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Chloroplasts are the green plastids which act as photosynthetic apparatus. In higher plants, they are mostly oval, spherical or discoid.

The major parts of chloroplast are:

1. Envelop:

  • Each chloroplast is bounded by two smooth selectively permeable cytoplasmic membranes with an inter-membrane space which is filled with fluid.
  • These  membranes are composed of lipo-protein sub-units.

2. Stroma:

  • It is the colourless hydrophilic ground substance (matrix) which fills the internal space of chloroplast.
  • It contains various enzymes required for the synthesis of glucose during dark phase of photosynthesis.
  • Matrix contains 70S ribosomes, 2-6 copies circular DNA, water and enzymes.
  • The most abundant enzyme is Rubisco (Ribulose Diphosphate Carboxylase)

3. Grana:

  • It is embedded in the ground substance-Stroma
  • It consists of many granums connected with each other by intergranal lamellae
  • Each granum is made up of stack of thylakoids.
  • Thylakoids are membrane-bound flattened, disc-shaped vesicles.
  • Each thylakoid consists of alternate layers of lipids and proteins embedded with quantasomes.
  • The chlorophyll pigments are organized into numerous photosynthetic units called quantasomes.
  • Each quantasome contains about 230 to 300 units of chlorophyll molecules.
  • They are capable of trapping light energy and converting it into ATP during the light reaction of photosynthesis.


  1. Chloroplasts are the site of photosynthetic reactions
  2. Evolution of oxygen
  3. Synthesis of ATP during phosphorylation
  4. Synthesis of glucose
  5. Photosensitivity in algae
  6. Formation of chromoplast
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