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.
After fertilization, the cells divide for about five days to form a ball of cells called a blastocyst. The blastocyst is essentially a hollow ball of cells containing an inner clump that is known as the inner cell mass. This clump is what give rise to embryonic stem cells if grown in a dish.