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.
1 A blastocyst is made up of an inner group of cells with an outer shell. 2  The inner group of cells will become the embryo. The embryo is what will develop into your baby.  The outer group of cells will become structures, called membranes, which nourish and protect the embryo.