Cell nuclei are membrane-bound structures found in eukaryotic cells, which include organisms like plants, animals, and fungi. The nucleus contains the cell's genetic material, organized as DNA in the form of chromosomes. This genetic information is crucial for regulating cell functions, growth, and reproduction. The nucleus is surrounded by a double membrane called the nuclear envelope, which protects the DNA and controls the movement of substances in and out of the nucleus. Within the nucleus, there is a region called the nucleolus, where ribosomal RNA is produced, essential for protein synthesis in the cell.