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My Pages On Different Subjects which Hyperlinked to all my Blog Posts

Saturday, 24 March 2012

PHOTOSYNTHESIS : Most Important Oxygen Producing Reaction of Earth.

is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can create their own food. In plants, algae, and cyanobacteria, photosynthesis uses carbon dioxide and water, releasing oxygen as a waste product. Photosynthesis is vital for all aerobic life on Earth. In addition to maintaining normal levels of oxygen in the atmosphere, photosynthesis is the source of energy for nearly all life on earth, either directly, through primary production, or indirectly, as the ultimate source of the energy in their food, the exceptions being chemoautotrophs that live in rocks or around deep sea hydrothermal vents. The rate of energy capture by photosynthesis is immense, approximately 100 terawatts, which is about six times larger than the power consumption of human civilization.As well as energy, photosynthesis is also the source of the carbon in all the organic compounds within organisms' bodies. In all, photosynthetic organisms convert around 100–115  petagrams of carbon into biomass per year.
Overall Reaction of Photosynthesis

Overall 3D structure of Plants important during Photosynthesis
3D -Microscopic Structure of Leaf
Microscopic Picture of Leaf and its different Structure
Microscopic picture of Leaf
The light dependent reactions of photosynthesis take place at specialised cell membranes,such as Thylakoid membrane
inside chloroplasts.That membrane is folded into the system pf stacked disks, called grana, and flatten channels.The interior spaces of the disks achannels are open to one another, so the membrane system actually forms a single compartment.The compartment is a reservoir for hydrogen ions, and it is tapped for ATP formation.The synthesis of
phosphorylated sugars and starch occurs in the stroma, a semifluid matrix that surrounds the thylakoid compartment.
       The internal organisation of a chloroplast might seem to be less than memorable, until you remember that we are taking about a very small space. If you clould lined up 2000 chloroplasts, one after another, the lineup would be no wider than your thumbnail.Imagine all the chloroplasts in one lettuce leaf, each a tiny factory of producing sugars and starch
and you begin to get a sense of the magnitude of metabolic events required to feed you and all other organism on earth.
Chloroplast ultrastructure:
1. outer membrane   2. intermembrane space  3. inner membrane (1+2+3: envelope) 4. stroma (aqueous fluid) 5. thylakoid lumen (inside of thylakoid) 6. thylakoid membrane 7. granum (stack of thylakoids) 8. thylakoid (lamella) 9. starch 10. ribosome 11. plastidial DNA
12. plastoglobule (drop of lipids)

A) Light Absorption:
1) In chloroplasts, light is absorbed by two types of photosystems (clusters of photosynthetic pigments embedded in the  
    thylakoid membrane).

2) Light absorption causes the transfer of electrons from photosystem 1 or 2 to an acceptor molecule,which will donate them toa transport system in the membrane.

B) Noncyclic pathway:
1) Exiting land plants rely mainly on noncyclic photophosphorylation,which yields ATP and NADPH.

2) In the non cyclic patheway, there is a one-way flow of electrons from photosystem 2 , through a trasport system, to
    photosystem 1, and on through a second trasport system.Electrons released from water molecules replace the electrons
    being expelled from photosystem 2.

3) During electron transfers, hydrogen ions picked up from the stroma are released inside the thylakoid compartment.
    Hydrogen ions derived from water molecules also accumulate here.Both activities establish concentration and electric
    gradients across the membrane.

4) Hydrogen ions flow down the gradients (through channel proteins that span the membrane), and the flow drives the
    joining of inorganic phosphate  and ADP to from ATP.

5) At the end of the second transport system,electrons are donated NADP+, which combines the H+ to form NADPH. The
    Electrons and hydrogen can be used directly in assembling organic compounds.

C) Cyclic pathway:
1) In cyclic photophosphorylation, excited electrons flow from photosystem 1, through a transport system, then back to
     photosystem. This pathway yields ATP only.

2) Operation of electron transport systems causes hydrogen ions to accumulate inside the thylakoid compartment.

3) Energy inherent in the resulting concentration and electric gradients between the compartment and the stroma is
    tapped to from ATP, just like it is in the non-cyclic pathway.

      12 H2O -----------> ELECTRON & HYDROGEN IONS ------------> USED IN FORMING -------------> 18 ATP, 12 NADPH, 12H+
                   6 O2
                 (Oxygen as
                  by product)


1) Carbon-di-oxide is fixed  to RuBP, making an unstable intemediate that is broken apart into two three carbon PGA

2) PGA is Phosphorylated (made more reactive) by ATP,and it receives H+ and electrons from NADPH.The result is

3) Through complex reactions, PGAL is rearranged into new RuBP molecules and into sugar phosphate.

4) It takes 6 turns of the Calvin-Benson cycle to produce one sugar phosphate(Only one very six PGAL molecules produced
    in the cycle is funneled into carbohydrate synthesis).

5) The suger phosphates are intemediates in the light-indipendent reactions; they can enter pathways by which many
    different carbohydrate end products form.
    18 ATP, 12 NADPH + 12H+  ----------------------------------> C6H12O6 ---> P-----> Typical sugar phosphate------>Carbohydrate
                                                          6H2O                                                                                              end product
                                                       (Water as                                                                                          (Sucrose,starch)

3D- Animation of Photosynthesis Process: 



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