5. Sodium-potassium pump: Protein mechanism found along the neuron membrane which transports 3 Na+ ions outside of the cell while also drawing 2 K+ ions into the cell; this is an active transport mechanism (requires energy (ATP) to function). 6.
What Is the Population Density of the United States? The population density of the United States is approximately 87.4 people per square mile, according to the 2010 U.S. Census. What Is the Most Densely Populated Continent? Perhaps not surprisingly, the most densely populated continent is Asia. Here are the population densities of the continents: 1  North America - 32 people per square mile. 2  South America - 73 people per square mile. 3  Europe - 134 people per square mile. 4  Asia - 203 people per square mile. 5  Africa - 65 people per square mile. 6  Australia - 6.4 people per square mile.
By 1900, the U.S.A. population jumped to 75,994,575. In 1920 the census counted more than a hundred million people (105,710,620). Another 100 million people were added to the United States population in just fifty years when the two hundred million barrier was reached in 1970 with 203,302,031 counted in the census. The 2000 Census counted a U.S.A. population of 281,421,906. Six years later the U.S. population had grown to 300 million.