Dark Reaction of
Photosynthesis
Every living on
earth depends on the process of producing energy on plants called
photosynthesis. Especially plants depend on photosynthesis for making food and
energy. Other organisms, including herbivores and carnivores, depend on it
indirectly because they depend on plants for food. Without plants, they
wouldn’t have the food, energy, and nutrients needed to survive. So that’s why
photosynthesis becomes the important process for all creatures. For photosynthesis
process itself, plants need sunlight to produce organic compounds, such as
lipids, proteins, and sugar. Then the organic compounds used to provide energy
for the plants. In photosynthesis solar energy is converted to chemical energy.
It is required directly in the first process of photosynthesis called Light
Dependent Process or Light Reactions. The direct energy of light in light
reaction process is to make energy carrier molecules that are used in the
second phase of photosynthesis. The second phase of photosynthesis called dark
reaction or also known as Calvin cycle doesn't directly depend on solar energy,
but it requires and processes some molecules that processed in light reaction
process. There are three steps inside Calvin cycle or dark reaction, and every
steps occurs in the stoma of the chloroplast.
The
first step called as fixation converts the carbon dioxide from the air into an
organic compound which cannot move away. In this step, carbon dioxide reacts
with Ribulose Bisphospahte (RuBP). This occurs under the influence of enzyme
ribulose bisphosphate groubs, and by accepting one more carbon atom from CO2
(Carbon dioxide) it should be converted into 6 carbons, and 2 phosphate
compounds. However, these compounds are immediately converted into 2 molecules
of glycerate3-phosphate (GP) which contains 3 carbons and one phosphate group.
This pathway, as taken from Wikipedia, is called C3 carbon fixation because the
first product is a 3-carbon compound.
The
second stage is called as carbon dioxide reduction. This stage named as it
because when CO2 (Carbon dioxide) reacts with H (Hydrogen) from reduced NADP as
a receptor of photosynthesis, it gains hydrogen and loses oxygen to become CH2O
(carbohydrates). Reduction is loss of oxygen. However, the CO2 is now part of
glycerate 3-phospate. Glycerate 3-phosphate is covered into triose phosphate
using reduced NADP and ATP. The reduced NADP provides the reducing hydrogen and
is converted back to NADP which is then reduced again in this stage. On the
other sides, ATP, as the product of NADP, is used to provide energy for the
conversion.
The
last phase of this process is called as Ribulose bisphosphate regeneration. In
this phase, ribulose monophosphate is converted into ribulose bisphosphate,
using a phosphate set from ATP. In a complex series of reactions, the remaining
ten molecules of triose phosphate are converted into 6 molecules. Thus reaction
which ribulose bisphosphate accepts carbon dioxide to become carboxylated is to
keep the cycle operating again.
As
the results of one turn of the calvin cycle are 2 Glycerate 3-phosphate
molecules, 3 ADP, and 2 NADP. They are regenerated and later used again in the
light reaction. It seems clearly, there are some connections between dark
reaction and light reaction of photosynthesis. What are processed in light
reaction is needed on dark reaction, and so does dark reaction. So that’s why,
Calvin cycle is important for photosynthesis in plants. In order to keep Calvin
cycle continuing, it doesn’t only depend on plant itself, but we as human also
take important act to keep Calvin cycle on photosynthesis running on. We have
to balance the ecosystem, for instance the conservation of soil and water has
to be kept because those factors indirectly influence the process of
photosynthesis especially Calvin cycle. What are produced on photosynthesis
process especially dark reaction process or Calvin cycle is not only important
for the plant. But also, it is important for all creatures’ life.
