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.
3. The blastocyst has an outer-layer of cells called the trophoblast, which will eventually form the protective placenta. Inside the trophoblast is a group of cells called the inner cell mass. The organism in a stage between zygote to fetus is called an embryo* and the cells are called embryonic stem cells.he blastocyst has an outer-layer of cells called the trophoblast, which will eventually form the protective placenta. Inside the trophoblast is a group of cells called the inner cell mass. The organism in a stage between zygote to fetus is called an embryo* and the cells are called embryonic stem cells.