Mitosis
Why do cells need to divide? Cells divide for three major reasons: Growth : From a single cell to a whole organism—cell division makes it possible. Repair & Replacement : Lost skin cells? A broken bone? Mitosis steps in to rebuild and replace. Reproduction : Life passes itself on through cell division—either asexually (like bacteria using binary fission) or sexually (via meiosis). Inside the nucleus of a eukaryotic cell, DNA usually exists as a loose tangle called chromatin . But before a cell divides, it bundles that DNA into chromosomes , thanks to proteins called histones . Each chromosome duplicates itself, creating sister chromatids —identical copies joined at a region called the centromere . Humans have: 46 chromosomes in body cells (diploid = 2n) 23 chromosomes in sex cells (haploid = n) Want to see chromosomes? Scientists use karyotypes , which visually arrange chromosomes by size and type. This helps identify the sex chromosomes (XX for females, XY f...