Photosynthesis

• The light-dependent reactions take place in the thylakoid membranes of the chloroplasts.
• This process generates ATP and NADPH, which are used in the Calvin cycle.
• Electrons from water molecules are excited to higher energy levels during photosystem II (PSII) and then transferred through an electron transport chain.
• Light energy is absorbed by pigments, mainly chlorophyll, which are located on the surface of the thylakoids.
• Electron transfer occurs between pigments within photosystem II, resulting in the formation of a high-energy electron that can be passed along the electron transport chain.
• The proton gradient produced by electron transport powers ATP synthesis via ATPase enzyme.
• The electron transport chain contains cytochrome b6f complex, plastocyanin, photosystem I and Fd (ferredoxin).
• The light-dependent reactions occur in the thylakoid membranes, while the Calvin cycle occurs in the stroma.
• Rubisco catalyses the carboxylation reaction where CO2 combines with ribulose bisphosphate (RuBP), forming two molecules of phosphoglyceric acid (PGA).
• Photosynthetic organisms use carbon dioxide as their source of carbon.
• NADPH is formed when NADP+ accepts hydrogen atoms from reduced ferredoxin.
• Photosystem I absorbs light energy and transfers electrons to ferredoxin, producing NADP+.
• Oxygen is released as a waste product and hydrogen ions are pumped across the thylakoid membrane.
• Water splits into oxygen gas and hydrogen ions at PSII.
• The remaining two photosystems use the energy from sunlight to excite electrons to higher energy states.
• Carbon dioxide enters the leaf through stomata and diffuses to the mesophyll cells.
• Inside the cell, Rubisco catalyzes the carboxylation reaction, converting RuBP into PGA.
• Carbon fixation is the process of converting atmospheric carbon into organic compounds through photosynthesis or other biological processes.
• Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) is an enzyme that plays a crucial role in the Calvin cycle by catalyzing the conversion of CO2 into RUBP.
• Chlorophyll a and b absorb different wavelengths of visible light.
• RuBP + CO2 → PGA
• Rubisco catalyses the carboxylation reaction between carbon dioxide and ribulose bisphosphate (RuBP) to form unstable molecules called 3-phosphoglyceric acid (PGA).
• Light-dependent reactions occur in chloroplasts and involve splitting water molecules to produce O2 and reducing power.
• C4 plants are adapted to hot and dry environments where water loss is high due to transpiration.