Chapter 17 (Part I)

Chapter 17 (Part I) - Chapter 17 Lecture Outline...

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Chapter 17 Lecture Outline Introduction What Am I? A. Most known organisms are animals. 1. Of the 1.7 million known species, three-fourths are animals. Animal diversity progressed through millions of years of evolution and natural selection. 2. Humans have a tendency to appreciate and study animals, but what is an animal? Do we know one when we see one, and how do we classify different animals? B. What am I? 1. The duck-billed platypus was a taxonomic nightmare when initially found by the first Europeans who visited Australia. It lays eggs and has a bill and webbed feet like a duck; it has fur and a tail like a beaver; it has mammary glands like any other mammal. So what is it? It’s a monotreme (an egg-laying mammal)! 2. Australia is full of special mammals called monotremes and marsupials. The niches that were being filled with placental mammals on other continents were left empty when Australia broke away from Pangaea. Without competition from other placental mammals, monotremes and marsupials filled in the empty niches and became the dominant mammals in Australia. Preview: Zoologists distinguish between animals with internal skeletons (vertebrates) and those without internal skeletons (invertebrates). All but one animal phylum (our own, phylum Chordata) are invertebrates (Module 18.14). I. Animal Evolution and Diversity Module 18.1 What is an animal? A. Animals are eukaryotic, multicellular heterotrophs that lack cell walls and obtain nutrition by ingestion (Figure 18.1A). This distinguishes animals from fungi that digest their food first and then absorb it. Animals have unique types of cell junctions (Module 4.18). Most animals have muscle cells for movement and nerve cells for sensory perception. Animals are, with the exception of the gametes, composed of diploid cells. B. The life cycle of most animals includes a dominant, diploid adult that produces eggs or sperm by meiosis. These gametes fuse to form a zygote. The zygote develops into the adult animal, passing through a series of embryonic stages, many of which are shared by most members of the animal kingdom (Figure 18.1B). C. In all animals, the embryonic stages include the blastula (hollow ball of cells) and, in most, a gastrula which is a saclike embryo with one opening and two layers of cells. The two cellular layers are called endoderm, which develops into the digestive tract, and the ectoderm, which becomes the outer layer of the animal and for some the nervous system. Most animals develop an additional layer of cells called the mesoderm, which forms the muscles and most of the internal organs. Preview: Embryonic development (Modules 27.9–27.15). D. In many animals, the gastrula develops into one or more immature stages, for example, larvae that develop into the sexually mature adults only after metamorphosis. NOTE:
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This note was uploaded on 03/10/2011 for the course BIOL 10 taught by Professor Kite during the Spring '11 term at Laney College.

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Chapter 17 (Part I) - Chapter 17 Lecture Outline...

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