KEY CONCEPT Photosynthesis requires a series of chemical reactions.

1. KEY CONCEPT Photosynthesis requires a series of chemical reactions.

2. Objectives • Describe the light-dependent reactions in which energy is captured. • Describe the light-independent reactions in which sugar is produced.

3. Vocabulary • Photosystem • Series of light-absorbing pigments and proteins that capture and transfer energy in the thylakoid membrane. • Electron Transport Chain • Series of proteins in the thylakoid and mitochondrial membranes that aid in converting ADP to ATP by transferring electrons. • ATP synthase • Enzyme that catalyzes the reaction that adds a high-energy phosphate group to ADP to form ATP. • Calvin Cycle • Process by which a photosynthetic organism uses energy to synthesize simple sugars from CO2.

4. The first stage of photosynthesis captures and transfers energy. • The light-dependent reactions include groups of molecules called photosystems.

5. Photosystem II captures and transfers energy. • chlorophyll absorbs energy from sunlight • energized electrons enter electron transport chain • water molecules are split • oxygen is released as waste • hydrogen ions are transported across thylakoid membrane

6. Photosystem I captures energy and produces energy-carrying molecules. • chlorophyll absorbs energy from sunlight • energized electrons are used to make NADPH • NADPH is transferred to light-independent reactions

7. The light-dependent reactions produce ATP. • hydrogen ions flow through a channel in the thylakoid membrane • ATP synthase attached to the channel makes ATP

8. The second stage of photosynthesis uses energy from the first stage to make sugars. • Light-independent reactions occur in the stroma and use CO2 molecules.

9. A molecule of glucose is formed as it stores some of the energy captured from sunlight. • carbon dioxide molecules enter the Calvin cycle • energy is added and carbon molecules are rearranged • a high-energy three-carbon molecule leaves the cycle

10. A molecule of glucose is formed as it stores some of the energy captured from sunlight. • two three-carbon molecules bond to form a sugar • remaining molecules stay in the cycle

11. Question/Answer • Where do the light-dependent reactions occur? • Thylakoid membrane of chloroplast • What is the source of the electrons in the electron-transport chain? • Chlorophyll • How are the electrons released from the water molecules used? • To replace energized electrons that leave the chlorophyll. What role do these electrons play? • What role do these electrons play? • They provide energy to move hydrogen ions into the thylakoid and to produce molecules of NADPH.

12. Question/Answer • What two energy carriers are produced? • NADPH and ATP • In what step is active transport occurring? Passive transport? • Step 3 • Step 6 • Where in the chloroplast do light-independent reactions occur? • Stroma • Where are ATP and NADPH coming from? • Light-dependent reactions • Why are these reactions called a cycle? • The five-carbon molecule of the process is regenerated, so the cycle continues.

13. Question/Answer • How does the Calvin Cycle build sugar molecules? • Carbon dioxide is added to five-carbon molecules in the cycle. Energy from ATP and NADPH is used in a series of chemical reactions that build the three-carbon molecules needed to form a six-carbon sugar.