Chapter 18 Lost Diversity

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Some microbes live in extreme conditions

• Microbial life exists practically everywhere on earth. – Including areas

with: • extremely high

temperatures • high pressure • extreme pH.

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Studying extreme environments gives us clues to the beginning of life on earth

• Areas deep in the ocean show the abiotic formation of simple organic molecules. – May help us to

understand reactions that occurred during the formation of life on earth.

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Some microbes live in extreme conditions • Investigating microbes that live in extreme

conditions is difficult. – May not be able to exist outside of their delicate

environment. – Cannot be cultured using normal techniques.

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Prokaryotic cells • Prokaryotes lack internal membrane-bound

organelles, and their DNA is not contained within a nucleus.

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Prokaryotic cells • Most prokaryotic organisms are unicellular and

microscopic. • Typically 1–10 microns, which is about 1/10 the thickness

of a human hair.

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Prokaryotic cells • Prokaryotes are an extraordinarily successful

product of evolution.

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Prokaryotic cells • Fossil evidence indicates that prokaryotes were the first

colonizers of our planet, and for nearly two billion years were its only life form.

• Prokaryotes are almost endlessly adaptive and can thrive just about anywhere.

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Identifying Prokaryotic cells • Biologists generally rely on DNA to identify

prokaryotic organisms. • Finding a unique DNA sequence in a sample means

the researchers have discovered a new organism.

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Prokaryotic cells • Two domains of life, Bacteria and Archaea, have

prokaryotic cells, but they each have distinct evolutionary histories.

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Prokaryotic cells - Archaea • Archaea are often found in more extreme

conditions than bacterial populations.

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• Archaea are similar to bacteria but they are genetically very different from bacteria.

• Archaea are sometimes known

as “extremophiles.” - They often live in very harsh conditions.

Prokaryotic cells - Archaea

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• Bacteria are prokaryotic cells with a diverse array of lifestyles.

• Most possess a cell wall, but their genetic diversity leads to a wide variety of differences in nutrition, metabolism, structure, and lifestyle.

Prokaryotic cells - Bacteria

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• Bacteria can be categorized by what they eat. – Some bacteria are autotrophs―they can make their own

food directly, using material from the nonliving environment.

– Some bacteria are heterotrophs―they must rely on other organisms to provide them with food.

Prokaryotic cells - Bacteria

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Bacteria - Cyanobacteria • One of the largest groups of autotrophic bacteria

are the cyanobacteria, which are found in oceans and freshwater, as well as on exposed rocks and soil.

• Cyanobacteria use the energy of sunlight to carry out photosynthesis.

• Many cyanobacteria also perform nitrogen fixation―the process of

converting atmospheric nitrogen into a form that plants can use to grow.

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Bacteria • Some heterotrophic

bacteria play an important role in decomposition and bioremediation projects.

• Many bacteria live in close association, or symbiosis, with other organisms. 4/2/2014

• Some bacteria are pathogens, or disease-causing agents.

• Many pathogenic bacteria cause disease by producing toxins that harm their hosts.

Bacteria

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• Bacteria display a variety of structural adaptations that suit their various lifestyles.

• Bacteria come in different shapes: spherical (cocci), rod-shaped (bacilli), and spiral (spirochetes).

Bacteria

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• Many bacteria have flagella (whiplike appendages extending from the surface of some bacteria, used in movement of the cell).

• Pili (short, hairlike appendages extending from the surface of some bacteria, are used to adhere to surfaces).

• Some bacteria are surrounded by a capsule (a sticky coating that adheres to surfaces).

Bacteria

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