1. A Population of Duckweed
Activity 2
A Population of Duckweed

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3. As you read the introduction, think about the following:
What is a population?
What is a community?
What examples of these terms did you read about in Activity 1, “Ecosystems and Change”?
Note that this Activity will continue for the length of the unit. Students do not need to delve deeper into population dynamics at this point, as that topic will be addressed in depth in later activities.

4. A population is a group of individuals of the same species that live in the same general area and are able to reproduce.
Populations of multiple species living in the same area are a community.

5. Challenge
How quickly can a population grow? How does the size of a population change through time?

6. Part A: Establishing a Baseline
Your group will be assigned an initial number of plants for your duckweed population.
Complete steps 1-6.
If appropriate, introduce the Organizing Data (OD) assessment variable here. More information on how to introduce and use this assessment variable is available in your Teacher’s Edition for this Activity and in Teacher Resources IV: Assessment.

7. Part B: Tracking the Population
Monitor your duckweed populations. Be sure to keep careful track of your population data.
At the end of the growing period, share your population data with the class.

8. Did the duckweed populations grow as expected?
How are population growth and sustainability related?
This class discussion should take approximately 20—25 minutes.

9. Analysis 1 Interpret your graph by answering the following questions:
A. What happened to your duckweed population over the study period?
B. Why do you think your population changed the way it did?
If appropriate, introduce the Analyzing Data (AD) assessment variable here. It can be used to score Analysis question one. More information on how to introduce and use this assessment variable, as well as a sample student response, is available in your Teacher’s Edition for this Activity and in Teacher Resources IV: Assessment.

10. Revisit the Challenge
How quickly can a population grow? How does the size of a population change through time?
Encourage students to compare the duckweed results to the different populations they have examined throughout the unit, particularly the different population graphs they looked at in Activity 14, “Investigating Population Growth Results.”

11. population growth rate
Key Vocabulary
carrying capacity
community
ecosystem
invasive species
limiting factor
organism
population
population growth rate
See Teacher Resources III: Literacy for more information on key vocabulary and the most effective strategies to enhance student vocabulary learning.
Note that bold words are formally defined in this activity. Words in regular font are used in the activity, but not formally defined. The definition of a key vocabulary word should not be discussed as a class prior to the formal definition being introduced.