I) The document discusses population explosion, which refers to the rapid increase in population that negatively impacts the environment. II) Reasons for population increase include improved medicine lowering death rates and birth rates rising. Immigration to developed nations has also increased population. III) Effects of overpopulation include increased air and water pollution, higher demand for food and resources, and more deforestation for housing and agriculture. Proper family planning and education are needed to control population growth in a sustainable way.