Question

The smallest prokaryotic cell is
A. Mycoplasma
B. Cyanobacteria
C. Bacteria
D. Bacillus

Answer 1

Hint: At 0.1 to 5.0 μm in diameter, prokaryotic cells are appreciably smaller than eukaryotic cells. It has diameters ranging from 10 to 100 μm. The small size of prokaryotes permit ions and organic molecules which enter them to rapidly disperse to other parts of the cell.

Complete answer:
Let's discuss the option and find the correct answer.
A. Mycoplasma : The signet-ring-shaped cell of Mycoplasma is gram-negative. The size of the cell is 0.2–0.3 μm. It is normally smaller than 1.0 μm. Mycoplasma is the smallest prokaryotic organism. It lacks a cell wall but has a stiff plasma membrane rich in sterols and lipoglycans. Hence option A is correct.
B. Cyanobacteria: Cyanobacteria are Photosynthetic Aquatic bacteria. Cyanobacterial cells home in size from 0.5-1 μm to 40 μm in diameter. The cell wall structure is alike to that of a gram-negative bacterium. Hence option B is incorrect.
C. Bacteria: Bacteria are mobile prokaryotic cells with characteristic peptidoglycan cell walls. Bacteria show a wide diversity of shapes and sizes called morphologies. Bacterial cells are around one-tenth the size of eukaryotic cells. They are typically 0.5–5.0 micrometres in length. Hence option C is incorrect.
D. Bacillus:Bacillus is a rod-shaped bacteria with average size 0.5-1.0 µm width and 1.0-4.0 µm long. Hence option D is incorrect.
Hence option A: mycoplasma is the correct answer.

Note: The longest cell in the human body is the neuron. Neurons are cells of the nervous system that process and impart information throughout the body. Blue-green algae, E. coli, and mycoplasma, this are the three examples of prokaryotic cells.