It is thought that organelles of eukaryotic organisms, such as mitochondria and chloroplasts (in plant cells) came from

It is thought that in evolutionary history of eukaryotic plant cell, the mitochondria and chloroplasts are originate from bacteria. That were once living with bacteria cells in symbiotic association and after million years they become the part of cells.

It is said that chloroplast originates from photosynthetic bacteria.

d.) circle motion requires a force to give it a centripetal acceleration.