Why are plastids needed in a cell?

Answer 1

Plastids are major organelles found only in plants and algae. Plastids are responsible for photosynthesis, storage of products like starch and for the synthesis of many classes of molecules such as fatty acids and terpenes which are needed as cellular building blocks and/or for the function of the plant.

Answer 2

ChloroPLASTS reduce carbon, chromoPLASTS add color (red tomatoes) and the other 5 or so plastidids have designated functions. Dr. Robert Wise has a book on it.