Organisms and Their Environment

Keywords: populations, biosphere, communities, ecosystems; Grade Level: fifth through eighth grade; Total Time for Lesson: 3 days; Setting: classroom

Concepts to Be Covered

  • The biosphere is the part of earth where all life is found, and it consists of biotic (living) factors as well as abiotic (nonliving) factors such as air, soil, water, and sunlight.
  • Populations are made up of all the members of a species living in the same place at the same time. A community includes all the populations of the area. The community and the abiotic factors make up the ecosystem.
  • An organism lives in its habitat within a community. The role or job of an organism within a community is its niche.

Goals for the Lesson

  • Students will be able to identify the biotic and abiotic factors in the biosphere.
  • Students will be able to describe the characteristics of populations.
  • Students will be able to compare a species' habitat and its niche within a community.

Subjects: science, math

Day 1


  1. Students will be given firsthand experience in determining the density of a population. Tell students they will learn more about populations and how populations interact with other populations and nonliving things in the environment.
  2. Have students brainstorm on all the types of organisms they might see on a walk in the woods. List them on the board. Tell students that these organisms share space, food, and nesting sites. Ask, "How does the number of individuals in a group affect each organism?" Tell them that they share their science classroom with other individuals. Ask, "How much space does each person have in your science classroom?" Tell students that they will be doing an activity to find out how much space each person has in your classroom.
  3. Have students work in pairs. Each pair needs one meterstick. One student should measure and the other should record. Then they can find the answers to the questions together. Give the following directions: Use a meterstick to measure the length and width of the classroom. Multiply the length and width to get the area of the classroom in square meters. Count the number of individuals in your class. Divide the number of square meters in the classroom by the number of individuals. How much space does each person have? Predict the amount of space each person would have if your class size doubled.
  4. If the student population is 30 and the classroom size is 240 square meters, then each student would have 8 square meters. Explain that if the population density of the classroom doubled, each person would have only 4 square meters. However, to calculate population density you divide the number of individuals in the population by the area to get individuals per unit area. In this case the population density would be:

30 students/240 square meters = 3 students/24 square meters = 1/8 = 0.125 students/square meter.

  1. Discuss the answers to the questions. Tell the students that since we now know that the number of individuals in a population determines the amount of space each has, we are ready to learn more about populations and how organisms and environments interact.

Lesson Procedure

  1. Define population on the board. Have students list the populations of living things that might be in the area where they live. List the characteristics of populations and explain each: population density, spacing and size.
  2. Show a graph of the world's population over time to illustrate how population size changes.
  3. Have students study the table below and explain what may have happened to change the population density.
Year Deer (in thousands) per 400 hectares
1905 5.7
1915 35.7
1920 142.9
1925 85.7
1935 25.7


Ask the following questions and discuss:

  • What advantages does a population that feeds on several kinds of organisms have over a population that eats only one kind of plant or animal?
  • Which would be easier, finding the size of a plant population or finding the size or an animal population?


Assign students to calculate the population density of Erie and compare it to New York City.

Day 2


  1. Show students models of the earth and moon.
  2. Ask them to compare and contrast the surfaces of each.
  3. Discuss that land, water, and air on earth is where all life exists and is called the biosphere, which extends from the deepest oceans to the upper atmosphere.


  1. Explain that in the biosphere living things depend upon and interact with each other and with the nonliving things in their environment.
  2. Show a picture of a pond.
  3. Ask students to identify the living and nonliving factors and list them on the board.
  4. Classify each as biotic or abiotic.
  5. Discuss that each species in the pond makes up a population; all the populations make up the community; the community and abiotic factors may up the ecosystem.
  6. Divide students into groups of four. Give each group four circles ( 2 in, 4 in, 6 in, and 8 in) of different colored construction paper, glue, and the labels population, ecosystem, individual and community.
  7. Ask each group to place the terms on the outside edges of the circles, the term that includes all of the others should be on the largest circle .
  8. Place the others in order until the smallest group is in the center circle. Discuss each group's results. See diagram.


Ask the following questions and discuss:

  • Name five biotic and five abiotic factors in the biosphere.
  • Ecosystems such as coral reefs are in a delicate balance. Hypothesize what would happen to that balance if one abiotic factor such as amount of sunlight suddenly changed.


  1. Assign students to find out how the eruption of Mt. St. Helen in Washington state in 1980 affected the population densities of area organisms.
  2. Have students choose an ecosystem and make a collage that shows the living and nonliving things that interact in it.

Day 3


  1. Tell students that each person lives in a population as part of a community. Have each student describe his/her population, community, habitat, and niche. (Students may describe themselves as humans, living in towns, inside houses and as students, brothers, sisters, etc.) Discuss answers.


  1. Divide students into groups of four and assign each group a different ecosystem that they may be familiar with such as a stream, garden plot or empty lot.
  2. Have each group identify the organisms found there. Have them make a list of all the populations present and infer the niche of each species. Each group will then draw their ecosystem and share it with the class.
  3. Explain the relationship between population, community and ecosystem. Point out that populations interact to make a community. Stress that communities and nonliving things make up the ecosystem.


Ask the following questions and discuss:

  • How is the habitat of a squirrel different from its niche?
  • What kinds of organisms live in a human habitat?
  • What might happen if two populations occupied the exact same niche?
  • Describe the difference between a population and a community.


Merrill Life Science (1995). New York: Glencoe Division of Macmillan/McGraw-Hill Publishing Company.


Rosemary Grove, Cathedral Center