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1.7.1Inquiry Process

Biological Classification — IB Biology HL Revision Notes & Topical Questions

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📚 IB Biology HL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
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Section 1 of 6Why Classify

Classification is the process of placing organisms into groups according to shared features.

Organise diversity
  • Organise diversity Millions of species exist, and grouping them makes it possible to study and talk about them clearly.
Predict features
  • Predict features Knowing the group of a new organism lets scientists predict features it probably shares with relatives.
Show relationships
  • Show relationships A natural classification places species together because they share a common ancestor.
Share names
  • Share names A universal scientific naming system avoids confusion caused by local common names.

Section 2 of 6Taxonomic Hierarchy

1
The largest group is the domain: Bacteria, Archaea or Eukarya.
2
Each domain is divided into kingdoms, and then each kingdom into phyla.
3
Phyla are split into classes, classes into orders, and orders into families.
4
Families are divided into genera, and each genus contains one or more species.
5
Each rank is a taxon, and every step down includes fewer organisms that are more similar.
RankHuman example
DomainEukarya
KingdomAnimalia
PhylumChordata
ClassMammalia
OrderPrimates
FamilyHominidae
GenusHomo
Speciessapiens

Section 3 of 6Binomial Nomenclature

Binomial Nomenclature
Two names
  • Two names Each species has a name made of its genus followed by its species, as in Homo sapiens.
Format
  • Format The genus begins with a capital letter, the species is lower case, and both are italicised or underlined.
Universal
  • Universal Scientists in every country use the same name, introduced by Linnaeus in the eighteenth century.
Natural classification
  • Natural classification Modern systems group organisms to include all descendants of a common ancestor.

Section 4 of 6Applying Classification

Applying Classification
Dichotomous keys
  • Dichotomous keys Keys use observable features to place an unknown organism in its group, step by step.
Molecular evidence
  • Molecular evidence Sequence similarities now guide placement more than appearance, because DNA reflects ancestry directly.
Clades
  • Clades A clade is an ancestor and all its descendants, and natural classification aims for every taxon to be a clade.
Limits
  • Limits Rank names are human conventions, so the same rank may represent very different ages of divergence.

Section 5 of 6Worked Example

Question Write the correct scientific name for the grey wolf and list its taxonomic ranks from largest to smallest if it is in genus Canis, family Canidae, order Carnivora, class Mammalia, phylum Chordata, kingdom Animalia, domain Eukarya.

  1. Binomial naming uses the genus first with a capital letter, then the species in lower case.
  2. The grey wolf species name is lupus, so the name is Canis lupus, written in italics or underlined.
  3. Order the ranks from largest to smallest: domain, kingdom, phylum, class, order, family, genus, species.
  4. Fill in each rankEukarya, Animalia, Chordata, Mammalia, Carnivora, Canidae, Canis, lupus.

Answer

  • Canis lupus;
    • Eukarya, Animalia, Chordata, Mammalia, Carnivora, Canidae, Canis, lupus.

Section 6 of 6Exam Checklist & Tips

1.7.1 – Key Points for the Exam

  • Taxonomy The science of classifying organisms.
  • Taxon A group of organisms at any rank.
  • Binomial name A two-part scientific name of genus and species.
  • Natural classification A classification based on evolutionary relationships.

Common Mistakes

  • Writing the species name with a capital letter, such as Homo Sapiens.
  • Using the species name alone without the genus.
  • Placing ranks in the wrong order.
  • Assuming that similar appearance always shows close relationship.

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