Question

The smallest living cells with the cell wall are

A. Mycoplasma

B. Viroids

C. Blue-green algae

D. Bacteria

Answer 1

Hint: The size of the organisms varies greatly. The size of the mycoplasma is the smallest unicellular organism. Bacteria including such as blue-green algae are the largest among all prokaryotes. Mycoplasma lacks a cell wall. Bacteria have definite cell membranes. 

Complete answer:

Option A- The members of Kingdom monera include the smallest living cells. Mycoplasma is the smallest living cell on earth but it does not have a cell wall. These are the unicellular organisms that can survive without oxygen. 

Option B- The size of the viroids is extremely small, ranging from 246 to 467 nucleotide-long genomes. They are mostly found in plants. They do not have an outer envelope. 

Option C- Blue-green algae also called as cyanobacteria have the size ranges from 0.5 to 0.6mm. It represents the largest prokaryotic organisms. 

Option D- Bacteria are microscopic, single-celled organisms. They are classified as prokaryotes. They lack a nucleus. They are surrounded by two protective covering: an outer cell wall and an inner cell membrane. The size of the bacteria is one-tenth the size of the eukaryotic cells. The size of the bacteria is typically 0.5-5.0 micrometers in length. Bacteria are the microorganisms which are known as the smallest living cell with a cell wall. From the above information we have found that bacteria are the smallest living cells with a cell wall.

Hence, the correct answer is option (D).

Note: The person with the unaided eye can see few species of bacteria, for example: Thiomargarita namibiensis is 0.5mm long while Epulopiscium fishelsoni is 0.7mm long. The smallest pathogenic agents are called viroids. Viroids reproduce within the host cell. Bacteria are found in three basic bacterial shapes: round (cocci), cylindrical, capsule shaped (bacillus), and spiral bacteria (spirilla). Bacteria can be good or bad for humans depending on their functions.