There are several stages but the crossing over starts on the second stage. And the actual crossing sides happens on the following stage. Hope this helped :)
Physical Factors:Physical factors that affect population distribution include altitude and latitude,relief,climate,soils,vegetation,water and location of mineral and energy resources.
Unicellular organisms are made up of only one cell that carries out all of the functions needed by the organism, while multicellular organisms use many different cells to function. Unicellular organisms include bacteria, protists, and yeast.
Usually simply by mixing with more solvent like adding more water to the solution. To dilute a solution means to add more solvent without the addition of more solute.