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| 1324653213 | Life Cycle of a Frog | The start of fertilization, the fusion of sperm and egg, which forms a zygote. Development proceeds with the cleavage stage, during which a series of cell divisions divide, or cleave, the zygote into a many-celled embryo. These cleavage divisions, which typically are rapid and lack accompanying cell growth, convert the embryo to a hollow ball of cells called a blastula. Next, the blastula folds in on itself, rearranging into a three-layered embryo, the gastrula, in a process called gastrulation. During organogenesis, the last major stage of embryonic development, local changes in cell shape and large-scale changes in cell location generate the rudimentary organs from which adult structure grow. Tail-bud embryo to larval stages to metamorphosis and finally to adult frog. (47.2) | 0 | |
| 1324653214 | Model Organisms | An organism selected for intensive scientific study based on features that make it easy to work with as in body size, life span, in the hope that findings will apply to other species. | 1 | |
| 1324653215 | Fertilization | The formation of a diploid zygote from a haploid egg and sperm. Molecules and events at the egg surface play a crucial role in each step of fertilization. | 2 | |
| 1324653216 | Acrosomal Reaction | The discharge of hydrolytic enzymes from the acrosome, a vesicle in the tip of a sperm, when the sperm approaches or contacts an egg. | 3 | |
| 1327359636 | Acrosome | A specialized vesicle at the tip of the sperm. | 4 | |
| 1327359637 | Fast Block to Polyspermy | By preventing additional sperm from fusing with the egg's plasma membrane, this depolarization acts as a fast block to polyspermy. | 5 | |
| 1327359638 | Cortical Reaction | A longer-lasting block to polyspermy is established by vesicles that lie just beneath the egg plasma membrane, in the rim of cytoplasm known as the cortex. Within seconds after a sperm binds to the egg, these vesicles, cortical granules, fuse with the egg plasma membrane. The secreted contents clip off sperm-binding receptors and cause the fertilization envelope to form. This acts as a slow block to polyspermy. | 6 | |
| 1327359639 | Slow Block to Polyspermy | The fertilization envelope and other changes in the egg's surface impede the entry of additional sperm nuclei and thus act s a longer-term slow block to polyspermy. | 7 | |
| 1327359640 | Fertilization in Mammals | Unlike sea urchins and most other marine invertebrates, terrestrial animals, including mammals, fertilize eggs internally. | 8 | |
| 1327359641 | Zona Pellucida | A sperm must travel through this layer of follicle cells before it reaches the zona pellucida, the extracellular matrix of the egg. Within the zona pellucida is a component that functions as a receptor for sperm. | 9 | |
| 1327359642 | Cleavage | Once fertilization is complete, many animal species undergo a succession of rapid cell divisions that characterized the cleavage stage of early development. | 10 | |
| 1327359643 | Blastomerers | Cleavage partitions the cytoplasm of the large fertilized egg into many smaller cells called blastomeres. | 11 | |
| 1327359644 | Blastula | A hollow ball of cells that marks the end of the cleavage stage during early embryonic development in animals. | 12 | |
| 1327359645 | Blastocoel | The fluid-filled cavity that forms in the center of a blastula. | 13 | |
| 1327359646 | Yolk | In frogs and many other animals, the distribution of yolk; stored nutrients, is a key factor influencing the pattern of cleavage. Nutrients stored in an egg. | 14 | |
| 1327359647 | Vegetal Pole | The point at the end of an egg in the hemisphere here most yolk is concentrated; opposite of animal pole. | 15 | |
| 1327359648 | Animal Pole | The point at the end of an egg in the hemisphere here the least yolk is concentrated; opposite of vegetal pole. | 16 | |
| 1327359649 | Holoblastic | Referring to a type of cleavage in which there is complete division of the egg; occurs in eggs that have little yolk; such as those of the sea urchin, or a moderate amount of yolk; such as those of the frog. | 17 | |
| 1327359650 | Meroblastic | Referring to a type of cleavage in which there is incomplete division of a yolk-rich egg, characteristic of avian development. | 18 | |
| 1327359651 | Regulation of Cleavage | The number of cleavage divisions varies among animals but appears to be controlled by a shared mechanism. | 19 | |
| 1327359652 | Morphogenesis | The development of the form of an organism and its structures. | 20 | |
| 1327359653 | Gastrulation | In animal development, a dramatic reorganization of cell and tissue movements in the hollow blastula-stage embryo folds inward producing a two-layered or three-layered embryo called a gastrula. | 21 | |
| 1327359654 | Gastrula | An embryonic stage in animal development encompassing the formation of three layers: ectoderm, mesoderm and endoderm. | 22 | |
| 1327359655 | Germ Layers | The cell layers produced by gastrulation are collectively called the embryonic germ layers. | 23 | |
| 1327359656 | Ectoderm | In the late gastrula, ectoderm form the outer layer. The outermost of the three primary germ layer in animal embryos; gives rise to the outer covering and, in some phyla, the nervous system, inner ear, and lens of the eye. | 24 | |
| 1327359657 | Endoderm | Lines the embryonic digestive compartment or tract. The innermost of the three primary germ layers in animal embryos; lines the archenteron and gives rise to the liver, pancreas lungs, and the lining of the digestive tract in species that have these structures. | 25 | |
| 1327359658 | Mesoderm | The middle primary germ layer in a triploblastic animal embryo; develop into the notochord, the lining of the coelom, muscles, skeleton, gonads, kidneys, and most of the circulatory system in species that have these structures. | 26 | |
| 1327359659 | Gastrulation in Sea Urchins | Gastrulation in the sea urchin begins at the vegetal pole of the blastula. | 27 | |
| 1327359660 | Archenteron | Extensive rearrangement of cells transforms the shallow depression into a deeper, narrower, blind-ended tube called the archenteron. | 28 | |
| 1327359661 | Blastopore | In a gastrula, the opening of the archenteron that typically develops into the anus in deuterostomes and the mouth in protostomes. | 29 | |
| 1327359662 | Gastrulation in Frogs | Begins when a group of cells on the dorsal side of the blastula begins to invaginate. | 30 | |
| 1327359663 | Dorsal Lip | The region above the blastopore on the dorsal side of the amphibian embryo. | 31 | |
| 1327359664 | Gastrulation in Chicks | The starting point for gastrulation in chicks is an embryo consisting of upper and lower layers; the epiblast and hypoblast, lying atop a yolk mass. | 32 | |
| 1327359665 | Primitive Streak | The pileup of cells moving inward at the blastoderm's midline produces a thickening called the primitive streak. | 33 | |
| 1327359666 | Gastrulation in Humans | Unlike the large, yolky eggs of many vertebrates, human eggs are quite small, storing little in the way of food reserves. | 34 | |
| 1327359667 | Blastocyst | The blastula stage of mammalian embryonic development, consisting of an inner cell mass, a cavity, and an outer layer, the trophoblast. In humans, the blastocyst forms 1 week after fertilization. | 35 | |
| 1327359668 | Inner Cell Mass | An inner cluster of cells at one end of a mammalian blastocyst that subsequently develops into the embryo proper and some of the extraembryonic membranes. | 36 | |
| 1327359669 | Trophoblast | The outer epithelium of a mammalian blastocyst. It forms the fetal part of the placenta, supporting embryonic development but not forming part of the embryo proper. | 37 | |
| 1327359670 | Extraembryonic Membranes | One of four membrane; yolk sac amnion, chorion, and allantois, located outside the embryo that support the developing embryo in reptiles and mammals. | 38 | |
| 1327612174 | Amniotes | Member of a clade of tetrapods named for a key derived character, the amniotic egg, which contains specialized membranes, including the fluid-filled amnion, that protect the embryo. Amniotes include mammals as well as birds and other reptiles. | 39 | |
| 1327612175 | Organogenesis | The process in which organ rudiments develop from the three germ layers after gastrulation. | 40 | |
| 1327612176 | Notochord | A longitudinal, flexible rod made of tightly packed mesodermal cells that runs along the anterior-posterior axis of a chordate in the dorsal part of the body. | 41 | |
| 1327612177 | Neural Tube | A tube of infolded ectodermal cells that runs along the anterior-posterior axis of a vertebrate, just dorsal to the notochord. It will give rise to the central nervous system. | 42 | |
| 1327612178 | Neural Crest | In vertebrates, a region located along the sides of the neural tube here it pinches off from the ectoderm. Neural crest cells migrate to various parts of the embryo and form pigment cells in the skin and parts of the skull, teeth, adrenal glands, and peripheral nervous system. | 43 | |
| 1327612179 | Somite | One of a series of blocks of mesoderm that exist in pairs just lateral to the notochord in a vertebrate embryo. | 44 | |
| 1327612180 | Mechanisms of Morphogenesis | Morphogenesis is a major stage of development in both animals and plants, but only in animals does it involve the movement of cells. | 45 | |
| 1327612181 | The Cytoskeleton in Morphogenesis | The cytoskeleton directs a different type of morphogenetic movement in promoting elongation of the archenteron in the sea urchin embryo. | 46 | |
| 1327612182 | Convergent Extension | A rearrangement of the cells of a tissue layer that causes the heet to become narrower; converge, while it becomes longer; extends. | 47 | |
| 1327612183 | Programmed Cell Death | Just as certain cells of the embryo are programmed to change shape or location, others are programmed to die. | 48 | |
| 1327612184 | Apoptosis | A type of programmed cell death, which is brought about by activation of enzymes that break down many chemical components in the cell. | 49 | |
| 1327612185 | Determination | The progressive restriction of developmental potential in which the possible fate of each cell becomes more limited as an embryo develops. At the end of determination, a cell is committed to its fate. | 50 | |
| 1327612186 | Differentiation | The process by which a cell or group of cells become specialized in structure and function. | 51 | |
| 1327612187 | Fate Mapping | One way to trace the ancestry of embryonic cells is direct observation through the microscope. | 52 | |
| 1327612188 | Fate Maps | Diagrams showing the structure arising from each region of an embryo. | 53 | |
| 1327612189 | Axis Formation | A body plan with bilateral symmetry is found across a range of animals, including nematodes, echinoderms, and vertebrates. The right-left axis is largely symmetrical, as the to sides are roughly mirror images of each other. | 54 | |
| 1327612190 | Restricting Developmental Potential | The range of structures to which it can give rise. | 55 | |
| 1327612191 | Totipotent | Describing a cell that can give rise to all parts of the embryo and adult, as well as extraembryonic membranes in species that have them. | 56 | |
| 1327612192 | Pattern Formation | The development of an animal's spatial organization, the arrangement of organs and tissues in their characteristic places in three-dimensional space. | 57 | |
| 1327612193 | Positional Formation | The molecular cues that control pattern formation. | 58 | |
| 1327612194 | Apical Ectodermal Ridge | A thickened area of ectoderm at the tip of the bud. | 59 | |
| 1327612195 | Zone of Polarizing Activity | A block of mesodermal tissue located underneath the ectoderm where the posterior side of the bud is attached to the body. | 60 | |
| 1327612196 | Cilia and Cell Fate | Ciliary function is essential for proper specification of cell fate in the human embryo. | 61 |
