4.3 Photosynthesis in Detail KEY CONCEPT Photosynthesis requires a series of chemical reactions.

4.3 Photosynthesis in Detail Objectives Describe the light-dependent reactions in which energy is captured. Describe the light-independent reactions in which sugar is produced.

4.3 Photosynthesis in Detail 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 CO 2.

4.3 Photosynthesis in Detail The first stage of photosynthesis captures and transfers energy. The light-dependent reactions include groups of molecules called photosystems.

4.3 Photosynthesis in Detail 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

4.3 Photosynthesis in Detail 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

4.3 Photosynthesis in Detail The light-dependent reactions produce ATP. –hydrogen ions flow through a channel in the thylakoid membrane –ATP synthase attached to the channel makes ATP

4.3 Photosynthesis in Detail Light-independent reactions occur in the stroma and use CO 2 molecules. The second stage of photosynthesis uses energy from the first stage to make sugars.

4.3 Photosynthesis in Detail 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

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

4.3 Photosynthesis in Detail 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.

4.3 Photosynthesis in Detail 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.

4.3 Photosynthesis in Detail 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.