Flashcards in Chapter 10 Questions Deck (4)
List the components of a photosystem and explain their function.
- Light Harvesting Complex: surrounds the photosystem
- Chlorophyll a: special because of their molecular environment
- Pigment Molecules: transfers the energy through the light harvesting complex
- Reaction Center: holds the primary e- acceptor
- Thylakoid Membrane: Holds the light harvesting complex
- Primary Electron acceptor: takes the e- from the special chlorophyll a
Trace electron flow through Photosystem 2 and Photosystem 1.
Two electrons enter photosystem II from hydrolysis, the splitting of water. These electrons are passed to special chlorophyll a molecules, P680 (named after the wavelength of light it absorbs best) in the reaction center. The electrons are passed up to the primary electron acceptor after being excited by light energy, and they then enter the first electron transport chain, consisting of several electron carriers and a cytochrome complex. This fall of electrons provides energy to synthesize ATP. The now low-energy electrons are passed to two additional special chlorophyll a molecules, P700, in photosystem I. Light energy once again excites the electrons, passing them on to another primary electron acceptor within the reaction center. Here they enter another electron transport chain, though with a different electron carrier and passing to NADP+ reductase. They are finally made into a molecule of NADPH, which is then passed away from the thylakoid and photosystems and into the stroma for the Calvin cycle.
Describe two important photosynthetic adaptations that minimize photorespiration.
One photosynthetic adaptation is C4 plants which preface the Calvin Cycle with an alternate mode of carbon fixation that forms a 4-carbon compound as its first product, this adaptation is advantageous in hot regions. Another adaptation is CAM plants which open their stomata during the night and close them during the day, the reverse of how normal plants behave. During the night they take in CO2 and store them in organic acids then during the day they close their stomata and when the light reactions can supply ATP and NADPH for the Calvin cycle, CO2 is released from the organic acids made the night before to become incorporated into sugar in the chloroplast.