Chemicals of Life
- The Leaf Structure
- The Process
- Photosynthesis Rate
Thinkquest Team 22016
It is important to remember that
O2 comes from water, not CO2.
Photosynthesis occurs in 2 phases the light and dark
|Light "harvesting" à
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
Election Transport à
|This transfer of
elections results in ATP and NADPH being formed. PS I is
responsible for the creation of NADPH.
When light is absorbed at PS I,
an election is displaced and transferred to an election acceptor.
This acceptor transfers the electron to NADP, reducing it to NADPH.
But if the chlorophyll at PS I keeps loosing electrons, it will
need to replace them. PS II does this.
When light hits the chlorophyll
at PS II, an electron is displaced and is sent, via electron
carriers, to PS I. Thus giving PS I its lost electron back. But
the PS II has lost an electron,
how does it get it back? The photolysis of water is the answer.
Water is split and an electron donated to PS II. Oxygen is given
off too this being 1 of the products of
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.
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.
|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
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.