Plastid is largest in size among the organelles present in the cytoplasm. They can be seen clearly under the microscope. Plastids are not present in Fungi, Bacteria and Animal Cells.
Plastid is mainly of two types:
- Leucoplastid or Leucoplast and
- Chromoplastid or Chromoplast.
Leucoplastids are colourless and Chromoplastids are coloured.
Chromoplastid again is of two types Chromoplast and Chloroplast.
Leucoplast: They are colourless, as they have no pigment. Leucoplast may be converted into Chromoplast or mainly chloroplast in contact with sunlight. In absence of light, the case may be reversed.
Position: Leucoplasts are present in the cells of organs like root, underground stem etc. which do not come in contact with sunlight.
Shape: Leucoplast may be semicircular or tubular in shape
Function: Their function is to store food.
Chromoplast: They are variously coloured, other than green, mostly yellow and red in colour. They are also variable in shape. Chromoplast occurred in the coloured part of plants. e.g. petals, coloured fruit and seeds, roots of carrot etc.
Function: Flowers are coloured and beautiful due to their presence.