This episode recounts thirteen important discoveries in biology, including Anton Van Leeuwenhoek's discovery of microorganisms, Robert Brown's identification of cell nuclei, and the discovery of Mitochondria. Here are the thirteen important discoveries: 1. Microorganisms (1674) 2. The Cell Nucleus (1831) 3. Archaea (1977) 4. Cell Division (1879) 5. Sex Cells (1884) 6. Cell Differentiation (late 19th century) 7. Mitochondria (late 19th century to the present) 8. The Krebs Cycle (1937) 9. Neurotransmission (late 19th to early 20th century) 10. Hormones (1903) 11. Photosynthesis (1770s) 12. Ecosystem (1935) 13. Tropical Biodiversity (15th century to the present).