Fresh water is any body of water with a low salt concentration. Organisms in fresh water various challenges which includes; Osmotic concentration such that fresh water is permanently dilute and most cells cannot function at this concentration of ions. Varying temperatures, variation in oxygen levels and reproduction and life cycle due to permanence of habitat and physiological difficulty of regulating osmotic concentration in larvae and juveniles.
        
             
        
        
        
Answer:
Because of recombination and independent assortment in meiosis, each gamete contains a different set of DNA. This produces a unique combination of genes in the resulting zygote. Recombination or crossing over occurs during prophase 
 
        
             
        
        
        
The tectonic plates move and shift due to Mantle convection
Mantle convection is caused by the magma in the mantle of the earth constantly being cooled near the crust and heated the closer it gets to the core and like normal convection the cool magma sinks towards the crust and the hot magma rises to the crust. this happens in a circular motion causing the crust to shift with the magma 
 
        
             
        
        
        
There is only a single proton so nothing to com apart