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- Contributed By: National Repository of Online Courses Science
Lesson 27, Prokaryotes
Prokaryotes are the smallest organisms in size, but they’re grand in
almost every other way. Their forms are ancient, represented in fossils
going back to the first life on Earth. If we count individuals, there
are far more prokaryotes today than all other organisms combined.
Prokaryotes can be found in every imaginable habitat, including some so
extreme that no other forms of life could survive there.
In this Lesson, we’ll survey the diversity of prokaryotic organisms.
Their external shapes may be simple, but their lifestyles and
biochemistry are very complex. Although some prokaryotes are well-known
causes of disease, many others are beneficial, and neither humans nor
any other species could survive without them.
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Lesson 28, Unicellular Eukaryotes
A diverse array of unicellular eukaryotic organisms exists almost
anywhere there is water. All unicellular eukaryotes are classified in
the kingdom Protista, along with the multicellular eukaryotes that
aren’t considered animals, plants, or fungi. The resulting grab-bag
kingdom is one of unexpected diversity in form and lifestyle. The
taxonomy of the protists is an unsettled scientific problem that is the
subject of intense research.
An exploration of protist diversity can begin in a drop of pond
water. In this Lesson, we’ll also explore the origins of the
eukaryotes, and look at a wide variety of protist organisms including
plantlike algae, one-celled predators, and slimy decomposers.
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