What cellular structure is essential for cell functions and contains both nuclear sap and chromatin?

The nucleus is the cellular structure that is essential for various critical cell functions, including the regulation of gene expression and the maintenance of the cell's genetic material. It serves as the control center of the cell, housing the chromatin, which is composed of DNA and proteins and plays a vital role in the packaging of genetic material as well as in the process of transcription.

Additionally, the nucleus contains nuclear sap, also known as nucleoplasm, which is a gel-like substance that fills the interior of the nucleus. This environment is crucial for the suspending components of the nucleus, allowing for processes such as the replication of DNA and the assembly of ribosomal subunits.

The combination of these components within the nucleus supports its key functions in cell growth, metabolism, and reproduction, reinforcing the importance of this organelle in cellular biology.