Summary: Three-Domain System of Classification
In this lecture, you will learn how scientists classify all living organisms using a modern system based on evolutionary relationships and cell structure.
We begin by revisiting the Five-Kingdom Classification proposed by Rebert Whittaker in 1969. This system grouped all organisms into five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia. It divided life forms into prokaryotes (Monera) and eukaryotes (all others).
Then, we move to a more advanced system called the Three-Domain System, introduced by Carl Woese in 1990. Based on molecular studies, he discovered that prokaryotes actually consist of two very different groups: Bacteria and Archaea. As a result, he classified life into three domains:
- Domain Archaea – ancient prokaryotes with unique features
- Domain Bacteria – typical modern-day prokaryotes
- Domain Eukarya – organisms with true nuclei, like plants, fungi, and animals
We will then focus on Domain Archaea, exploring:
- Their cell structure (membrane and wall differences)
- Their genetic similarities with eukaryotes
- Their unique metabolism, like methane production
- Their asexual reproduction methods (no mitosis or meiosis)
You will also discover the importance of Archaea in science and industry, such as:
- Enzymes used in biotechnology
- Biogas production in sewage treatment
- Metal extraction from ores
Finally, we will look at the main groups of Archaea:
- Methanogens
- Halobacteria
- Thermococci
- Thaumarchaeota