Explain why the transition from prokaryotic to eukaryotic cells is considered a major step in the history of life on Earth.

Prokaryotic cells lack a membrane‑bound nucleus, so transcription and translation occur in the same compartment, limiting regulation. Eukaryotic cells have a nucleus, separating these processes and allowing more complex gene regulation.

Eukaryotes possess membrane‑bound organelles such as mitochondria and the endoplasmic reticulum, which compartmentalise metabolic pathways and increase efficiency.

The endosymbiotic acquisition of mitochondria (and chloroplasts) gave eukaryotes a large boost in energy production via aerobic respiration, providing the energy required for more complex cellular functions.

These features together enabled the evolution of multicellular organisms and greater biological complexity, marking a major step in life’s history.