Photosynthesis

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Photosynthesis flash cards
Shareef Akbari
Flashcards by Shareef Akbari, updated more than 1 year ago
Shareef Akbari
Created by Shareef Akbari about 7 years ago
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Question Answer
What is the ultimate source of energy in almost all ecosystems? sunlight
What is the point of the light reactions? To convert solar energy to chemical energy
What is the overall equation for photosynthesis? 3CO2+6H2O -> C3H6O3 + 3O2 + 3H2O
Which pigment is essential for photosynthesis? Chlorophyll a
What is a photosystem? Organized group of 250-400 pigment molecules combined within thylakoid membrane that acts as a light gathering antenna complex
What is the reaction centre? Complex of proteins and 2 chlorophyll a molecules
How is ATP formed in the light reactions?? The cleavage of H20 gives electrons to P680, but the H+ ions that are left get forced out of the lumen. Once the electrons that were given to P680 go down the "steps" to Cytbf/f complex, there is a conformational change and the Cyt bf/f complex opens as an H+ channel. This allows H+ to go down its gradient, providing the energy required for ATP synthesis.
How is NADPH made in the light reactions Once the electrons pass Cyt Bf/f complex, they get transferred down a chain of proteins to P700, which gets excited by light as well. This increases the energy of P700, and electrons pass down another chain as well until they're given to the final electron acceptor, NADP+. Electrons bind to NADP+ and H+ to form NADPH
What is cyclic photophosphorylation? Happens in photosystem one, where the same elctron keeps binding to P700 over and over again, and the cycle produces ATP through Cyt bf/f
What is the ratio of ATP to NAPDH that is required for the dark reactions? 9ATP:6NADPH
What is the point of the dark reactions? To create sugar
What is rubisco? Most abundant enzyme on the planet. Adds 3CO2 to 3 5 carbon RuBP molecules. This turns into 6 3 carbon PGA molecules. Uses CO2 and produces O2
What is PGAL? Output of the calvin cycle. Used to make sugars.
What happens to C3 photosynthesis when there is a low concentration of CO2? RUBISCO uses O2 as a substrate, produces CO2. Does not form ATP, sugar or NADPH. Called photorespiration.
What are 2 ways that plants have developed to combat the problem with C3 photosynthesis? C4 and CAM
What are the steps in C4 photosynthesis? 1. CO2 enters substomatal chamber 2. CO2+3C molecule -> 4C molecule in mesophyll cells 3. 4C molecule is sent to bundle sheath cells 4. 4C molecule is broken down into CO2 in bundle sheath cells. 5. CO2 enters calvin cycle
How did CAM plants figure out how to beat the problems in C3 photosynthesis? Split up photosynthesis to happen at different times of the day. Light reactions happen during the day when stomata are closed so water can't escape because it's hot. Dark reactions happen at night when stomata are open so CO2 can get in.
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