PHOTOSYNTHESIS IN HIGHER PLANTS NEET, Light Reaction & Photophosphorylation – PS-I, PS-II, ATP & NADPH formation, cyclic and non-cyclic photophosphorylation.
Course Description
Photosynthesis in Higher Plants involves two main stages: Light Reaction and Dark Reaction.
- Light Reaction occurs in the presence of sunlight, where pigments absorb light energy to generate ATP and NADPH. It includes photophosphorylation, which can be:
- Non-cyclic (involving both PS-I and PS-II)
- Cyclic (involving only PS-I)
- The splitting of water (photolysis) in PS-II releases oxygen as a byproduct.
- Dark Reaction occurs in the stroma without direct light involvement. It includes the Calvin Cycle (C3 Cycle), where RuBisCO fixes CO₂ to synthesize glucose. Some plants follow the C4 Cycle (Hatch and Slack Pathway), where CO₂ is initially fixed into a four-carbon compound in mesophyll and bundle sheath cells, reducing photorespiration and enhancing photosynthetic efficiency.
Environmental factors such as light intensity, carbon dioxide concentration, temperature, and water availability significantly affect the rate of photosynthesis. While C3 plants are common in temperate regions, C4 plants thrive in hot and arid conditions due to their specialized mechanism. Additionally, CAM plants like cacti use a modified pathway to minimize water loss.
Overall, photosynthesis is not just the foundation of the plant’s food production but also the main source of oxygen, making it indispensable for sustaining life on Earth and maintaining the balance of the ecosystem.
