| Feature | Non-Cyclic Photophosphorylation | Cyclic Photophosphorylation |
|---|---|---|
| Photosystems Involved | Involves both **Photosystem I (PS I)** and **Photosystem II (PS II)** working in series. | Involves **Photosystem I (PS I)** only. PS II is completely inactive here. |
| Electron Flow Path | The electron expelled from PS II does not return; it is a one-way flow (Z-scheme). | The expelled electron cycles back to the same reaction center via carriers. |
| Photolysis of Water | Occurs on the inner side of the thylakoid membrane, splitting water. | Does not occur; there is no splitting of water molecules. |
| End Products | Produces both **ATP** and **NADPH**, along with oxygen ($O_2$) evolution. | Produces **ATP only**. No NADPH is synthesized, and no oxygen is released. |
| Anatomical Location | Occurs in the **grana lamellae** where both PS I and PS II are present. | Occurs in the **stroma lamellae**, which lack PS II and NADP reductase enzyme. |
Looking for more NCERT-focused Biology notes, diagrams, MCQs and NEET preparation resources?
Explore NEET Biology →Mastering the intricate energetic pathways of plant life requires a deep look at how chloroplasts harvest light and fix carbon. In our previous guide, we broke down the core differences between C_3 and C_4 plants. In this section, we provide detailed, step-by-step solutions to the remaining critical textbook questions from the Class 11 Photosynthesis in Higher Plants NCERT chapter.
❓ Step-by-Step NCERT Exercise Solutions (Continued)
Q6: What are the two parts of a chloroplast where light and dark reactions occur respectively?
Answer: The chloroplast is a double-membrane, highly specialized organelle where the two phases of photosynthesis are spatially separated to maximize chemical efficiency:
Light Reaction (Photochemical Phase): Occurs in the Thylakoid membranes and Grana lamellae. This is where chlorophyll pigments absorb solar energy to split water and generate ATP and NADPH.
Dark Reaction (Biosynthetic Phase): Occurs in the fluid matrix called the Stroma. This matrix contains all the essential enzymes (like RuBisCO) required to fix carbon dioxide into glucose using the energy packets produced in the light phase.
Q7: Which property of the pigment chlorophyll enables it to act as a primary light-harvesting molecule?
Answer: Chlorophyll a acts as the primary reaction center molecule due to several specific chemical and physical properties:
Light Absorption Spectrum: It has a remarkable ability to absorb light energy at specific wavelengths, predominantly in the blue and red regions of the visible light spectrum.
Electron Excitation: When a photon of light hits chlorophyll a, its valence electrons absorb the energy and get excited to a higher energy state.
Electron Transfer: Instead of losing this absorbed energy as heat or fluorescence, excited chlorophyll a can eject this high-energy electron and pass it directly to a primary electron acceptor. This initiates the entire electron transport chain (Z-scheme) of the light reaction.
Answer: Photophosphorylation is the process of synthesizing energy-rich ATP molecules from ADP and inorganic phosphate (P_i) using solar energy. Plants utilize two distinct pathways to achieve this:
Answer: Photorespiration (also known as the C_2 cycle) occurs in C_3 plants when light intensities and temperatures are high, and internal CO_2 concentrations drop. Under these specific conditions, the active site of the dual-nature enzyme RuBisCO binds with oxygen (O_2) instead of CO_2.
It is labeled as a highly wasteful evolutionary process because:
No Sugar Synthesis: It does not lead to the production of glucose or any useful chemical food reserves.
No ATP or NADPH Generation: Instead of producing energy packets, it actively consumes ATP to run its metabolic loops.
Loss of Fixed Carbon: It leads to the destruction of previously fixed photosynthetic carbon, releasing it back into the atmosphere as carbon dioxide (CO_2).
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