SACE Biology – Topic 4-1: The Origin of Life on Earth

These flashcards cover key concepts in the Origin of Life on Earth: fossil evidence, chemical origins, RNA world, protocell formation, oxygenation events, LUCA, and endosymbiotic theory.

Approximately how long has life existed on Earth according to current evidence?

About 3.5–3.7 billion years

What are stromatolites?

Layered bacterial mats that trap sediment; they represent the oldest known fossils of life

What early-Earth experiment by Miller and Urey demonstrated that organic molecules could form abiotically?

A 1953 spark-discharge experiment that produced 13 of the 20 naturally occurring amino acids from water, methane, ammonia, and hydrogen

Which environmental feature is hypothesised as a possible birthplace of life due to chemical-rich, warm water and energy sources?

Hydrothermal (deep-sea) vents

What does the RNA World hypothesis propose about the earliest genetic material?

RNA was the primary carrier of genetic information before DNA

What are ribozymes?

Catalytic RNA molecules capable of accelerating biochemical reactions

Which part of the ribosome acts as a ribozyme, catalysing peptide-bond formation?

The rRNA component

Why did DNA likely replace RNA as the main genetic material?

DNA is chemically more stable

Why did proteins replace most ribozymes over evolutionary time?

Proteins possess superior catalytic efficiency

What is the Last Universal Common Ancestor (LUCA)?

The most recent common ancestor of all life currently on Earth

How do lipids naturally form protocell-like structures in water?

Their polar heads and non-polar tails self-assemble into micelles or vesicles

What crucial event about 2 billion years ago dramatically altered Earth’s atmosphere?

The rise of oxygenic photosynthesis, increasing atmospheric O₂

What was one catastrophic effect of the initial rise in atmospheric oxygen?

Mass die-off of anaerobic prokaryotes for which oxygen was toxic

Which protective atmospheric layer formed as oxygen accumulated, reducing UV radiation?

The ozone layer

What does the endosymbiotic theory state about mitochondria and chloroplasts?

They as prokaryotes that were engulfed becoming symbiotic organelles

Name one piece of evidence that mitochondria and chloroplasts were once independent prokaryotes.

They possess circular DNA similar to bacteria/ they divide by binary fission

How do mitochondria and chloroplasts replicate inside eukaryotic cells?

By binary fission independent of the cell nucleus

Why can membranes be considered a key step toward cellular life?

They create internal environments with distinct chemical conditions, enabling specialized reactions

What does “endosymbiosis” mean?

one organism living inside another in a mutualistic relationship

Which prokaryotic trait of mitochondria and chloroplasts supports endosymbiosis besides DNA shape?

Presence of 70S ribosomes similar to bacterial ribosomes

What atmospheric oxygen percentage did early photosynthetic bacteria raise it to, triggering evolutionary change?

Roughly 0.45 %—enough to be toxic to many anaerobes