Topic 8.2: Photosynthesis Flashcards Preview

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Flashcards in Topic 8.2: Photosynthesis Deck (22)
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What are phtosystems?(2)

collections of chlorophyll molecules; act a light-gathering "antenna complex"


Where are the photosystems located?

in the thylakoid membrane


What are the characteristics of photosystem II? (2)

chlorophyll a is the most dominant pigment; P680 absorbs 680 nm wavelength of red light


What are the characteristics of photosystem I?(2)

chlorophyll b is the most dominant pigment; P700 absorbs 700 nm wavelength of red light


What is the electron transport chain of photosynthesis?(9)

uses light energy, ATP, and NADPH; NADPH (stored) energy goes to Calvin cycle; photosystem II absorbs light; excited electron passes from chlorophyll to "primary electron acceptor"; need to replace electron in chlorophyll; enzyme extracts electrons from H2O and supplies them to chlorophyll; to do this the enzyme spilts the H2O; oxygen combines with another oxygen to form O2; O2 is released


How does the light reactions elevate electrons?(2)

photosystem II generates energy as ATP; photosystem I generates reducing powers as NADPH


What is cyclic photophosphorylation?(3)

if photosystem I can't pass electron to NADPH, it cycles back to photosystem II and makes more ATP, but no NADPH; coordinates light reactions to Calvin cycle; Calvin cycle uses more ATP than NADPH


What is the Calcin cycle?(5)

occurs in the stroma of the chloroplast; needs ATP and NADPH; first phase is fixation where Rubisco (enzyme) fixes CO2 to an existing 5-Carbon Sugar (RuBP), splitting it into 2 3-Carbon Sugars (PGA); the next phase is reduction where ATP donates a phosphate to PGA making it G3P and ATP becomes ADP, then NADPH trades that phosphate for an electron and the carbohydrate is reduced; the final phase is where only one PGAL leaves to be further modified and the rest are recharged with an additional phosphate and then rearranged into 3 RuBP


What is the gas exchange in the stomates?(3)

CO2 in for the Calvin Cycle; O2 out from the light reactions; H2O out for the light reactions


How do stomates control water loss from leaves?(4)

stomates close to conserve water; guard cells; if gaining water the stomates open; if losing water the stomates close; adaptation to living on land


What is the problem with closed stomates?(3)

O2 builds up from light reaction; CO2 is depleted in Calvin Cycle; causes problems in the Calvin cycle


What is the problem in the Calvin Cycle when the stomates are closed?(2)

Rubisco normally binds carbon to RuBP which leads to the reduction of RuBP and the building of sugars in photosynthesis; when O2 concentration is high the Rubisco bonds oxygen to RuBP which leads to the oxidation of RuBP and the breakdown of sugars in photorespiration


What is the impact of photorespiration?(7)

oxidation of RuBP; short circuit of Calvin cycle; loss of carbons to CO2; decreases photosynthetic output by siphoning off carbons; no ATP (energy) produced; no C6H12O6 (food) produced; if photosynthesis could be reduced, plant would become 50% more efficient; strong selection pressure


How do you reduce photorespiration?

separate carbon fixation from the Calvin cycle


What are the characteristics of C4 plants?(6)

physically separate carbon fixation from Calvin cycle; different enzyme to capture CO2 in PEP carboxylase which stores carbon in 4-Carbon compounds; different leaf structure; adaption to hot, dry climates; have to close stomates a lot; sugar cane, corn, other grasses


What are the characteristics of CAM plants?(8)

separate carbon fixation from Calvin cycle by time of day; open stomates fix carbon (capture CO2) during night; store carbon in organic acids such as malic and isocitric acid; perform Calvin cycle during day; different adaptation to hot, dry climates; succulents, some cacti, pineapple; in day close stomates and release CO2 from storage compounds to Calvin cycle; increases concentration of CO2 in cells


What are the characteristics of PEP carboxylase?(3)

higher affinity for CO2 than O2 therefore better than Rubisco; fixes CO2 in 4-Carbon compounds; regenerates CO2 in inner cells for Rubisco


What are the parts of the C3 plant cell?(7)

upper epidermis; palisade mesophyll cell; vein; bundle sheath cell; spongy mesophyll cell; lower epidermis; stroma


What are the parts of a C4 plant cell?(6)

upper epidermis; mesophyll cell; vein; bundle sheath cell; lower epidermis; stroma


What occurs in the outer cells during C4 photosynthesis?(5)

light reaction; carbon fixation; punps CO2 to inner cells; keeps O2 away from inner cells; keeps O2 away from Rubisco


What occurs in the inner cells of C4 photosynthesis?(2)

calvin cycle; glucose to veins


Why is C3 photosynthesis a problem?(6)

possible evolutionary baggage; Rubisco evolved in high CO2 atmosphere; there wasn't strong selection against active site Rubisco accepting both CO2 and O2; today it makes a difference; 21% O2 vs. 0.03% CO2; photorespiration can drain away 50% of carbon fixed by Calvin cycle on a hot, dry day

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