Question

Which of the following organisms completely lack a cell wall, they are the smallest living cells known and can survive without oxygen?
A. Mycoplasma
B. Euglenoids
C. Slime molds
D. All of the above

Answer 1

Hint:These organisms are naturally resistant to antibiotics that target cell wall synthesis since they do not have a cell wall. These belong to the order Mycoplasmataceae. They are the minutest and the simplest free-living prokaryotes and are also referred to as ‘mollicutes’.

Complete answer: 1. This is a genus of bacteria, which is pathogenic in nature, lacking a cell wall around their cell membranes. This characteristic feature makes them resistant to antibiotics that target the cell wall.
2. Mycoplasma is an organism with these characteristics. The mode of nutrition among the organisms of this genus can be parasitic or saprotrophic.
3. Mycoplasma species are intracellular pathogens which means they grow inside their host. The controlled osmotic environment of the host cells makes cell walls unnecessary for mycoplasma. This mechanism enables the mycoplasma to exist without cell walls.
4. Due to the absence of cell walls, mycoplasma rapidly dies if it is placed in an environment with very high or very low salt concentrations.
5. Mycoplasma, being facultative anaerobes, can thrive where there is little law and no oxygen.
6. The energy production (in the form of Adenosine triphosphate) in mycoplasma is done by the process of fermentation which does not require oxygen.
7. The diameter of the smallest coccus capable of reproduction is about 300 nm.
The correct answer to this question is option A i.e. Mycoplasma

Additional information:
The mycoplasma cell contains organelles required for growth and replication. These are plasma membrane, ribosomes, and double stranded circular DNA molecules.

Note:Mycoplasma is also termed as Pleuropneumonia like organisms (PPLO).