CH_42_STUDENT_OUTLINE

CH_42_STUDENT_OUTLINE - Chapter 42: Animal Development What...

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Chapter 42: Animal Development
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What Is Animal Development? The process by which an animal proceeds from fertilized egg through adulthood and eventually death Animals demonstrate two possible forms of development Indirect development Direct development
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Indirect Development When the juvenile has different morphology from adult Most invertebrates and some vertebrates (amphibians) Adults make large numbers of eggs, each with a small yolk (food storage) An immature larva emerges from egg Metamorphosis produces sexually mature adults
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larva adult adult larva
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Fig. 42-1
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Direct Development When the juvenile resembles the adult form Reptiles, birds, mammals, and some invertebrates Newborn is a sexually immature version of the adult Adults produce fewer offspring but are more developed and advanced at birth in terms of levels of development
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Reptiles, Birds, and Mammals Produce Similar Extraembryonic Membranes Reptiles, birds, and mammals produce amnionic eggs Embryo encased in protective shell and liquid-filled space Act as “private pond” Allows embryo to be less dependent on the external environment for development
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Reptiles, Birds, and Mammals Produce Similar Extraembryonic Membranes Amnionic eggs contain 4 extra embryonic membranes: Chorion: lines shell, involved in O2 and CO2 exchange with environment Amnion: encloses embryo in watery environment Allantois: surrounds and isolates wastes Yolk sac: contains stored food
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Reptile Mammal shell yolk sac allantois embryo amnion chorion
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How Does Development Proceed? Multistage process including: 1. Cleavage 2. Gastrulation 3. The formation of adult structures 4. Sexual maturation
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Cleavage Begins the Process Cleavage: Zygote divides mitotically without an increase in size A solid round ball of cells is formed (morula) The morula develops an internal cavity (blastocoel) Becomes a blastula
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Gastrulation Forms Three Tissue Layers An indentation (blastopore) forms and cells fold inward to form 3 layers: Endoderm : inner layer, digestive and respiratory tracts Mesoderm : middle layer; muscle and skeleton Ectoderm : outer layer; epidermis, circulatory, and nervous system A 3-layered embryo ( gastrula ) forms
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Gastrulation Forms Three Tissue Layers Table 42-1
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Author Animation: Overview of Animal Development
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Adult Structures Develop Organs form ( organogenesis ) from each embryonic cell layer Organs “sculpted” by programmed death of excess cells (1) some cells die unless they receive a chemical “survival signal” (only motor neurons that connect with muscles live) (2) some cells live unless they receive a chemical “death signal” (webbing in human toes)
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Sexual Maturation Is Controlled by Genes and the Environment Age and environment can stimulate hormone release and sexual development Nutrition and early sexual contact may accelerate maturation
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How Is Development Controlled? Through regulation of gene transcription
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CH_42_STUDENT_OUTLINE - Chapter 42: Animal Development What...

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