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.
The blastocyst is made up of three layers: 1  The ectoderm (which will become the skin and nervous system) 2  The endoderm (which will become the digestive and respiratory systems) 3  The mesoderm (which will become the muscle and skeletal systems).