Biology · Unity and diversity

A3.2 — Classification and cladistics

Biology · SL / HL · syllabus-mapped notes

1. A3.2.1

   Need for classification of organisms

   Explain why organisms need to be classified.

2. A3.2.2

   Difficulties classifying organisms into the traditional hierarchy of taxa

   Explain why the traditional hierarchy of taxa does not always match evolutionary divergence.

3. A3.2.3

   Advantages of classification corresponding to evolutionary relationships

   Explain the advantage of a classification that follows evolutionary relationships.

4. A3.2.4

   Clades as groups of organisms with common ancestry and shared characteristics

   Define a clade, and state what evidence places organisms in the same one.

5. A3.2.5

   Gradual accumulation of sequence differences as the basis for estimates of when clades diverged from a common ancestor

   Explain the molecular clock, and why it gives only estimates of divergence times.

6. A3.2.6

   Base sequences of genes or amino acid sequences of proteins as the basis for constructing cladograms

   Construct a cladogram from base or amino acid sequence data.

7. A3.2.7

   Analysing cladograms

   Deduce evolutionary relationships, common ancestors and clades from a cladogram.

8. A3.2.8

   Using cladistics to investigate whether the classification of groups corresponds to evolutionary relationships

   Explain how cladistics is used to test whether an existing classification matches evolution.

9. A3.2.9

   Classification of all organisms into three domains using evidence from rRNA base sequences

   State the classification of all organisms into three domains, based on rRNA sequences.