Ecosystem Structure and Function — Revision Notes

⚡ 30-Second Revision

Ecosystem: — Biotic + Abiotic components interacting.
Biotic: — Producers (autotrophs), Consumers (heterotrophs), Decomposers (saprotrophs).
Abiotic: — Temp, light, water, soil, nutrients.
GPP: — Total photosynthesis. $GPP = NPP + R$.
NPP: — Biomass available to consumers. $NPP = GPP - R$.
Decomposition Steps: — Fragmentation $\rightarrow$ Leaching $\rightarrow$ Catabolism $\rightarrow$ Humification $\rightarrow$ Mineralization.
Energy Flow: — Unidirectional, non-cyclic. Follows 10% Law.
10% Law: — Only 10% energy transferred to next trophic level.
Nutrient Cycling: — Cyclic. Gaseous (C, N) vs. Sedimentary (P, S).
Factors affecting decomposition: — Warmth, moisture, N-rich detritus (faster); Lignin, chitin, low temp, anaerobic (slower).

2-Minute Revision

Ecosystems are functional units of nature where living (biotic) and non-living (abiotic) components interact. Biotic components include producers (plants), consumers (animals), and decomposers (bacteria, fungi).

Abiotic factors are physical and chemical elements like temperature, light, water, and soil. Ecosystem functions include productivity, decomposition, energy flow, and nutrient cycling. Productivity measures biomass creation: Gross Primary Productivity (GPP) is total photosynthesis, while Net Primary Productivity (NPP) is GPP minus respiration, representing energy available to consumers.

Decomposition is the breakdown of dead organic matter, occurring in steps: fragmentation, leaching, catabolism, humification, and mineralization, crucial for nutrient return. Energy flows unidirectionally from the sun through trophic levels, with only about 10% transferred at each step (10% Law), leading to energy loss as heat.

Nutrient cycling, unlike energy flow, is cyclic, ensuring elements like carbon and nitrogen are continuously reused, either through gaseous or sedimentary reservoirs.

5-Minute Revision

An ecosystem is the fundamental unit of ecology, encompassing all living organisms (biotic components: producers, consumers, decomposers) and their interactions with the non-living physical and chemical environment (abiotic components: light, temperature, water, soil). The structure of an ecosystem refers to its species composition and stratification, while its function involves four key processes: productivity, decomposition, energy flow, and nutrient cycling.

Productivity is the rate of biomass production. Gross Primary Productivity (GPP) is the total rate of photosynthesis, while Net Primary Productivity (NPP) is the GPP minus the energy lost by producers during respiration ($NPP = GPP - R$).

NPP is the energy available to herbivores. Decomposition is the breakdown of complex organic detritus into simpler inorganic substances by decomposers. This multi-step process includes: 1. Fragmentation (physical breakdown by detritivores), 2.

Leaching (water-soluble nutrients seep into soil), 3. Catabolism (enzymatic degradation by microbes), 4. Humification (formation of stable humus), and 5. Mineralization (release of inorganic nutrients from humus).

Factors like warm, moist conditions and nitrogen-rich detritus accelerate decomposition, while lignin, chitin, low temperature, and anaerobic conditions slow it down.

Energy flow is unidirectional and non-cyclic, originating from the sun and moving through different trophic levels (producers $\rightarrow$ primary consumers $\rightarrow$ secondary consumers $\rightarrow$ tertiary consumers).

The 10% Law states that only about 10% of the energy from one trophic level is transferred to the next, with the rest lost as heat. This limits the length of food chains. Nutrient cycling (biogeochemical cycles) involves the continuous movement of essential elements (e.

g., carbon, nitrogen, phosphorus) between biotic and abiotic components. These are either gaseous cycles (reservoir in atmosphere, like carbon and nitrogen) or sedimentary cycles (reservoir in Earth's crust, like phosphorus).

Understanding these interconnected processes is vital for comprehending ecosystem stability and sustainability.

Worked Example (10% Law):

If producers in an ecosystem have $100,000,J$ of energy, calculate the energy available to tertiary consumers.

Producers: — $100,000,J$
Primary Consumers: — $10$ of $100,000,J = 10,000,J$
Secondary Consumers: — $10$ of $10,000,J = 1,000,J$
Tertiary Consumers: — $10$ of $1,000,J = 100,J$

So, only $100,J$ would be available to tertiary consumers.

Prelims Revision Notes

Ecosystem Structure and Function: NEET Quick Recall

I. Ecosystem Definition & Components:

Ecosystem: — Structural & functional unit of nature; biotic + abiotic interactions.
Biotic Components:

* Producers (Autotrophs): Photosynthetic (plants, algae) or chemosynthetic bacteria. Base of food chain. * Consumers (Heterotrophs): * Primary (Herbivores): Eat producers. * Secondary (Carnivores/Omnivores): Eat primary consumers. * Tertiary (Top Carnivores/Omnivores): Eat secondary consumers. * Decomposers (Saprotrophs): Bacteria & fungi. Break down dead organic matter.

Abiotic Components: — Non-living factors: Temperature, light, water, soil, inorganic nutrients ($CO_2, O_2, N_2, P, Ca$), organic substances (proteins, carbs, lipids).
Stratification: — Vertical distribution of species (e.g., forest canopy, understory, ground layer).

II. Ecosystem Functions:

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Productivity: — Rate of biomass production.

* GPP (Gross Primary Productivity): Total rate of organic matter production (total photosynthesis). * NPP (Net Primary Productivity): GPP - Respiration (R). Biomass available to consumers. $NPP = GPP - R$. * Secondary Productivity: Rate of new organic matter formation by consumers. * Highest NPP/unit area: Tropical rainforests. Lowest: Deserts, deep oceans.

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Decomposition: — Breakdown of complex organic detritus into inorganic substances.

* Detritus: Dead plant/animal remains, fecal matter. * Steps (FLCHM mnemonic): * Fragmentation: Detritivores break detritus into smaller particles. * Leaching: Water-soluble inorganic nutrients seep into soil.

* Catabolism: Microbial enzymes degrade detritus. * Humification: Formation of dark, amorphous, resistant humus (nutrient reservoir). * Mineralization: Release of inorganic nutrients from humus.

* Factors Affecting Rate: * Faster: Warm, moist, aerobic conditions; N-rich, water-soluble detritus. * Slower: Low temp, anaerobic; lignin/chitin-rich detritus.

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Energy Flow: — Unidirectional, non-cyclic.

* Sun $\rightarrow$ Producers $\rightarrow$ Primary Consumers $\rightarrow$ Secondary Consumers $\rightarrow$ Tertiary Consumers. * 10% Law (Lindeman's Law): Only ~10% of energy transferred to next trophic level; 90% lost as heat. * Energy pyramids are always upright (except for biomass in some aquatic ecosystems).

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Nutrient Cycling (Biogeochemical Cycles): — Cyclic movement of elements.

* Gaseous Cycles: Reservoir in atmosphere (e.g., Carbon Cycle, Nitrogen Cycle). * Sedimentary Cycles: Reservoir in Earth's crust (e.g., Phosphorus Cycle, Sulfur Cycle).

III. Key Distinctions:

Ecosystem vs. Community: — Ecosystem includes biotic + abiotic; Community is only biotic.
Energy Flow vs. Nutrient Cycling: — Energy is unidirectional & lost; Nutrients are cyclic & reused.

Vyyuha Quick Recall

To remember the steps of decomposition in order, think: For Lazy Cats, Humans Mineralize.

Fragmentation
Leaching
Catabolism
Humification
Mineralization