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.
It is known as a blastocyst and has two parts: 1  An outer layer of cells, or trophectoderm, will form the placenta that supports the embryo as it grows inside the uterus. 2  An inner clump of cells, called the inner cell mass, is a ball of 10â20 cells. 3  These cells are undifferentiated, or unspecialized. An outer layer of cells, or trophectoderm, will form the placenta that supports the embryo as it grows inside the uterus. 2  An inner clump of cells, called the inner cell mass, is a ball of 10â20 cells. 3  These cells are undifferentiated, or unspecialized.