Concept and uses of classification systems

Classification organises the enormous variety of living organisms into manageable groups based on the features that they share.

Key Definition A species is defined as a group of organisms that can reproduce to produce fertile offspring.

Binomial System

• Gives every species a unique two-part scientific name, made up of the genus followed by the species
• Is an internationally agreed system of naming, which prevents the confusion caused by the use of different common names in different countries and languages

Dichotomous Keys

• Provide a practical tool for identifying organisms by working through a series of paired, two-choice questions based on observable features

Extended At Extended level, classification systems aim to reflect evolutionary relationships, grouping organisms by common ancestry rather than by surface-level similarity alone.

DNA Base Sequence Comparison

• Comparing the sequence of bases in DNA has strengthened this approach, because organisms that share a more recent common ancestor have base sequences in their DNA that are more similar than those that share only a distant common ancestor
• This is because they have had less time for mutations to introduce differences between their base sequences
• This molecular evidence can correct misclassifications based on physical features, as it reveals true genetic relationships regardless of outward appearance