MS SastryLeigh High School1

Overall Photosynthesis Reaction = 6CO2 + 6H2O  C6H12O6 + 6O2

Photosynthesis has 2 parts: Light Dependent Reaction and Light Independent Reactions (a.k.a Calvin’s Cycle)

Noncyclic photophosphorylation (Z scheme)
(essentially takes energy in the form of light and electrons from H2O to make energy-rich ATP and NADPH)
Called ‘Noncyclic’ because electron does not return to PSII, but is replaced by water. / Process / Location / Input / Output / Details
Light Dependent Reaction
PSII
PS II has ‘chlorophyll a’ molecule in the Rection Center that absorbs light at 680 nm; Other pigments around chlorophyll’ a’ absorb light energy and pass it on to it. / Thylakoid membrane – chlorophyll a / Light, H2O
Water splits to make output
ADP and Pi (inorganic phosphate) / 2H+, 2 e-
½ O2
Electron from H2O replces PS II electron
ATP (see ETC and ATP Synthase) / Chlorophyll ‘a’ molecule in PSII absorbs light, causing electron to be excited. This electron is ejected from chlorophyll, and it moves to a ‘primary electron acceptor’ (PEA) and then to compounds in the electron transport chain (more electronegative atom accepts the electron and it loses energy). Finally this electron replaces the “lost” electron in PSI
PSIIe- PEA  ETC (ATP made using ATP Synthase)  PSI
Light Dependent Reaction
PSI
PS I has ‘chlorophyll a’ molecule in the Rection Center that absorbs light at 700nm; / Thylakoid membrane – chlorophyll a / Light,
e- from PSII,
NADP+ / NADPH (Hydrogen carrier—carries hydrogen from water to stroma to link with oxygen and carbon to make glucose) / PSI also loses electron when light strikes it, energy from electron used to make NADPH.
PSIe- ETC NADPH
(No ATP in PSI)
*Phosphorylation is a generl term – here it refers to ADP gaining a Phosphate group to turn into ATP.
(ADP + Pi = ATP) / Cyclic Photophosphorylation
PSII Only
Does NOT involve PSI / Thylakoid membrane
-chlorophyll a / Light, ADP, Pi / ATP / Ejected electron from chlorophyll ‘a’ in PSII eventually flows back to PSII (hence CYCLIC). NO WATER!
This makes ATP through ETC and ATP Synthase as in Noncyclic Potophosphorylation.
PSIIe- PEA  ETC PSI
Electron Transport Chain / Thylakoid membrane / e- from PSII
Cytochromes and other protein or lipid electron carriers in the thylakoid membrane / H+ ions pumped from stroma into thylakoid lumen / As electron moves through ETC, it is passed through several redox(reduction/oxidation) reactions
ATP Synthase / Thylakoid membrane / H+ ions flow back through the ATP Synthase enzyme in the thylakoid membrane (go from thylakoid lumen into stroma)
ADP, Pi / ATP / H+ ions move back into stroma allowing ATP to be synthesized. ATP remains in the stroma to help puttogether the glucose.
Used to be incorrectly named as DARK reactions! / Light Independent Reaction/Calvin Cycle in C3 plants / Stroma / CO2
NADPH
ATP
(RUBISCO—enzyme that fixes CO2) / C6H12O6
NADPH+
ADP + Pi / First, a C3 compound is made (G3P), then 2 of these G3P combine to make sugar (glucose has 6 carbons). Then glucose links to make different polysaccharides and disaccharides. (fructose, sucrose, starch, cellulose, etc.)

Light dependent rections make ATP and NADPH (carries H atom from water) usin the energy of light.. Light independent reactions use ATP and NADPH to put C, O, and H together to make C6H12O6 (C fixation). . Light independent reactions also yield the NADP+ and ADP needed for light reactions.


Process / Location / Input / Output / Details
Photorespiration / Thylakoid, stroma / Light, LOW CO2, H2O / no glucose / Wasteful process that occurs on hot, dry, days (CO2 levels in plant decrease; O2 levels increase inside the leaf causing RUBISCO – the enzyme in Calvin’s cycle to change from fixing C to fixing ‘O’)
C3 Plants / Thylakoid, stroma of Mesophyll cell / Light, CO2, H2O / C6H12O6 / Normal days, C3 plants can produce glucose
Light, CO2, H2O / NO glucose / Hot dry days when stomata close
C4 Plants
(Corn, Sugarcane) / Mesophyll cell / CO2, H2O / 4-carbon compound malate
(needs ATP, so some ATP is lost in this process) / Even on hot, dry days when stomata close, C4 plants can make glucose. To prevent photorespiration C4 plants take in CO2 and fix it into 4-carbon compound in the mesophyll cell; then, they move the 4 carbon compound away from the LOW CO2 area (mesphyll cell) into another area – the bundle sheath cells which surround the xylem and phloem in the veins. These bundle sheath clls release the CO2 from the 4 C malate compound and now RUBISCO can fix the CO2 into glucose fine and dandy even when stomata are closed!
Bundle Sheath Cell / CO2 is released from 4-carbon compound malate / Glucose is formed.
CAM plants
(crassulacean acid metabolism)
Desert plants / Night.
(Mesophyll cell) / CO2 / Organic compound / To prevent photorespiration, CAM plants take in CO2 at night; fix CO2 into glucose during day when stomta are closed
Day.
(Mesophyll cell / Organic compound from night time releases the CO2 / C6H12O6 / CAM and C4 are both strategies to avoid *photorespiration.

*When stoma close to prevent water loss on hot, dry days, this results in side effects—inability to absorb CO2 that is needed for photosynthesis.

Photosynthesis / Cell Respiration
Has 2 parts:
1) Light dependent—ATP, NADPH
2) Light independent—fixes CO2 as C6H12O6 / Has 4 parts
  1. Glycolysis—splits glucose into 2 pyruvate, 2 ATP (net), 2 NADH
  2. Shuttle – 2 NADH (may be used to yield only 4 ATP instead of 6ATP as it consumes some energy)
  3. Krebs cycle—releases 6CO2 from glucose, 2 ATP, 6 NADH, 2 FADH2

If a student volunteer types up more points for comparison, I will edit and post it on the website – it will be a GREAT study tool for you!