1. 8-3 The Reactions of Photosynthesis
Photo Credit: ©Stone
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Inside a Chloroplast
Chloroplasts contain thylakoids—saclike photosynthetic membranes.
Single
thylakoid
Chloroplast
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Inside a Chloroplast
Thylakoids are arranged in stacks known as grana. A singular stack is called a granum.
Granum
Chloroplast
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Inside a Chloroplast
Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters called photosystems, which are the light-collecting units of the chloroplast.
Photosystems
Chloroplast
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Inside a Chloroplast
The reactions of photosystems include: the light-dependent reactions and the Calvin cycle.
The light-dependent reactions take place within the thylakoid membranes.
The Calvin cycle takes place in the stroma, which is the region outside the thylakoid membranes.
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6. Light- dependent reactions
Inside a Chloroplast
H2O
CO2
Light
NADP+
ADP + P
Light- dependent reactions
Calvin Cycle
Calvin cycle
The process of photosynthesis includes the light-dependent reactions as well as the Calvin cycle.
Chloroplast O2
Sugars
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Electron Carriers
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.
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Electron Carriers
One carrier molecule is NADP+ that transports electrons.
NADP+ accepts and holds 2 high-energy electrons along with a hydrogen ion (H+).
This converts the NADP+ into NADPH.
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Electron Carriers
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.
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10. Light-Dependent Reactions
What happens in the light-dependent reactions?
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11. Light-Dependent Reactions
The light-dependent reactions require light (input).
The light-dependent reactions produce (output) oxygen gas and convert ADP and NADP+ (inputs) into the energy carriers ATP and NADPH (outputs).
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12. Light-Dependent Reactions
The light-dependent reactions use (input) water, ADP, and NADP+.
The light-dependent reactions produce (output) oxygen, ATP, and NADPH.
These compounds provide the energy to build energy-containing sugars from low-energy compounds.
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13. As a table, use whiteboards to…
… write and/or illustrate the light-dependent reactions.

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The Calvin Cycle
What is the Calvin cycle?
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The Calvin Cycle
The Calvin cycle uses ATP and NADPH (inputs) from the light-dependent reactions to produce high-energy sugars (output).
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.
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The Calvin Cycle
1. 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.
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The Calvin Cycle
2. 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.
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The Calvin Cycle
3. 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+
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The Calvin Cycle
4. 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+
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20. 6-Carbon sugar produced Sugars and other compounds
The Calvin Cycle
5. The 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
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21. 5-Carbon Molecules Regenerated Sugars and other compounds
The Calvin Cycle
6. 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
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The Calvin Cycle
The two sets of photosynthetic reactions work together.
The light-dependent reactions trap sunlight energy in chemical form.
The Calvin cycle uses that chemical energy to produce stable, high-energy sugars from carbon dioxide and water.
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8-3
In plants, photosynthesis takes place inside the
thylakoids.
chloroplasts.
photosystems.
chlorophyll.
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8-3
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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8-3
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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8-3
What is another name for the Calvin cycle?
light-dependent reactions
light-independent reactions
electron transport chain
photosynthesis
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8-3
Which of the following factors does NOT directly affect photosynthesis?
wind
water supply
temperature
light intensity
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28. END OF SECTION