Which structures perform the function of mitochondria in bacteria?

Select the correct statement regarding prokaryotic cells.

Which of the following statements about a bacterial cell is/are correct?
$(i)$ Mesosome is formed by the extensions of plasma membrane into the cell.
$(ii)$ The pili are elongated tubular structures made up of a protein.
$(iii)$ Flagellum is composed of filament,hook,and basal body.
$(iv)$ Ribosomes are about $30 \; nm$ by $50 \; nm$ in size.

Which of the following is a characteristic of a prokaryotic cell?

Which cell organelle is absent in anaerobic bacteria?

What are the infoldings of the cell membrane in bacteria called?