Rethinking Classification Schemes Chapter 1 Enrichment

Name
Date
Class
Chapter 1
Enrichment
LESSON 2
Rethinking Classification Schemes
Early classification schemes for life
included only two kingdoms—Animalia
and Plantae. As time passed, more distinct
groups of organisms were discovered. After
microscopes were developed, scientists were
able to view tiny organisms not easily seen
by the unaided eye. Prokaryotes, which are
unicellular organisms, were discovered, and
a new kingdom—Kingdom Monera—was
added to the classification scheme.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Still More Changes
Five kingdoms—Animalia, Plantae,
Fungi, Protista, and Monera were organized
under two domains—Prokarya and Eukarya.
Recall that prokaryotic cells do not contain
internal, membrane-bound structures.
Prokaryotes include bacteria and were
grouped in Kingdom Monera. In contrast,
the cells of eukaryotes do contain internal,
membrane-bound structures. Eukaryotes
include plants, animals, fungi, and protists.
In 1977 some scientists realized there
was much more to Prokarya than
previously thought. Previously, unicellular
organisms called archaea were considered
to be bacteria; they look very similar to
bacteria when they are viewed under a
microscope. However, genetic tests
showed that archaea are very different
from bacteria. For that reason, Prokarya is
now organized into two separate
domains—Bacteria and Archaea. Life is
now classified into three domains rather
than two—Bacteria, Archaea, and Eukarya.
Hardy Life-Forms
Archaea have an amazing ability to
thrive in harsh habitats. Scientists have
discovered these tiny life-forms near
scalding hydrothermal vents on the
seafloor. They also have been found in icy
antarctic waters. They even live 600 m
below ground.
Some of these same harsh conditions are
found on Mars and certain moons in the
solar system. Scientists theorize that
organisms similar to archaea could be
present below the surface of these bodies in
space.
Engineers also are studying archaea.
They hope these unusual life-forms can be
used in the production of common items.
For example, archaea might help improve
the cleaning ability of cold-water
detergents, make fragrances last longer, and
reduce food spoilage.
Applying Critical-Thinking Skills
Directions: Respond to each statement.
1. Consider Imagine you are a scientist. Decide what criteria you would consider before
establishing a new domain for a life-form.
2. Infer which facts indicate that ancestors of archaea might be among the first life-forms
on Earth.
Classifying and Exploring Life
37