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Ecosystem - Ecosystem Structure and Function

Grade 12CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Ecosystem Structure: Includes both biotic (living organisms) and abiotic (physico-chemical) factors. A characteristic physical structure is Stratification, which is the vertical distribution of different species occupying different levels, such as trees in the top layer and herbs at the bottom.

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Productivity: The rate of biomass production. Gross Primary Productivity (GPPGPP) is the total organic matter produced during photosynthesis. Net Primary Productivity (NPPNPP) is the remaining energy after respiration (RR).

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Secondary Productivity: This is defined as the rate of formation of new organic matter by consumers.

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Decomposition: The process where decomposers break down complex organic matter (detritus) into inorganic substances like CO2CO_2, H2OH_2O, and nutrients. It involves fragmentation, leaching, catabolism, humification, and mineralization.

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Energy Flow: Energy flow in an ecosystem is unidirectional. According to the 10%10\% Law, only 10%10\% of the energy is transferred to each higher trophic level; the rest is lost as heat.

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Ecological Pyramids: These represent the relationship between producers and consumers at different trophic levels in terms of number, biomass, and energy. While most pyramids are upright, the Pyramid of Biomass in the sea is often inverted (Phytoplankton << Fish).

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Pyramid of Energy: This pyramid is always upright because energy is invariably lost as heat when it flows from one trophic level to the next, adhering to the laws of thermodynamics.

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Nutrient Cycling: Also known as biogeochemical cycles, these involve the movement of nutrient elements through the various components of an ecosystem. They are categorized into Gaseous (e.g., Nitrogen, Carbon) and Sedimentary (e.g., Phosphorus, Sulphur) cycles.

📐Formulae

NPP=GPP−RNPP = GPP - R

Percentage of energy transfer=Energy at higher trophic levelEnergy at lower trophic level×100\text{Percentage of energy transfer} = \frac{\text{Energy at higher trophic level}}{\text{Energy at lower trophic level}} \times 100

Productivity units=g m−2 yr−1 or kcal m−2 yr−1\text{Productivity units} = g \, m^{-2} \, yr^{-1} \text{ or } kcal \, m^{-2} \, yr^{-1}

💡Examples

Problem 1:

In a pond ecosystem, if the producers capture 1,000,000 J1,000,000 \, J of sunlight energy, calculate the energy available to the tertiary consumers following the 10%10\% Law.

Solution:

  1. Sunlight available: 1,000,000 J1,000,000 \, J
  2. Energy captured by Producers (1%1\% of sunlight): 1,000,000×0.01=10,000 J1,000,000 \times 0.01 = 10,000 \, J
  3. Primary Consumers: 10,000×0.10=1,000 J10,000 \times 0.10 = 1,000 \, J
  4. Secondary Consumers: 1,000×0.10=100 J1,000 \times 0.10 = 100 \, J
  5. Tertiary Consumers: 100×0.10=10 J100 \times 0.10 = 10 \, J

Explanation:

Plants capture only about 1%1\% of the incident solar radiation. Thereafter, as per Lindeman's 10%10\% law, only 10%10\% of the energy stored in one trophic level is passed to the next.

Problem 2:

Calculate the Net Primary Productivity (NPPNPP) of a forest ecosystem where the Gross Primary Productivity (GPPGPP) is 2,500 kcal m−2 yr−12,500 \, kcal \, m^{-2} \, yr^{-1} and the respiration loss is 30%30\%.

Solution:

GPP=2,500 kcal m−2 yr−1GPP = 2,500 \, kcal \, m^{-2} \, yr^{-1} Respiration loss (RR) = 30%30\% of 2,500=0.30×2,500=750 kcal m−2 yr−12,500 = 0.30 \times 2,500 = 750 \, kcal \, m^{-2} \, yr^{-1} NPP=GPP−RNPP = GPP - R NPP=2,500−750=1,750 kcal m−2 yr−1NPP = 2,500 - 750 = 1,750 \, kcal \, m^{-2} \, yr^{-1}

Explanation:

NPPNPP represents the actual biomass available for consumption by heterotrophs after the producers have met their own respiratory requirements.

Ecosystem Structure and Function - Revision Notes & Key Diagrams | CBSE Class 12 Biology