- The Leaf Structure
- The Process
- Photosynthesis Rate
- Photosynthesis Test
It is important to remember that O2 comes from water,
Photosynthesis occurs in 2 phases the light and dark reaction.
The Light Reaction
|Light "harvesting" -||In chloroplasts, there are thylakoids, which have
Pigment molecules around them. These pigment molecules funnel light photons to the chlorophyll a molecules in the reaction centre. As the chlorophyll molecule absorbs this energy, its electrons move to a higher energy level creating an excited chlorophyll molecule. It can now pass this energy onto the chlorophyll molecule next to it, thus exciting it, and making itself normal again.
Electrons are being transport through these 2 centres:
Election Transport -
|This transfer of elections results in ATP and
NADPH being formed. PS I is responsible for the creation of NADPH.
ATP is also formed by the transfer of electrons, and is made by ADP and an inorganic phosphate. The flow of electrons from PS II to PS I creates hydrogen ions(H+), and a steep concentraion gradient. The passage of H+ out of the thylakoids, provides the energy for ATP to be synthesised in the presence of ATPase. This is called non-cyclic photophosphorylation. The H+ ions also provide the hydrogen for reducing NADP to NADPH.
So the light reaction creates energy by phosphoralyation producing ATP, and by adding electrons to NADP to create NADPH.
The Dark Reaction
This reaction occurs in the stroma of the chloroplast. This stage is mainly concerned with the synthesizing of carbohydrates from CO2. This occurs in a number of steps, with different enzymes along the way.
The Calvin Cycle -
|Firstly CO2 is
combined with RuBP(a 5 carbon organic compound). The enzyme RuBP
carboxylase is needed here.This "fixes" the CO2.
Thus a 6 carbon mocule is created, which is very unstable, so it splits immediately into 2 molecules (3 carbons each), of glycerate 3-phosphate(GP).
GP is then reduced to GALP, a 3 carbon sugar. This reduction used hydrogen from NADPH. Energy for this comes from NADPH and ATP. The 3 carbon sugar is built up to a 6 carbon sugar, which can be converted to starch.
Some of the 3C sugar isnt converted into 6C, but goes into the regeneration of RuBP, for the continuation of this cyclic process.