Question

Mesosomes are found in
A. Yeast
B. Aspergillus
C. Mucor
D. Cyanobacteria

Answer 1

Mesosomes are the invaginated structures formed by the localized infoldings of the plasma membrane. These structures can also be defined as the extension of the plasma membrane into the cell wall.

Complete answer:
Mesosomes are found in several heterotrophic bacteria. These invaginated structures are in the form of vesicles, tubules of lamellar whorls. It is present in cytoplasm which aids in increasing the surface area in photosynthetic prokaryotes, cyanobacteria, wherein it carries the photosynthetic pigments.
Most of the time, mesosomes are found in association with nuclear areas or near the site of cell division but absent in eukaryotes. The lamellar whorl can be observed in Nitrobacter, Nitro monas and Nitrococcus. The invagination of plasma membranes leads to the formation of vesicles. The structure of the vesicle becomes interrupted due to constriction however this constriction does not cause a complete separation of tubules. Closely packed spherical vesicles are seen in Chromatium and Rhodospirillum rubrum.
Functions:

Synthesis of a cell wall.
DNA replication.
Distribution of daughter cells, respiration, secretions
Mesosomes sometimes play a role in reproduction. During the process of binary fission, a cross wall is formed that results in the formation of two cells. Mesosomes initiate the formation of septum and attach bacterial DNA to the cell membrane. It separates bacterial DNA into each daughter cell. Also, the infoldings of mesosomes increases the surface area of plasma membranes which in turn increases absorption of nutrients.

Therefore, the correct option is D, Cyanobacteria.

Note: The cyanobacterial plasma membrane is selectively permeable, lacks cholesterol, and has a high proportion of protein to phospholipid. It fuses with photosynthetic lamellae giving rise to lamellosomes or mesosomes in the cytoplasm. Lamellosomes are similar in functions to mesosomes. Also, the cytoplasm lacks eukaryotic organelles such as chloroplasts, mitochondria, endoplasmic reticulum, but possesses photosynthetic apparatus, ribosomes, and a large number of subcellular inclusions such as glycogen and the genetic material.