Textbook Answer Key 
                    Textbook: Environmental Science 
                     
                    Chapter 1: Populations and Communities 
                      Section 1 Assessment 
                         1.  a. A habitat provides food, water, shelter and other things an organism needs to reproduce. b. The 
                              organism might die 
                         2.   a. Biotic factors are the living parts of a habitat that an organism interacts with; abiotic factors are 
                              the nonliving parts. b. Biotic—grass, birds, snake, badger, bison, prairie dogs; abiotic—soil, air, 
                              temperature, sunlight c. All organisms need water to carry on life processes. Plants and algae 
                              need sunlight to make food in photosynthesis. Other organisms depend directly or indirectly on 
                              the plants and algae for food.  
                         3.    a. Organism, population, community, ecosystem b. A community because a community consists 
                              of different populations living together c. Sample answer: If a population that is a food source for 
                              another population decreases, then the second population may decrease due to starvation.  
                    Section 1 Skills Lab 
                    Note: Store-bought potting soil may result in better, more uniform growth. 
                    Expected Outcome:  The plants will grow and thrive as long as not too little and not too much water is 
                    provided and that the plants receive sunlight. Plants may decline if they become too crowded or if 
                    nutrients in the soil are depleted. 
                    Analyze and Conclude:  
                         1.  Biotic factors: plants, any microscopic organisms in the soil; abiotic factors: gravel, soil, charcoal, 
                              water, air, light 
                         2.  Yes, light, an abiotic factor 
                         3.  Sample answer: The insect probably would not survive because it would eat the plants faster than 
                              they could grow. 
                         4.  Paragraphs should explain that the model shows how biotic and abiotic factors interact within an 
                              ecosystem. The model is closed, not as complex, contains fewer orgainisms than ecosystem. 
                     Design an Experiment:  Students should include both plants and animals in their ecosystem. Make sure 
                    students let the water stand uncovered for a few days before adding it to the ecosystem to get rid of 
                    

	
	








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                    Section 2 Assessment 
                       1.  a. Direct observation, indirect observation, sampling, mark and recapture b. Sampling; there would 
                            be too many mushrooms over too large an area to count them individually. 
        2.     a. Join—birth, immigration; leave—death, emigration b. 500 mice c. Some mice  may have 
          immigrated into the population 
        3.  3.   a. Food and water, space, weather  b. Any of the following: A population cannot grow beyond 
          the number that can be supported by the amount of food and water available, if organisms do not 
          have enough space, some will not be able to reproduce or survive; severe weather conditions can 
          kill members of a population. c. Sample answer: A severely cold winter could kill large numbers of 
          pigeons and reduce the population. 
        4.  Math Practice: If population size > carrying capacity, then population size will decrease. The 
          carrying capacity is the largest population an area can support. If there are more individuals than an 
          area can support, they won’t all survive so the population will decrease. 
       Section 2 Skills Lab 
           Note:  Tell students that each square represents a turtle and that some of the “turtles” have been     
          marked with a dot on one side. In Step 2, clarify that the 15 marked turtles refer to the bottom box 
          in the second column of the table, “Number Marked.” Students may assume that more turtles 
          recaptured with marks mean a bigger population, and fewer turtles with marks mean a smaller 
          population. Point out that the opposite can be true too, because unmarked turtles added (birth, 
          immigration) since the last count. 
          Expected Outcome: The number of marked turtles recaptured will vary. Therefore, students’ estimates 
          of the total population of Year 4 will also vary. 
          Analyze and Conclude:  
          1.  The estimated totals for Years 1-3 are 60, 48 and 40. Total number captured for Year 4 now 
            is 10. If 0 are recaptured, the total population cannot be determined. If 1 is recaptured, the 
            estimated total is 150; if 2, 75; if 3, 50; if 4, 38; if 5, 30; 6, 25; if 7, 21; if 8, 19; if 9, 17; if 10, 
            15.  
          2.  Year 4 will vary. 
          3.  The turtle population declined steadily from Year 1 to Year 3. Possible causes include limited 
            food, overcrowding, weather conditions, disease, predation and use of chemicals in the pond. 
          4.  Most students will probably predict a continuing decline in the population. 
          5.  Sample answer: Mark and recapture is useful because it allows scientists to study a 
            population over time. It is most useful when a population is fairly large, concentrated in one 
            area, and can’t be observed directly or indirectly. 
       More to Explore:  The estimated total population would increase to 88. 
       Section 3 Assessment  
          1.  a. Adaptations are the behaviors and physical characteristics that allow organisms to live 
            successfully in their environments. b. The sharp fangs enable the snake to bite into its prey c. 
            Snakes with sharper fangs could capture more prey and thus be able to survive and reproduce. 
            They pass this trait, sharp fangs, on to their offspring. 
          2.    a. Competition, predation, and symbiosis b. Possible answers: Competition—Two species 
            of birds that eat the same type of insects; predation—a snake eating a mouse; symbiosis—
            stinging ants nesting in an acacia tree 
          3.     a. Mutualism, commensalism and parasitism b. Mutualism—both species benefit; 
            commensalism—one species benefits and the other is      neither harmed nor helped; 
            parasitism—one species is helped and the other species is harmed. c. Parasitism is most 
            likely. One species is being harmed (the plant). 
       At- Home Activity 
          Feeding Frenzy: Organisms seen at the feeder will vary, but most students will see several 
          varieties of birds. Some may also see squirrels and other small animals. Suggest that students use 
          a bird guide to identify the birds they see.  
       Section 4 Assessment 
          1.  a. Primary succession is the series of changes that occur in an area where no soil or organisms 
            exist. Secondary succession is the series of changes that occur after a disturbance in an 
            existing ecosystem. 
            b. Before primary succession, not even soil is present, so the process is relatively slow. 
            Secondary succession generally occurs more rapidly than primary succession. 
            c. Secondary succession; before the sidewalk was built, soil was present and an ecosystem 
            had existed there. 
          At-home Activity 
          Community changes: Suggest that students take notes so that they will remember what the person 
          said. Have students present their summaries followed by a class discussion, focusing on any 
          examples of succession they identified. 
       Chapter 1 Review and Assessment 
          Organizing Information: a. direct observation b. indirect observation c. sampling d. mark-and- 
          recapture studies 
          Reviewing Key Terms 
          1.  b,  2. c, 3.  b, 4. c, 5. d 6. True, 7. False; population, 8. True, 9. False; competition 10. False; 
            host 
       Checking Concepts 
            11. Sample Answer: Biotic—trees, birds; abiotic—sunlight, soil 
            12. Plants and algae use the energy of sunlight to combine water and carbon dioxide to make 
            their own food during photosynthesis.  All consumers in that ecosystem feed directly or 
            indirectly on plants and algae. 
            13. Ecologists count the number of organisms in a small area, and then multiply by the 
            number of units in the entire area to estimate the entire population. 
            14. Give an example showing how space can be a limiting factor for a population. 
            15. What are two adaptations that prey organisms have developed to protect themselves? 
            Describe how each adaptation protects the organism. 
       Thinking Critically 
              16. Studying the entire population of the species usually is not possible because the population 
       is too large or spread out. 
                 17. Answers may include indirect observation (counting egg clusters), sampling (counting the 
       number in a small area and then multiplying by the number of units in the entire area), or mark and 
       capture 
               18. Organisms within a species share the same niche. Because individuals within a species are 
       more similar, they will share many of the same advantages and disadvantages in surviving in a certain 
       environment, which intensifies competition for the limited resources. Members of two different species 
       may share some parts of a habitat but do not usually compete for all resources in the same way. 
              19. Primary succession; there is no soil present and only pioneer organisms are shown. 
       Math Practice 
          20. If birth rate> death rate, population size increases. If death rate>death rate, population size 
       decreases. If immigration>emigration, population size increases. IF immigration