Symbiotic Strategies
Lesson Overview

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GRADE LEVEL: Grades 9-12

TIME ALLOTMENT: Five 45-minute class periods

OVERVIEW: This lesson focuses on symbiosis and ecological relationships. Students will investigate the many ways that species that live in close proximity to each other might interact in an ecosystem, whether via competition or predation or through an ongoing symbiotic relationship such as mutualism, commensalism, or parasitism. Segments drawn from the NATURE episode The Secret Lives of Sharks and Rays and an online interactive featuring the malaria parasite will be used to provide specific examples of these interactions. The students will discover that all ongoing ecological relationships, even parasitic or predatory ones, have evolved over long periods of time and are integral to the maintenance of the balance and stability of an ecosystem.

The lesson then moves to a discussion of the ways that ecosystems can be thrown out of balance, often as a result of human action. A video segment showing the barbaric practices of the shark fin harvesting industry is used as a case in point of a human behavior that places a species in peril. Students will brainstorm ideas for restoring the relationship between sharks and humans to a healthy balance and will view an optimistic video segment featuring the ecotourism industry. As a culminating activity, students will select a case study for which to formulate an “Ecosystem Action Plan.” They will research an ecosystem thrown out of balance by human action and will prepare a presentation for the class describing the problem and suggesting three possible actions that could be taken to rectify the imbalance.

SUBJECT MATTER: Biology/ Living Environment


  • Define and describe the possible ecological relationships between species that coexist in an ecosystem
  • Classify specific interspecies relationships as mutualistic, commensal, or parasitic
  • Understand that ecological relationships evolved over time and are integral to maintaining the balance and stability of ecosystems
  • Name factors that can throw ecosystems out of balance
  • Describe human actions that have contributed to ecosystem imbalance and species decline
  • Suggest remedial actions to ameliorate human-caused imbalances in ecological relationships


National Science Education Standards


All students should develop understanding of:

The interdependence of organisms

  • Organisms both cooperate and compete in ecosystems. The interrelationships and interdependencies of these organisms may generate ecosystems that are stable for hundreds or thousands of years.
  • Human beings live within the world’s ecosystems. Increasingly, humans modify ecosystems as a result of population growth, technology, and consumption. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening current global stability, and if not addressed, ecosystems will be irreversibly affected.

New York State Regents Core Curriculum Alignments

Living Environment Core Curriculum

Standard 1: Students will use mathematical analysis, scientific inquiry, and engineering design, as appropriate, to pose questions, seeks answers, and develop solutions.

Key Idea 1: The central purpose of scientific inquiry is to develop explanations of natural phenomena in a continuing and creative process.

Performance Indicator 1.1: Elaborate on basic scientific and personal explanations of natural phenomena, and develop extended visual models and mathematical formulations to represent one’s thinking.

1.1a scientific explanations are built by combining evidence that can be observed with what people already know about the world.

Performance Indicator 1.2: Hone ideas through reasoning, library research, and discussion with others, including experts.

1.2a Inquiry involves asking questions and locating, interpreting, and processing information from a variety of sources.

1.2b Inquiry involves making judgments about the reliability of the source and relevance of information.

Standard 4: Students will understand and apply scientific concepts, principles, and theories pertaining to the physical setting and living environment and recognize the historical development of ideas in science.

Key Idea 1: Living things are both similar to and different from each other and from nonliving things.

Performance Indicator 1.1: Explain how diversity of populations within ecosystems relates to the stability of ecosystems.

1.1c In all environments, organisms compete for vital resources. The linked and changing interactions of populations and the environment compose the total ecosystem.

1.1d The interdependence of organisms in an established ecosystem often results in approximate stability over hundreds and thousands of years. For example, as one population increases, it is held in check by one or more environmental factors or another species.

1.1f Every population is linked, directly or indirectly, with many others in an ecosystem. Disruptions in the numbers and types of species and environmental changes can upset ecosystem stability.

Key Idea 6: Plants and animals depend on each other and their physical environment.

Performance Indicator 6.1: Explain factors that limit growth of individuals and populations.

6.1g Relationships between organisms may be negative, neutral, or positive. Some organisms may interact with one another in several ways. They may be in a producer/consumer, predator/prey, or parasite/host relationship or one organism may cause disease in, scavenge, or decompose another.

Performance Indicator 6.3: Explain how the living and nonliving environments change over time and respond to disturbances.

6.3c A stable ecosystem can be altered, either rapidly or slowly, through the activities of organisms (including humans), or through climatic changes or natural disasters. The altered ecosystem can usually recover through gradual changes back to a point of long-term stability.

Key Idea 7: Human decisions and activities have had a profound impact on the physical and living environment.

Performance Indicator 7.1 Describe the range of interrelationships of humans with the living and nonliving environment.

7.1a The Earth has finite resources; increasing human consumption of resources places stress on the natural processes that renew some resources and deplete those resources that cannot be renewed.

7.1c Human beings are part of the Earth’s ecosystems. Human activities can, deliberately or inadvertently, alter the equilibrium in ecosystems. Humans modify ecosystems as a result of population growth, consumption, and technology. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening current global stability, and if not addressed, ecosystems may be irreversibly affected.

Performance Indicator 7.3 Explain how individual choices and societal actions can contribute to improving the environment.



NATURE: The Secret World of Sharks and Rays, selected segments

Clip 1: “Shark and Turtle”

A battle between a loggerhead turtle and a shark.

Clip 2: “Unlikely travel companions”

A variety of symbiotic relationships exist between sharks and other marine species.

Clip 3: “Sharks and fishermen”

Sharks and fishermen compete for the same catch.

Clip 4: “Collapse of sharks”

This clip shows the destructiveness of the shark fin and shark cartilage industries.

Clip 5: “Sharks in our future”

If sharks can be shown to have value while alive, their future may be bright.

Access the streaming and downloadable video segments for this lesson at the Video Segments Page.

Web sites

Malaria games from
This site provides two games – the mosquito game and the parasite game – to help students understand the transmission of malaria.

Life Cycle of a Malaria Parasite Interactive Tour
This flash-based interactive tour provides a detailed explanation of each stage of the malaria parasite’s life cycle.


For each student:

  • Ecological Relationships Student Organizer (PDF) (RTF)

For each group (3-4 students):

  • Malaria Student Organizer (PDF) (RTF)
  • Computer with Internet access
  • Ecosystem Action Plan Student Organizer (PDF) (RTF)

For the teacher:

  • One computer with Internet access for class demonstration
  • Teacher Answer Key (PDF) (RTF)
  • Ecosystem Action Plan Assessment Rubric (PDF) (RTF)


Prior to teaching this lesson, you will need to:

Preview all of the video clips and Web sites used in the lesson.

Download the video clips used in the lesson to your classroom computer, or prepare to watch them using your classroom’s Internet connection.

Bookmark the Web sites used in the lesson on each computer in your classroom. Using a social bookmarking tool such as or diigo (or an online bookmarking utility such as portaportal) will allow you to organize all the links in a central location.

Gather the necessary materials as outlined above in “Materials” in advance of teaching the lesson.

Next: Proceed to Activities

  • Holly Dungan

    I thought this was a great video enhanced lesson to help students really get the picture of symbiotic relationships. It was as though a light bulb went on in most of my student’s head’s after this lesson.

  • Horoscope@Email

    Men have always been on a quest for love. Finding the true partner is never ending. Man has employed the help of witchcraft, and every conceivable ways just to find that elusive perfect partner in life. Some or a growing number have turned to astrology and the horoscope. Can it finally find the best partner and make things better?

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  • Maya Rainwater

    Is there anymore relasonships with sharks?

  • Mary Schappert

    I ended up integrating two of the lessons out of this unit into my curriculum- nice job. Wonderful resource.

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