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IB Biology HL A3.2 Classification and Cladistics Hl Only Questions

Practise using taxonomy, cladograms, molecular evidence and molecular clocks to infer evolutionary relationships and classification.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Arrange taxonomic ranks, define clades as common ancestors plus descendants, and identify closest relatives or sister groups from shared derived features.
  • Construct cladograms from sequence, trait or distance data and apply parsimony to choose the tree requiring the fewest changes.
  • Interpret roots, nodes and branch order to infer common ancestors, divergence sequence and what a cladogram can establish.
  • Use molecular evidence, including conserved chloroplast sequences, to expose convergence and justify taxonomic reclassification.
  • Relate DNA or amino-acid substitutions to divergence time using molecular-clock evidence.
  • Use rRNA and molecular features such as ribosomes, histones, introns, membrane lipids and cell walls to classify Archaea, Eubacteria and Eukarya.

Covered syllabus points

A3.2.1 (HL)—Need for classificationA3.2.2 (HL)—Difficulties with traditional hierarchyA3.2.3 (HL)—Advantages of evolutionary classificationA3.2.4 (HL)—CladesA3.2.5 (HL)—Molecular clockA3.2.6 (HL)—Constructing cladogramsA3.2.7 (HL)—Analysing cladogramsA3.2.8 (HL)—Testing classification correspondenceA3.2.9 (HL)—Three domains classification

Question 1

[Maximum number: 7]

Evolution causes gene pools to change over time and new species to be formed.

Explain how a newly discovered plant species would be classified and named.

Question 2

[Maximum number: 1]

Which is the hierarchy of taxa in order of increasing numbers of species?

A

genus, family, order, class

B

class, order, genus, family

C

genus, family, class, order

D

class, order, family, genus

Question 3

[Maximum number: 8]

Evolution is the change in the heritable characteristics of a population.

Explain how evolutionary relationships and cladograms can be used for classification.

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