Taxonomy, binomials and evolutionary trees

Lesson page: echoesof.science/school/classification/ages-15-16/ · Pupil worksheet: echoesof.science/school/classification/ages-15-16/print/

Learning aims

Describe the three domains and the taxonomic hierarchy.
Apply the rules of binomial nomenclature.
Explain that classification reflects evolutionary relationships and changes with evidence (e.g. fungi).
Design, test and evaluate a dichotomous key, including a log₂ efficiency argument.

Lesson plan

Time	Activity
5 min	Starter: list the dog from domain to subspecies; what does each step add?
10 min	Read the text; discuss the fungi case.
20 min	Build the key, calculate the mean steps, test on another group.
5 min	Redesign one branch.
5 min	Binomial game or quiz.

Materials for the experiment

Cards with pictures of 16 different organisms (mix of invertebrates, vertebrates, plants and fungi)
Large sheet of paper
A stopwatch
A partner group

Safety: Picture cards only; no specimens are needed.

Common misconceptions

Pupils may think…	Actually…
Organisms that look alike must be closely related.	Closely related organisms do not always look alike; classification follows common ancestry.
Classification is fixed once and for all.	Trees are hypotheses and change with new data, as the fungi example shows.
Organisms next to each other in a key are closely related.	A key is an identification tool based on convenient features, not on ancestry.

Worksheet answers

Domain Eukarya, kingdom Animalia, phylum Chordata, class Mammalia, order Carnivora, family Canidae, genus Canis, species Canis lupus, subspecies Canis lupus familiaris.
Fungi lack chloroplasts and cannot photosynthesise; they secrete enzymes and absorb nutrients; Whittaker (1969) gave them their own kingdom, and molecular evidence shows they are more closely related to animals than to plants.
Minimum 4 steps (2⁴ = 16). Real keys are longer because observable features rarely split a group exactly in half, so some branches are longer.
It is the best explanation of relationships based on the evidence so far; new data such as DNA sequences can change it.

Quiz answers

What are the three domains of life? Bacteria, Archaea and Eukarya. Kingdoms sit inside the domains.[1]
Which order of ranks is correct, from largest to smallest? Phylum, class, order, family. Kingdom, phylum, class, order, family, genus, species.[1]
In Canis lupus familiaris, what does 'familiaris' name? The subspecies. The domestic dog is a subspecies of Canis lupus.[1]
Why do scientists not classify only by appearance? Closely related organisms do not always look alike. Classification should reflect common ancestry.[1]
What kind of evidence showed that fungi are closer to animals than to plants? Molecular (genetic) evidence. Genetic analysis revealed the relationship.[5]
What is the minimum number of steps a dichotomous key needs to separate 32 organisms? 5. 2⁵ = 32, and each step has two choices.[7]

Going further

Compare a key based on appearance with a published phylogenetic tree for the same 16 organisms. Which organisms are grouped differently, and why?

Sources used in this lesson

[1] Biology 2e, 20.1 Organizing life on Earth (OpenStax (Rice University)): reliability High
[2] Concepts of Biology, 12.1 Organizing life on Earth (OpenStax (Rice University)): reliability High
[3] What's in a name? Naming (Harvard Museum of Natural History): reliability High
[4] The wonderful world of fungi (Royal Botanic Gardens, Kew): reliability High
[5] Three reasons fungi are not plants (American Society for Microbiology): reliability High
[7] Classification: making a dichotomous key (lesson plan) (US National Park Service): reliability High

Full list with links and a note on each source's reliability: echoesof.science/school/classification/sources/

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