the membrane directly.
ATP synthase
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
2 NADP+ 2 2
NADPH 36

37. Light-Dependent Reactions
The cell membrane contains a protein called ATP synthase that allows H+ ions to pass through it.
ATP synthase
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
2 NADP+ 2 2
NADPH 37

38. Light-Dependent Reactions
l. As H+ ions pass through ATP synthase, the protein rotates.
ATP synthase
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
2 NADP+ 2 2
NADPH 38

39. Light-Dependent Reactions
m. As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP.
ATP synthase
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
ADP
2 NADP+ 2 2
NADPH 39

40. Light-Dependent Reactions
Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well.
ATP synthase
+ O2
2H2O
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
ADP
2 NADP+ 2 2
NADPH 40

41. ATP synthase + O2 2H2O ADP 2 NADP+ 2 NADPH 2
The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
ADP
2 NADP+ 2 2
NADPH 41

42. End of Part 2

43. B. The Calvin Cycle
Also called the light independent (aka Calvin cycle, aka “dark phase”)reactions
ATP and NADPH formed by the light-dependent reactions contain an abundance of chemical energy, but they are not stable enough to store that energy for more than a few minutes.
3. During the Calvin cycle plants use the energy that ATP and NADPH contain to build high-energy compounds that can be stored for a long time. 43

44. The Calvin Cycle 44

45. a. Six carbon dioxide molecules enter the cycle from the atmosphere and combine with six 5-carbon molecules.
CO2 Enters the Cycle
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.
The Calvin Cycle 45

46. b. The result is twelve 3-carbon molecules, which are then converted into higher-energy forms.
The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 46

47. The energy for this conversion comes from ATP and high-energy electrons from NADPH.
Energy Input 12
12 ADP 12
NADPH
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.
12 NADP+
The Calvin Cycle 47

48. c. Two of twelve 3-carbon molecules are removed from the cycle.
Energy Input 12
12 ADP 12
NADPH
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.
12 NADP+ 48

49. The 2 removed molecules are used to produce sugars, lipids, amino acids and other compounds.12
12 ADP 12
NADPH
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.
12 NADP+
6-Carbon sugar produced
Sugars and other compounds 49

50. d. The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to begin the next cycle. 12
12 ADP
6 ADP 12
NADPH 6
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.
12 NADP+
5-Carbon Molecules Regenerated
Sugars and other compounds 50

51. The Calvin Cycle
The two sets of photosynthetic reactions work together.
a. The light-dependent reactions trap sunlight energy in chemical form.
b. The light-independent reactions use that chemical energy to produce stable, high-energy sugars from carbon dioxide and water. 51

52. C. Factors Affecting Photosynthesis
1. Temperature, Light, and Water
Temperature
Among most important factors that affect photosynthesis are temperature, light intensity, and availability of water.

53. Reactions made possible by enzymes that function best b/w 0oC and 35oC
Above or below these temps could slow down rate of photosynthesis
Low temps, may stop entirely

54. b. Light Intensity of light affects rate of photosynthesis
High light intensity increases rate of photosynthesis
After intensity reaches a certain level, plant reaches maximum rate of photosynthesis

55. c. Water Water is one of raw materials of photosynthesis
Shortage of water can slow or stop photosynthesis
Water loss can damage plant tissues
Plants that live in dry conditions often have waxy coatings on leaves to reduce water loss
May also have biochemical adaptations that make photosynthesis more efficient under dry conditions

56. 2. Photosynthesis Under Extreme Conditions
a. To conserve water: plants in bright, hot conditions close small openings in leaves that normally admit carbon dioxide
Keeps plants from drying out
Causes carbon dioxide w/in leaves to fall to very low levels
Photosynthesis slows down or stops

57. 3. C4 Photosynthesis
Animation
a. Specialized chemical pathway that allows them to capture very low levels of carbon dioxide to pass it on to Calvin cycle
1st compound formed in pathway contains 4 carbon atoms
c. Enables photosynthesis to keep working under intense light and high temperatures
d. Requires extra energy in form of ATP to function
e. Examples: corn, sugar cane, sorghum

58. 4. CAM Plants
a. Carbon dioxide becomes incorporated into organic acids during photosynthesis
Process called Crassulacean Acid Metabolism
b. Admit air into leaves only at night
c. In cool darkness, carbon dioxide is combined w/ existing molecules to produce organic acids, “trapping” carbon w/in leaves
d. During daytime, leaves tightly sealed to prevent loss of water  compounds release carbon dioxide  enable carbohydrate production
Examples: pineapple, cacti, “ice plants” (near freeways along west coast to retard brush fires and prevent erosion)