The Fundamental Unit of Life — Science STD 9 — Question

1. Nucleus.

Explanation:
A eukaryotic cell has a nucleus bounded by a double wall membrane structure known as a nuclear membrane. The nuclear membrane is a discontinuous membrane having nuclear pores, which act as a protein channel for regulating the exchange of materials between cytoplasm and nucleoplasm. The nucleus contains the chromatin threads and the nucleolus. The gel-like texture of the nucleoplasm embedded with chromatin threads gives it a dense appearance.