Introduction To Photosynthesis

                        PHOTOSYNTHESIS:

Chemically photosynthesis is a redox process in which CO2 is reduced into glucose. Water act as reducing agent which is oxidized into oxygen. Bioenergetically photosynthesis can be defined as a energy conversion process in which energy poor molecules such as water and carbondioxide change into energy rich molecules such as glucose. The extra energy was absorbed in the form of sunlight by photosynthetic pigments

ACTION SPECTRUM:

Full range of electromagnetic radiation in the universe is called ELECTROMAGNETIC SPECTRUM. Visible light is only the small part of spectrum(From 380nm to 750nm) which is not only seen by us but qalso effective for the process of photosynthesis. The effectivness of different wavelength(colours) of visible light is primarily depend on its absorption in plant body. As different wavelength of light differently absorbed in  plant body so each wavelength of light has its own effectivness for the proces of photosynthesis. The graph which show the effectivness of different wavelength of light for the process of photosynthesis is called ACTION SPECTRUM.  Detailed analysis of action spectrum tell us thatblue(430nm) and red(670nm) was most effective for the process of photosynthesis

PHOTOSYNTHETIC PIGMENTS:

Pigment is any substance that absorbed light energy. Photosynthetic pigments are present in thylakoid membrane. In higher plants there are two major type of pigments
1- Chlorophyll
2-Carotenoids

CHLOROPHYLL:

Chlorophyll absorb mainly red,blue,voilet and orange wavelengths. Yellow and green are least absorbed. There are two main type of chlorophyll
1-Chlorophyll a is a bluish green pigment and found in all photosynthetic orgnism except photosynthetic bacteria.
2-Chlorophyll b is yellowish green pigmenet and found in all photosynthetic organisms except brown,red algae and photosynthetic organisms
algae also have some other type of chlorophylls which are chlorophyll c,d,e. Bacteria has another type of chlorophyll which is BACTERIOCHLOROPHYLL
Chlorophyll a=C55H7205N4Mg
Chlorophyll b=C55H70O6N4Mg
A molecule of chlorophyll consist of head and two tails. Head composed of porphyrin ring with Mg in centre. Porphyrin ring consist of four pyrole ringle. Each pyrole ring consist of N and four C. The nitrogen atom of pyrole ring interact with centeral Mg. The difference between chlorophyll a and b is that in chlorophyll a consist of CH3 at second pyrole ring and chloropyhll b consist of CHO at second pyrole ring. The head of chlorophyll is hydrophillic and exposed to surface of thylakoid membrane. Tail of chloropyll is hydrophobic and embedded into the thylakoid membrane

Carotenoids:

Carotenoids are terpenoid lipids. They absorb light mainly in blue-voilet range. They act as acessory pigments along with chlorophyll b. They absorb light enery and pass it to chlorophyll a. In this way they provide protection to chlorophyll a from excess of light. They also attract insects,birds and other animal for pollination
There are two types of carotenoids
1-Carotene(It is orange pigment,composed of isoprenoid unit and found in all photosynthetic eukaryotes.
2-Xantophyll is yellow in colour

       Arrangement Of pigments:             

For efficient absorption and utilization of energy, the photosynthetic pigment are arrangend in the forms of cluster in thylakoid membrane. These clusters are known as PHOTOSYSTEM. The peripheral part of photosystem is called antenna complex it contain acessory pigments such as chlorophyllb and carotenoids. The centeral part of photosystem is called REACTION CENTRE. It only contain chlorophyll a. Due to reaction centre or chlorophyll-a photosystem has two types
1-Photosystem--1(Chlorophyll-a in reaction centre of this photosystem absorb maximun light of wavelength 700nm. Due to which it also known as P-700)
2-Photosystem-2(Chlorophyll-a in reaction centre of this chlorophyll absorb light of maximum wavelength 680nm. Due to which it is also known as P-680)
These two photosystem are named in the order of their discovery not in the order in which they are found in thylakoid membrane. During light reaction first P-680 use then P-700 used

             ROLE OF CARBONDIOXIDE IN PHOTOSYNTHESIS:

Carbondioxide act as carbon source. Plant are known as autotroph because they convert inorgananic molecule into organic molecule. Air consist of 0.03% of carbondioxide. Land plant use atmospheric carbondioxide. Dissolved carbondioxide and carbonates or bicarbonates was used by aquatic photosynthetic organism. Carbondioxide use in dark reaction or Kalvin cycle.

ROLE OF WATER IN PHOTOSYNTHESIS:

Water act as proton and electron donor in photosynthesis. During photosynthesis of PS-680 or Photosystem-2 absorb light energy electron of chlorophyll-a excited and leave it. These electrons accepted by primary electron acceptor. After loosing electron chlorophyll-a molecule in reaction centre of PS-680 become electron deficient. When water react with this oxidized state of chlorophyll-a it split into 2H+,2e- and oxygen. Oxygen release as byproduct while electron was accepted by chlorophyll-a molecule to remove electron deficiency. Actually this splitting of water occur when light is present because due to absorbance of light energy chlorophyll electron excited and leave it so that's why this splitting of water is known as PHOTOLYSIS OF WATER. Role of water in photosynthesis was first time hypothesized by VAN NEIL in 1930. This hypothesis was confirmed in 1940