A. how do the earth’s physical factors influence population density? when population growth increases in an area, what is happening to the birth rate and age structure of that population? (site 1)

The physical factors of the Earth affect population density by becoming a key determinant in which the individuals opts to live. The majority of the individuals desires to live in an area closer to their place of interest, where the climate is accessible and favorable. When there is an elevation in population, the rate of birth becomes high, and the age structure of the population becomes like a pyramid that signifies that more of the individuals in the population belongs to a younger age.  

Earth’s physical factors greatly influence population density

It is because on physical factors people depends. Physical factors that affect population density are water, climate, land shape, vegetation, soils and availability of natural resources etc. If these factors are present in large quantity then the population density will be higher and vice versa.

When population growth increases in an area, the population of a country has a triangle-shaped age structure which represents higher population of younger individuals and lower number of aged people.

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equal distribution i think.

the endomembrane system i think