Lesson 1 of 12 · 6 min

From Aristotle to two kingdoms

NCERT §2 (introduction)

The club's first attempt at sorting uses the oldest rule there is: anything green goes under 'plants', anything that moves goes under 'animals'. Within a day the list has fungi in the plant column and a green swimming cell nobody can place.

The story this chapter follows: Meera's monsoon notebook

During the monsoon, Meera's school science club keeps a notebook of everything alive around them: green scum on the school pond, mould spreading over a forgotten slice of bread, curd setting in the canteen, the biogas plant at a dairy farm, a tobacco field with mottled leaves, and grey-green crusts on the compound wall. By the end of the term every entry has to go into one of five kingdoms, or be marked as something that fits none of them.

The lesson in notes

In short

People have always sorted living things, at first without scientific criteria, simply by how they could be used for food, clothing and shelter.

Aristotle made the earliest attempt at a more scientific basis. He split plants by simple form into trees, shrubs and herbs, and split animals into those with red blood and those without.

In the time of Linnaeus a Two Kingdom system, Plantae and Animalia, took in every plant and every animal.

The two kingdom system drew no line between prokaryotes and eukaryotes, between unicellular and multicellular organisms, or between photosynthetic green algae and non-photosynthetic fungi.

Sorting into plants and animals was easy to do and understand, but many organisms fitted neither group, so the scheme was eventually judged inadequate.

Beyond outward form, biologists wanted classification to use cell structure, the nature of the cell wall, mode of nutrition, habitat, methods of reproduction and evolutionary relationships.

Plantae and Animalia have remained in every later system, but which organisms belong inside them, and how many other kingdoms exist, has been understood differently by different scientists.