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Archaea Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) To access a customizable version of this book, as well as other interactive content, visit www.ck12.org CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2012 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution/NonCommercial/Share Alike 3.0 Unported (CC BY-NC-SA) License (http://creativecommons.org/licenses/by-nc-sa/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/terms. Printed: January 30, 2013 www.ck12.org C ONCEPT Concept 1. Archaea 1 Archaea • Distinguish between bacteria and archaea. What organisms can grow in the hot springs of Yellowstone National Park? In the 1970s, a new group of organisms was identified. Unlike other organisms, these organisms could thrive in temperatures near 100ºC, the boiling point of water! This new group of organisms was named archaea. What are Archaea? For many years, archaea were classified as bacteria. Like the bacteria, archaea lacked a nucleus and membranebound organelles and, therefore, were prokaryotic cells. However, when scientists compared the DNA of the two prokaryotes, they found that there were distinct differences. They concluded that there must be two distinct types of prokaryotes, which they named archaea and bacteria. Even though the two groups might seem similar, archaea have many features that distinguish them from bacteria: 1. The cell walls of archaea are distinct from those of bacteria. While bacteria have cell walls made up of the polymer peptidoglycan, most archaea do not have peptidoglycan in their cell walls. 2. The plasma membranes of the archaea are also made up of lipids that are distinct from those in bacteria. 3. The ribosomal proteins of the archaea are similar to those in eukaryotic cells, not those in bacteria. Although archaea and bacteria share some fundamental differences, they are still similar in many ways: 1. They both are single-celled, microscopic organisms that can come in a variety of shapes (Figure 1.1). 2. Both archaea and bacteria have a single circular chromosome of DNA and lack membrane-bound organelles. 3. Like bacteria, archaea can have flagella to assist with movement. Obtaining Food and Energy Most archaea are chemotrophs and derive their energy and nutrients from breaking down molecules in their environment. A few species of archaea are photosynthetic and capture the energy of sunlight. Unlike bacteria, which 1 www.ck12.org FIGURE 1.1 Archaea shapes can vary widely, but some are bacilli (rod-shaped). can be parasites and are known to cause a variety of diseases, there are no known archaea that act as parasites. Some archaea do live within other organisms. But these archea form mutualistic relationships with their host, where both the archaea and the host benefit. In other words, they assist the host in some way, for example by helping to digest food. Reproduction Like bacteria, reproduction in archaea is asexual. Archaea can reproduce through binary fission, where a parent cell divides into two genetically identical daughter cells. Archaea can also reproduce asexually through budding and fragmentation, where pieces of the cell break off and form a new cell, also producing genetically identical organisms. Vocabulary • archaea: Single-celled organism with no nucleus and a different cell wall than bacteria, often thriving in extreme environments. • binary fission: Type of asexual reproduction in bacteria where a single cell divides into two cells. • chemotroph: Organism that obtains energy by breaking down chemical compounds in the environment. • mutualistic relationship: Symbiotic relationship in which both species benefit; mutualism. Summary • Archaea are prokaryotes, but they differ from bacteria in their DNA and biochemistry. • Most archaea are chemotrophs, but some are photosynthetic or form mutualistic relationships. • Archaea reproduce asexually through binary fission, fragmentation, or budding. 2 www.ck12.org Concept 1. Archaea Practice Use the resource below to answer the questions that follow. • Introduction to the Archaea at http://www.ucmp.berkeley.edu/archaea/archaea.html. 1. What are the three domains of life? 2. Why was the name Archaeabacteria misleading? 3. What pigment do Archaea use to carry out photosynthesis? What does this pigment do that allows the organisms to make ATP? Review 1. How are archaea different from bacteria? 2. Compare how bacteria reproduce to how archaea reproduce. 3