Identify the structure at the arrow?

Identify the structure at the arrow?

• A. Euchromatin
• B. Heterochromatin
• C. Nucleolus
• D. Nucleus

Answer: (C)

The structure at the arrow is the nucleolus. It’s the region inside the nucleus where ribosomal RNA genes are transcribed and ribosomal subunits begin to form. The nucleolus appears as a distinct, dense body within the nucleus and is not enclosed by its own membrane. Euchromatin and heterochromatin are forms of chromatin inside the nucleus, not separate bodies. Euchromatin is lightly packed and associated with active transcription, while heterochromatin is tightly packed and usually transcriptionally silent. The nucleus is the entire membrane‑bound organelle housing all nuclear components, including the nucleolus. So the arrow points to this specialized substructure responsible for ribosome production.

The structure at the arrow is the nucleolus. It’s the region inside the nucleus where ribosomal RNA genes are transcribed and ribosomal subunits begin to form. The nucleolus appears as a distinct, dense body within the nucleus and is not enclosed by its own membrane.

Euchromatin and heterochromatin are forms of chromatin inside the nucleus, not separate bodies. Euchromatin is lightly packed and associated with active transcription, while heterochromatin is tightly packed and usually transcriptionally silent. The nucleus is the entire membrane‑bound organelle housing all nuclear components, including the nucleolus. So the arrow points to this specialized substructure responsible for ribosome production.