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Explain 20% of the topic which is important
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The Living World: the most important 20%
Focus on these 4 areas. They cover most of the chapter and common exam questions.
1. Biodiversity, identification, nomenclature, classification
- Biodiversity means the variety and number of living organisms on Earth.
- We need a common system because local names vary from place to place.
- Identification: recognising an organism correctly.
- Nomenclature: giving it a universal scientific name.
- Classification: arranging organisms into groups based on similarities and differences.
- The study of identification, naming and classification is called taxonomy.
- Systematics includes taxonomy plus evolutionary relationships among organisms.
One-line difference:
Taxonomy = identification + nomenclature + classification.
Systematics = taxonomy + evolutionary relationships.
Taxonomy = identification + nomenclature + classification.
Systematics = taxonomy + evolutionary relationships.
2. Binomial nomenclature
Every organism has a two-word scientific name, introduced by Carolus Linnaeus.
Example: Mango = Mangifera indica
Human = Homo sapiens
Human = Homo sapiens
Rules
- The name has two words:
- First word = Genus
- Second word = specific epithet/species name
- Names are Latin or Latinised.
- Printed names are written in italics.
- If handwritten, underline each word separately.
- Genus begins with a capital letter.
- Specific epithet begins with a small letter.
Example: Homo sapiens
- Homo = genus
- sapiens = specific epithet
3. Taxonomic hierarchy: learn this sequence perfectly
Taxonomic categories are ranks used to classify organisms.
Species → Genus → Family → Order → Class → Phylum/Division → Kingdom
Mnemonic: Smart Girls Find Out Classy People Kind.
| Category | Meaning | Example |
|---|---|---|
| Species | Similar organisms that can be closely related | Homo sapiens |
| Genus | Group of related species | Homo |
| Family | Group of related genera | Hominidae |
| Order | Group of related families | Primata |
| Class | Group of related orders | Mammalia |
| Phylum | Group of related classes in animals | Chordata |
| Division | Equivalent of phylum in plants | Angiospermae |
| Kingdom | Highest category in this chapter | Animalia / Plantae |
Key idea: As we move from species to kingdom, the number of common characteristics decreases, while the number of organisms included increases.
4. Important examples
Human classification
- Species: Homo sapiens
- Genus: Homo
- Family: Hominidae
- Order: Primata
- Class: Mammalia
- Phylum: Chordata
- Kingdom: Animalia
Mango classification
- Species: Mangifera indica
- Genus: Mangifera
- Family: Anacardiaceae
- Order: Sapindales
- Class: Dicotyledonae
- Division: Angiospermae
- Kingdom: Plantae
Must-memorise answers
Why are organisms classified?
Because there are millions of organisms. Classification makes their study, identification and understanding easier.
Because there are millions of organisms. Classification makes their study, identification and understanding easier.
What is a taxon?
A taxon is a unit or category of classification, such as species, genus, family, etc.
A taxon is a unit or category of classification, such as species, genus, family, etc.
What is the basic unit of classification?
Species.
Species.
Phylum is used for?
Animals.
Animals.
Division is used for?
Plants.
Plants.
The highest taxonomic category here is?
Kingdom.
Kingdom.
If you remember only one thing:
Binomial nomenclature rules + Species to Kingdom sequence + examples of human and mango are the highest-yield parts.
Binomial nomenclature rules + Species to Kingdom sequence + examples of human and mango are the highest-yield parts.
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