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Ecosystems

Nutrient cycling and the Gersmehl model

  • 3 things to know
  • Component 3 Section B

Overview

Nutrient cycle, three stores in the Gersmehl model and transfers between the stores in the Gersmehl model.

What you need to know

Answer each one before you reveal it.

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Key term

What is a nutrient cycle?

Key term

Name the three stores in the Gersmehl model.

Key term

Name the transfers between the stores in the Gersmehl model.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is a nutrient cycle?

    Model answer

    A nutrient cycle is the circulation of mineral elements between the living and non-living parts of an ecosystem. Nitrogen, phosphorus, potassium and calcium are the main nutrients involved.

  2. 2

    Name the three stores in the Gersmehl model.

    Model answer

    Biomass, litter and soil are the three stores. Circle size in the model is proportional to the amount held in each.

  3. 3

    Name the transfers between the stores in the Gersmehl model.

    Model answer

    Litter fall moves nutrients from biomass to litter, and decay moves them from litter to soil. Uptake by roots returns nutrients from the soil to the biomass.

  4. 4

    Name the inputs and outputs in the Gersmehl model.

    Model answer

    Precipitation adds nutrients from the atmosphere, and weathering of parent rock adds them from below. Losses occur through surface runoff from the litter and leaching from the soil.

  5. 5

    What is leaching?

    Model answer

    Leaching is the removal of soluble nutrients as water percolates down through the soil. Heavy rainfall in the tropics makes leaching rapid.

  6. 6

    What is litter fall?

    Model answer

    Litter fall is the transfer of dead leaves, branches and animal remains from the biomass to the ground surface. The rate depends on the type of vegetation and on the season.

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