Light Dependent Reactions (Stage 1)
PS II (wavelength p680)
-Photons strike the chlorophyll in Photosystem 2 (PS II) and an electron absorbs the energy and becomes excited (photoexcitation), but has nothing to do with this energy.
-The electron travels from PS II (1st protein complex of 4) along the Electron Transport Chain (via mobile electron carriers) to harness the energy; across a series of reactions the electrons lose their energy.
-The energised electrons from PS II that were picked up by electron carriers are transported to the 2nd protein complex, the Cytochrome Complex. -The cytochrome complex stands in between PS II and PS I (which are all embedded in the thylakoid membrane), and uses the lost energy from the electrons to pump hydrogen ions into the thylakoid.
-Now missing an electron, the chlorophyll molecule will split a H20 molecule in cooperation with PS II to steal its electron and replenish the one it lost, the by-products of this process are hydrogen ions (single protons) and oxygen.
**By-product of oxygen is the reason behind the survival of living organisms.
PS I (wavelength p700)
The 'tired' electrons becomes re-energised by some photons as it reaches Photosystem 1 (PS I) and travels on another electron carrier, where all of the energy is used to help make NADPH (similar to ATP) by an enzyme, which combines 2 electrons and 1 Hydrogen ion with NADP+. (NADP+ + 2 e- + 1 H+ = NADPH).
**Products of light dependent reactions: Chemical energy in the form of ATP and NADPH, as well as the by-product O2.
Light Independent Reactions/Calvin Cycle (Stage 2)
**Doesn't require light energy from photons, uses energy derived from ATP and NADPH to fuel processes
Carbon Fixation (1st phase of Calvin Cycle)
-Begins in the Stroma (empty space of chloroplast). Involves fixing a CO2 molecule onto Ribulose-Bisphosphate or RuBP (the starting and end point of the 'cycle'), with the help of an enzyme called RuBisCo (which converts inorganic carbon into organic carbon), which causes it to become unstable.
-So this new 6-Carbon chain has to break apart, creating 2 molecules of 3-Phosphoglycerate, which occurs to 3 molecules of RuBP (explained later).
**If RuBisCo reacts with O2 instead of CO2, it creates a toxic by-product known as phosphoglycolate (process of photorespiration) believed to alter enzymatic functions.
Reduction (2nd phase)
-ATP combines a phosphate group onto the 3-Phosphoglycerate molecules and then NADPH packs some electrons, creating 2 molecules of Glyceraldehyde 3-Phosphate (G3P).
-G3P is a high-energy, 3-carbon compound that plants can convert into many carbohydrates such as glucose, or cellulose or starch.
G3P is also known as PGAL
Regeneration (3rd and last phase)
-9 ATP molecules and 6 NADPH are required to convert the 3 RuBP started with into 6 G3Ps, however only 1 G3P can leave the cycle - with the other 5 G3Ps needed to regenerate the original 3 RuBP, completing 1 round of the cycle.
**G3P is considered the ultimate product of photosynthesis as the glucose gained from it is the energy used by all cells
Require water, light and carbon dioxide
CO2 enters the plant through the stomata
Plant absorbs photons from the sun using the pigment “chlorophyll”
Inside the chloroplasts there are things called thylakoids, which have the lumen inside the structure and the stroma outside the structure
It all starts in photosystem II
Photons strike the chlorophyll and excite the electrons in the chlorophyll
The cytochrome complex uses some of the energy from the electron to pump more hydrogen protons into the thylakoid.
The hydrogen protons, now inside the thylakoid, are brought into the ATP synthase. The ATP synthase packs the Hydrogen proton onto the ADP making ATP
The original electron, now completing its journey, is moved into PSI where it is reenergized by a photon. The Re energized electron then moves into the…