Passive transport vs active transport sounds like what it is. In passive transport, there is no energy needed to get the molecules across the cell membrane, whereas in active transport, energy is expended getting the molecules across the membrane. Basically in active transport the ATP in your cells gives one of it’s phosphates to the transport proteins in your cell membrane and it lets select molecules in. These molecules are moving through a concentration gradient during active transport(with the help of ATP), from an area of low concentration to an area of high concentration.
The fertilized egg begins a rapid descent to the uterus. The period of rest in the tube appears to be necessary for full development of the fertilized egg and for the uterus to prepare to receive theegg. ... At the end of this transition period, the embryo becomes a mass of very organized cells, called a blastocyst.
