Classification and Biodiversity
Classification
Classification is the process of sorting living organisms into groups based on their similarities and differences. It helps scientists study relationships between organisms.
The Linnaean System
Carl Linnaeus (1735) developed a hierarchical classification system with seven levels (taxa). From broadest to most specific:
Kingdom → Phylum → Class → Order → Family → Genus → Species
A helpful mnemonic: King Philip Came Over For Good Spaghetti
Example — human classification:
| Level | Human classification |
|---|---|
| Kingdom | Animalia |
| Phylum | Chordata |
| Class | Mammalia |
| Order | Primates |
| Family | Hominidae |
| Genus | Homo |
| Species | sapiens |
Binomial Nomenclature
Linnaeus also introduced binomial nomenclature — every species is given a two-part Latin name:
- First name = genus (capitalised)
- Second name = species (lowercase)
- Always written in italics (or underlined if handwritten)
Examples: Homo sapiens (human), Panthera leo (lion), Escherichia coli (bacterium)
Three-Domain System
Carl Woese proposed the three-domain system (1990s) based on analysis of ribosomal RNA (genetic analysis rather than physical features):
| Domain | Characteristics | Examples |
|---|---|---|
| Archaea | Primitive bacteria; often live in extreme environments (hot springs, salt lakes); no nucleus | Methanogens, thermophiles |
| Bacteria | True bacteria; no nucleus (prokaryotes); diverse | E. coli, Salmonella |
| Eukarya | All organisms with cells containing a nucleus | Animals, plants, fungi, protists |
The three-domain system replaced the old five-kingdom system because genetic analysis revealed that what were classified as bacteria were actually two very different groups (Archaea and Bacteria).
Why Classification Changes
Classification systems change as new evidence emerges:
- DNA sequencing reveals evolutionary relationships that physical features alone cannot show
- Chemical analysis (e.g. protein comparison) can support or contradict traditional groupings
- New species are discovered, and some organisms are reclassified
Biodiversity
Biodiversity is the variety of all the different species of organisms on Earth, or within an ecosystem. High biodiversity indicates a healthy ecosystem.
Biodiversity depends on:
- The number of different species in an area (species richness)
- The population size of each species (abundance)
Why Biodiversity Matters
- Ecosystems with high biodiversity are more stable and resilient — if one species is lost, others can fill its role
- Many species provide direct benefits: food, medicines, materials
- Ecological services: pollination, water purification, carbon storage
- Ethical responsibility to protect other species
Threats to Biodiversity
Human activities are rapidly reducing biodiversity:
| Threat | How it reduces biodiversity |
|---|---|
| Habitat destruction | Deforestation, urbanisation, and farming destroy habitats — species lose their homes |
| Pollution | Air, water, and land pollution poison organisms and damage ecosystems |
| Overexploitation | Overfishing, overhunting, and overharvesting reduce populations below sustainable levels |
| Climate change | Changing temperatures and weather patterns alter habitats faster than species can adapt |
| Introduction of invasive species | Non-native species outcompete, prey on, or spread disease to native species |
Deforestation
Cutting down large areas of forest reduces biodiversity by:
- Destroying habitats for countless species
- Reducing carbon dioxide absorption (trees absorb CO₂ for photosynthesis)
- Increasing greenhouse gases (burning trees releases stored carbon)
- Causing soil erosion and flooding
- Disrupting the water cycle (less transpiration)
Conservation Programmes
Efforts to maintain biodiversity include:
- Breeding programmes in zoos and wildlife parks for endangered species
- Seed banks — storing seeds of rare plant species
- Nature reserves and national parks — protecting habitats from development
- Reintroduction programmes — releasing captive-bred organisms into the wild
- Legislation — laws protecting endangered species (e.g. CITES — Convention on International Trade in Endangered Species)
- Hedgerow and habitat restoration — recreating lost habitats
- Recycling and reducing waste — reducing demand for raw materials
- Reducing deforestation — sustainable forestry, protected forests, replanting
Maintaining Biodiversity and the Future
Scientists argue that maintaining biodiversity is important for:
- Future medicine — many drugs are derived from organisms (e.g. aspirin from willow bark, penicillin from fungi)
- Food security — genetic diversity in crops protects against disease
- Ecosystem stability — biodiverse ecosystems provide clean air, water, and fertile soil
Exam Tips
- Know all seven levels of the Linnaean classification system and the correct order
- The three-domain system is based on genetic analysis (RNA), not physical features
- Biodiversity questions often ask you to evaluate conservation methods — discuss advantages and limitations
- Deforestation is a common 6-mark topic — link it to habitat loss, climate change, and reduced biodiversity