Photosynthesis
PHOTOSYNTHESIS
EXPLAINING ANATOMY FOR PHOTOSYNTHESIS.
Photosynthesis is the crucial process which drive the life
over our planet and maintain the oxidative environment.
Here we know about the photosynthesis but let first discuss
about the various mode of nutrition present in our environment.
There are mainly two types of mode of nutrition:-
1.
Heterotrophic
2.
Autotrophic
Autotrophic mode of nutrition is of mainly two types
I.
Photoautotroph
II.
Chemoautotroph
Photoautotroph is of two types one
who use oxygen to synthesize there food and the other who not use oxygen as
oxygenic and anoxygenic respectively.
Here we study about oxygenic mode
of photosynthesis.
Litteraly the word photo stands
for the light or photon therefore photosynthesis stands for stnthesising food
in presence of light.
In plants this process of
photosynthesis takes place within the
cytoplasmic organell chloroplast, a membrane bond organell .
Chloroplast having mainly three structural region.
1.
Double membrane bond structure
2.
Stroma
3.
Thyllakoid (diagram)
 |
| Chloroplast |
 |
| Thyllakoid section |
Photosynthesis is a process for synthesizing organic products by utilizing sunlight as a
source of energy, by inhaling CO2 as a
source of carbon and by absorbing water
as a source of hydrogen and byproduct oxygen.
Chemical formula diagram of photosynthesis.
This is the chemical formula representation of
photosynthesis, proposed by Van Niel in 1941.
This is the sum of three individual reactions.
THREE REACTION REPRESENTATION
Here you can notice that the byproduct oxygen is released from water not through carbon dioxide.
Further the whole explanation for the process of
photosynthesis moves around this chemical reaction, that is where this reaction
takes place, from where the contents of photosynthesis is reached to there site
and what are there source and also what is the final product of photosynthesis.
Green leafs are food factory for plant where
the process of photosynthesis takes place.
-
In C3
plant photosynthesis occurs within chloroplast containing mesophyll cells .
-
C4 plants
having special Kranz anatomy of leaf in
these certain processes takes place within the mesophyll cell and
remaining process is completed within a
thick walled structure encircling the vascular bundles known as bundle sheath.
Have you noticed it that the
process of photosynthesis in C3 plant
completes within a single cell of mesophyll while this process within C4 plants completes inside the two cells-
mesophyll and bundle sheath.
Let first understand the anatomy of
leaf:-
DIAGRAM FOR LEAF ANATOMY.
T.S view of Dicot leaf under
Electron microscope shows us several components of leaf, they are:-
·
Coverig of cuticle over leaf surface
·
Adaxial epidermis
·
Palisade mesophyll
·
Spongy mesophyll
·
Vascular bundle imprignated within Bundle sheath
·
Abaxial epidermis with stomatal opening.
The anatomy of Dicotyledon leaf
is:-
Anatomy of leaf:- leaf contains the upper most layer of water
impermeable cuticle, then a layer of cell for adaxial epidermis, then two types
of mesophyll found first is pallisade mesophyll
without intercellular space and then spongy mesophyll with air space, in
between these vascular bundles impregnated with bundle sheath is present whose
combined structure take the shape of veins and veinlets, at the bottom-most
point before lower cuticle, abaxial epidermis layer is present, in dicot leaf
stomatal aperture is found at abaxial epidermis.
Palisade mesophyll have the number
of chloroplast while in spongy mesophyll chloroplast is least.
These cells have the structure similar to plant cell havin cell wall,
mitochondria, chloroplast, nucleus, large vacuole, golgi body, Endoplasmic
Reticulum, DNA, RNA and so on.
Process of photosynthesis takes place within the chloroplast, a double
membrane bond organell, part of endosymbiont theory, having fluid filled space
called stroma, coin like structure called Thyllakoid piled over one another
known as granum as singular, each granum remain in contact with each other
through stromal lamellae and some starch and phosphate granules. Chloroplast
cell is similar to the prokaryotic cell or it
is a prokaryotic cell which use the eukaryotic cell as host during the
period of evolution .
This whole is the required anatomy which are usefull to us in
understanding the process of photosynthesis.
Only the difference in the Kranz anatomy leaf
is bundle sheath of the cell contain large number of chloroplast, grana are
absent, thick walls impervious to gaseous exchange and no intercellular
space. while the C3 plant lack these
specification.
Take a view of chloroplast and
there structural materials.
DIAGRAM OF CHLOROPLAST
DIAGRAM OF THYLLAKOID
In the chloroplast two reactions
take place, one is Light rection and the other is Dark reaction. In light
reaction light is utilised for exciting the electrons present in the
chlorophyll and transporting it through ETS to the NADP, where the assimilatory
power NADPH is formed.
If the light reaction takes place
in the thyllakoid then the involvement of photopigment System II & I both
occur one after the another respectively. When the light reaction takes place
within the stromal lamellae then there is the absence of photopigment system
II, therefore this reaction excited electron again comes back to the same and
not form the NADPH. On the basis of there pathway these reactions are also
termed as
NON-CYCLICPHOTOPHOSPHORYLATION & CYCLIC-PHOTOPHOSPHORYLATION as in non-cyclic
photophosphorylation the pathway of
electron form a structure of “Z” therefore this process is also called as
z-scheme.
Here the term photophosphorylation
stand for the addition of phosphoryl group(OPO3H2) in the presence of light. Or
it is not wrong to say phosphorylation Product is ATP.
DIAGRAM OF Z-SCHEME.
DARK REACTION
The dark reaction takes place
within the stroma of chloroplast here the assimilatory powers produced during
the Light reaction being used, which may be through the calvin cycle or the CAM
pathway. In this process fixation of carbon also takes place.
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