The sites of hematopoiesis in the developing embryo in the correct temporal order is which of the following?
a. yolk sac, fetal liver, bone marrow
b. yolk sac, aorta, fetal liver
c. fetal liver, bone marrow
d. yolk sac, placenta, bone marrow

A.

Explanation: During embryogenesis, there are several sites for hematopoiesis. In week 3 it begins in the Yolk Sac, in Pander´s Island or Wolff´s Island. In week 5 hematopoiesis starts on the fetal liver and until week 12 hematopoiesis begins in the bone marrow, spleen, and thymus.

volcanoes (an event in the geosphere) release a large amount of particulate matter into the atmosphere. these particles serve as nuclei for the formation of water droplets (hydrosphere). rainfall (hydrosphere) often increases following an eruption, stimulating plant growth (biosphere).

which

what is a measurement of the earth’s history divided into time periods?

> fossil record <

sedimentary rock

> geologic time scale <

radioactive elements