It is surrounded by a nuclear membrane which is very much like the cell membrane . If you stain the cell, the absorbs the stain very quickly. When you stain the cell, a material in the nucleus, called chromatin , shows up. When cells divide in reproduction, the chromatin forms tiny hairlike threads of many shapes called chromosomes . The chromosomes control heredity.
Some cells show another structure in the nucleus, called the nucleolus.
Mitochondria are rodshaped structures scattered through the cytoplasm. Mitochondria control chemical reactions that release energy produced in cells. They do this by using en zymes.