Question

Hypothesize abiut the location of photosynthesis based on leaf pigments

Answer 1

Photosynthesis takes place in the green leaves of the plants and parts of the plant.The most active photosynthetic tissue in higher plants is the mesophyll leaves .Mesophyll cells have many chloroplasts,which contain the specialised light absorbing green pigments called the chlorophyll.In photosynthetic eukaryotes ,photosynthesis occurs in the subcellular organelle known as the chloroplast .This double membrane enclosed organelle posses a third system of membranes called thylakoids..A stack of thylakoids forms a granum .Adjacent grana are connected by unstacked membranes called stroma lamellae.The fluid compartment surrounding the thylakoids ,called the stroma.Chlorophyll and cartenoids are embedded in the thylakoids which helps in photosynthesis i,e. trapping the light energy and synthesis of ATP and NADPH   and since they are light driven ,so they are called light reaction.In stroma,enzymatic reaction incorporate CO2 into the plant leading to the synthesis of sugar ,which turns into starch .Here it is light driven but are dependent on the products of light reaction ,so it is called called dark reaction.

A chromatographic separation of the leaf pigments show that the colour of leaves is due to four pigments.

a)Chlorophyll a-Bright or blue green in the chromatogram

b)Chlorophyll b:- yellow or green

c) Xanthophylls-yellow

d) Carotene- Yellow to orange yellow

Of these ,Chlorophyll a is the primary photosynthetic pigment

Chlorophyll has a tadpole structure .It consist of a porphyrin head and phytol tail.

Other than primary chlorophyll a , all other are assesory pigments .Carotenoids protect plant from excessive heat and prevent photo-oxidation of chlorophyll pigments.And antenna molecules absorb light of different wavelengths and transfer the energy to chlorophyll molecule.

Photosynthetic pigments are group of pigments which take part in the conversion of light energy into chemicl energy .The photosynthetic units are called photosystem I (PS I) and photosystem II(PS II) .Each unit has a reaction center of a specific chlorophyll a molecule which absorbs light energy of longer wavelength .These center can release electron upon absorption of energy .In PS-I ,the reaction center of chlorophyll a has absorption peak at 700 nm ,hence it's called P700 while in PS II,the reaction center has an absorption maximum at 680 nm and is called P680.Reaction center is sorrounded by light harvesting molecules .These absorb  photons of different wavelength and transfer this energy to reaction center .Harvesting molecules occur in form of specific complexes called light harvesting complexes (LHC) called LHC-I and LHC-II .The pigment molecules of these complexes are bound to proteins .These helps to make photsynthesis more efficient .