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## World in the Balance

### Course, Subject

Biology/Living Environment, Math, Science & Technology

### Objective

To calculate how long it takes a country's population to double in size and to investigate factors affecting growth rate.

PBS - NOVA

### Duration

Two 40-minute class periods

### Materials

• Printable Teachers Guide
• copy of the "Double Up" student handout (PDF or HTML )
• copy of the "Calculating Population Growth" student handout (PDF or HTML )
• copy of the "Growth Rates Worldwide" student handouts (PDF or HTML)
• calculator
• graph paper

### Description

In this lesson, students use various science methods to figure out how long it will take the world's population to double. Population growth is an important topic, since we have to make sure that there are going to be enough resources to sustain a growing population.

### Website(s)

NOVA - World in the Balance

### Procedure

1. Since 1800, human population has grown from one billion to six billion people. Over the next half century, that number is projected to rise to nine billion. Tell students that in this activity they will investigate how long it takes the populations of different countries and territories to double.

• Before class, refer to the "Growth Rates Worldwide" student handouts to create a list of six to eight countries for each team. Try to make sure that each team's list includes countries with a range of growth rates and that the class data set represents countries on all of the continents (excluding Antarctica, which has no indigenous population). Choose countries with a growth rate of more than 0.044 to ensure that the rate will double in a reasonable time frame (Norway, with a rate of 0.044, takes 160 years to double; Japan, with a rate of 0.011, takes 630 years). See Activity Answer on page 5 for some sample doubling rates. Don't choose countries with negative growth rates as they will never double.

• Organize the class into teams of four and provide copies of the student handouts and other materials to each team. Assign each team its set of countries.

• Define the meaning of growth rate: the increase in a country's population during a period of time expressed as a percentage of the population at the start of that time. For example, if a town had 75 people in 1980 and 100 people in 1981, the growth rate for the year would be 33 percent.

• Explain to students that they will be using 10-year compounded growth rates to determine when each country's population will double. The 10-year growth rate is based on annual growth rates from 2003 from the U.S. Bureau of Census International Database. The starting population for each country will be 50 individuals, and for this activity, the growth rate will be assumed to be constant.

• Use the steps on the "Calculating Population Growth" student handout to demonstrate how to calculate future population sizes using the growth rate data.

• After teams have doubled the populations of all of their assigned countries, have teams graph their countries' population growths. Ask students to put the number of years on the x-axis in increments of 10 and the number of individuals on the y-axis in increments of five. Then ask students to draw the best-fit curve.

• If necessary, help students see that population growth is not a linear function; i.e., it produces a curved graph rather than a straight-line graph. Have teams answer the questions on their student handouts and hold a class discussion about their conclusions.

• Create a class histogram on the blackboard, posterboard, or an overhead to compare population doubling for each country. The histogram will need to have an upper time value of the country that takes the longest to double and should have an upper population size value of 150. Ask each team to represent each of its countries with a data point and an abbreviation of the country's name. Examine the histogram with students. Where do most of the countries in the class data set fall on the histogram? What else do students observe about the histogram? (Remind students that this does not represent all the world's countries.)

• Have students brainstorm a list of factors they think might affect growth rate (e.g., birthrate, death rate, access to medical care, nutrition, immigration, education, and income).

• Ask students to choose the four lowest and the four highest growth rate countries among their data sets or from the larger data table representing all the countries. Organize the class into teams belonging to two groups:
1. Have one group use print and Internet resources to research some factors that contribute to low growth rates and the possible environmental, social, and economic impacts on the people within those populations.
2. Have the other group research factors contributing to high growth rates and the corresponding impacts on people in its populations.
Have each team write a two-page report on its findings. Students can find some of this information in the CIA World Factbook, World Bank Group Data Profile tables, and CountryReports.org

• To conclude the lesson, discuss with students some of the factors affecting growth rates in the countries they researched. Do students see any commonalities among low-growth rate countries? Among high-growth rate countries? What are some of the differences between the factors among low-growth rate and high-growth rate countries?
• As an extension, have students choose countries with a negative growth rate and calculate the time it takes for a population to decrease to half its original size given an initial population size of 100 individuals. Then have them research reasons for negative growth rates.

Click on the link below to view the answer sheet for the activity. There is a sample graph and table to view as well.