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.
A cnidocyte is a type of venomous cell that is found in  coelenterates. A nematocyst, meanwhile, is a specialized organelle  found inside the nematocysts of coelenterates.