Asked in FBISE Biology 2022 SLO — Paper 1 2022

During human embryonic development, first site of RBC formation is

Correct answer: A. Yolk sac

  • A. Yolk sac
  • B. Allantois
  • C. Notochord
  • D. Blastocyst

Explanation

In the human embryo, the first site of blood formation is the yolk sac. Later in embryonic life, the liver becomes the most important red blood cell-forming organ, but it is soon succeeded by the bone marrow, which in adult life is the only source of both red blood cells and the granulocytes.

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About Embryonic Development

Embryonic development begins after fertilization with cleavage and formation of the morula and blastula, followed by gastrulation and the establishment of germ layers. It includes organ formation, tissue differentiation and early growth, rather than the later increase in size associated with postnatal development.

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