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SPI Biology · Biodiversity and Classification

Five Kingdoms and the Ranks of Classification

Whittaker sorted all living things into five kingdoms, and inside each kingdom organisms are placed in ranks from the broad kingdom down to the single species.

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Why this matters

Four questions in the bank, three EASY and one MODERATE: who gave the five kingdom system (from the 2022 paper), the order of the ranks, the protist that links plants and animals, and the protists whose silica walls cover the seabed. Learn the five kingdoms, the ranks in order and two famous protists.

Concept 1 of 2: Whittaker's five kingdoms and the ranks

Classification is sorting: first into a few large boxes (kingdoms), then smaller and smaller boxes inside them, until each box holds one kind of organism, a species. The five kingdoms are told apart by two questions: is the cell with or without a nucleus, and is the body one cell or many?

Definition

  • R H Whittaker (1969) gave the five kingdom system: Monera, Protista, Fungi, Plantae, Animalia.
  • Carolus Linnaeus gave binomial nomenclature: every organism has a two part name, genus then species (Homo sapiens).
  • Ranks, from the top down: kingdom, phylum (division for plants), class, order, family, genus, species.
  • From the bottom up it is the reverse: species, genus, family, order, class, phylum or division, kingdom.
  • Species is the basic unit: organisms that can breed with each other.
KingdomCellBodyExample
MoneraNo true nucleusOne cellBacteria, blue green algae
ProtistaTrue nucleusOne cellAmoeba, Euglena, diatoms
FungiTrue nucleus, cell wall of chitinMostly many cells, cannot make foodYeast, mushroom, Rhizopus
PlantaeTrue nucleus, cell wall of celluloseMany cells, make their own foodMoss, fern, mango
AnimaliaTrue nucleus, no cell wallMany cells, eat foodEarthworm, fish, human
Whittaker's system covers all living things, not just animals.
Ranks top down: kingdom, phylum or division, class, order, family, genus, species.
Practice this conceptself-check · 5 quick reps

The same idea in a real exam question:

SPI · 2022 · SPI Entrance Examination 2022 · Q103Easy

Example 1 · Biodiversity and Classification · Five Kingdoms and the Ranks of Classification

____ is the pioneer of the modern day, five kingdom classification system of multicellular animals.

Putting class below order

Going up, order comes before class: species, genus, family, order, class, phylum, kingdom. A list that puts class before order on the way up is wrong.

Robert Hooke for classification

Robert Hooke first saw cells. The five kingdom system is Whittaker's, and the two part naming of species is Linnaeus's.
Drill 1 more on whittaker's five kingdoms and the ranks

Concept 2 of 2: Protists: Euglena, diatoms and their relatives

Protists are single cells with a true nucleus. Some behave like tiny plants, some like tiny animals, and one, Euglena, behaves like both.

Definition

  • Euglena: has chloroplasts and makes food by photosynthesis like a plant, but has no cell wall, swims with a flagellum and can take in food like an animal. So it is the connecting link between plants and animals.
  • Diatoms: have cell walls of silica. When they die the walls pile up on the seabed as diatomaceous earth.
  • Amoeba: moves and feeds with false feet (pseudopodia).
  • Paramecium: moves with cilia; has no chloroplasts.
  • Plasmodium: causes malaria.
ProtistMoves byKnown for
EuglenaFlagellumLink between plants and animals
Euglena has chloroplasts; Paramecium has none.
DiatomsDrift in waterSilica walls, deposits on the seabed
AmoebaFalse feet (pseudopodia)Changes its shape
ParameciumCiliaSlipper shape
PlasmodiumCarried by mosquitoesCauses malaria
Practice this conceptself-check · 3 quick reps

The same idea in a practice question:

Practice questionEasy

Example 2 · Biodiversity and Classification · Five Kingdoms and the Ranks of Classification

____ is a connecting link between plant and animal as it has both plant and animal characters. They have chloroplasts to perform photosynthesis, like plants.

Calling a moss a protist

Marchantia and Funaria (moss) are true plants, bryophytes, made of many cells. Euglena, the plant-animal link, is a single-celled protist.

Protozoa or bacteria for seabed silica

The silica on the seabed comes from the walls of diatoms, which are protists with glass-like silica walls.
Drill 1 more on protists: euglena, diatoms and their relatives

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Reference tables (2)

Whittaker's five kingdoms and the ranks5 rows
KingdomCellBodyExample
MoneraNo true nucleusOne cellBacteria, blue green algae
ProtistaTrue nucleusOne cellAmoeba, Euglena, diatoms
FungiTrue nucleus, cell wall of chitinMostly many cells, cannot make foodYeast, mushroom, Rhizopus
PlantaeTrue nucleus, cell wall of celluloseMany cells, make their own foodMoss, fern, mango
AnimaliaTrue nucleus, no cell wallMany cells, eat foodEarthworm, fish, human
Whittaker's system covers all living things, not just animals.
Ranks top down: kingdom, phylum or division, class, order, family, genus, species.
Protists: Euglena, diatoms and their relatives5 rows
ProtistMoves byKnown for
EuglenaFlagellumLink between plants and animals
Euglena has chloroplasts; Paramecium has none.
DiatomsDrift in waterSilica walls, deposits on the seabed
AmoebaFalse feet (pseudopodia)Changes its shape
ParameciumCiliaSlipper shape
PlasmodiumCarried by mosquitoesCauses malaria

Watch out for (4)

Test yourself on a real paper

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