Answer:
Population density naturally varies a great deal within each country according to climatic conditions, topography, mineral deposits, rainfall, soil cultivation, etc
Cancer or cell death could happen I got it right in my test
Cellular differentiation is the process that results in the formation of more specialized cells that are ought to perform specific function in the body. Undifferentiated cells tend to perform more than one function like stem cell. Example of differentiated cell is liver cell, heart cell etc.
Differentiation process occurs many time during the growth of the organism to form organs and hence, organ system. Differentiation is a must process for the full development of an organism.