What is the difference between population growth and population size?

Correct answer: Size is the number at one time, while growth is the change over time

The correct answer is A: population size is the number of people present at a particular time, whereas population growth is the increase or decrease in that number over a period. For example, if a town has 20,000 people in a given year, 20,000 is its population size at that time. If it has 22,000 people five years later, the change of 2,000 represents growth. Growth is affected by births, deaths, immigration, and emigration. Option A is correct because it separates a population’s amount from the change in that amount. Option B is wrong because population concepts describe people, not weather. Option C is wrong because birth rate is only one factor affecting growth, and a river is unrelated. Option D is wrong because size and growth answer different questions: “How many people are there?” and “How has the number changed?” Memory cue: size is a snapshot; growth is a moving change.