Chapter 37

Chapter 37 - Chapter 37: Animal Development What Is Animal...

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Unformatted text preview: Chapter 37: Animal Development What Is Animal Development? The process by which an animal proceeds from fertilized egg through adulthood and eventual death Animals demonstrate two possible forms of development Indirect development Direct development Indirect Development When the juvenile has different morphology from adult Most invertebrate and some vertebrate (amphibians) Adults make large number of eggs, each with a small yolk (food reserve) An immature larva emerges from egg Metamorphosis produces sexually mature adults larva adult adult larva larva adult adult larva What type of development is this? How does it differ from the other type? Direct Development When the juvenile resembles the adult form Reptiles, birds, mammals, and some invertebrates Newborn is a sexually immature version of adult Adults produce fewer offspring, but are more developed What type of development is this? How does it differ from the other type? Reptiles, Birds, and Mammals Produce Similar Extraembryonic Membranes Reptiles, birds, and mammals produce amnionic eggs Embryo encased in protective shell and liquid-filled space Acts as private pond Allows the embryo to be less dependent on the external environment for development Reptiles, Birds, and Mammals Produce Similar Extraembryonic Membranes Amnionic eggs contain 4 extra-embryonic membranes: Chorion : lines shell, involved with O 2 and CO 2 exchange with environment Amnion : encloses embryo in watery environment Allantois : surrounds and isolates wastes Yolk sac : contains stored food Reptile Mammal shell yolk sac allantois embryo amnion chorion Reptile Mammal shell yolk sac allantois embryo amnion chorion What role does each membrane play? Difference between shelled & non-shelled eggs? How Does Development Proceed? Multistage process including: 1. Cleavage 2. Gastrulation 3. The formation of adult structure 4. Sexual maturation Cleavage Begins the Process Cleavage : Zygote divides mitotically without an increase in size A solid round of ball of cells is formed ( morula ) The morula develops an internal cavity ( blastocoel ) Becomes a blastula 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 sceleton Ectoderm : outer layer; epidermis, circulatory, and nervous system A 3-layered embryo ( gastrula ) forms 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 muscle live) (2) Some cells live unless they receive a chemical death signal (webbing in human toes) Sexual Maturation Is Controlled by Genes and the Environment...
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Chapter 37 - Chapter 37: Animal Development What Is Animal...

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