Photosynthesis
Plants
are able to convert water and carbon dioxide to be their food, organic
compound, especially sugar by using sunlight energy. The process of converting
is called photosynthesis. Photosynthesis involves two reactions: light reaction
and light-independent reaction.
The
first reaction is the light reaction which is also called light-dependent
reaction. This reaction occurs in thylakoid membrane of the chloroplasts. It uses
light energy to synthesize ATP and NADPH,
the form of energy that is ready to be used by plants and humans. In this case,
plants use ATP and NADPH to provide energy for the next reaction. The equation
for the light-dependent reactions
is:
2 H2O
+ 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+
+ 3 ATP + O2
Two water
molecules are separated by photolysis process which uses light energy. That is
because 2 NADP+ need to be reduced, and it can happen if 2 H+
exist. ADP (Adenosine Triphosphate) transform into ATP by adding phosphate
molecule to it. As seen in the equation, at the end of reaction, there are
NADPH, ATP, H+ and O2- as the products of photolysis which are not used in the reaction.
The next reaction is light-independent
reaction. This reaction is often called Calvin cycle or dark reaction. An
enzyme is needed to capture CO2 from the air. The enzyme is called RuBisCO. The equation for light-independent reaction is:
3 CO2 + 9 ATP + 6 NADPH +
6 H+ → C3H6O3-phosphate + 9 ADP + 8
Pi + 6 NADP+ + 3H2O
There are
several step occurring before C3H6O3-phosphate exists at the end of reaction. Carbon dioxide combines
with a five-carbon sugar, RuBP (ribulose
1,5-bisphosphate),
to produce two molecules of a
three-carbon compound which is called
GP
(glycerate 3-phosphate). If a molecule of phosphate is added, GP becomes PGA (3-phosphoglycerate). The
existence of ATP and NADPH from
the light-dependent stage makes GP reduced
to G3P (glyceraldehyde 3-phosphate). This product becomes PGAL (3-phosphoglyceraldehyde) or even triose
phosphate. Triose is a 3-carbon sugar
whose in the equation is written as C3H6O3-phosphate. Five of
six molecules of the G3P are
used to regenerate RuBP so the process can continue. As seen in
the equation, the results of reaction are C3H6O3-phosphate, ADP and Pi- the result of ATP usage, NADP+- the result of
NADPH usage, H2O- the combination of H+ with O2
which remain after used to form C3H6O3-phosphate.
In short, photosynthesis is a very complicated process.
It is a wonderful ability that plants have. We need to save them in order to
save our life. As explained before, in two reactions, the basic thing that we
need is produced. The former produces O2 that we use to breathe. The
latter produce C3H6O3-phosphate that we eat in form of fruit or seed. So, let’s keep our earth green!
