Question

Which organism does not have a true nucleus?
A. Bacterium
B. Archaebacterium
C. Cyanobacterium
D. All of the above

Answer 1

Hint: Prokaryotes are organisms that lack the true nucleus because they do not contain an envelope surrounding the nuclear membrane.

Complete answer:
The nuclear material of prokaryotes is not bound by a nuclear membrane. No distinctive nucleus is present in them. The nuclear region of the prokaryotes is known as a nucleoid which is concentrated in a small region containing their genomic DNA.
Prokaryotes do not have a well-defined nucleus as well as membrane-bound cell organelles like mitochondria. The size of a prokaryotic cell ranges between micron to micron. Among all other prokaryotes, bacterial cells are very common and they even multiply faster. Bacterial cells are found everywhere and are ten times smaller than most plants and animals.
Their nucleus contains more than two loops of DNA within the cytoplasm which is not bound in any envelope.
Examples of prokaryotic cells are Bacterial cells, Archeal cells, Blue-green algae, Mycoplasma, etc..
Therefore all the options mentioned above fall under the category of prokaryotic cells and thereby, satisfy the condition of not having a nucleus.
So, the correct answer is “Option D”.

Additional Information:
Examples of prokaryotes are Escherichia coli, Cyanobacteria, subclasses of Archaebacteria like Sulfolobus acidocaldarius archaebacterium.
The absence of the nucleus has its advantages. The prokaryotes can accept plasmid from their surroundings and synthesize proteins for any genetic code that they want.
But the disadvantage is that it makes the prokaryotic cell prone to viral infections because transcription and translation processes are naked and easily accessible.

Note:
All the early life forms have evolved gradually. Similarly, there was the evolution of cells from prokaryotic to eukaryotic. Therefore, all of the above are examples of prokaryotic cells that do not have a true nucleus.