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Chapter 26 The Tree of Life: - page 10 / 18

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It is clear that they provided life with opportunities for adaptive radiations into newly vacated ecological niches.

Concept 26.3 As prokaryotes evolved, they exploited and changed young Earth

The oldest known fossils are 3.5-billion-year-old stromatolites, rocklike structures composed of layers of cyanobacteria and sediment.

If bacterial communities existed 3.5 billion years ago, it seems reasonable that life originated much earlier, perhaps 3.9 billion years ago, when Earth first cooled to a temperature where liquid water could exist.

Prokaryotes dominated evolutionary history from 3.5 to 2.0 billion years ago.

The early protobionts must have used molecules present in the primitive soup for their growth and replication.

Eventually, organisms that could produce all their needed compounds from molecules in their environment replaced these protobionts.

A rich variety of autotrophs emerged, some of which could use light energy.

The diversification of autotrophs allowed the emergence of heterotrophs, which could live on molecules produced by the autotrophs.

Prokaryotes were Earth’s sole inhabitants from 3.5 to 2.0 billion years ago.

These organisms transformed the biosphere of the planet.

Relatively early, prokaryotes diverged into two main evolutionary branches, the bacteria and the archaea.

Representatives from both groups thrive in various environments today.

Metabolism evolved in prokaryotes.

The chemiosmotic mechanism of ATP synthesis is common to all three domains—Bacteria, Archaea, and Eukarya.

This is evidence of a relatively early origin of chemiosmosis.

Transmembrane proton pumps may have functioned originally to expel H+ that accumulated when fermentation produced organic acids as waste products.

The cell would have to spend a large portion of its ATP to regulate internal pH by driving H+ pumps.

The first electron transport pumps may have coupled the oxidation of organic acids to the transport of H+ out of the cell.

Lecture Outline for Campbell/Reece Biology, 7th Edition, © Pearson Education, Inc. 26-10

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