Plastids are particular feature of plant cell. They contains pigments and impart colours to the plants .
On the basis of pigments, plastids are of following types-
Chloroplast –This plastid contains Chlorophyll. This traps photo-energy for photosynthesis.
Chromoplast – These are colour plastids other than chloroplast. Chromoplast contain fat soluble pigments like carotenoids,xanthophylls etc.
Leucoplast- These are colourless plastid and store nutrients These are of following types.
Amyloplasts-store carbohydrates.
Elaioplasts-store oils and fats.
Aleuroplast-store proteins.
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| Amyloplast of Potato |
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| Chromoplast in fruits and flowers |
Structure of chloroplast
Chloroplast is a double membrane bound cell organelle like mitochondria. Space inside to the inner membrane of chloroplast is filled with fluid i.e. “Stroma” . In stroma many plate like membranous sacs are found and known as “Thylakoids” .These thylakoids are filled with chloroplast. Thylakoids are arranged in in stacks like of the piles of coins i.e. “Grana”(sing-Granum). Stroma lamellae connect thylakoids of different grana.
In stroma circular DNA, 70S ribosomes are present like in mitochondria.So it is a semi-autonomous cell organelle.
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Function of Chloroplast
Chloroplast are found in the mesophyll cells of leaves of plants. In chloroplast ,process of photosynthesis takes place. Light-reaction of photosynthesis occurs in thylakoids because photo-energy(Sunlight) trapping chlorophyll is present inside thylakoids while Dark-reaction of photosynthesis takes place in stroma of chloroplast.
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| Figure showing process of photosynthesis in chloroplast |
