Photosynthesis: Light Reactions, Calvin Cycle, and ATP Synthesis

Core Principles of Photosynthesis

The Light-Dependent Reactions

1. When oxygen is released during photosynthesis, what is it a direct by-product of?

   It is a direct by-product of splitting water molecules.

2. What is the role of pigment molecules in a light-harvesting complex?

   Within the thylakoid membranes, they absorb and transfer light energy to the reaction-center chlorophyll.

3. What is directly associated with photosystem I?

   It is directly associated with receiving electrons from the thylakoid membrane's electron transport chain.

4. How can one detect the lack of photosystem II in certain photosynthetic organisms?

   The most effective method is to test for the liberation of O2 in the presence of light, as photosystem II is responsible for splitting water to release oxygen.

Electron Flow and ATP Synthesis

5. What are the products of linear electron flow?

   The primary products are ATP and NADPH.

6. If the Calvin cycle consumes more ATP than NADPH, where do the extra ATP molecules originate?

   The extra ATP molecules are generated through cyclic electron flow.

7. If a thylakoid is punctured, disrupting the proton gradient, what process is most directly affected?

   This damage most directly affects the synthesis of ATP, which depends on the chemiosmotic gradient across the thylakoid membrane.

8. Where are ATP synthase complexes located in a plant cell?

   They are found in both the thylakoid membrane and the inner mitochondrial membrane.

9. When does ATP synthesis via chemiosmosis occur in photosynthetic cells?

   It occurs during both photosynthesis and cellular respiration.

The Calvin Cycle and Reaction Products

10. In which part of photosynthesis are O2 molecules produced?

    Molecular oxygen is produced during the light-dependent reactions alone.

11. Where do the light reactions and the Calvin cycle occur?

    The light reactions take place in the thylakoid membranes, while the Calvin cycle occurs in the stroma of the chloroplast.

12. Where does the Calvin cycle take place?

    The Calvin cycle takes place in the stroma of the chloroplast.

13. What is the primary function of the Calvin cycle?

    Its primary function is to synthesize simple sugars, like glucose, from carbon dioxide.

14. What is produced during the light reactions of photosynthesis?

    The light reactions produce ATP, NADPH, and O2.

15. What are the products of the Calvin cycle?

    The Calvin cycle produces glucose, ADP, and NADP+.

General Photosynthesis and Cellular Concepts

16. Why do most plants appear green?

    Most plants are green because their primary pigment, chlorophyll, reflects green light while absorbing other wavelengths for energy.

17. What supplies the energy that excites the P680 and P700 reaction centers?

    The energy is supplied by photons from light.

18. How do mitochondria and chloroplasts differ in energy conversion?

    Mitochondria transfer chemical energy from food to ATP, whereas chloroplasts transform light energy into the chemical energy of ATP.

19. What key energy-converting organelles are found in plant cells?

    Plant cells contain both mitochondria and chloroplasts.

20. What is the main advantage of C4 and CAM photosynthesis over the C3 strategy?

    Their primary adaptive advantage is that they help the plant conserve water and synthesize glucose more efficiently under hot, dry conditions.