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Biology - Ecosystems (Biotic and Abiotic components, Food chains, Food webs)

Grade 8ICSE

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

🔑Concepts

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An ecosystem is a self-sustaining structural and functional unit of the biosphere where biotic and abiotic components interact.

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Abiotic components include non-living factors such as light, temperature, water (H2OH_2O), soil, and atmospheric gases like O2O_2, CO2CO_2, and N2N_2.

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Biotic components consist of living organisms categorized into Producers (Autotrophs), Consumers (Heterotrophs), and Decomposers (Saprotrophs).

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Producers, mainly green plants, convert solar energy into chemical energy through photosynthesis: 6CO2+6H2O→SunlightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{\text{Sunlight}} C_6H_{12}O_6 + 6O_2.

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Consumers are divided into primary (herbivores), secondary (carnivores), and tertiary (top carnivores) based on their position in the food chain.

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A Food Chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another.

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A Food Web is a network of many interconnected food chains, representing the complex feeding relationships in an ecosystem.

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Energy flow in an ecosystem is unidirectional, meaning it moves from producers to higher trophic levels and cannot flow back.

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Lindeman's 10% Law: Only about 10%10\% of the energy available at one trophic level is transferred to the next higher level; the rest is lost as heat during respiration and metabolic activities.

📐Formulae

6CO2+6H2O→ChlorophyllSunlightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} C_6H_{12}O_6 + 6O_2

Energy at Trophic Level (n)=Energy at Level (n-1)×0.10\text{Energy at Trophic Level (n)} = \text{Energy at Level (n-1)} \times 0.10

Biomass=Total mass of living matter in a given area\text{Biomass} = \text{Total mass of living matter in a given area}

💡Examples

Problem 1:

In a food chain consisting of Grass →\rightarrow Grasshopper →\rightarrow Frog →\rightarrow Snake, if the Grass captures 20,000 J20,000 \text{ J} of solar energy, calculate the energy available to the Snake.

Solution:

  1. Producer (Grass): 20,000 J20,000 \text{ J}
  2. Primary Consumer (Grasshopper): 20,000×0.10=2,000 J20,000 \times 0.10 = 2,000 \text{ J}
  3. Secondary Consumer (Frog): 2,000×0.10=200 J2,000 \times 0.10 = 200 \text{ J}
  4. Tertiary Consumer (Snake): 200×0.10=20 J200 \times 0.10 = 20 \text{ J}.

Explanation:

According to the 10%10\% law of energy transfer, each subsequent trophic level receives only one-tenth of the energy from the previous level.

Problem 2:

Identify the components in the following sequence: Paddy→Paddy \rightarrow Mouse →\rightarrow Snake →\rightarrow Peacock.

Solution:

Paddy: Producer; Mouse: Primary Consumer (1st1^{st} Order); Snake: Secondary Consumer (2nd2^{nd} Order); Peacock: Tertiary Consumer (3rd3^{rd} Order/Top Carnivore).

Explanation:

This is a terrestrial food chain where energy flows from the autotroph (PaddyPaddy) to various levels of heterotrophs.

Problem 3:

Why is a food web more stable than a food chain?

Solution:

A food web provides multiple alternative pathways for energy flow. If one species in a web becomes extinct or decreases in number, consumers can switch to an alternative food source.

Explanation:

Unlike a linear food chain where the removal of one link disrupts the entire flow, the complexity of a food web ensures the survival of the ecosystem by maintaining biological balance.