The cell is the basic unit of life. Prokaryotes (e.g. bacteria) have no membrane-bound nucleus. Eukaryotes (plants, animals, fungi) have a true nucleus. Key organelles: Cell membrane (controls entry/exit), Nucleus (contains DNA, controls cell activities), Cytoplasm (site of chemical reactions), Mitochondria (ATP production – powerhouse), Ribosomes (protein synthesis), Chloroplasts (photosynthesis – plants only), Vacuole (storage), Cell wall (plants – rigidity).