How It Works: Classification and Why It Changes
Part of Classification — GCSE Biology
This how it works covers How It Works: Classification and Why It Changes within Classification for GCSE Biology. Classification systems, taxonomy, and evolutionary relationships It is section 4 of 11 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 4 of 11
Practice
25 questions
Recall
20 flashcards
How It Works: Classification and Why It Changes
Classification is the process of grouping living organisms based on their similarities and differences, making it easier for scientists to study and communicate about life on Earth. The system in use today was established by Carl Linnaeus in the 18th century and is called the Linnaean hierarchy.
Organisms are grouped at progressively finer levels — from Kingdom (broadest) down to Species (most specific). At each level, organisms share more characteristics with each other. Two organisms in the same genus are more closely related than two organisms that share only a kingdom.
Classification systems are not fixed — they change as new evidence becomes available. For most of history, organisms were classified by their physical appearance and structure (morphology). This worked for many groups but led to errors when unrelated organisms happened to look similar (convergent evolution). The development of DNA sequencing in the 20th century revolutionised classification: by comparing the DNA sequences of organisms directly, scientists can determine more accurately how closely related they are and how recently they shared a common ancestor.
Carl Woese used ribosomal RNA (rRNA) sequences to re-examine the classification of microorganisms. He discovered that organisms previously classified as bacteria fell into two fundamentally different groups — true bacteria and archaea — which are as different from each other at the molecular level as either is from eukaryotes. This led to his proposal of the three-domain system, which now supersedes the five-kingdom system for most scientific purposes.