Criteria for classifying organisms

The idea

Organisms are grouped by broad, then finer features: external features, mode of nutrition, internal structures, cell structure, ecological role, reproduction and genetic similarity (DNA); similar features suggest evolution from common ancestors.

Grouping a plant

The same organism can fit into different groups depending on the criterion chosen. A plant can be grouped by its size, or by the way it gets food.

Why does the same organism fit into more than one group?

• Different features can be used as the criterion
• Scientists change the organism
• Organisms have no features

Which criterion?

Tap the bin where each feature belongs.

Broad first, then finer

Scientists begin with broad, easily visible features and then look at finer ones. The book lists seven criteria. Similar features suggest that organisms have evolved from common ancestors.

Organisms are grouped by broad, then finer features: external features, mode of nutrition, internal structures, cell structure, ecological role, reproduction and genetic similarity (DNA). Similar features suggest evolution from common ancestors.

• Criterion | Example from the book
• External features | shape, size, body organisation
• Mode of nutrition | autotrophic or heterotrophic
• Internal structures | skeletal patterns, organs, tissues
• Cell structure | unicellular or multicellular, eukaryote or prokaryote, cell wall
• Ecological role | producer, consumer or decomposer
• Reproduction | asexual and/or sexual
• Genetic similarity | similarities in inherited features, studied using DNA

Notes

Organisms are grouped by broad, then finer features. Similar features suggest evolution from common ancestors.

Check yourself

In what order do scientists usually look at features?

Producer, consumer or decomposer is which criterion?

Similarities in inherited features, studied in detail, use ...

What do similar features in organisms suggest?

• DNA first, then visible features. DNA is a detailed feature. Scientists often start with broad visible features.
• Finer features first, then visible ones. The book says scientists look at broad and easily visible features and then at more detailed ones.
• Broad, easily visible features first, then more detailed ones — correct. Yes!
• Ecological role — correct. Yes!
• Mode of nutrition. Mode of nutrition means autotrophic or heterotrophic.
• Reproduction. Reproduction means asexual and/or sexual methods.
• Shape and size. Shape and size are external features that can be seen directly.
• DNA — correct. Yes!
• Skeletal patterns. Skeletal patterns are internal structures.
• They always live in the same habitat. The book says similar features suggest common ancestors. It does not link them to one habitat.
• They belong to the same species. Organisms can share features and still be different species. The book says similar features suggest common ancestors.
• They have evolved from common ancestors — correct. Yes!