Ecosystem — Revision Notes

⚡ 30-Second Revision

Ecosystem — Biotic + Abiotic interactions.
Producers — Autotrophs (plants, algae).
Consumers — Heterotrophs (herbivores, carnivores, omnivores).
Decomposers — Bacteria, fungi (break down detritus).
GPP — Total photosynthesis. NPP: GPP - Respiration ($NPP = GPP - R$).
Decomposition Steps — Fragmentation $ightarrow$ Leaching $ightarrow$ Catabolism $ightarrow$ Humification $ightarrow$ Mineralization.
Energy Flow — Unidirectional. 10% Law: Only $approx 10$ energy transferred to next trophic level.
Food Chain — Linear. Food Web: Interconnected chains.
Pyramid of Energy — Always upright.
Pyramid of Biomass — Can be inverted (aquatic).
Pyramid of Number — Can be inverted (parasitic) or spindle-shaped.
Carbon Cycle — Reservoir: Atmosphere ($CO_2$), Oceans. Processes: Photosynthesis, Respiration, Decomposition, Combustion.
Phosphorus Cycle — Reservoir: Rocks. No gaseous phase. Processes: Weathering, Absorption, Decomposition.

2-Minute Revision

An ecosystem is a dynamic unit where living (biotic) and non-living (abiotic) components interact, facilitating energy flow and nutrient cycling. Producers (plants) form the base, converting solar energy into organic matter (GPP), with NPP being the energy available to consumers after respiration.

Energy flows unidirectionally, losing about 90% at each trophic level (10% Law), which explains why the pyramid of energy is always upright. Food chains (grazing, detritus) and complex food webs illustrate these feeding relationships.

Decomposition, a crucial process involving fragmentation, leaching, catabolism, humification, and mineralization, recycles nutrients from dead organic matter back into the ecosystem. Key nutrient cycles, like carbon (atmospheric reservoir, human impact from fossil fuels) and phosphorus (sedimentary reservoir, no gaseous phase), ensure continuous nutrient availability.

Understanding these processes and their graphical representations (ecological pyramids) is fundamental for NEET.

5-Minute Revision

Ecosystems are the fundamental functional units of nature, comprising biotic (producers, consumers, decomposers) and abiotic (physical and chemical) components. Producers, mainly plants, capture solar energy to synthesize organic matter, measured as Gross Primary Productivity (GPP).

Net Primary Productivity (NPP = GPP - Respiration) is the energy available to the next trophic level. Energy flow is strictly unidirectional, following the 10% Law, meaning only about 10% of energy is transferred between successive trophic levels, with the rest lost as heat.

This principle ensures that the pyramid of energy is *always* upright, unlike pyramids of number or biomass, which can be inverted (e.g., inverted biomass pyramid in aquatic ecosystems due to rapid phytoplankton turnover).

Decomposition is the breakdown of dead organic matter (detritus) by decomposers (bacteria, fungi) into inorganic nutrients. Its steps are fragmentation (physical breakdown), leaching (soluble nutrients seep), catabolism (chemical breakdown), humification (humus formation), and mineralization (nutrient release). Factors like temperature, moisture, and detritus composition significantly affect its rate.

Nutrient cycling, or biogeochemical cycles, ensures the continuous availability of essential elements. The Carbon Cycle involves atmospheric $CO_2$ and oceanic reservoirs, with photosynthesis, respiration, decomposition, and combustion as key processes.

Human activities, especially fossil fuel burning, significantly impact this cycle. The Phosphorus Cycle is sedimentary, with rocks as the main reservoir, and lacks a gaseous phase. Understanding these interconnected processes and their implications is vital for NEET.

Prelims Revision Notes

Ecosystems: NEET Quick Recall

1. Definition & Components:

Ecosystem — Functional unit of nature; biotic + abiotic interactions.
Biotic — Producers (autotrophs, e.g., plants, phytoplankton), Consumers (heterotrophs: herbivores, carnivores, omnivores), Decomposers (bacteria, fungi).
Abiotic — Non-living factors (e.g., sunlight, water, soil, temperature, minerals).

2. Ecosystem Functions:

Productivity — Rate of biomass production.

* GPP (Gross Primary Productivity): Total organic matter produced via photosynthesis. * NPP (Net Primary Productivity): GPP - Respiration (R). Energy available to next trophic level. (Units: $g^{-2}yr^{-1}$ or $kcal,m^{-2}yr^{-1}$).

Decomposition — Breakdown of detritus (dead organic matter) into inorganic substances.

* Steps: Fragmentation (detritivores) $ightarrow$ Leaching (water-soluble nutrients) $ightarrow$ Catabolism (enzymes) $ightarrow$ Humification (humus formation) $ightarrow$ Mineralization (nutrient release). * Factors: Temperature, moisture, chemical composition of detritus (lignin/chitin slow, N/sugars fast), aeration.

Energy Flow — Unidirectional, non-cyclic.

* Source: Sun (except deep-sea vents). * 10% Law (Lindeman's Law): Only $approx 10$ energy transferred to next trophic level; $90$ lost as heat/unutilized. * Food Chain: Linear sequence (GFC: producer $ightarrow$ herbivore $ightarrow$ carnivore; DFC: detritus $ightarrow$ decomposer $ightarrow$ detritivore). * Food Web: Interconnected food chains, provides stability.

Nutrient Cycling (Biogeochemical Cycles)

* Gaseous: Reservoir in atmosphere (e.g., Carbon, Nitrogen). * Sedimentary: Reservoir in Earth's crust (e.g., Phosphorus, Sulfur). * Carbon Cycle: Atmospheric $CO_2$, oceanic reservoir. Processes: Photosynthesis (uptake), Respiration, Decomposition, Combustion (release). Human impact: Fossil fuels, deforestation. * Phosphorus Cycle: Rock reservoir. No gaseous phase. Processes: Weathering, absorption by plants, decomposition.

3. Ecological Pyramids:

Pyramid of Energy — *Always upright*. Reflects 10% law; energy decreases at higher trophic levels.
Pyramid of Biomass — Can be upright (most terrestrial) or *inverted* (e.g., aquatic: phytoplankton biomass < zooplankton biomass at a given time).
Pyramid of Number — Can be upright (grassland), *inverted* (parasitic food chain), or spindle-shaped (tree ecosystem).

4. Key Terms:

Standing Crop — Total living biomass at a trophic level at a given time.
Standing State — Amount of inorganic nutrients present in an ecosystem at a given time.
Trophic Level — Position in food chain.
Humus — Dark, amorphous, slow-decomposing organic matter, nutrient reservoir.

Vyyuha Quick Recall

Please Don't Eat Nice Peaches.

Productivity
Decomposition
Energy Flow
Nutrient Cycling
Pyramids

This mnemonic helps recall the five main functional aspects of an ecosystem.