organisms perform some basic processes which help in the survival and
perpetuation of race. This is called life process
autotrophic and produce their own food by photosynthesis.
This is the
only process on earth which can utilize the energy present in sun light and
also adds oxygen to the atmosphere and makes our living possible.
is defined as a photochemical reaction during which carbon dioxide and water in
presence of sunlight and chlorophyll are utilized for the production of
reaction of photosynthesis can be written as
6CO2+12H2O --- -------------→ C6H12O6+6CO2+6H20
In plants, leaf
constitutes the main photosynthetic organ as it contains large surface area to
receive more sunlight and its internal organization is more suitable for
transverse section of a leaf shows that it covered by epidermis on both
surfaces. At some places, epidermis is interrupted by a large number of
openings called stomata. The central opening is called stoma. Each stoma is
surrounded by two kidney shaped cells called guard cells. These stomata
regulate the exchange of gases from the leaves. The tissue enclosed between the
two epidermal layers is called mesophyll. It is differentiated into palisade
and spongy parenchyma. This mesophyll cells contains abundant chloroplasts.
chloroplast are oval shaped and are filled with colorless fluid called stroma. Inside
the stroma, many disc like structures called thylakoid membranes are observed.
These thylakoids are present like the piles of a coin called grana. The grana
are connected by stroma thylakoid. Inside the thylakoids membranes, chlorophyll
molecules are situated. These chlorophyll molecules trap solar energy from the sunlight.
Vascular bundles are located in the central region of the leaf.
Mechanism of photosynthesis:
of photosynthesis is divided into two phases.
Light reaction: The process takes place only in the
presence of light. So it is named as light reaction.
is essential for the process is transported from roots to stems and leaves.This
light reaction taken place in the grana of thylakoids of chloroplast. The
chlorophyll molecule traps the solar energy and this light activated
chlorophyll split the water molecule by a process called photolysis. In this reaction,
oxygen is released and is escaped into atmosphere. Then NADP molecule is
activated by the electrons to produce NADPH2 and ADP molecule by
utilizing energy from the electron converts into ATP. Thus during light
reaction, light energy is converted into chemical energy in the form of ATP and
NADPH2.oxygen is the byproduct.
takes place in the absence of light. So it named as dark reactions.
dioxide is essential for this process is obtained from atmosphere and it enters
through the stomata into the cells of leaf. The entire dark phase is carried
out in the stroma of chloroplast. CO2 in the presence of ATP and NADPH2
which is produced in the light reaction is utilized for the production of
glucose, which is a carbohydrate.