Classification and evolution

Classification

Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species

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Binomial naming of species

The binomial system of naming species uses two Latin names (genus and species) to give each organism a unique, universally accepted scientific name.

Its advantage is that it avoids confusion from common names, allowing scientists worldwide to accurately identify and communicate about the same species.

Written with two capital letters and italics

5 Kingdoms

Organisms are classified into five kingdoms based on observable features such as cell structure, number of cells, and method of nutrition.

Early classification used similarities in visible characteristics like presence of nucleus, cell walls, and feeding type.

Prokaryotae, protictista, fungi, plantae and animalia

Prokaryotae

Unicellular organisms with no nucleus (DNA is circular and free in cytoplasm) or membrane bound organelles.

Have cell walls but not made of cellulose.

Examples include bacteria.

Protocstita

Mostly unicellular organisms with a nucleus present.

Can be autotrophic or heterotrophic.

Includes algae and protozoa.

Fungi

Mostly multicellular (some unicellular like yeast).

Cell walls made of chitin.

Saprotrophic nutrition (feed on dead organic matter).

Plantae

Multicellular organisms with cellulose cell walls.

Contain chloroplasts and carry out photosynthesis.

Autotrophic nutrition.

Animalia

Multicellular organisms with no cell walls.

Heterotrophic nutrition (ingest food).

Usually have nervous coordination and mobility.

Evidence for 3 domain

Modern classification uses genetic analysis (DNA sequencing) and comparison of biological molecules like ribosomal RNA (rRNA) and proteins to determine relationships between organisms.

DNA analysis shows how similar organisms are by comparing base sequences, revealing evolutionary relatedness more accurately than visible traits.

rRNA comparisons are especially important because they change slowly over time and show deep evolutionary relationships.

3 domains

Bacteria: prokaryotic, unicellular organisms with cell walls (not peptidoglycan in Archaea), no nucleus, circular DNA.

Archaea: prokaryotic, unicellular, genetically distinct from bacteria, often found in extreme environments.

Eukarya: organisms with eukaryotic cells (nucleus + membrane-bound organelles), includes animals, plants, fungi, and protoctists.

3 domain vs 5 kingdoms

Kingdom system (5 kingdoms): based mainly on observable features like cell type, number of cells, and nutrition.

Domain system (3 domains): based on genetic and molecular evidence (DNA and rRNA comparisons).

Domain system is more accurate and shows deeper evolutionary relationships.

Kingdom system groups some organisms incorrectly (e.g. all prokaryotes together).

Relationship between classification and phylogeny

Classification is the organisation of organisms into groups based on similarities.

Phylogeny is the study of evolutionary relationships between organisms.

Modern classification systems are based on phylogeny, grouping organisms by shared ancestry.

Darwin and Wallace

Darwin and Wallace independently developed the theory of evolution by natural selection, explaining how organisms with advantageous traits survive and reproduce more successfully.

Fossil evidence: shows progressive change and extinction in species through rock layers, including transitional forms linking ancestral and modern species (homologous structure pentadactyl limb showing a common ancestor which adapted to function).

Genomic DNA evidence: comparison of DNA base sequences (genomes) shows closely related species have more similar DNA

Molecular evidence: similarities in proteins (e.g. amino acid sequences of cytochrome c / mitochondrial proteins)

Intraspecific vs interspecific variation

Intraspecific variation: differences between individuals of the same species (e.g. human height, leaf size in a plant species).

Interspecific variation: differences between different species (e.g. cats vs dogs, bacteria vs plants).

Continuous vs discontinues variation

Continuous variation: shows a full range of values with no clear categories; usually controlled by many genes and environment (e.g. height in humans, mass in animals, leaf length in plants).

Discontinuous variation: shows distinct categories with no intermediates; usually controlled by a single gene (e.g. blood group in humans, flower color in some plants, antibiotic resistance in bacteria).

Types of adaptations

Anatomical: physical features (e.g. cactus spines reduce water loss, thick fur for insulation).

Physiological: internal processes (e.g. enzyme function at high temp, osmoregulation in kidneys).

Behavioural: actions (e.g. migration, huddling for warmth).

Different taxonomic groups similar anatomy

Similar structures in different taxonomic groups are due to convergent evolution.

Occur when unrelated species evolve similar features because of similar environmental pressures.

These are analogous structures (e.g. wings in birds and insects).

Homolgous structures

Homologous structures are similar anatomical features in different species due to shared evolutionary ancestry.

They may have the same basic structure but different functions (e.g. human arm, whale flipper, bat wing).

Evidence of divergent evolution, where related species adapt to different environments.

Shows how species have evolved from a common ancestor.

Natural selection

Genetic variation exists within a population due to different alleles.

Selection pressure (e.g. predators, disease, environment) favours individuals with advantageous characteristics.

These individuals are more likely to survive and reproduce (higher reproductive success).

They pass on advantageous alleles to offspring, increasing their frequency over time.

Over generations, the population shows an increased proportion of advantageous traits (evolution).

Pesticide resistane

Some insects have genetic variation that makes them resistant to pesticides.

Pesticide kills non-resistant insects, but resistant ones survive and reproduce.

Over time, the population becomes mostly resistant due to natural selection.

Drug resistance

Some bacteria have mutations that make them resistant to antibiotics.

Antibiotics kill non-resistant bacteria, but resistant ones survive and multiply rapidly.

This leads to antibiotic-resistant strains, making infections harder to treat.