Chapter 19: lifes origin and early evolution

RNA world hypothesis

hypothesis that RNA served as the genetic information of early life

endosymbiont hypothesis

hypothesis that mitochondria and chloroplasts evolved from bacteria

iron-sulfur world hypothesis

hypothesis that the metabolic reactions that led to the first cells took place on the porous surface of iron-sulfide-rich rocks at hydrothermal vents

Precambrian Era

interval from earths formation to 541 million years ago

The prevalence of _______ in living organisms is taken as support for the idea that life arose near deep-sea vents.

iron-sulfide cofactors

protocell

membranous sac that contains interacting organic molecules; hypothesized to have formed prior to the earliest life forms

Evolution of ___________ increased the energy available to cells, making a larger genome and processes such as membrane trafficking possible.

mitochondria

Infoldings of the plasma membrane into the cytoplasm of some ancestral cells may have evolved into the ___________.

nuclear envelop and ER membranes

An abundance of ___________ in earths early atmosphere would have interfered with assembly of organic compounds.

oxygen

The evolution of ________ resulted in the eventual formation of the ozone layer.

oxygen-producing photosynthesis

Hadean eon

prcambrian interval that runs from earths formation to 4 billion years ago

Archean eon

precambrian interval extending from 4 billion years ago to 2.5 billion years ago. first eon for which there is evidence of life.

Among prokaryotes, only the cyanobacteria ________.

produce oxygen during photosynthesis

According to one hypothesis, negatively charged clay particles played a role in early ___________.

protein formation

The first eukaryotes were ___________.

protists

An RNA that functions as an enzyme is a _______.

ribozyme

Which of the following is NOT true of conditions during the Hadean eon?

rocks began to rust

stromatolite

rocky, layered structure that forms over time as a mat of aquatic prokaryotic cells traps sediments

Describe how scientists have tested the hypothesis that simple organic molecules could have formed on the early Earth.

small organic molecules that serve as the building blocks for living things can be formed by nonliving mechanisms

set of events in order

the big bang, liquid water appears, origin of protocells, onset of oxygen-releasing pathway of photosynthesis, emergence of the first eukaryotes, origin of chloroplasts

Astrobiology

the scientific study of life's origin and distribution in the universe

List three locations where the building blocks of Earth's first life may have formed.

these molecules form in space, near hydrothermal vents, and may have formed in the atmosphere of the early earth

Stanley millers experiment demonstrated that ___________.

under some conditions, amino acids can assemble spontaneously from inorganic materials

hydrothermal vent

underwater opening from which mineral-rich water heated by geothermal energy streams out

ozone layer

upper atmospheric region rich in ozone that screens out incoming ultraviolet radiation

big bang theory

well-supported hypothesis that the universe originated by a nearly instant distribution of matter through space

Describe the likely origins of the eukaryotic nucleus, endomembrane system, mitochondria, and chloroplasts.

A nucleus and other membrane-bound organelles are defining features of eukaryotic cells. The nucleus and endomembrane system could have arisen through modification of infoldings of the plasma membrane. Mitochondira and chloroplasts evolved through endosymbiosis and are descended from bacteria.

Explain what caused the increase in oxygen in Earth's air and waters.

Evolution of the oxygen-releasing pathway of photosynthesis in cyanobacteria resulted in the oxygenation of earths atmosphere and waters.

Describe the oldest fossils of early life and the environments in which these fossil cells lived.

Fossils indicate that by about 3 billion years ago prokaryotic cells were widespread in the ocean.

List the proposed steps that led to the first cellular life.

Metabolic reactions may have begun when molecules became concentrated on clay particles or inside tiny rock chambers near hydrothermal vents

Explain the RNA world hypothesis

RNA can serve as an enzyme, as well as a genome. An RNA world may have preceded evolution of DNA-based genomes.

ribozyme

RNA that functions as an enzyme

List the probable traits of LUCA, the last common ancestor of all life.

The ancestor of all modern life arose by about 4 billion years ago. The first cells were most likely anaerobic and prokaryotic.

Describe how the increase in oxygen affected the existing organisms and how it set the stage for the later movement of life onto land.

The rise in oxygen favored organisms that could detoxify oxygen or use it in aerobic respiration. Addition of oxygen to the atmosphere led to formation of the ozone layer, which allowed life to move onto land.

Describe the properties of laboratory-produced protocells.

Vesicle-like structures with outer membranes form spontaneously when certain organic molecules are mixed with water. (fatty acid membrane)

A stromatolite is a structure ____________.

consisting of layered bacteria and sediment

Explain what study of ancient rocks has revealed about conditions of the early Earth.

during earths early years meterorites pummeled the planets surface and volcanic eruptions were common, as earth cooled liquid water began to pool on its surface, earths early atmosphere had no oxygen gas

The host cell in the endosymbiosis that produced the first chloroplasts was an ____________.

early eukaryote

Which of the following events did NOT occur during the precambrian era?

evolution of the first plants

proterozoic eon

final eon of the precambrian era, 2.5 billion to 541 million years ago