Plastid =
The term plastid was introduced by E. Haeckel in 1866. With the exception of some protists,(eg, Euglena, dinophyceae, diatoms) plastids are restricted to plants only. Plastids are semi-autonomous organelles having DNA and double membrane envelope which store or synthesise various types of organic compounds. Plastids develop from colourless precursors called proplastids which have the ability to divide and differentiate into various types of plastids.
Type of plastids =
1. Leucoplasts = Leucoplasts
Colourless, occur in non-green
cells. Their main function is storage.
According to the stored products
they are Amyloplasts (store
starch), Elaioplasts or lipidoplasts
or oleoplasts (store lipids or fat) and
Aleuroplasts or proteoplasts or
proteinoplasts (store proteins).
2.Chromoplast =Chromoplasts
Yellow or reddish in colour
due to presence of carotenoid
pigments. They lack chlorophyll.
They are mainly present in cells
of petals and ripe fruit and
impart them various colours.
They also synthesise membrane
lipids.
3.Chloroplast =The term plastid of Chloroplasts Greenish in colour, contain photosynthetic pigments-chlorophylls and carotenoids. Synthesise
food from inorganic materials, using light energy
Funcation =Energy Transduction
Chloroplasts have unique ability to trap solar energy and transform it into chemical energy, which is essential for all living organisms to support their life activities. Photosynthesis Chloroplasts are the centres of photosynthesis or formation of organic compounds from inorganic raw materials Consumption of CO2.
They pick up carbon dioxide and use the same in photosynthesis Thus, keep the percentage of carbon dioxide balanced in the atmosphere as it is being constantly added through respiration and combustion.
Liberation of oxygen Chloroplasts liberate oxygen which is passed into the atmosphere. Thus, keep the balance of oxygen constant in the atmosphere
since it is being used up in respiration and combustion
Microbodies=Microbodies Minute, simple, spherical sacs, bounded by single unit membrane which absorb molecular oxygen and take part in oxidation.
