Mesosomes are extensions of plasma membrane into the cell in the form of vesicles, tubules and lamellae.
These are of two types : Septal mesosome and Lateral mesosome.
(a)Septal mesosome may be involved in cell wall formation, chromosome replication and distribution of chromosomes to daughter cells, secretory processes and increase in plasma membrane surface area and enzymatic content.
(b)Lateral mesosome contains respiratory enzymes often called chondroid.