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Chapter 13

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Western University
Biology 1225
Michael Butler

Chapter 13: Early Life Forms and the Viruses Overview Life originated on Earth more than 3.8 billion years ago. Its origin and subsequent evolution have been linked to the physical and chemical evolution of the universe, the stars, and our solar system. In the past century, many studies and experiments have provided indirect evidence that life originated under conditions that presumably existed on the early Earth. In comparison to the age of the Earth, humans (Homo sapiens) have been around for only a very short period of time. Humans are a recent offshoot of the primate group. Human evolution has been marked by trends that involved changes in our bones, muscles, teeth, sensory systems, and the brain. Much of the material that is discussed in the chapter comes under the title of a branch of science called TAXONOMY, which is the science of the naming and categorization of organisms according to their evolutionary similarities. Naturalists and biologists have documented more than 1.4 million species that exist on the Earth today, and perhaps millions more wait to be discovered and classified. Classification systems are used to organize species into categories based on their evolutionary relatedness. In Chapter 13 and 14, you will examine several different ways of classifying organisms. You will then examine the wondrous array of organisms and their characteristics, beginning with the simplest organisms and proceeding to the most complex. Responsibilities You do not need to memorize dates for major events in the history of life on Earth. Be sure that you know what conditions were like on the early, primitive Earth and how those conditions (such as the development of the gases in the atmosphere) contributed to the appearance of life, the evidence is that the first cells to evolve were bacteria that only undertook anaerobic metabolism, since there was no free atmospheric oxygen at that time to allow aerobic metabolism. In section 13.3 you will only be responsible for the discussion on endosymbiosis. In section 13.4 you should concentrate on being able to identify the general structural features of all viruses, that at a minimum a virus consists of nucleic acid (either RNA or DNA but never both), held inside a protein based shell called a protein coat in your textbook but termed acapsid by people who study viruses. Viruses do not have cytoplasm, at most will contain only one or two enzymes that have a specialized purpose in their infection process, and are absolute obligate parasites of cells. For section 13.6 you should know in general terms just how to define what a protist is, and to be able to give the identifying features of each type of protist, I am not really interested in having you be able to identify and name all of the numerous kinds of algae, water molds, slime molds and so on. So for instance, for protozoa you would simply need to know that they are so grouped because of their animal-like, behavior (although of course they are not animals- because they consist of only a single cell), or you should know that algae are photosynthesizing organisms that range in size from single cells to use seaweed, can be of various pigmentation's, and can live in fresh or seawater. 1. Members of the Kingdom Animalia share a list of common features. Select from each pair of terms or phrases the one which is characteristic of true animals by underlining your choice. (Be sure that you know what each term means.) - prokaryotic, eukaryotic - heterotrophic, au
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