Interdependence in nature is illustrated by the transfer ...



Student Name: __________________________________________

Interdependence in nature is illustrated by the transfer of energy through trophic levels. The diagram below depicts the transfer of energy in a food web of an Arctic lake located in Alaska

a) Choosing organisms from four different trophic levels of this food web as examples, explain how energy is obtained at each trophic level.

b) Describe the efficiency of energy transfer between trophic levels and discuss how the amount of energy available at each trophic level affects the structure of the ecosystem.

c) If the cells in the dead terrestrial plant material that washed into the lake contained a commercially produced toxin, what would be the likely effects of this toxin on this food web? Explain.

Scoring Rubric:

|(A) TROPHIC LEVEL EXPLANATION - 3 possible points |Possible Points |

|List - example of four organisms correlated to proper trophic level. |1 |

|T.L #0 - (Detritivores) - Snails - larvae of Chironomids - Larvae of Caddis Flies | |

|T.L #1 - (Producers/autotrophs) Phytoplankton - Algae - Aquatic plants - Dead terrestrial plant |1 |

|T.L #2 - (First order or primary consumers) Zooplankton - Snails - Larvae of Chironomids - Larvae of Caddis Flies |1 |

|T.L #3 - (Second order consumers) Grayling - Sculpin- Lake Trout |1 |

|T.L #4 - (Third order consumers) Lake trout | |

|Producers obtain energy by photosynthesis |1 |

|Consumers obtain energy by digestion or assimilation (must link to specific consumer or level) |1 |

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|(B) ENERGY TRANSFER (Efficiency – effect on ecosystem structure) – 4 possible points |Possible Points |

|Note: Point must be earned from either Efficiency or Ecosystem Structure to earn 4 point maximum! | |

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|Efficiency | |

|• 10% rule or overall inefficient |1 |

|• why inefficient (e.g. cellular respiration, never eaten, wastes, heat, metabolism) |1 |

|• thermodynamics - increase in entropy |1 |

|• primary - net - gross productivity |1 |

|• life history - energy value varies per life stage |1 |

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|Ecosystem Structure | |

|• number of level thus indicated as 4-5 maximum |1 |

|• pyramid of energy |1 |

|• pyramid of biomass |1 |

|• pyramid of numbers |1 |

|• standing crop effect as related to phytoplankton and zooplankton |1 |

|(C) TOXIN FROM DEAD TERRESTRIAL PLANT (Effect) – 4 possible points |Possible Points |

|(1 pt) for each effect.... but must link one secondary effect to earn maximum |1 |

|(1 pt) for each correct interdependent pathway as a secondary effect | |

| |1 |

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