Photosynthesis in Higher Plants

Chloroplast, pigments involved in photosynthesis

  • Chloroplast (semi-autonomous organelle) occurs in all the green parts of the plant with a double membrane, enclosing a proteinaceous matrix, called stroma.
  • Stroma is the location of the dark reaction of photosynthesis, which possesses flattered sac-like structures, namely thylakoids, which are stacked in some places to form grana, which is the site of light reaction of photosynthesis.
  • The functional unit of the chloroplast is quantasome (or) photosynthetic unit; that consists of photosystem (ps) inside which photosynthetic pigments are present.
  • The photosystem is of 2 types (i) Photosystem 1 (ps1) and (ii) Photosystem 2 (ps2).
  • The uppermost portion of thylakoid region is termed as non-appressed thylakoid and rest bottom layers in grana are termed as appressed thylakoid. Every granum is connected with each other by a stromal/lamellar thylakoid.
  • Non-appressed and stromal thylakoid possess Ps1 and appressed thylakoid possesses Ps2 system.
  • Photosynthetic pigments which absorb light of specific wavelengths in the visible region possess conjugated double bonds.
  • The main pigment is chlorophyll that is four types Chl.a, Chl.b, Chl.c and Chl.d, which are soluble in organic solvents like ether (or) ketone.
  • Tadpole-like structure in chlorophyll consists of 2 main groups such as porphyrin (Head) and phytol (Tail)
  • Mg – Porphyrin complex is present in chlorophyll, where all the pyrrole rings are connected by methine bridges.
  • Chlorophyll ‘a’ is universal.
  • Chl.b differs from Chl-a in having – CHO group instead of a methyl(=CH3) group at the 3rd carbon atom.
  • Carotenoids are phycobilins are 2 important accessory pigments.
  • Carotenoids are of 2 types – (i) Carotenes (ii) Xanthophylls, responsible for yellow, brown to reddish colour.
  • Phycoerythrin and phycocyanin are the types of phycobilins which are present in Red algae and Blue-green algae respectively. Phycocyanin does not possess Mg2+.

View this video for the topic from 33:49 to 55:09

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