Ch. 15: the evolution of microbial life
Terms in this set (35)
Earth was formed about
4.6 billion years ago.
The first living things
- Prokaryotes evolved by about 3.5 billion years ago,
- began oxygen production about 2.7 billion years ago,
- lived alone for more than a billion years,
- continue in great abundance today.
The first eukaryotes
- Single-celled eukaryotes first evolved about 2.1 billion years ago.
- Multicellular eukaryotes first evolved at least 1.2 billion years ago.
Rise in animal diversity
- All the major phyla of animals evolved by the end of the Cambrian explosion, (Cambrian time period, explosion in diversity) which
- began about 540 million years ago
Life moves onto land
- Plants and fungi first colonized land about 500 million years ago and
- were followed by amphibians that evolved from fish.
We may never know for sure how life on Earth began. Today, most biologists think it is possible that life on early Earth evolved from simple cells produced by
- chemical and
- physical processes.
physical rather than biological; not derived from living organisms.
-devoid of life; sterile.
According to one hypothesis, the first organisms were products of chemical evolution in 4 stages:
1. Abiotic synthesis of organic monomers
2. Abiotic synthesis of polymers
3. Formation of pre-cells
4. Origin of self-replicating molecules
Stage 1: Abiotic Synthesis of Organic Monomers
An apparatus was built to mimic the early Earth atmosphere and included
- hydrogen gas (H2), methane (CH4), ammonia (NH3), and water vapor (H2O),
- sparks that were discharged into the chamber to mimic the prevalent lightning of early Earth, and
-a condenser that cooled the atmosphere, causing water and dissolved compounds to "rain" into the miniature "sea."
After the apparatus had run for a week
an abundance of organic molecules essential for life had collected in the "sea," including amino acids, the monomers of proteins.
These laboratory experiments
- have been repeated and extended by other scientists and
- support the idea that organic molecules could have arisen abiotically on early Earth.
Stage 2: Abiotic Synthesis of Polymers
Researchers have brought about the polymerization of monomers to form polymers, such as proteins and nucleic acids, by dripping solutions of organic monomers onto:
- hot sand,
- clay, or
Stage 3: Formation of Pre-Cells
A key step in the origin of life was the isolation of a collection of abiotically created molecules within a membrane.
Laboratory experiments demonstrate that pre-cells could have formed
spontaneously from abioticallyproduced organic compounds. They
- have a selectively permeable surface,
- can grow by absorbing molecules from their surroundings
Stage 4: Origin of Self-Replicating Molecules
Life is defined partly by the process of inheritance, which is based on self-replicating molecules.
One hypothesis is that the first genes were short strands of RNA that replicated themselves
- without the assistance of proteins,
- perhaps using RNAs that can act as enzymes, called ribozymes.
- can be called the "RNA world"
-lived and evolved all alone on Earth for about 2 billion years.
- are found wherever there is life,
- have a collective biomass that is at least ten times that of all eukaryotes,
- thrive in habitats too extreme for any eukaryote,
- cause about half of all human diseases, and
- are more commonly benign or beneficial.
prokaryote and eukaryotes
-bateria and archaea
-fungi, protists, plants, animal
Compared to eukaryotes, prokaryotes are
- much more abundant and
- typically much smaller.
Prokaryotes living in soil and at the bottom of lakes, rivers, and oceans help to
decompose dead organisms and other organic waste material, returning vital chemical elements to the environment.
The Structure and Function of Prokaryotes
- lack a membrane-enclosed nucleus,
- lack other membrane-enclosed organelles,
- typically have cell walls exterior to their plasma membranes, but
- display an enormous range of diversity.
The three most common shapes of prokaryotes are
1. spherical (cocci),
2. rod-shaped (bacilli), and
3. spiral or curved.
-All prokaryotes are unicellular
Some species exist as
groups of two or more cells
-grouped together and work together as colonies
About half of all prokaryotes are
mobile, and many of these travel using one or more flagella.
Most prokaryotes can reproduce
- by dividing in half by binary fission and
- at very high rates if conditions are favorable.
-binary fission (split in 2)
Some prokaryotes form endospores
- thick-coated, protective cells
- produced when the prokaryote is exposed to unfavorable conditions.
-resistant inner layer of the membrane or wall inside the cell
- eukaryotes that are not fungi, animals, or plants,
- mostly unicellular, and
- ancestral to all other eukaryotes.
- consists of multiple clades (kingdoms)
Eukaryotic cell nucleus evolved by
the infolding of the plasma membrane of a prokaryotic cell to form the endomembrane system
Other eukaryotic organelles arose via endosymbiosis
- Endosymbiosis refers to one species living inside another host species
-eukaryotic organelles came from organelles entering the cell / forming a beneficial partnership within the cell
-new plastids and mitochondria are formed similarly to binary fission
-plastids and mitochondria have their own circular DNA
is a more general association between organisms of two or more species.
Protists obtain their food
in a variety of ways
are autotrophs, producing their food by photosynthesis
Other protists are
-Some protists eat bacteria or other protists.
-Other protists are fungus-like and obtain organic molecules by absorption.
derive their nutrition from a living host, which is harmed by the interaction
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