Lecture 4 - Photosynthesis II | Plant Metabolism - Botany PDF Download

 Page 1


Photosynthesis II 
 
 
0            Institute of Lifelong Learning, University of Delhi                                                               
                                 
 
 
Lesson Prepared under MHRD project “National Mission 
on Education through ICT” 
 
Discipline: Botany 
Paper: Plant Plant Metabolism 
National Coordinator: Prof. S.C. Bhatla 
 
Lesson: Photosynthesis II 
Lesson Developer: Dr Basudha Sharma 
MM (PG) College, Modinagar, Uttar Pradesh 
 
Lesson Reviewer: Dr Girish Mishra, Department of Botany, 
University of Delhi 
 
Language Editor: Namrata Dhaka 
Department/College: Department of Genetics, University of Delhi, 
South Campus 
 
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
 
 
Page 2


Photosynthesis II 
 
 
0            Institute of Lifelong Learning, University of Delhi                                                               
                                 
 
 
Lesson Prepared under MHRD project “National Mission 
on Education through ICT” 
 
Discipline: Botany 
Paper: Plant Plant Metabolism 
National Coordinator: Prof. S.C. Bhatla 
 
Lesson: Photosynthesis II 
Lesson Developer: Dr Basudha Sharma 
MM (PG) College, Modinagar, Uttar Pradesh 
 
Lesson Reviewer: Dr Girish Mishra, Department of Botany, 
University of Delhi 
 
Language Editor: Namrata Dhaka 
Department/College: Department of Genetics, University of Delhi, 
South Campus 
 
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
 
 
Photosynthesis II 
 
 
1            Institute of Lifelong Learning, University of Delhi                                                               
Chapter: Photosynthesis II 
Table of content 
? Carbon fixation 
? Calvin-Benson cycle 
? Steps of Calvin cycle 
? Carboxylation 
? Reduction 
? Formation of Sugars and Regeneration of Rubilose 
1,5-bisphosphate(RuBP)  
? Stoichiometry of Calvin cycle 
? Regulation of Calvin cycle  
? Photochemical changes 
? Activation of enzymes by light 
? Transport of intermediates   
? Regulation by metabolites 
? Photorespiration/C2 cycle/Glycolate metabolism 
? Significance of photorespiration 
? Mechanisms to avoid photorespiration 
? Hatch and Slack Pathway/C4 cycle 
? Three variants of HSK pathway 
? Regulation of C4 cycle 
? Photosynthetic efficiency of C3 and C4 
? Crassulacean Acid Metabolism 
? Ecological significance of CAM 
? Regulation of CAM cycle 
? Factors affecting photosynthesis 
? External factors 
? Light 
? Carbon dioxide 
? Temperature 
? Water 
? Internal factors 
? Chlorophyll content 
? Metabolic factors 
? Anatomy of leaf 
Page 3


Photosynthesis II 
 
 
0            Institute of Lifelong Learning, University of Delhi                                                               
                                 
 
 
Lesson Prepared under MHRD project “National Mission 
on Education through ICT” 
 
Discipline: Botany 
Paper: Plant Plant Metabolism 
National Coordinator: Prof. S.C. Bhatla 
 
Lesson: Photosynthesis II 
Lesson Developer: Dr Basudha Sharma 
MM (PG) College, Modinagar, Uttar Pradesh 
 
Lesson Reviewer: Dr Girish Mishra, Department of Botany, 
University of Delhi 
 
Language Editor: Namrata Dhaka 
Department/College: Department of Genetics, University of Delhi, 
South Campus 
 
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
 
 
Photosynthesis II 
 
 
1            Institute of Lifelong Learning, University of Delhi                                                               
Chapter: Photosynthesis II 
Table of content 
? Carbon fixation 
? Calvin-Benson cycle 
? Steps of Calvin cycle 
? Carboxylation 
? Reduction 
? Formation of Sugars and Regeneration of Rubilose 
1,5-bisphosphate(RuBP)  
? Stoichiometry of Calvin cycle 
? Regulation of Calvin cycle  
? Photochemical changes 
? Activation of enzymes by light 
? Transport of intermediates   
? Regulation by metabolites 
? Photorespiration/C2 cycle/Glycolate metabolism 
? Significance of photorespiration 
? Mechanisms to avoid photorespiration 
? Hatch and Slack Pathway/C4 cycle 
? Three variants of HSK pathway 
? Regulation of C4 cycle 
? Photosynthetic efficiency of C3 and C4 
? Crassulacean Acid Metabolism 
? Ecological significance of CAM 
? Regulation of CAM cycle 
? Factors affecting photosynthesis 
? External factors 
? Light 
? Carbon dioxide 
? Temperature 
? Water 
? Internal factors 
? Chlorophyll content 
? Metabolic factors 
? Anatomy of leaf 
Photosynthesis II 
 
 
2            Institute of Lifelong Learning, University of Delhi                                                               
? Summary 
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 4


Photosynthesis II 
 
 
0            Institute of Lifelong Learning, University of Delhi                                                               
                                 
 
 
Lesson Prepared under MHRD project “National Mission 
on Education through ICT” 
 
Discipline: Botany 
Paper: Plant Plant Metabolism 
National Coordinator: Prof. S.C. Bhatla 
 
Lesson: Photosynthesis II 
Lesson Developer: Dr Basudha Sharma 
MM (PG) College, Modinagar, Uttar Pradesh 
 
Lesson Reviewer: Dr Girish Mishra, Department of Botany, 
University of Delhi 
 
Language Editor: Namrata Dhaka 
Department/College: Department of Genetics, University of Delhi, 
South Campus 
 
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
 
 
Photosynthesis II 
 
 
1            Institute of Lifelong Learning, University of Delhi                                                               
Chapter: Photosynthesis II 
Table of content 
? Carbon fixation 
? Calvin-Benson cycle 
? Steps of Calvin cycle 
? Carboxylation 
? Reduction 
? Formation of Sugars and Regeneration of Rubilose 
1,5-bisphosphate(RuBP)  
? Stoichiometry of Calvin cycle 
? Regulation of Calvin cycle  
? Photochemical changes 
? Activation of enzymes by light 
? Transport of intermediates   
? Regulation by metabolites 
? Photorespiration/C2 cycle/Glycolate metabolism 
? Significance of photorespiration 
? Mechanisms to avoid photorespiration 
? Hatch and Slack Pathway/C4 cycle 
? Three variants of HSK pathway 
? Regulation of C4 cycle 
? Photosynthetic efficiency of C3 and C4 
? Crassulacean Acid Metabolism 
? Ecological significance of CAM 
? Regulation of CAM cycle 
? Factors affecting photosynthesis 
? External factors 
? Light 
? Carbon dioxide 
? Temperature 
? Water 
? Internal factors 
? Chlorophyll content 
? Metabolic factors 
? Anatomy of leaf 
Photosynthesis II 
 
 
2            Institute of Lifelong Learning, University of Delhi                                                               
? Summary 
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Photosynthesis II 
 
 
3            Institute of Lifelong Learning, University of Delhi                                                               
Learning outcomes: 
After reading this lesson you should be able to 
? Describe the various steps involved in the light independent reactions. 
? Explain the historical aspect associated with the discovery of dark reactions. 
? Explain the function and carboxygenase and oxygenase activity of rubisco. 
? Generate a visual representation of Calvin cycle, photorespiration, C4 cycle and 
CAM cycles. 
? Explain the significance of photorespiration. 
? Describe calvin cycle and calculate the number of ATP and NADPH molecules 
required for the fixation of one molecule of CO
2.
 
? Describe the various methods adopted by plants for concentrating CO
2.
 
? Explain the mechanism and significance of photorespiration. 
? Identify the factors associated with photosynthesis. 
? Relate the importance of Kranz anatomy with C4 cycle . 
? Give reasons for the photosynthetic efficiency of C4 plants. 
? Describe the three pathways associated with hatch and slack pathway. 
? Explain why the C4 plants are able to reduce photorespiration. 
? Explain the similarities and differences associated with C3, C4 and CAM cycle. 
? Understand the mechanism and ecological significance of CAM pathway. 
 
 
 
 
 
 
 
 
 
Page 5


Photosynthesis II 
 
 
0            Institute of Lifelong Learning, University of Delhi                                                               
                                 
 
 
Lesson Prepared under MHRD project “National Mission 
on Education through ICT” 
 
Discipline: Botany 
Paper: Plant Plant Metabolism 
National Coordinator: Prof. S.C. Bhatla 
 
Lesson: Photosynthesis II 
Lesson Developer: Dr Basudha Sharma 
MM (PG) College, Modinagar, Uttar Pradesh 
 
Lesson Reviewer: Dr Girish Mishra, Department of Botany, 
University of Delhi 
 
Language Editor: Namrata Dhaka 
Department/College: Department of Genetics, University of Delhi, 
South Campus 
 
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
 
 
Photosynthesis II 
 
 
1            Institute of Lifelong Learning, University of Delhi                                                               
Chapter: Photosynthesis II 
Table of content 
? Carbon fixation 
? Calvin-Benson cycle 
? Steps of Calvin cycle 
? Carboxylation 
? Reduction 
? Formation of Sugars and Regeneration of Rubilose 
1,5-bisphosphate(RuBP)  
? Stoichiometry of Calvin cycle 
? Regulation of Calvin cycle  
? Photochemical changes 
? Activation of enzymes by light 
? Transport of intermediates   
? Regulation by metabolites 
? Photorespiration/C2 cycle/Glycolate metabolism 
? Significance of photorespiration 
? Mechanisms to avoid photorespiration 
? Hatch and Slack Pathway/C4 cycle 
? Three variants of HSK pathway 
? Regulation of C4 cycle 
? Photosynthetic efficiency of C3 and C4 
? Crassulacean Acid Metabolism 
? Ecological significance of CAM 
? Regulation of CAM cycle 
? Factors affecting photosynthesis 
? External factors 
? Light 
? Carbon dioxide 
? Temperature 
? Water 
? Internal factors 
? Chlorophyll content 
? Metabolic factors 
? Anatomy of leaf 
Photosynthesis II 
 
 
2            Institute of Lifelong Learning, University of Delhi                                                               
? Summary 
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Photosynthesis II 
 
 
3            Institute of Lifelong Learning, University of Delhi                                                               
Learning outcomes: 
After reading this lesson you should be able to 
? Describe the various steps involved in the light independent reactions. 
? Explain the historical aspect associated with the discovery of dark reactions. 
? Explain the function and carboxygenase and oxygenase activity of rubisco. 
? Generate a visual representation of Calvin cycle, photorespiration, C4 cycle and 
CAM cycles. 
? Explain the significance of photorespiration. 
? Describe calvin cycle and calculate the number of ATP and NADPH molecules 
required for the fixation of one molecule of CO
2.
 
? Describe the various methods adopted by plants for concentrating CO
2.
 
? Explain the mechanism and significance of photorespiration. 
? Identify the factors associated with photosynthesis. 
? Relate the importance of Kranz anatomy with C4 cycle . 
? Give reasons for the photosynthetic efficiency of C4 plants. 
? Describe the three pathways associated with hatch and slack pathway. 
? Explain why the C4 plants are able to reduce photorespiration. 
? Explain the similarities and differences associated with C3, C4 and CAM cycle. 
? Understand the mechanism and ecological significance of CAM pathway. 
 
 
 
 
 
 
 
 
 
Photosynthesis II 
 
 
4            Institute of Lifelong Learning, University of Delhi                                                               
Introduction 
As discussed in the chapter Photosynthesis - Part I, light energy is harvested by the 
photosynthetic unit consisting of reaction centre pigment (chlorophyll a) protein complex 
located on the thylakoid membrane and the antennae pigments. Two reaction centres, 
Photosystem I and II, cooperate to form ATP, a source of chemical energy, NADPH, 
source of hydrogen, and molecular oxygen.  The flow of electrons form the two 
photosystem through the different complexes results in the formation of electrochemical 
H+ gradient which results in photophosphorylation.  ATP and NADPH thus generated are 
used in the chemical reduction of carbon dioxide to form sugars in the light independent 
reactions. In this Chapter we shall discuss the steps involved in this reduction of carbon 
dioxide. 
 
Figure: Light dependent reactions of photosynthesis occur in thylakoid while the light 
independent reactions take place in the stroma of chloroplasts.  
Source: http://setarosite.org/images/biobook_images/photosynthesis_light_dark.gif (cc) 
Carbon fixation 
Carbon fixation refers to the conversion of CO
2
 into complex organic compounds 
(carbohydrates) through photosynthesis. Fixation of CO
2
 and formation of sugars is a 
complicated process and was detected initially by techniques like autoradiography and 
chromatography. However, now photosynthetic products can be identified and analysed 
by nuclear magnetic resonance (NMR) and mass spectrometry.  High performance liquid 
chromatography (HPLC) is used to separate the various photosynthetic products.