Cell Organelles
The specialized structures inside a cell: the nucleus stores DNA, mitochondria make ATP, ribosomes build proteins, the endoplasmic reticulum and Golgi apparatus process and ship them, and lysosomes digest waste.
Prokaryotes (bacteria) lack a nucleus and membrane-bound organelles; eukaryotes (plants, animals, fungi) have both. Cells that need lots of energy, like cardiac muscle, are packed with mitochondria — structure tracks function.