AP Biology Questions on Light-Dependent Reactions: Exam Prep

📚 Quick Study Guide

• ☀️ Light-dependent reactions occur in the thylakoid membranes of the chloroplasts.
• 💧 Water ($H_2O$) is split, providing electrons and protons ($H^+$), and releasing oxygen ($O_2$).
• ⚡ Light energy is absorbed by chlorophyll and other pigments, exciting electrons.
• ➡️ Excited electrons move through an electron transport chain (ETC), releasing energy.
• ⚙️ This energy is used to pump protons ($H^+$) across the thylakoid membrane, creating a proton gradient.
• 🧪 Chemiosmosis: $H^+$ ions flow down their concentration gradient through ATP synthase, driving the synthesis of ATP.
• ⚛️ NADP+ is reduced to NADPH, carrying high-energy electrons. The overall reaction can be represented as: $2H_2O + 2NADP^+ + 3ADP + 3Pi + light \rightarrow O_2 + 2NADPH + 3ATP$

Practice Quiz

1. Which of the following is a direct product of the light-dependent reactions of photosynthesis?
   1. ATP
   2. Glucose
   3. $CO_2$
   4. RuBP
2. What is the primary role of water in the light-dependent reactions?
   1. To absorb light energy.
   2. To provide electrons for the electron transport chain.
   3. To release carbon dioxide.
   4. To produce glucose.
3. Where does the oxygen released during photosynthesis come from?
   1. Carbon dioxide ($CO_2$).
   2. Water ($H_2O$).
   3. Glucose ($C_6H_{12}O_6$).
   4. ATP.
4. Which of the following is the main purpose of the electron transport chain in the light-dependent reactions?
   1. To directly produce glucose.
   2. To generate a proton gradient for ATP synthesis.
   3. To split water molecules.
   4. To fix carbon dioxide.
5. What molecule is the final electron acceptor in the light-dependent reactions?
   1. $CO_2$
   2. $O_2$
   3. $NADP^+$
   4. RuBP
6. The movement of protons ($H^+$) through ATP synthase is best described as:
   1. Active transport.
   2. Facilitated diffusion.
   3. Osmosis.
   4. Simple diffusion.
7. Which of the following energy conversions occurs during the light-dependent reactions?
   1. Chemical energy to light energy.
   2. Light energy to chemical energy.
   3. Chemical energy to kinetic energy.
   4. Kinetic energy to potential energy.