What are the three phases of early embryonic development in animals, and what key events occur during each phase?
What will be an ideal response?
The three phases of early embryonic development in animals are cleavage, gastrulation, and organogenesis. During cleavage, the zygote divides multiple times, producing a larger number of smaller cells. The result is a morula, a tightly packed ball of cells. Next, the morula develops a liquid-filled cavity (the blastocoel) and becomes a blastula. The second phase of early embryonic development is gastrulation, during which the three tissue layers–ectoderm, mesoderm, and endoderm–form. The gastrula also contains the archenteron, which will become the digestive tube. The third phase of early embryonic development is organogenesis. During organogenesis, the organs begin to form. In vertebrates, the first important event in organogenesis is the development of the neural tube, which represents the future brain and spinal cord.
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A. anal-oral sexual activity. B. insect vectors. C. contaminated food and water. D. infected animals.
The ____ phylum of seedless vascular plants has about 1000 known living species, including those in the genera
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a. Hepatophyta b. Monilophyta c. Bryophyta d. Lycophyta e. Anthocerophyta
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