Primary and Secondary Productivity — Revision Notes

⚡ 30-Second Revision

Primary Productivity: — Rate of organic matter synthesis by producers.

- GPP (Gross Primary Productivity): Total photosynthesis/chemosynthesis. - NPP (Net Primary Productivity): GPP - Respiration (R) of producers. Energy available to consumers. - Formula: $ext{NPP} = \text{GPP} - \text{R}$

Secondary Productivity: — Rate of new organic matter formation by consumers.

- GSP (Gross Secondary Productivity): Total energy assimilated by consumer. - NSP (Net Secondary Productivity): GSP - Respiration (R) of consumers. Energy available to next trophic level. - Formula: $ext{NSP} = \text{GSP} - \text{R}$

Units: — $ext{kcal m}^{-2} \text{yr}^{-1}$ or $ext{g m}^{-2} \text{yr}^{-1}$.
10% Law: — Only ~10% energy transfers to next trophic level; 90% lost as heat.
Factors affecting Primary Productivity: — Light, Temperature, Water, Nutrients (N, P).
High NPP Ecosystems: — Tropical rainforests, coral reefs, estuaries.
Low NPP Ecosystems: — Deserts, open oceans, tundra.
Productivity vs. Standing Crop: — Productivity is a rate; Standing Crop is biomass at a point in time.

2-Minute Revision

Productivity in ecology measures the rate of biomass production. It's categorized into primary and secondary. Primary productivity is the foundation, representing the rate at which producers (plants, algae) convert inorganic matter into organic compounds, primarily through photosynthesis.

Gross Primary Productivity (GPP) is the total amount produced, while Net Primary Productivity (NPP) is GPP minus the energy producers use for their own respiration (NPP = GPP - R). NPP is the crucial energy available to herbivores and decomposers.

Secondary productivity is the rate at which consumers (animals) convert the organic matter they ingest into their own biomass. Similar to primary, it has Gross Secondary Productivity (GSP) and Net Secondary Productivity (NSP), where NSP is GSP minus consumer respiration.

A key principle is the 10% law, stating that only about 10% of energy transfers from one trophic level to the next, with the rest lost as heat, explaining why food chains are short. Factors like light, temperature, water, and essential nutrients significantly influence primary productivity.

Remember, productivity is a rate, distinct from standing crop, which is the total biomass at a given moment.

5-Minute Revision

Let's consolidate the core concepts of primary and secondary productivity, essential for NEET. Productivity is fundamentally the rate of biomass accumulation. Primary productivity is the initial energy capture by autotrophs.

Gross Primary Productivity (GPP) is the total organic matter produced via photosynthesis or chemosynthesis. However, producers, like all organisms, respire to sustain themselves. The energy lost in this process is 'R'.

Thus, Net Primary Productivity (NPP), the energy available to the rest of the ecosystem (herbivores and decomposers), is calculated as $ext{NPP} = \text{GPP} - \text{R}$. For instance, if a plant fixes $1000,\text{J}$ (GPP) but uses $200,\text{J}$ for respiration, its NPP is $800,\text{J}$.

Secondary productivity focuses on consumers. It's the rate at which heterotrophs convert assimilated food into their own biomass. Gross Secondary Productivity (GSP) is the total energy assimilated from food.

Again, consumers respire, so Net Secondary Productivity (NSP), the energy available to the next trophic level, is $ext{NSP} = \text{GSP} - \text{R}$ (consumer respiration). Secondary productivity is always lower than primary productivity due to the 10% law of energy transfer, which states that only about 10% of energy moves from one trophic level to the next, with the remaining 90% lost as heat during metabolic processes.

This explains the pyramid of energy and biomass.

Key factors influencing primary productivity include solar radiation (energy source), temperature (affects enzyme activity), water availability (reactant and transport medium), and essential nutrients (e.

g., N, P). Tropical rainforests and coral reefs are examples of highly productive ecosystems due to optimal conditions, while deserts and open oceans have low productivity due to limiting factors. Remember the units: $ext{kcal m}^{-2} \text{yr}^{-1}$ or $ext{g m}^{-2} \text{yr}^{-1}$.

Crucially, distinguish productivity (a rate) from standing crop (total biomass at a specific time). An ecosystem can have high standing crop (e.g., a mature forest) but moderate NPP, or low standing crop but high NPP (e.

g., an algal bloom with rapid turnover).

Prelims Revision Notes

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Productivity Definition: — Rate of biomass production per unit area per unit time. Units: $ext{kcal m}^{-2} \text{yr}^{-1}$ or $ext{g m}^{-2} \text{yr}^{-1}$.
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Primary Productivity: — By producers (autotrophs) from inorganic sources.

* Gross Primary Productivity (GPP): Total rate of photosynthesis/chemosynthesis. Total energy fixed. * Net Primary Productivity (NPP): GPP minus producer respiratory losses (R). $ext{NPP} = \text{GPP} - \text{R}$. This is the energy available to herbivores and decomposers.

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Secondary Productivity: — By consumers (heterotrophs) from consuming other organisms.

* Gross Secondary Productivity (GSP): Total energy assimilated by the consumer. * Net Secondary Productivity (NSP): GSP minus consumer respiratory losses (R). $ext{NSP} = \text{GSP} - \text{R}$. This is the energy available to the next trophic level.

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Energy Flow & 10% Law:

* Energy flows unidirectionally from sun to producers to consumers. * Only about 10% of energy is transferred from one trophic level to the next (Lindeman's 10% Law). * The remaining 90% is lost as heat during metabolic processes (respiration), unconsumed biomass, and waste products. * This explains why food chains are short (typically 3-5 trophic levels) and energy/biomass pyramids are broad at the base and narrow at the top.

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Factors Affecting Primary Productivity:

* Solar Radiation: Primary energy source. Higher light intensity generally increases GPP. * Temperature: Affects enzyme activity in photosynthesis; optimal range exists. * Water Availability: Essential reactant for photosynthesis and nutrient transport.

Limiting in deserts. * Nutrient Availability: Essential minerals (N, P, K, Mg) are crucial for plant growth. Often limiting in oceans and some terrestrial soils. * Species Characteristics: Photosynthetic efficiency of dominant plant species.

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Global Productivity Patterns:

* Highest NPP per unit area: Tropical rainforests, coral reefs, estuaries, wetlands. * Lowest NPP per unit area: Deserts, open oceans, tundra. * Despite low NPP per unit area, open oceans contribute significantly to global NPP due to their vast area.

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Productivity vs. Standing Crop:

* Productivity: A rate (e.g., $ext{g m}^{-2} \text{yr}^{-1}$). Dynamic. * Standing Crop: Total biomass present at a given time (e.g., $ext{g m}^{-2}$). Static. * Example: Algal bloom (low standing crop, high NPP); Mature forest (high standing crop, moderate NPP).

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Ecological Significance: — Productivity is a key indicator of ecosystem health, capacity to support life, and carbon sequestration potential.

Vyyuha Quick Recall

Plants Grow Plenty, Now People Partake. Respiration Reduces Resources.