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Ecology and Environment - Ecosystem

Grade 12ICSEBiology

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

🔑Concepts

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Ecosystem Structure: An ecosystem consists of biotic (producers, consumers, decomposers) and abiotic components (temperature, light, H2OH_2O, soil). Stratification refers to the vertical distribution of different species occupying different levels, such as trees in the top strata and grasses in the bottom.

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Productivity: Primary production is the amount of biomass produced per unit area over a time period by plants during photosynthesis. Gross Primary Productivity (GPPGPP) is the rate of production of organic matter, while Net Primary Productivity (NPPNPP) is the available biomass for consumption by heterotrophs.

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Decomposition: The process of breaking down complex organic matter into inorganic substances like CO2CO_2, H2OH_2O, and nutrients. The steps include fragmentation, leaching, catabolism, humification, and mineralization.

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Energy Flow: Energy flow in an ecosystem is unidirectional. It follows the First and Second Laws of Thermodynamics. Only about 1−5%1-5\% of incident solar radiation (or 2−10%2-10\% of PARPAR - Photosynthetically Active Radiation) is captured by producers.

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Trophic Levels: Organisms occupy a specific place in the food chain based on their source of nutrition. The 10%10\% Law states that only 10%10\% of the energy is transferred to each trophic level from the lower trophic level.

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Ecological Pyramids: Graphical representation of trophic structures. Includes Pyramid of Number, Pyramid of Biomass, and Pyramid of Energy. Note that the Pyramid of Energy is always upright, while others can be inverted (e.g., biomass in a sea ecosystem).

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Ecological Succession: The gradual and fairly predictable change in the species composition of a given area. It starts with a pioneer species and ends in a stable climax community. Primary succession occurs in newly cooled lava or bare rocks; secondary succession occurs in abandoned farm lands or burnt forests.

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Nutrient Cycling (Biogeochemical Cycles): The movement of nutrient elements through various components of an ecosystem. Includes Gaseous cycles (e.g., Carbon, Nitrogen) where the reservoir is the atmosphere, and Sedimentary cycles (e.g., Phosphorus, Sulphur) where the reservoir is the Earth's crust.

📐Formulae

NPP=GPP−RNPP = GPP - R (where RR is Respiration losses)

Net Community Productivity=NPP−Consumption by Heterotrophs\text{Net Community Productivity} = NPP - \text{Consumption by Heterotrophs}

Trophic Efficiency=Energy at trophic level nEnergy at trophic level n−1×100\text{Trophic Efficiency} = \frac{\text{Energy at trophic level } n}{\text{Energy at trophic level } n-1} \times 100

10% Law: En+1=En×0.1010\% \text{ Law: } E_{n+1} = E_n \times 0.10

6CO2+12H2O→Light/ChlorophyllC6H12O6+6H2O+6O26CO_2 + 12H_2O \xrightarrow{\text{Light/Chlorophyll}} C_6H_{12}O_6 + 6H_2O + 6O_2

💡Examples

Problem 1:

In a grazing food chain, if the Net Primary Productivity (NPPNPP) at the producer level is 20,000 J20,000 \text{ J}, calculate the amount of energy available to the tertiary consumer following Lindeman's 10%10\% law.

Solution:

EProducer=20,000 JE_{\text{Producer}} = 20,000 \text{ J} EPrimary Consumer=20,000×0.10=2,000 JE_{\text{Primary Consumer}} = 20,000 \times 0.10 = 2,000 \text{ J} ESecondary Consumer=2,000×0.10=200 JE_{\text{Secondary Consumer}} = 2,000 \times 0.10 = 200 \text{ J} ETertiary Consumer=200×0.10=20 JE_{\text{Tertiary Consumer}} = 200 \times 0.10 = 20 \text{ J}

Explanation:

According to the 10%10\% Law, only 10%10\% of the energy available at one trophic level is transferred to the next. The energy decreases significantly as we move up the food chain.

Problem 2:

Explain why the pyramid of biomass in a sea ecosystem is often inverted.

Solution:

In a sea ecosystem, the producers are tiny phytoplanktons. Although they have a high rate of reproduction, their 'standing crop' biomass at any given time is much lower than the biomass of the zooplankton and fish that feed on them.

Explanation:

The pyramid of biomass depends on the 'standing crop' (weight of living matter) at a specific time. Because fish are large and long-lived compared to phytoplanktons, their total biomass exceeds that of the producers.

Ecosystem - Revision Notes & Key Diagrams | ICSE Class 12 Biology