Photosynthesis Flashcards
photosynthesis
- converts light energy to chemical bond energy + carbon fixed into organic compounds
- formula: 6CO2 + 12H2O (light)→ C6H12O6 + 6H2O + 6O2
2 processes of photosynthesis
light-dependent or light-independent reactions
light-dependent uses light energy to produce ATP that powers light-independent (Calvin cycle that produces sugar)
photosynthetic pigments
absorb light energy and provides energy for photosynthesis
2 major groups of pigments in plants
chlorophylls and carotenoids
chlorophyll a and chlorophyll b
green pigments, absorbs all wavelengths of light in red/blue/violet range
carotenoids
yellow/orange/red pigments, absorbs lights in blue/green/violet ranges
ex: xanthophyll (carotenoid with slight chemical variation), phycobilins found in red algae and absorb lights in blue and green range
antenna pigments
capture light in wavelengths that are not captured by chlorophyll a
(includes chlorophyll b + carotenoids)
passes energy along to chlorophyll a, which directly transforms light energy to sugar
action spectrum
graph comparing wavelengths of light vs rate of photosynthesis
purpose of chlorophyll a
directly involved in light reactions of photosynthesis
structure: large molecule with single mg atom in head surrounded by alternating double and single bonds (porphyrin ring) attached to long hydrocarbon tail
chloroplast
- contains photosynthetic pigmenets that carry out photosynthesis with enzymes
- contains grana where light-dependent reactions occur, consist of layer of membranes called thylakoids (site of photosystems 1 and 2)
- contains stroma where light-independent reactions occur
photosystems
- light-harvesting complexes in thylakoid membranes of chloroplasts
- has reaction center with chlorophyll a and region with hundreds of antenna pigement molecules that funnel energy into chlorophyll a
- PS I and II work together in light reactions (named in order of discovery and not order of function, PS II works before PS I)
few hundred photosystems in each thylakoid
- PS I absorbs light best in 700 nm range, aka P700
- PS II absorbs light best in 680 nm range, aka P680
light-dependent reactions
light absorbed by photosystems, and electrons flow through ETC
2 routes for electron flow:
- noncyclic flow
- cyclic photophosphorylation
noncyclic photophosphorylation
electrons enter 2 ETCs, and produces ATP and NADPH:
1. energy absorbed by P680, electrons from double bonds in head of chlorophyll a become energized and move to higher energy level to be captured by a primary electron acceptor
2. photolysis (splitting of water) provides electrons to replace those lost from chlorophyll a in P680, splits water into 2 electrons, 2 protons (H+), and 1 oxygen (2 oxygen combine and is released as waste product)
3. electrons from P680 pass along ETC with cytochromes/other proteins and end up in P700, flow is exergonic and provides energy to produce ATP by chemiosmosis
4. ATP formed by chemiosmosis (protons from photolysis pumped by thylakoid membrane from stroma into thylakoid space (lumen), diffuses down gradient through synthase channels and into stroma), ATP produced here provides energy to power Calvin cycle
5. NADP becomes reduced when picking up 2 protons released from water in P680, newly formed NADPH carries hydrogen to Calvin cycle to make sugar
6. energy absorbed by P700, electrons from head of chlorophyll a become energized and are captured by primary electron receptor (energy that escapes here replaced with electrons from PS II, also produces NADPH instead of ATP)
light → P680 oxygen released → ATP produced → P700 → NADPH produced
this ATP synthesis is called photophosphorylation because it is powered by light energy
cyclic photophosphorylation
- solely produces ATP (nothing else)
- occurs when chloroplast runs low on ATP (Calvin cycle uses a lot of energy)
- electrons from P680 ETC to P700 to primary electron acceptor, and back to cytochrome complex in P680 ETC
