Evolution of Eukaryotes

Objectives

• Summarize the endosymbiotic theory
• Summarize life in the late Precambrian
• Summarize life in the Paleozoic Era

Eukaryotic cells evolved about 2 billion years ago. It is explained by the endosymbiotic theory.

Endosymbiosis occurred when a large cell engulfed a smaller cell.

The small cell was not digested but lived inside the large cell. The cells formed a symbiotic relationship.

Some small cells supplied energy not only for themselves but also for the large cells. They became mitochondria.

Other small cells used sunlight to make food. They became chloroplasts.

Evidence

• Organelle DNA is short, circular, and unlike nuclear DNA
• Organelle membranes are like prokaryote membranes
• Organelle ribosomes are similar to bacterial ribosomes
• Reproduction is by binary fission

While mitochondria and chloroplast biochemical pathways are similar to prokaryotes', host cells' are similar to Archaebacteria.

Made possible by endosymbiosis, new eukaryotic cells were efficient.

New characteristics

• Multicellularity
• Cell specialization
• Large size

Late Precambrian Period

Earth's Changes

• Continents drifted
• CO2 levels rose and fell

Organisms Adapted (or died)

• Sexual reproduction
• Some cells started to colonize
• Multicellularity

Sexual Reproduction

• Increased chances that some would survive
• Increased speed of evolution

Cell colonies led to specialization. Colonies were more efficient than individual cells.

Multicellularity

• Cells couldn't live independently
• Organism was bigger and more efficient

Mass extinction occurred at the end of the Precambrian Period 544 million years ago.

Paleozoic Era

Paleozoic Era began with a burst of new life in the "Cambrian Explosion." Sponges evolved and trilobites were abundant.

Ordovician Period

• Oceans filled with many invertebrates
• First fish evolved
• Plants colonized land for first time

Silurian Period

• Corals appeared
• Fish continued to evolve
• On land, vascular plants appeared
• Vascular plants grew larger than nonvascular

Devonian Period

• First seed plants evolved
• Fish with lobe fins evolved - could breath air

Carboniferous Period

• Forests left deposits of carbon that turned to coal
• The first amphibians evolved
• Then reptiles evolved

Permian Period

• Major land masses collided to form Pangea
• Temperatures were extreme
• Climate was dry

The era ended with the biggest mass extinction ever, the Permian Extinction. Exact cause unknown.