Cell nucleus (labels) - illustration

Diagram of an cell nucleus:
1. Nuclear envelope
1.a. Outer membrane
1.b. Inner membrane
2. Nucleolus
3. Nuceleoplasm
4. Chromatin
4.a. Heterochromatin
4.b. Euchromatin
5. Ribosomes
6. Nuclear pore

Illustration courtesy of Mariana Ruiz, via Wikimedia Commons.