A heat engine gives greater efficiency when run with a large temperature difference. In the oceans the temperature difference between surface and deep water is greatest in the tropics, although still a modest 20 to 25 Â°C.
A blastocyst is a cellular mass that forms early in the process of embryo development in mammals. In humans, this stage of embryogenesis occurs five days after fertilization, when there are fewer than 100 cells in the mass.
Within the blastocyst, there are two types of cells. In the interior is the inner cell mass, a portion of which will begin to divide at a very rapid pace and become the developing fetus. It is surrounded by a fluid-filled cavity called the blastocoele.