Reading Essentials for Biology Glencoe (794133), страница 12
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What words come to mind when you hear the term humanpopulation? Think about some of the concepts you learned in the previous section. Do they apply tohuman populations? Write your thoughts on the lines below.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnIdentify theMain Point Skim the sectionand highlight the main ideaof each paragraph.A census, which counts all the people who live in a country, istaken every ten years in the United States.
It also collects information about where people live and their economic condition.The United Nations keeps similar information for each countryin the world. The study of information about human populationsis called demography (de MAH gra fee). Information about populations includes size, density, distribution, movement, birthrates,and death rates.Human population has grown at a rapid rate in recent years.Scientists estimate that it took from the time of the first humansto 1800 for the world human population to reach 1 billion.
In1930, there were 2 billion people. In 1999, there were 6 billionpeople. If this rate continues, scientists estimate that in 2050there will be 9 billion people on Earth.What factors affect the growth of humanpopulations?1. How are humans differentfrom other populations?________________________________________________________________________40Chapter 4Remember that populations can keep growing as long as theyhave enough resources. Human populations are different fromother populations because humans can consciously change theirenvironment.
Humans can grow their own resources by farmingand raising farm animals. Humans can control limiting factors suchas disease. Many illnesses that killed people in the past can now betreated with medicine. People live longer and they are able to produce more children. The children grow up and they produce morechildren, causing the population to grow.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.World PopulationNameDateClassSection4.2Human Population, continuedHow can you determine the growth rateof a population?To determine the growth rate of a population, you need toconsider different factors.
Those factors are illustrated in thechart below.Factors that Addto a PopulationFactors that Subtractfrom a PopulationBirthsDeathsPeople moving into a populationPeople moving out of a populationThe birthrate is the number of live births per 1000 people ina given year. The death rate is the number of deaths per 1000people in a given year. Keeping track of people who move intoand out of a population is not always possible. As a result, it iseasier to use the birthrate and death rate to calculate the Population Growth Rate (PGR).
The following formula is used tocalculate PGR:Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Birthrate – Death Rate = Population Growth RateWhen the birthrate of a population is the same as the deathrate, then the PGR is zero. It is important to remember, though,that if the PGR is zero, it does not mean that the population isremaining exactly the same. It means that new people are enteringthe population (through birth) at the same rate that people areleaving the population (through death).
The population is changing, but it is stable. Your school population will help you understand this idea. If new students arrive at the same rate that studentsgraduate, the population of your school remains the same eventhough the students that make up the population change each year.What is the effect of a positive growth rate?When the PGR is above zero, or positive, it means that morepeople are entering the population than are leaving. The population is growing. The PGR is positive when there are more birthsthan deaths in the population. A PGR also can be less than zero,or negative. This happens when there are more deaths than births.Doubling time is the time needed for a population to doublein size.
Doubling only happens with growing populations. A negative growth rate means that a population will not double. A slowgrowth rate means that it will take a long time for the populationto double. Doubling time can be calculated for a population.READING ESSENTIALS2. Interpret If the population growth rate is positive it means there are(Circle your choice.)a. more births thandeaths.b. more deaths thanbirths.Chapter 441NameDateClassSection4.2Human Population, continued80+75–7970–7465–6960–6455–5950–5445–4940–4435–3930–3425–2920–2415–1910–145–90–4You may have filled out a survey that asked if you were betweenthe ages of 10 and 14 or between the ages of 15 and 19.
Youranswer tells where you are in the age structure of the population.Age structure refers to the number of people at each differentage level. Scientists are interested in the ages of the population,and how many people are males and how many are females. Thisinformation tells the scientists if the population is stable, growing,or becoming smaller.Scientists put age inforPopulation Distribution Per Age Range for Several Countriesmation into a graph calledan age structure graph. TheStable growthRapid growthSlow growthgraph shows at a glance theMaleages of the largest group inFemaleReproductivethe population.
When ayearslarge amount of the population is made up of children, then the populationis experiencing rapidgrowth. When there aremore adults than children,the population is declining.When the amount of peo4 2 0 2 4 8 6 4 2 0 2 4 6 8 12 10 8 6 4 2 0 2 4 6 8 10 12ple in the different agePopulation (percent of total for each country)levels is about equal, thepopulation is stable.Does environment affect population growth?3. Interpret a Graph Inthe age structure graphabove, which country hasthe smallest percentageof people in the 80+ agegroup? (Circle yourchoice.)a. stable growth countryb.
rapid growth countryc. slow growth country42Chapter 4The needs of human populations are different all over theworld. Some are concerned with basic needs such as food andwater. Some need to maintain the healthy conditions they alreadyhave.
Sometimes populations grow too fast. In these populations,there is not enough food, water, or living space for everyone.Maybe the population creates more waste than can be handled.Sometimes the conditions of the environment cause disease tospread, or pollution affects the water. These things affect the stability of human populations. The environment plays an importantpart in the growth of populations.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.AgeWhat is the age structure of a population?NameDateClassSection4.2Human Population, continued◗ After You ReadMini Glossaryage structure: proportions of a population thatare at different age levelsbirthrate: number of live births per 1000 population in a given yeardeath rate: number of deaths per 1000 population in a given yeardemography (de MAH gra fee): study of population characteristics such as growth rate, agestructure, and geographic distributiondoubling time: time needed for a population todouble in size1.
Review the terms and their definitions in the Mini Glossary above. Circle the four key termsthat scientists use to gather important information about a population.2. Use the table below to review what you have read. Place each of the characteristics from thelist that follows the table under the correct heading.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Increasing PopulationDecreasing PopulationWill not have doubling timePositive growth rateMore adults than childrenMore children than adultsWill have doubling timeNegative growth rateVisit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about human population.READING ESSENTIALSChapter 443NameDateClassSection5.1 Vanishing Species◗ Before You ReadSC.G.2.4.5 The student understands that the amount of life any environment can supportis limited and that human activities can change the flow of energy and reduce the fertilityof Earth.
Also covers SC.D.2.4.1, SC.G.1.4.1, SC.G.2.4.2, SC.G.2.4.6Dinosaurs are probably the most familiar organisms that are extinct, or no longer exist. Many plantsand animals that are alive today are in danger of dying out. Think of one animal and one plant thatwould change the way you live if they became extinct. Write the names of those organisms on thelines below and tell why you think each is so important.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnIdentifyThreats to BiodiversityHighlight all the threats tobiodiversity that you readabout in this section.1.
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