True nucleus is absent in :a)Volvoxb)Anabaenac)Mucod)VaucheriaCorrect answer is option 'B'. Can you explain this answer?

Question

Answer

Because it belongs to kingdom monera which is prokaryotic and prokaryotic don't contain nuclear membrane...

Answer

Vaucheria is a yellow-green alga belonging to family Vaucheriaceae under the kingdom Plantae.

Volvox is a green alga belonging to family Volvocaceae under the kingdom Plantae.

Anabaena is a blue-green alga belonging to phylum Cyanobacteria under the kingdom Monera

Mucor is a fungus belonging to phylum Zygomycota under the kingdom Fungi.

Vaucheria, Volvox, and Mucor have domain Eukaryota while Anabaena has domain Prokaryota. Eukaryotes have membrane-bound well-defined nucleus whereas, Prokaryotes do not have a membrane-bound nucleus because, in them, the genetic material lies freely in the cytoplasm. Hence, the true nucleus is absent in Anabaena.

Answer

True nucleus is absent in Anabaena

Anabaena is a genus of filamentous cyanobacteria that belongs to the phylum Cyanobacteria. It is a photosynthetic bacterium found in freshwater environments. Anabaena exhibits a unique feature in terms of its cellular organization, particularly the absence of a true nucleus.

Structure of Anabaena
Anabaena has a filamentous structure composed of numerous cells joined end to end. The filament is surrounded by a gelatinous sheath that provides protection and helps in adhesion. Each cell within the filament is called a heterocyst or vegetative cell and performs specific functions.

Absence of a true nucleus
Unlike eukaryotic cells, including plant and animal cells, Anabaena does not possess a true nucleus. Instead, it has a region called the nucleoid that contains the genetic material, which is a single circular DNA molecule. The nucleoid is not enclosed within a nuclear membrane or surrounded by a nuclear envelope, as observed in eukaryotes.

Nucleoid region
The nucleoid region in Anabaena is irregularly shaped and located towards the center of the cell. It is not separated from the cytoplasm by a nuclear membrane. The genetic material within the nucleoid region is not associated with histone proteins, which are commonly found in eukaryotic DNA.

Importance of absence of true nucleus
The absence of a true nucleus in Anabaena allows for efficient and rapid gene expression. It eliminates the need for transcription and translation processes to occur in separate compartments. This feature is advantageous for Anabaena as it enables quick adaptation to changing environmental conditions.

Summary
In summary, Anabaena, a filamentous cyanobacterium, lacks a true nucleus. Instead, it possesses a nucleoid region where the genetic material is located. This unique cellular organization allows for efficient gene expression and adaptation to varying environmental conditions.

Answer

Anabena

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