An organ is a structure made up of two or more tissue types that work together to perform a specific function.
A blastocyst is a ball of cells that develops early in a pregnancy, around five to six days after a sperm fertilizes an egg. It implants in your uterine wall and develops into an embryo, then a fetus.
Fertilization initiates the early phases of embryonic development. Fertilization is closely monitored to ensure that just one sperm unites with one egg. The zygote undergoes cleavage after fertilization to generate the blastula.
Members of major taxonomic groups of animals are classified as protostome or deuterostome based on how they grow as embryos.
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