After this activity, student should be able to:

• Describe the biosphere and discuss its components.
• Describe how population and population density affect an organism.
• Identify how engineers apply knowledge of population density to the development of space, such as land and building capacity.

Let's review what the biosphere is. It is the part of our planet where life is found, and includes living things like animals and plants, as well as nonliving things, like air, soil, water and sunlight. The Earth's biosphere contains different types of environments and ecosystems, such as tropical rain forests, deserts, grasslands and arctic climates. Can you think of some living and nonliving things that you could find in these different environments? (Possible answers: Rocks, soil, sunlight, water, plants and animals.)

Let's brainstorm on all the types of organisms you might see on a walk in a nearby park. (Write a list that is visible for the entire class, such as on the classroom board or overhead projector.) These organisms share some things. What do they share? They share the same space and air and water and food resources. How does the number or amount of organisms in a space affect each organism? (Possible answers: Results in fewer resources for each organism, including food, space to live, energy, air, etc.)

The sharing of space and resources happens in all environments. For example, what happens if there is only one dog in a house that drinks from a water bowl? What happens to the water if you have three dogs drinking form that same water bowl? That's right; the amount of water per dog is decreased. It may even run out. What might happen to the space in this classroom if the number of students were doubled or tripled? Would that put a strain on any of our resources, such as chairs, desks or paper? Do you think there is a limit to the number of students permitted in a classroom at one time? Why? (For example, for safety in an emergency evacuation, to keep from over heating the room [body heat from so many people], etc.)

The amount of organisms in a particular environment is called its population. Populations are made up of all the members of a species living in the same place at the same time. Population density is the population per unit of land area; for example, persons per square kilometer of land. Population density helps us describe how much space an organism has in that unit of land, which helps us understand how the resources (water, food, etc.) might be divided. Engineers need to know about the population distribution and density to design a community's areas and systems, such as transportation (roads, highways, traffic, parking, bridges), structures (homes, schools, farms, offices, stores), parks and open space, public works infrastructure (power, water, sewers, landfills), and resources (how much water is available for a community to drink and use). During the design and planning phases, safety engineers also review building plans and building safety code requirements to set occupancy limits for safe emergency evacuation.

Who knows what a biodome is? A biodome is a closed structure that contains an environment. Engineers create and study biodomes to better understand how things interact with each other in a specific environment. Biodomes contain both biotic (living) and abiotic (nonliving) factors, just like the biosphere, and are constructed to represent a specific ecosystem or environment, such as a desert or tropical rain forest. A biodome acts as an artificial habitat for the plants and organisms that the engineer decides to place within it. Engineers want to determine the conditions in which a biodome environment is in equilibrium, or in a state in which all the different living and nonliving things exist in a balance, without any disappearing.

Let's consider a biodome of a tropical environment about the size of a shoebox. Could you put a population of 10 medium-sized insects in it? 10,000? What is the number of insects that you think could comfortably survive within it? What might happen if you have too many insects (too large an insect population)? (Possible answers: The insects may eat all of the food or use all of the resources, resulting in insect death.)

Now, let's think about our own classroom — a room that we share with each other and the teacher. What is the population of our class? How much space does each person have in our classroom? What might happen if we try to fit the entire school into our classroom? Well, today we are doing an activity to find out the population density and exactly how much space each person has in your classroom right now.

Before the Activity

With the Students

Help speed along the measuring process by first showing students a good way to measure the classroom with their meter sticks. Then they can get to the rest of the worksheet sooner.

Some students require more help than others in performing the worksheet calculations. They also may need an explanation of the units, how to write them, and what they mean. Take time to discuss the units (meters and square meters), write them on the board and have students provide examples, for example, velocity can be measured in meters per second.

Lead the class in several example population density problems. For example, if a student and his/her sibling were together in their living room with the dimensions of 5 meters by 5 meters, find the population density of the room. Write the problems on the board and label the units for the class to refer to during the activity.

It may be necessary to bring the unit of land into perspective, for example, an acre (~4,047 square meters) is about the size of the playground's soccer field (90 x 45 meters = 4,050 square meters).

Have students approximate other population densities, such as those of their city, county, state or country. What would an engineer do with this information?

Have the class consider how population density and distribution affects different activities. For example, have the students discuss how much food their cafeteria makes each day, how many books are available in the library, how many grocery stores in a town, or how many parking spaces near a sports arena.

Have students make measurements and counts around their school, and calculate population densities, for example, bicycles in the bike rack area, cars in the parking lot, drinking fountains in the school building, people in an school assembly in the auditorium or cafeteria, or trash cans on the school grounds.

Bush, Mark B. Ecology of a Changing Planet, Second Edition. Saddle River, NJ: Prentice Hall, 2000.

Dictionary.com. Lexico Publishing Group, LLC. Accessed October 9, 2006. (Source of some vocabulary definitions, with some adaptation) http://www.dictionary.com

World Population Trends, World Population Information. Last modified August 24, 2006. Population Division/International Programs Center, U.S. Census Bureau. Accessed October 9, 2006. http://www.census.gov/ipc/www/world.html