1. The Reactions of Photosynthesis
Photosynthesis song ~ Enjoy!
Photo Credit: ©Stone

2. Inside a Chloroplast Inside a Chloroplast
In plants, photosynthesis takes place inside chloroplasts.
Plant
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Chloroplast
Plant cells

3. Inside a Chloroplast Chloroplast
Chloroplasts contain thylakoids—saclike photosynthetic membranes.
Single
thylakoid
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Chloroplast

4. Inside a Chloroplast Chloroplast
Thylakoids are arranged in stacks known as grana. A singular stack is called a granum.
Granum
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Chloroplast

5. Inside a Chloroplast Chloroplast
Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters called photosystems, which are the light-collecting units of the chloroplast.
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Photosystems
Chloroplast

6. Inside a Chloroplast
The light-dependent reactions take place within the thylakoid membranes.
The Calvin cycle (AKA: light-independent reaction) takes place in the stroma, which is the region outside the thylakoid membranes.
The two sets of photosynthetic reactions work together.
The light-dependent reactions trap sunlight energy in chemical form.
The light-independent reactions use that chemical energy to produce stable, high-energy sugars from carbon dioxide and water.

7. Light- dependent reactions
Inside a Chloroplast
H2O
CO2
Light
NADP+
ADP + P
Light- dependent reactions
Calvin Cycle
Calvin cycle
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The process of photosynthesis includes the light-dependent reactions as well as the Calvin cycle.
Chloroplast O2
Sugars

8. Electron Carriers
When electrons in chlorophyll absorb sunlight, the electrons gain a great deal of energy.
Cells use electron carriers to transport these high- energy electrons from chlorophyll to other molecules.
One electron carrier molecule is NADP+ it transports electrons by accepting & holds 2 high-energy electrons along with a hydrogen ion (H+). This converts the NADP+ into NADPH.
The conversion of NADP+ into NADPH is one way some of the energy of sunlight can be trapped in chemical form.
The NADPH carries high-energy electrons to chemical reactions elsewhere in the cell.
These high-energy electrons are used to help build a variety of molecules the cell needs, including carbohydrates like glucose.

9. Light-Dependent Reactions
The light-dependent reactions require light.
The light-dependent reactions produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH.
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10. Electron Transport: notes & FYIs
2 Photosystems: I & II (Ancient Greek: phos = light and systema = assembly)
Each system is identified by its wavelength of light (700 and 680 nanometers, respectively for PSI and PSII in chloroplasts).
These are functional & structural units of photosynthesis: that deal with the absorption of light and the transfer of energy and electrons.
They are both found in the thylakoid membranes of chloroplasts for plants, and algae, or in the cytoplasmic membrane of photosynthetic bacteria, such as cyanobacteria.
Each contain chlorophyll molecules, that can convert light energy into chemical energy.
A photon of light causes an electron to reach a high energy level.
Both photosystems, the energized electron must be passed to a chlorophyll molecule in the reaction center before it can leave the photosystem.
Both contain carotenoid molecules.

11. PS I & PS II
Photosystem I (PS I) is so named because it was discovered before photosystem II (PSII).
These discoveries were in the late 20th century. (1950’s – 1960’s)
 Light reactions take place in the ________________ membrane.
1.) PS II - Light excites the electrons in Chlorophyll a
2.) PS II – These electrons move to a primary electron acceptor
3.) PS II – The Electron Transport Chain: transfers these electrons via
series of molecules.
4.) PS I – Light excites the electrons in Chlorophyll a
– These electrons move to a primary electron acceptor & are
replaced by electrons from PS II.
5.) PS I – 2nd Electron Transport Chain: transfers these electrons &
combine with NADP + to make NADPH
Another Presentation on Photosynthesis I (Just another way to see the same material presented.)
Photosyn video by kids (Nice overview!)
Calvin Cycle Video (Your teacher really gets a kick out of this one.)

12. MORE IMAGES SHOWING PHOTOSYNTHESIS
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14. Copyright Pearson Prentice Hall

15. Light-Dependent Reactions
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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.

16. Light-Dependent Reactions
Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level.
Photosystem II
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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.

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

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

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

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

21. Light-Dependent Reactions
As plants remove electrons from water, oxygen is left behind and is released into the air.
Photosystem II
+ O2
2H2O
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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

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

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

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

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

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

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

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

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

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

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

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

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

34. 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
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The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen.
ADP
2 NADP+ 2 2
NADPH

35. LIGHT-DEPENDENT REACTIONS
The light-dependent reactions use water, ADP, and NADP+.
The light-dependent reactions produce oxygen, ATP, and NADPH.
These compounds provide the energy to build energy- containing sugars from low-energy compounds.

36. THE CALVIN CYCLE ~ LIGHT INDEPENDENT!
ATP and NADPH formed by 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.
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.
The Calvin cycle uses ATP and NADPH from the light- dependent reactions to produce high-energy sugars.

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

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

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

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

41. 6-Carbon sugar produced Sugars and other compounds
The Calvin Cycle
The molecules are used to produce sugars, lipids, amino acids and other compounds. 12
12 ADP
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NADPH
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.
12 NADP+
6-Carbon sugar produced
Sugars and other compounds

42. 5-Carbon Molecules Regenerated Sugars and other compounds
The Calvin Cycle
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
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NADPH 6
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.
12 NADP+
5-Carbon Molecules Regenerated
Sugars and other compounds

43. Chemiosmosis
The diffusion of ions across a selectively-permeable membrane. Primarily relates to the synthesis of ATP by the movement of hydrogen ions across a membrane during cellular respiration.
Hydrogen ions (protons) will diffuse from an area of high proton concentration to an area of lower proton concentration.
It’s the diffusion of water across a membrane, that is why it is called chemiosmosis.

44. CARBON FIXATION
This is a process that allows gaseous carbon dioxide to convert into a solid compound.
Mostly deals with the photosynthesis processes found in autotrophs (organisms that produce their own food), whereby carbon dioxide is changed into sugars.

45. CALVIN CYCLE
This is the most common biological method of carbon fixation.
In plants, there are three types of carbon fixation during photosynthesis: C3 C4
CAM
**Next few slides is a conglomerate of information from a variety of sources including wikipedia.
**Wikipedia, is a like an encyclopedia; however, anyone can edit it.
So, you always have to do back up research to verify the information that you are reading.

46. A little more about C3, C4, & CAM…
C3 plants that use the Calvin cycle for the initial steps that incorporate CO2 into organic matter, forming a 3-carbon compound as the first stable.
C4 plants that preface the Calvin cycle with reactions do incorporate CO2 into a 4-carbon compound.
C4 plants have a distinctive internal leaf anatomy. Tropical grasses, such as sugar cane and maize are C4 plants, but there are many broadleaf plants that are C4. Overall, 7600 species of terrestrial plants use C4 carbon fixation, representing around 3% of all species.
CAM-plants that use Crassulacean acid metabolism as an adaptation for arid conditions.
CO2 enters through the stomata during the night and is converted into organic acids, which release CO2 for use in the Calvin cycle during the day, when the stomata are closed.
The jade plant (Crassula ovata) and cacti are typical of CAM plants Sixteen thousand species of plants use CAM.[3]

47. The Calvin Cycle Steps:
Takes place in the stroma.
Steps:
1.) CO2 combines with RuBP to form to molecules of PGA
2.) PGA is converted to PGAL.
3.) Most of PGAL is converted back to RuBP.
(Some PGAL is used to make organic compounds.)
RuBP – Ribulose-1,5-bisphosphate (5 Carbon Molecule)
used in carbon fixing of the Calvin Cycle.
PGAL – Phosphoglyceraldehyde (3-Carbon Molecule)

48. Factors Affecting Photosynthesis
Many factors affect the rate of photosynthesis, including:
Water
Temperature
Intensity of light
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49. In plants, photosynthesis takes place inside the
thylakoids.
chloroplasts.
photosystems.
chlorophyll.
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50. Energy to make ATP in the chloroplast comes most directly from
hydrogen ions flowing through an enzyme in the thylakoid membrane.
transfer of a phosphate from ADP.
electrons moving through the electron transport chain.
electrons transferred directly from NADPH.
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51. NADPH is produced in light-dependent reactions and carries energy in the form of
ATP.
high-energy electrons.
low-energy electrons.
ADP.
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52. What is another name for the Calvin cycle?
light-dependent reactions
light-independent reactions
electron transport chain
photosynthesis
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53. Which of the following factors does NOT directly affect photosynthesis?
wind
water supply
temperature
light intensity
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