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Pond-water Populations
Administration Procedures
Grades 5-8 Performance Task
Contributed by: Oregon State Department of Education


Students will predict the effect of changing a component of a simple system such as a food web. Students will design and carry out an investigation to test how fertilizers or other factors affect the growth of algae or other organisms in aquarium or pond water.

The task assesses students' understanding of scientific inquiry including the following skills: observation, background research, scientific procedures (including investigation design, measurement techniques, and error analysis), data collection, data display, scientific questions, formulating a hypothesis, measurement skills.

This task is designed to take students approximately 10 hours, depending on viability of organisms in pond water, 1-2 weeks.

Overall Task Content Area:

Life Science

Specific Knowledge Areas:

Balance of populations in ecosystems

Performance Expectations:

  • conducting investigations
  • using equipment
  • gathering, organizing, and representing data
  • formulating conclusions from investigational data

National Science Education Standards:

8 A SI 1: Abilities necessary to do scientific inquiry: Grades 5-8

1.2 Design and conduct a scientific investigation. Students should develop general abilities, such as systematic observation, making accurate measurements, and identifying and controlling variables. They should also develop the ability to clarify their ideas that are influencing and guiding the inquiry, and to understand how those ideas compare with current scientific knowledge. Students can learn to formulate questions, design investigations, execute investigations, interpret data, use evidence to generate explanations, propose alternative explanations, and critique explanations and procedures.

1.4 Develop descriptions, explanations, predictions, and models using evidence. Students should base their explanation on what they observed, and as they develop cognitive skills, they should be able to differentiate explanation from description providing causes for effects and establishing relationships based on evidence and logical argument. This standards requires a subject knowledge base so the students can effectively conduct investigations, because developing explanations establishes connections between the content of science and the contexts within which students develop new knowledge.

1.7 Communicate scientific procedures and explanations. With practice, students should become competent at communicating experimental methods, following instructions, describing observations, summarizing the results of other groups, and telling other students about investigations and explanations.

8 C LS 4: Populations and ecosystems: Grades 5-8

4.4 The number of organisms an ecosystem can support depends on the resources available and abiotic factors, such as quantity of light and water, range of temperatures, and soil composition. Given adequate biotic and abiotic resources and no disease or predators, populations (including humans) increase at rapid rates. Lack of resources and other factors, such as predation and climate, limit the growth of populations in specific niches in the ecosystem.

(Use the "hot" link on the PALS home page to check the full text of related National Science Education Standards, if desired.)

National Council of Teachers of Mathematics:

AL1: Understand patterns, relations and functions:
Grades 6-8 f. represent, analyze, and generalize a variety of patterns with tables, graphs, words, and, when possible, symbolic rules

DAP3: Develop and evaluate inferences and predictions that are based on data:
Grades 6-8 c. use observations about differences between two or more samples to make conjectures about the populations from which the samples were taken

AL4: Analyze change in various contexts:
Grades 6-8 e. use graphs to analyze the nature of changes in quantities in linear relationships

PS2: Solve problems that arise in mathematics and in other contexts:
Grades 6-8

COM4: Use the language of mathematics to express mathematical ideas precisely:
Grades 6-8

REP3: Use representations to model and interpret physical, social, and mathematical ideas:
Grades 6-8

General Instructions to the Teacher:

This task is designed to take students 10 hours, depending on viability of organisms in pond water, 1-2 weeks. .

Students should be ready to work as soon as periods begin. A central supply area, if needed, should be easily accessible. All supplies should be clearly labeled.

Materials for " Pond Water Populations":

The student will need:

  • jars with lids
  • graduated cylinder or measuring cup
  • eye droppers
  • microscopes
  • tap water
  • thermometer
  • a light source
  • a heat source
  • aquarium water
  • slides & cover slips
  • liquid fertilizer
  • reference book for identification of protists, algae (optional)
  • materials from home

Advance Preparation:

  • Students will design an investigation to test how one variable affects the growth of organisms in water. The teacher sets up a control jar filled with half tap water (aged three days or de-chlorinated) and half aquarium (or pond) water which contains algae. The lid is secured on the jar and the jar is placed in indirect sunlight.
  • Students are then given materials to set up another jar and test how the change of one variable affects the growth of algae in the water. Students set up their own control jars.
  • Introduce pond as a closed ecosystem with biotic and abiotic factors. Ask: "Which factors influence or change the balance of populations in the closed ecosystem of the pond?"
    • Factors to consider:
    • light
    • temperature
    • introduction of a different organism (animal or plant)
    • nutrients
    • plants
    • type of container
    • location of measurement within container
    • size of container
  • Expand discussions into larger populations & discover limiting factors and biomes; endangered species; mycorrhyza; adaptations; natural selection; and evolution


  • Be careful.
  • Teachers and students should always exercise appropriate safety precautions and utilize appropriate laboratory safety procedures and equipment when working on science performance tasks.


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