AP Biology Questions on Photosystem Function

📚 Quick Study Guide

• ☀️ Photosystems: Light-dependent reaction centers in the thylakoid membranes of chloroplasts. They capture light energy and convert it into chemical energy.
• 💡 Photosystem II (PSII): The first photosystem in the sequence. It absorbs light best at 680 nm and uses this energy to split water molecules ($H_2O$) into electrons, protons ($H^+$), and oxygen ($O_2$). This process is called photolysis.
• 💧 Electron Source (PSII): Water ($H_2O$) is the electron donor, replenishing electrons lost by chlorophyll.
• ⚡️ Electron Transport Chain (ETC): Electrons from PSII are passed along an ETC, releasing energy used to pump protons ($H^+$) into the thylakoid lumen, creating a proton gradient.
• 🧪 Photosystem I (PSI): The second photosystem. It absorbs light best at 700 nm. It receives electrons from the ETC and re-energizes them using light.
• 🧬 NADPH Formation (PSI): Electrons from PSI are used to reduce $NADP^+$ to $NADPH$, which is then used in the Calvin cycle.
• 🔢 ATP Synthase: The proton gradient created by the ETC drives ATP synthase, which phosphorylates ADP to ATP (photophosphorylation).
• 🌍 Cyclic vs. Non-Cyclic Electron Flow: In non-cyclic electron flow, both PSII and PSI are involved, producing ATP and NADPH. In cyclic electron flow, only PSI is involved, producing ATP but no NADPH.

Practice Quiz

1. Which of the following is the primary function of Photosystem II?
   1. A. To produce NADPH
   2. B. To split water molecules and release oxygen
   3. C. To fix carbon dioxide
   4. D. To produce ATP
2. What molecule is the final electron acceptor in Photosystem I?
   1. A. $O_2$
   2. B. $H_2O$
   3. C. $NADP^+$
   4. D. $CO_2$
3. The energy from the electron transport chain in photosynthesis is used to:
   1. A. Directly synthesize glucose
   2. B. Pump $H^+$ ions into the thylakoid lumen
   3. C. Split carbon dioxide
   4. D. Reduce oxygen to water
4. What is the original source of electrons for Photosystem II?
   1. A. NADPH
   2. B. ATP
   3. C. $H_2O$
   4. D. $CO_2$
5. Which of the following is produced by cyclic electron flow in photosynthesis?
   1. A. NADPH only
   2. B. ATP and NADPH
   3. C. ATP only
   4. D. Oxygen only
6. At what wavelength does Photosystem I (PSI) absorb light most efficiently?
   1. A. 400 nm
   2. B. 580 nm
   3. C. 680 nm
   4. D. 700 nm
7. What is the role of the antenna pigments in a photosystem?
   1. A. To split water molecules
   2. B. To directly excite the reaction center chlorophyll
   3. C. To capture light energy and transfer it to the reaction center
   4. D. To produce ATP