Quiz

Topics Covered in the MCQs: Photosynthesis

Light-Dependent Reactions

1. Photosystems I and II:

• Light Absorption: Chlorophyll pigments within photosystems I and II absorb light energy, exciting electrons to higher energy levels.
• Photoexcitation and Electron Transport: Excited electrons are ejected from the chlorophyll molecules and transferred through a series of electron carriers.
• Water Splitting: In photosystem II, water molecules are split into oxygen, hydrogen ions, and electrons. The released oxygen is a byproduct of photosynthesis.
• Proton Gradient Formation: As electrons move through the electron transport chain, energy is used to pump protons across the thylakoid membrane, creating a proton gradient.

2. ATP Synthesis:

• Chemiosmosis: The proton gradient created across the thylakoid membrane drives the synthesis of ATP. Protons flow through ATP synthase, a protein complex embedded in the membrane, which catalyzes the phosphorylation of ADP to ATP.

3. NADPH Production:

• Electron Transfer: Electrons from the electron transport chain are transferred to NADP+, reducing it to NADPH. NADPH is a high-energy electron carrier that will be used in the Calvin cycle to reduce carbon dioxide.

Overall Goal of Light-Dependent Reactions:

The primary goal of the light-dependent reactions is to convert light energy into chemical energy stored in ATP and NADPH. These energy-rich molecules are essential for the subsequent dark reactions, or Calvin cycle, where glucose is synthesized.