Photosynthesis MCQs for NEET — Botany Questions with Answers

CAM (Crassulacean Acid Metabolism) plants open their stomata at night to minimize water loss while allowing CO2 to enter for photosynthesis. During the day, the stomata are closed to conserve water. This adaptation is particularly useful in arid conditions.

In the light reactions of photosynthesis, water (H2O) acts as the electron donor to Photosystem II (PSII), which contains P680 chlorophyll molecules. Water is split into oxygen, protons, and electrons through a process called photolysis. The electrons released from water replenish the electron deficit in P680 after it gets excited by light energy.

The reduction of ADP to ATP in photosynthesis occurs through a process known as chemiosmosis, which involves a high concentration of H+ ions (protons) across the thylakoid membrane. This proton gradient drives ATP synthesis as protons flow back across the membrane through ATP synthase.

The process of ATP formation from ADP in the presence of light in chloroplasts is called photophosphorylation. This process uses the energy from light to add a phosphate group to ADP, forming ATP, and it occurs in the thylakoid membranes of chloroplasts during the light reactions of photosynthesis.

O₂ (oxygen) is the by-product of photosynthesis. During the light-dependent reactions of photosynthesis, water molecules are split (photolysis) to release oxygen, electrons, and protons. The oxygen is then released as a by-product.

The reduction of carbon occurs in the stroma of the chloroplast. This is where the Calvin cycle takes place, utilizing ATP and NADPH produced in the light-dependent reactions to fix carbon dioxide into organic molecules.

Cyclic photophosphorylation occurs mostly in stroma lamellae membrane and in this process, only ATP is released.

The fixation and reduction of CO₂ in the Calvin cycle (also known as the dark reaction) occur in the presence of ATP and NADPH, which are generated during the light reactions of photosynthesis. ATP provides the necessary energy, while NADPH provides the reducing power for the conversion of CO₂ into glucose.

Photolysis of water in photosynthesis involves the splitting of water molecules into oxygen, protons, and electrons. This process is catalyzed by the oxygen-evolving complex (OEC) of photosystem II, which requires manganese (Mn++) and chloride (Cl-) ions to function properly.