Course 2.1Lesson 1 of 3

From two kingdoms to five

Aristotle and Linnaeus used two kingdoms, plants and animals. This did not separate organisms with and without a nucleus, single-celled and many-celled ones, or those that make their food and those that do not. R. H. Whittaker proposed five kingdoms in 1969: Monera, Protista, Fungi, Plantae and Animalia. He used the cell structure, the body organisation, the mode of nutrition, the reproduction and the evolutionary relationships.

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Plants and animals, and the rest

Where would you put a mushroom? It grows in the soil and does not move, so it looks like a plant. But it has no chlorophyll. Where would you put a bacterium, or a single green cell of an alga? Questions like these made biologists change their system again and again.

The two-kingdom system

Aristotle was the earliest to try a scientific basis for classification. He sorted plants into trees, shrubs and herbs, and animals into those with red blood and those without it.

Later, Linnaeus put all organisms into two kingdoms: Plantae and Animalia. This system was easy to use, but it did not separate:

eukaryotes (cells with a true nucleus) from prokaryotes (cells without one);
single-celled organisms from many-celled ones;
photosynthetic organisms (the green algae) from non-photosynthetic ones (the fungi).

Many organisms fitted neither kingdom. Bacteria, blue-green algae, fungi, mosses and ferns were all put with the plants, because they have a cell wall.

What should we look at?

The answer was to look at more than the shape of the body. Biologists took into account:

the structure of the cell, and the nature of the cell wall;
the body organisation: one cell, a loose group of cells, or tissues and organs;
the mode of nutrition: does the organism make its own food, or take it from others?
the way of reproduction;
the evolutionary relationships between organisms.

Whittaker's five kingdoms

In 1969, R. H. Whittaker proposed five kingdoms: Monera, Protista, Fungi, Plantae and Animalia. This is the system that the NCERT book follows.

Five boxes, one for each kingdom. Monera: prokaryotic cell, no nuclear membrane, wall that is not of cellulose, one cell, food made by itself or taken from others; examples bacteria and cyanobacteria. Protista: eukaryotic cell with a nuclear membrane, wall in some, one cell, food made by itself or taken from others; examples Amoeba, Euglena and diatoms. Fungi: eukaryotic cell, wall of chitin, body of threads called hyphae, food absorbed, heterotrophic; examples mushroom, Rhizopus and yeast. Plantae: eukaryotic cell, wall of cellulose, tissues and organs, food made by photosynthesis, autotrophic; examples mango, fern and moss. Animalia: eukaryotic cell, no cell wall, organ systems, food eaten, heterotrophic; examples fish, frog and bird.

Feature	Monera	Protista	Fungi	Plantae	Animalia
Cell type	prokaryotic	eukaryotic	eukaryotic	eukaryotic	eukaryotic
Cell wall	present, not of cellulose	present in some	present, of chitin	present, of cellulose	absent
Nuclear membrane	absent	present	present	present	present
Body organisation	cellular	cellular	many cells, loose tissue	tissues and organs	tissues, organs and organ systems
Mode of nutrition	autotrophic or heterotrophic	autotrophic or heterotrophic	heterotrophic	autotrophic	heterotrophic

Autotrophic means that the organism makes its own food. Heterotrophic means that it takes food made by others.

A key to the five kingdoms

You should find that a mushroom (a nucleus, many cells, no photosynthesis, a wall of chitin) lands in Fungi. Switch photosynthesis on, and the same cells become Plantae.

The key is simplified, and it has exceptions. Yeast is a single-celled fungus, and some protists make their own food. The system is a tool, not a law.

Try it in Python

This program is the key as a function. It takes four features and gives a kingdom.

Practise with new numbers

Common mistakes

Putting fungi with the plants. Fungi have no chlorophyll, and their wall is of chitin, not cellulose.
Thinking every single cell is a bacterium. Protists are single cells with a true nucleus.
Forgetting the date and the name. Whittaker, 1969, five kingdoms.
Treating the key as a law. Yeast and some green protists break it.

Remember these

The two-kingdom system did not separate prokaryotes from eukaryotes, single-celled from many-celled, or photosynthetic from non-photosynthetic organisms.
Whittaker proposed five kingdoms in 1969: Monera, Protista, Fungi, Plantae and Animalia.
He used the cell structure, the body organisation, the mode of nutrition, the reproduction and the evolutionary relationships.
Only the Monera are prokaryotes. The other four kingdoms are eukaryotes.