Photosynthesis - AP Biology

1. What is the overall equation for photosynthesis?

   $6 \text{CO}_2 + 6 \text{H}_2\text{O} + \text{light} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6 \text{O}_2$. Converts light energy, water, and $\text{CO}_2$ into glucose and oxygen.

2. What is the role of carbon dioxide in photosynthesis?

   Carbon source for glucose synthesis. Fixed into organic molecules during the Calvin cycle.

3. Identify the three phases of the Calvin cycle.

   Carbon fixation, reduction, regeneration. Sequential steps that convert $\text{CO}_2$ into glucose precursors.

4. Which three-carbon carbohydrate is exported as the net product of the Calvin cycle and can be used to make glucose?

   Glyceraldehyde-3-phosphate (G3P). For every three $\text{CO}_2$ fixed, the cycle yields one net G3P; glucose and other carbohydrates are built from G3P rather than produced directly by the cycle.

5. Which light spectrum is least absorbed by chlorophyll a?

   Green. Chlorophyll reflects green light rather than absorbing it.

6. What is the initial electron donor in photosystem II?

   Water (H$_2$O). Split to provide electrons and release oxygen gas.

7. Which component of the chloroplast contains chlorophyll?

   Thylakoid. Membrane structures that house photosynthetic pigments.

8. What molecule is produced by ATP synthase during photosynthesis?

   ATP. Energy currency synthesized via chemiosmosis in thylakoids.

9. In which part of the chloroplast does the Calvin cycle take place?

   Stroma. Fluid-filled space surrounding thylakoids where carbon fixation occurs.

10. What type of light do carotenoids absorb?

    Blue and green light. Accessory pigments that broaden photosynthetic light absorption.

11. During linear photosynthetic electron flow, which reduced electron carrier is produced using electrons energized by photosystem I?

    NADPH. Electrons energized by photosystem I are passed along a short electron transport chain and ultimately transferred to NADP⁺ (by the enzyme NADP⁺ reductase), reducing it to NADPH.

12. What is the significance of the Z-scheme in photosynthesis?

    Represents electron flow in light reactions. Shows energy changes as electrons move between photosystems.

13. What process in photosynthesis generates a proton gradient across the thylakoid membrane?

    Electron transport chain. Creates proton concentration difference for ATP synthesis.

14. Which molecule is regenerated in the Calvin cycle to accept CO$_2$?

    Ribulose bisphosphate (RuBP). Five-carbon acceptor molecule for $\text{CO}_2$ in carbon fixation.

15. What is the main difference between C3 and C4 plants?

    C4 plants fix CO$_2$ into a 4-carbon compound. Spatial separation reduces photorespiration in hot climates.

16. What molecule is the primary electron carrier in photosynthesis?

    NADP$^+$. Accepts electrons to form NADPH for the Calvin cycle.

17. What enzyme catalyzes the fixation of CO$_2$ in the Calvin cycle?

    Rubisco. Catalyzes the first step of carbon fixation in photosynthesis.

18. What is the energy source for ATP synthesis during photosynthesis?

    Proton gradient. Chemiosmotic force drives ATP synthase rotation.

19. What is the main purpose of cyclic electron flow?

    Produce ATP without NADPH. Balances ATP/NADPH ratio for optimal Calvin cycle function.

20. What does NADPH provide in the Calvin cycle?

    Reducing power. Donates electrons for carbon dioxide reduction reactions.

21. Which molecule acts as the primary carrier of chemical energy in cells?

    ATP. Stores and transfers energy in phosphate bonds.

22. What is the role of ATP in photosynthesis?

    It supplies energy for the Calvin cycle. ATP made in the light reactions powers the formation of carbohydrate (G3P) and the regeneration of the carbon acceptor RuBP, but it does not directly drive the initial fixation of $\text{CO}_2$ by rubisco.

23. Identify the two main stages of photosynthesis.

    Light-dependent reactions and Calvin cycle. Light reactions produce ATP/NADPH; Calvin cycle fixes carbon.

24. In which organelle does photosynthesis occur?

    Chloroplast. Contains thylakoids and stroma where photosynthetic reactions occur.

25. What is the primary function of photosystem I?

    Produce NADPH. Reduces $\text{NADP}^+$ to NADPH using light energy.

26. Which gas is a byproduct of photosynthesis?

    Oxygen. Released when water molecules are split in photosystem II.

27. What is the primary pigment involved in photosynthesis?

    Chlorophyll. Green pigment that absorbs light energy for photosynthesis.

28. Name the 3-carbon molecule produced in the Calvin cycle.

    Glyceraldehyde-3-phosphate (G3P). Precursor molecule used to synthesize glucose and regenerate RuBP.

29. What does the term 'photophosphorylation' refer to?

    ATP synthesis using light energy. Light-driven phosphorylation of ADP to form ATP.

30. What is the source of energy that drives the light-dependent reactions?

    Sunlight. Provides photons that excite chlorophyll electrons.

31. In which part of photosynthesis is oxygen produced?

    Light-dependent reactions. Water splitting in photosystem II releases oxygen gas.

32. Which molecule supplies energy used in the reduction and RuBP-regeneration stages of the Calvin cycle?

    ATP. ATP supplies energy for converting fixed carbon into G3P and for regenerating RuBP, while NADPH supplies the reducing power (electrons) for the reduction step.

33. What is photorespiration?

    A process where oxygen is fixed instead of CO$_2$. Wasteful process where rubisco binds oxygen instead of $\text{CO}_2$.

34. Where in the chloroplast do light-dependent reactions occur?

    Thylakoid membranes. Contain photosystems and electron transport chains.

35. What is the role of water in the light-dependent reactions?

    Electron donor. Provides electrons when split by photosystem II.

36. What is the function of accessory pigments?

    Expand the range of light absorption. Capture wavelengths chlorophyll cannot absorb efficiently.

37. What adaptation allows CAM plants to minimize water loss?

    Stomata open at night. Temporal separation prevents water loss during hot days.

38. Which molecule is reduced to form NADPH in photosynthesis?

    NADP$^+$. Electron acceptor that becomes reducing agent NADPH.

39. What is RuBP and its role in photosynthesis?

    5-carbon sugar involved in CO$_2$ fixation. Acceptor molecule that binds with $\text{CO}_2$ in carbon fixation.

40. Which photosystem absorbs light at 680 nm?

    Photosystem II. P680 reaction center splits water and begins electron flow.

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