Carolus Linnaeus placed all living organisms into two kingdoms; Plantae and Animalia. The two-kingdom classification was later found to be inadequate because it places organisms with a true nucleus (eukaryotes) with those without a true nucleus (prokaryotes).
Prokaryotes Vs. Eukaryotes
| Prokaryotes: | Eukaryotes: | |
| 1. | No distinct nucleus. | Distinct nucleus present. |
| 2. | No nuclear membrane. | Nuclear membrane present. |
| 3. | Nuclear materials scattered on the cytoplasm. | Nuclear materials not scattered on the cytoplasm. |
| 4. | No membrane-bounded organelles. | Membrane bounded organelles present. |
| 5. | Exist only in simple forms. | Exist in complex forms. |
| 6. | They are primitive. | They are more advanced. |
| 7. | Bacteria and blue-green algae are examples of prokaryotic cells. | Fungi, plant and animal cells are examples of eukaryotic cells. |
Green photosynthetic plants were also placed with non-green plants.
Under the basis of the difference between eukaryotes and prokaryotes cells, as well as the mode of nutrition, scientist R.H Whittaker proposed the five kingdom classification, in 1969.
Biologists now favour classifying organisms using the five-kingdom classification.
The five kingdoms are;
- Monera
- Protista
- Fungi
- Plantae
- Animalia
The prokaryotes were placed under the Kingdom Monera while the eukaryotes were classified under four kingdoms: Protista, Plantae, Fungi & Animalia.
The five kingdom way of classifying living organisms still presents problems as some organisms such as lichen and viruses do not fit into any of these kingdoms. Viruses are not included in the five kingdom classification because they do not have a cell structure and cannot reproduce, so they are currently not considered living things. However, there are still debates going on, as some scientists are of opinion that they are in fact living things.
Advantages of the Five Kingdom Classification:
- When compared to the two kingdom classification, it is better and more natural.
- It separates unicellular and multicellular organisms.
- It separates autotrophs and heterotrophsA heterotroph is an organism that consumes other organisms in a food chain. The term stems from the Greek words hetero for “other” and trophe for “nourishment.” More.
- It places the fungi in a separate group (Kingdom Fungi) as it has a different mode of nutrition.
- Prokaryotes (Kingdom Monera) are placed in a separate group (Kingdom Monera).
Problems of the Five Kingdom Classification:
The five-kingdom classification system has many limitations particularly in classifying the lower organisms.
- Fungus and algae do not fit into the same kingdom.
- Viruses cannot also fit into any kingdom because they have both living and non-living characteristics.
Summary:
The five kingdom classification was devised by Robert Harding Whittaker in 1969.
The five-kingdom classification according to the revolutionary trend is;
1. Kingdom Monera
2. Kingdom Protista
3. Kingdom Fungi
4. Kingdom Plantae
5. Kingdom Animalia
Gaining
i like this topic cause it considers historical events . such as the first attempt in classifying living organisms by a greek philosopher Aristotle.