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 GRANUM







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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