Biology (NTSE/Olympiad)  

1. The cell


Plastids :
Introduction :
• Plastids are organelles enclosed by a double membrane found in all plants.
Historical Account :
E.Heckel (1865) gave the term plastid. Plastids are largest cell organelles.
Ultrastructure :
• Plastids occur in most plant cells and are absent in animal cells.
• Plastids are self replicating organelles like mitochondria i.e. they have the power to divide.
Schimper divided plastids into three types :
(a) Chromoplast - Coloured plastids
(except green colour)
(b) Chloroplast - Green coloured plastids
(c) Leucoplast - Colourless plastid.
• Plastids also have double membrane but no cristae.
Functions of Plastids :
• Chloroplasts trap solar energy and utilized it to manufacture food for the plant.
• Chromoplast impart various colour of flower to attract insect for pollination.

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