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Photosynthesis Energy for Life Ⓒ Richard Mayberry
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Two Stages: Light Phase & Dark Phase
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The Light Reactions
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Light Phase Light Energy from the sun powers photosynthesis.
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Light Phase This Energy enters the chloroplasts of plant cells.
Light Energy Light Phase Chlorophyll Coated Thylakoid Disks in Grana This Energy enters the chloroplasts of plant cells.
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Light Phase Chlorophyll converts light to chemical energy.
Light Energy Light Phase Chlorophyll Coated Thylakoid Disks in Grana Chlorophyll converts light to chemical energy.
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Light Phase Some of this energy breaks bonds in water. H H H H
Light Energy Light Phase Chlorophyll Coated Thylakoid Disks in Grana Breaks Bonds O H H O H H Some of this energy breaks bonds in water.
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Light Phase Oxygen gas is released by the cell. O2 H H H H
Light Energy Light Phase Chlorophyll Coated Thylakoid Disks in Grana O2 O H H O H H Oxygen gas is released by the cell.
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Light Phase Hydrogens are collected by NADP molecules. O2 H H NADP
Light Energy Light Phase Chlorophyll Coated Thylakoid Disks in Grana O2 H H NADP NADPH2 H H Hydrogens are collected by NADP molecules.
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Light Energy O2 O2 H H NADP NADPH2 H H Chlorophyll Coated Thylakoid Disks ADP P P ADP in Grana Some of the energy makes ATP molecules by bonding ADP and Phosphate. Light Phase
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The Dark Reactions
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Dark Phase RuBP CO2 CO2 combines with RuBP to form a 6-carbon sugar.
Unstable 6-Carbon Sugar CO2 CO2 combines with RuBP to form a 6-carbon sugar. Dark Phase
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Dark Phase PGA RuBP CO2 The sugar splits into two PGA molecules.
Unstable 6-Carbon Sugar CO2 The sugar splits into two PGA molecules. Dark Phase
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Dark Phase PGA RuBP ATP CO2 PGA ADP ATP gives a phosphate to PGA.
Unstable 6-Carbon Sugar CO2 PGA ATP gives a phosphate to PGA. Dark Phase
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Dark Phase ATP PGA PGA~P RuBP ADP ATP CO2 PGA PGA~P ADP
Unstable 6-Carbon Sugar ATP ADP CO2 PGA PGA~P PGA~P has extra energy for the next step. Dark Phase
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Dark Phase ATP PGA PGA~P RuBP P ADP ATP CO2 PGA PGA~P ADP
Unstable 6-Carbon Sugar ATP ADP CO2 PGA PGA~P Removing the phosphate releases energy. Dark Phase
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Dark Phase NADP ATP NADPH2 PGA PGA~P RuBP P ADP ATP CO2 PGA PGA~P P
Unstable 6-Carbon Sugar ATP ADP CO2 PGA PGA~P P The energy helps NADPH add hydrogen to the PGA. Dark Phase
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Dark Phase NADPH2 NADP ATP ADP PGA PGA~P PGAL RuBP P NADPH2 NADP ATP
Unstable 6-Carbon Sugar NADPH2 NADP ATP ADP CO2 PGA PGA~P P This results in production of PGAL molecules. Dark Phase
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The plant has: 3 "Options" for PGAL
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PGAL PGAL Dark Phase Respiration
To Cytoplasm PGAL Send both PGAL’s out for immediate respiration. Dark Phase
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or
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PGAL PGAL P GLUCOSE Dark Phase ATP ADP ATP ADP
Combine 2 PGAL’s and remove the phosphates to make Glucose. Dark Phase
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or
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PGAL PGAL CH2O Calvin Cycle RuBP H2O Dark Phase
Combine 2 PGAL’s and split into multiple products. Dark Phase
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is the most efficient as it "recycles" everything except the
The Calvin Cycle is the most efficient as it "recycles" everything except the water and carbon dioxide
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PGAL PGAL CH2O C6H12O6 Calvin Cycle RuBP H2O GLUCOSE
X 6 PGAL H2O C6H12O6 GLUCOSE Six Calvin Cycles produce enough carbohydrate to make molecule of glucose
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Photosynthetic energy from the Sun . . . . . . passes up the food chain to all living things.
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