Exam 3 - Exam 3 Chapter 32 The Animal Kingdom The crown...

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Exam 3 Chapter 32 The Animal Kingdom The crown Kingdoms are basically divided based on nutrition. o Plants are photosynthetic. Fungi feed by absorption and animals feed by consumption. Animals are eukaryotic, multicellular, and heterotrophic. They lack cell walls but have a coating on their cells called collagen. They have specialized muscle and nerve cells. They reproduce sexually. The diploid phase is dominant and animals are only haploid for the time it takes to reproduce. They cannot survive haploid. Animals are composed of tissue developed from embryonic layers that differentiate. There is a larval stage in animals, which in some involves a metamorphosis. Larvae are sexually immature and morphologically distinct from the adult. They all have HOX genes, which regulate the pattern of development in animals. They turn on certain genes at the right time in order to develop the organism. o This is the basis of evolutionary developmental biology. Only animals have these. Early growth of an animal o Meiosis forms the egg and sperm. o The zygote is the fertilized egg. o Then as cells multiply (called cleavage), we reach the eight cell stage. o Then a blastula is formed. It grows out and cells are able to move forming a hollow ball. o Then there is the process of gastrulation where there is infolding of the blastula. This will form the digestive system. There can be two or three layers that differentiate. o The next stage is the larval stage, before birth or hatching or whatever. Choanoflagellates may have been the first attempt at multicellular organisms. Their flagella bring in food via phagocytosis. They are found in the water and can swim away from a colony when it becomes too large and start a new one. The feeding cells of sponges are identical to choanoflagellates. Sponges are the most primitive animals. They have no symmetry, or tissue. Origins of Animal Diversity Animals are believed to have evolved from a colonial flagellated protist 675-875 million years ago. May have resembled choanoflagellates. Animals underwent rapid diversification at the beginning of the Cambrian period 542 million years ago. This was during the Paleozoic era. o This diversification took place over a span of 15 million years. o All major animal body plans that are in existence today evolved at this time. o Many of the animal body plans of this time period appear bizarre. This is likely because they did not survive and became extinct. One example of this is hallucigenia. All animals were marine until plants began to exist on land. There are three hypotheses as to what caused the rapid diversification of the Cambrian period. o First, there was selective pressure on the species, due to having to compete with other species.
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