18.1.5—Characteristic features of kingdoms

The main Eukarya kingdoms are Protoctista, Fungi, Plantae and Animalia. Kingdom classification combines cell structure, body organisation and nutrition; one visible feature is rarely enough.

Protoctista — a broad group of eukaryotic organisms outside the other three kingdoms; members vary widely in cell structure, feeding and body form.
Fungi — eukaryotic heterotrophs with non-cellulose cell walls; they obtain nutrients by extracellular digestion and absorption, including from decaying material or living hosts.
Plantae — multicellular eukaryotes with cellulose cell walls, large vacuoles and usually chloroplasts; they are autotrophs and form complex body systems.
Animalia — multicellular eukaryotes with no cell walls; they are heterotrophs with varied feeding mechanisms and specialised cells that can form tissues and organs.

Classify from combined evidence:

1. Confirm the organism is eukaryotic.
2. Record cell-wall and organelle features, body organisation and the way nutrition is obtained.
3. Compare the whole feature pattern with the four kingdom profiles.
4. State the best-supported kingdom while keeping exceptions and the broad Protoctista boundary in view; do not infer a kingdom from multicellularity or one cell feature alone.

Plants and fungi are not defined by being multicellular, and fungi are not autotrophs. The kingdom profiles are evidence-based teaching groupings; this card does not extend into virus nucleic-acid classification.