In humans, the yolk sac is the
site of origin for blood cells and primordial germ cells. The human yolk sac is
a membrane located outside the embryo and it is connected by a tube through the
umbilical opening to the embryo's midgut. The yolk sac serves as an early site
for the formation of blood and in time, is incorporated into the primitive gut
of the embryo.
Explanation:
Cell membranes are selectively permeable. Some solutes cross the membrane freely, some cross with assistance, and others do not cross at all. A few lipophilic substances move freely across the cell membrane by passive diffusion. ... Large molecules do not cross intact cell membranes, except in certain special cases.
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They are known as evolutionary biologists. Strictly speaking, anthropology is split up into a number of disciplines - physical (sometimes known as biological) anthropology is the study of evolution as it relates to human beings. Further to this, scientists who study evolution in the fossil record are known as evolutionary palaeobiologists or simply palaeobiologists.
I think the answer you’re looking for is
D. Carbon, hydrogen, and oxygen
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