Question

Prokaryotes, have a cell wall surrounding the cell membrane except in
A) Bacteria
B) Mycoplasma
C) Blue green algae
D) All of the above

Answer 1

Hint: Most prokaryotes have a rigid cell wall surrounding the plasma membrane. The significant component of this cell wall is peptidoglycan or murein. Plasma membrane or cell membrane is the outermost layer of a cell and provides structural support to the cell.

Complete answer:
Option A: Cell wall is present in the wide domain of bacteria. In both the gram-positive and gram-negative bacteria do have well walls outside their cell membrane, although their composition and construction are quite different in both cases and this difference probably determines their virulence as well. Therefore, this option is incorrect.
Option B: Mycoplasma is the genus of bacteria that lack a rigid cell wall outside the cell membrane. In spite of being prokaryotes, they do not have a cell wall. They are bound only by a “unit” membrane. Therefore, this is the correct option.
Option C: Blue-green algae (Cyanobacteria) also have rigid cell walls. But the composition is a little bit different from that of bacteria. Therefore, this option is incorrect.
Option D: Bacteria and blue-green algae have cell walls surrounding their plasma membrane, but the mycoplasma doesn’t have. Hence, this option is inevitably incorrect.

Thus, the correct answer is option (B) Mycoplasma.

Note:
i) Eukaryotic plant cells also have a cell wall surrounding the cell membrane but this is composed of cellulose.
ii) Animal cells lack cell walls.
iii) The function of cell walls in prokaryotic cells includes providing support, protection as well as structure.