Basic process of photosynthesis
Photosynthesis is a process where by energy from light is harvested and used to drive synthesis of carbohydrates from carbon dioxide and water.

Physics of light
Quantum is the elemental unit of energy. Photon is a quantum of electromagnetic energy and it is particle of light.

Chloroplast structure
Chloroplast is a plant subcellular organelle where photosynthesis takes place. Outer membrane of chloroplast is permeable. Inner membrane encloses stroma. Thylakoid is flattened membrane surrounded vesicle. This is the place where light reaction occurs. In stroma, fluid surrounding the thylakoids is the place where the dark reaction occurs. Chlorophylls are the green pigments; they are present in the thylakoid membrane of chloroplast. They absorb deep blue and red light. Secondary light absorbing pigments are called accessory pigments. They are carotenoids and phycobilins. Photosystems are the light absorbing pigments of thylakoid membrane arranged in functional sets.

Light reaction and photophosphorylation
Photosystems are of two types: PS I P700, PS II P680. Components of photosystem I and II transfer the electrons from water to NADP. Light is absorbed by these photosystems and electrons are transferred from water to NADP. Photophosphorylation is a process where the light energy captured by the photosynthetic organisms is transformed into the phosphate bond energy of ATP. During the transfer of electrons, ATP is synthesized. Electron flow is cyclic. As a result oxygen is not released and ATP is formed as a result of proton gradient created by Cytochrome bf pump.

Dark reaction – Calvin cycle
Second step of photosynthesis is called Calvin’s cycle and it is a dark reaction. There are two stages here, I and II.  In Stage I carbon dioxide is incorporated into 5 carbon ribulose bisphosphate. In stage II ribulose bisphosphate is the regenerated.

Photorespiration
Photorespiration is the process wherein oxygen consumption occurs in illuminated temperature zone of plants under high oxygen and low carbon dioxide. Oxygen is consumed and carbon dioxide is released. Moreover, ATP is expended without benefit.

C4 pathway
C4 cycle is the pathway adopted by C4 plants to conserve the carbon dioxide released via photorespiration. It occurs in mesophyll cells. Carbon dioxide is incorporated to form 4 carbon oxaloacetate.

Photosynthesis is a process where by energy from light is harvested and used to drive synthesis of carbohydrates from carbon dioxide and water. Photophosphorylation is a process where the light energy captured by the photosynthetic organisms is transformed into the phosphate bond energy of ATP. Components of photosystem I and II transfer the electrons from water to NADP. Second step of photosynthesis is called Calvin’s cycle and it is a dark reaction. There are two stages here, I and II. Stage I is carbon dioxide fixation and stage II is the regeneration phase. Photorespiration is the process wherein oxygen consumption occurs in illuminated temperature zone of plants under high oxygen and low carbon dioxide. C4 cycle is the pathway adopted by C4 plants to conserve the carbon dioxide released via photorespiration. It occurs in mesophyll cells.

• General concept map to explain the photosynthesis features.
• Animated map to show the processes taking place in chloroplast.
• Pictorial explanation of light absorption.
• Photosystem I and II, cyclic electron flow are diagrammatically represented.

Basic process of photosynthesis

• Introduction
• Definition

Physics of light

• Electromagnetic spectra
• Light absorption

Chloroplast structure

• Outline
• Light absorbing structures
• Accessory pigments
• Photosystem

Light reaction and photophosphorylation

• Role of light harvesting molecules
• Excitation of reaction center
• Photosystem I and II
• Cytochrome bf complex
• Light absorption by photosystems
• Summary – Transfer of electrons
• Definition – Photophosphorylation
• Coupling of ATP synthesis
• Cyclic electron flow

Dark reaction – Calvin cycle

• Stage I – Carbon dioxide fixation
• Stage II – Regeneration phase

Photorespiration

• Definition
• Process

C4 pathway

• Definition
• Pathway