Photosynthesis Energy for Life Ⓒ Richard Mayberry

Two Stages: Light Phase & Dark Phase

The Light Reactions

Light Phase Light Energy from the sun powers photosynthesis.

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.

Light Phase Chlorophyll converts light to chemical energy. Light Energy Light Phase Chlorophyll Coated Thylakoid Disks in Grana Chlorophyll converts light to chemical energy.

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.

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.

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.

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

The Dark Reactions

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

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

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

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

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

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

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

The plant has: 3 "Options" for PGAL

PGAL PGAL Dark Phase Respiration To Cytoplasm PGAL Send both PGAL’s out for immediate respiration. Dark Phase

or

PGAL PGAL P GLUCOSE Dark Phase ATP ADP ATP ADP Combine 2 PGAL’s and remove the phosphates to make Glucose. Dark Phase

or

PGAL PGAL CH2O Calvin Cycle RuBP H2O Dark Phase Combine 2 PGAL’s and split into multiple products. Dark Phase

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

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

Photosynthetic energy from the Sun . . . . . . passes up the food chain to all living things.