Q.Differentiate between primary productivity and secondary productivity. OR Maximum number of trophic levels is hardly 3-5 in terrestrial ecosystems. Explain, why ?
🔒You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Primary Productivity Factors
Let’s begin with something you already know. Imagine a farmer planting wheat. The yield at harvest depends on the quality of the seed, the fertility of the soil, the amount of sunlight and water, and the farmer’s skill. Now scale that up to an entire country or the whole world. The “primary productivity” of an ecosystem is simply the rate at which plants (the primary producers) capture sunlight and convert it into chemical energy through photosynthesis. It is the foundation of all food chains — without it, there would be no food for animals, no timber, no fuel, and no oxygen.
For a commerce or humanities student, think of primary productivity as the natural income of an ecosystem. Just as a business needs raw materials and labour to produce goods, an ecosystem needs sunlight, water, nutrients, and temperature to produce plant matter. The factors that influence how fast or slow this production happens are called primary productivity factors.
What the NCERT textbook says
The NCERT Class 12 Biology chapter on Ecosystem defines primary productivity as “the rate of biomass production” by plants. It is expressed in terms of weight (grams per square metre per year) or energy (calories per square metre per year). The textbook lists the following factors that control primary productivity:
- Sunlight – the energy source for photosynthesis. More sunlight generally means higher productivity, but too much can be harmful.
- Temperature – affects enzyme activity in plants. Most plants work best between about 20°C and 30°C.
- Water availability – without water, photosynthesis stops. Deserts have low productivity; rainforests have high productivity.
- Nutrients – especially nitrogen, phosphorus, potassium, and magnesium. Poor soils (like those in some tropical regions after deforestation) limit growth even if sunlight and water are abundant.
- Carbon dioxide concentration – CO₂ is the raw material for making glucose. Higher CO₂ can boost productivity up to a point.
- Plant type and health – different species have different photosynthetic efficiencies. A healthy, mature forest is more productive than a degraded grassland.
Primary productivity is not the same as the total amount of plant matter present. It is the rate of production — how much new plant matter is created per unit time. A dense old forest may have a huge standing biomass but low productivity if most trees are not actively growing. A young, fast-growing plantation can have high productivity even with less total biomass.
Why it matters for a humanities/commerce student
You might wonder: why should a future economist, lawyer, or manager care about plant growth rates? Here is the connection:
- Agriculture and food security – Productivity factors determine crop yields. Understanding them helps in planning irrigation, fertiliser use, and selecting crops for a region.
- Climate change policy – Forests act as carbon sinks. Their productivity determines how much CO₂ they can absorb. International agreements like the Paris Accord rely on accurate estimates of forest productivity.
- Resource economics – Timber, paper, biofuels, and even medicines depend on primary productivity. A country’s natural capital is partly measured by its ecosystem productivity. …
This question offers a choice between comparing primary and secondary productivity, and explaining why terrestrial food chains stay short, so both parts are answered below. …
Primary productivity is production of new organic matter by green plants (producers); secondary productivity is the rate at which that organic matter is converted into new biomass by the consumers that eat it.
Primary productivity: defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis.
- Gross Primary Productivity (GPP): the total rate of production of organic matter, including the matter used up by the plant's own respiration.
- Net Primary Productivity (NPP) = GPP − Respiration losses (R): the productivity actually available to consumers (herbivores, decomposers) for consumption.
- Expressed as g m⁻² yr⁻¹ (biomass) or kcal m⁻² yr⁻¹ (energy). It varies from ecosystem to ecosystem depending on the plant species, environmental factors, and availability of nutrients.
Secondary productivity: defined as the rate of formation of new biomass by consumers (herbivores and other heterotrophs). Consumers assimilate the organic matter (plant/animal biomass) they feed on and convert a fraction of it into their own body mass — this rate of biomass build-up by consumers is the secondary productivity.
OR — Why terrestrial food chains rarely have more than 3–5 trophic levels:
According to the ten per cent law (Lindeman's law), only about 10% of the energy available at one trophic level is transferred to the next trophic level; the remaining ~90% is lost mainly as heat during respiration and other metabolic activities, and some is lost as unutilised/undigested matter. Because of this progressive, large loss of usable energy at every step: …
Showing the 12 most recent of 15 on this concept.
- CBSE 2026Set ANNUAL1 markMCQQ.The primary productivity in an ecosystem is expressed as :(a) gm-2yr-1(b) gm-2yr(c) Kcalm-2yr(d) Kcalm-2
›Reveal solutionSolution
Primary productivity is a rate, so it is expressed as the mass of organic matter (or energy) produced per unit area per unit time.
Primary productivity is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. Because it is a RATE, it must include a time term, and it is conventionally expressed either as g m⁻² yr⁻¹ (mass basis) or as kcal m⁻² yr⁻¹ (energy b …
- CBSE 2026Set ANNUAL1 markMCQQ.If gross primary productivity minus respiration losses then we get:(a) Productivity(b) Net Primary Productivity(c) Secondary Productivity(d) Primary production
›Reveal solutionSolution
GPP minus respiration losses equals Net Primary Productivity (NPP).
Primary productivity is the rate at which producers (plants) fix energy through photosynthesis. Gross primary productivity (GPP) is the total organic matter produced. Producers themselves use up part of this energy in respiration (R). The amount left after subtracting respiration is available to consumers and is called Net Primary Productivity …
- CBSE 2026Set ANNUAL1 markQ.Write True or False. The Amazon rainforest is known as the "lungs of the planet" because it produces a large amount of carbon dioxide.
›Reveal solutionSolution
False — the Amazon rainforest is the "lungs of the planet" because it releases huge amounts of oxygen by photosynthesis, not carbon dioxide.
In the CBSE/NCERT Ecosystem chapter, the Amazon forest is described as contributing an estimated 20% of the total oxygen in Earth's atmosphere. Green plants during photosynthesis take in CO₂ and release O₂; this is why the forest is nicknamed the l …
- CBSE 2025Set F1 markMCQQ.Which of the following absorbs the maximum amount of solar energy?(a) Plantation(b) Cropping(c) Growing grass(d) Culturing algae
›Reveal solutionSolution
A plantation absorbs the most solar energy.
The amount of solar energy absorbed by a vegetation type depends on its leaf area index (canopy density) and standing biomass. Among the options, a plantation of trees has the largest, multi-layered canopy and the highest leaf area, so it intercepts and absorbs more incoming solar radiation than fie …
- CBSE 2025Set ANNUAL1 markMCQQ.In the equation, GPP-R=NPP, R represents(a) Respiration losses(b) Radiant energy(c) Reasoning(d) Recycling
›Reveal solutionSolution
Net Primary Productivity equals Gross Primary Productivity minus the respiratory losses of the producers.
Gross Primary Productivity (GPP) is the total rate of production of organic matter (biomass) during photosynthesis by producers in an ecosystem. However, a significant part of this fixed energy is used up by the plants themselves in their own respiration (metabolic maintenance) — this is termed Respiration losses (R). What remains after subtracting these respiration losses is the Net Primary Productivity (NPP), i.e., GPP − R = NPP — the biomass/energ …
- CBSE 2024Set 57/1/11 markMCQQ.The rate of formation of new organic matter by consumers, and the biomass available for consumption of herbivores as well as decomposers are referred to as: (A) Gross primary productivity and Net primary productivity (B) Net primary productivity and Secondary productivity (C) Secondary productivity and Net primary productivity (D) Secondary productivity and Gross primary productivity
›Reveal solutionSolution
Secondary productivity measures the rate at which consumers (herbivores, carnivores) form new organic matter, while net primary productivity represents the biomass actually available to herbivores and decomposers after plants have used some energy for their own respiration.
The question asks us to match two distinct ecological concepts: the productivity of consumers and the biomass available for the next trophic level. Understanding these terms requires clarity about how energy flows through an ecosystem and how we measure productivity at different levels.
Gross primary productivity is the total rate at which producers (plants, algae) capture solar energy and convert it into chemical energy through photosynthesis. Think of it as the gross income of the ecosystem—the entire amount of organic matter synthesized before any deductions.
Net primary productivity is what remains after plants subtract their own respiratory losses from gross primary productivity. The formula is simple: NPP = GPP – Respiration by plants. This is the actual biomass available to herbivores and decomposers—the net income, if you will. It represents the stored energy in plant tissues that can be consumed by the next trophic level.
Now, when herbivores eat plants and carnivores eat herbivores, they too produce new organic matter in their own bodies. This rate of formation of new organic matter by consumers—whether herbivores, carnivores, or any heterotroph—is called secondary productivity. It's analogous to primary productivity but occurs at the consumer level rather than the producer level.
NoteThe term "secondary" doesn't mean less important; it simply indicates that this productivity depends on primary producers. Consumers cannot synthesize organic matter from inorganic sources—they must consume existing organic matter and convert it into their own biomass. …
- CBSE 2024Set A11 markMCQQ.Net Primary Productivity (NPP) is equal to(a) GPP(b) GPP + R(c) GPP / R(d) GPP – R
›Reveal solutionSolution
Net Primary Productivity is Gross Primary Productivity minus respiratory losses.
Gross Primary Productivity (GPP) is the total rate of organic matter produced by photosynthesis. Plants use part of this for their own respiration (R). The remaining biomass available for consumption by heterotrophs is the Net P …
- CBSE 2024Set ANNUAL1 markMCQQ.The amount of biomass or organic matter produced per unit area over a certain time period by plants during photosynthesis is(a) Primary productivity(b) Secondary productivity(c) Net primary productivity(d) Productivity
›Reveal solutionSolution
Primary productivity is defined as the amount of biomass or organic matter produced by producers (plants) per unit area over a period of time through photosynthesis.
Primary productivity is expressed as weight (g/m^2/yr) or energy (kcal/m^2/yr) and is the basic production of organic matter by autotrophs. It is further divided into Gross Primary Productivity (GPP, the total rate of production including matter used up in respiration) and Net Primary Productivity (NPP = GPP minus respiratory losses, the biomass actually available to consumers). Th …
- CBSE 2024Set ANNUAL1 markMCQQ.Assertion (A) : Net primary productivity is greater than gross primary productivity. Reason (R) : A part of net primary productivity goes waste during respiration.(a) Assertion (A) and Reason (R) both are true and Reason (R) is the correct explanation of Assertion (A).(b) Assertion (A) and Reason (R) both are true, but Reason (R) is not the correct explanation of Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) and Reason (R) both are false.
›Reveal solutionSolution
Actually GPP is greater than NPP, not the other way round, because respiratory losses are subtracted from GPP, not from NPP.
Gross Primary Productivity (GPP) is the total rate of production of organic matter by producers through photosynthesis. Net Primary Productivity (NPP) is what remains after subtracting the respiratory losses (R) of the producers: NPP = GPP − R. This means GPP is always greater than NPP, so the Assertion (that NPP is greater than GP …
- CBSE 2024Set ANNUAL1 markQ.Write full name of G.P.P.
›Reveal solutionSolution
GPP is the total rate of organic matter (biomass) production by producers through photosynthesis, before respiratory losses are subtracted.
In an ecosystem, Gross Primary Productivity (GPP) is the total amount of organic matter (biomass) produced by producers (green plants) per unit area per unit time during photosynthesis. A part of this GPP is used up by the plants themselves in respiration (Respiratory loss, R); what remains after subtract …
- CBSE 2023Set ANNUAL1 markQ.The rate of biomass production is called ________. (Fill in the blank)
›Reveal solutionSolution
Productivity refers to the rate at which biomass is produced per unit area over a period of time by plants (primary producers) or consumers (secondary producers).
Productivity is defined as the rate of biomass production. It is expressed in terms of weight (g^-2) or energy (kcal m^-2) produced per unit area per unit time.
- Gross Primary Productivity (GPP) is the total rate of production of organic matter during photosynthesis. …
- CBSE 2021Set D1 markMCQQ.Secondary productivity is related to(a) Producers(b) Herbivores(c) Carnivores(d) None of these
›Reveal solutionSolution
Secondary productivity is the rate of formation of new organic matter by consumers (heterotrophs), starting with herbivores.
Gross primary productivity is the rate at which producers fix energy. Secondary productivity is the rate at which consumers (heterotrophs) assimilate and store energy in new biomass. In a grazing food chain the first consumers are the herbivores, so seco …
🎓Unlock everything free for 14 days
- ✓Full step-by-step solutions
- ✓Concept-first explanations
- ✓Methods, shortcuts & mistakes
- ✓PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.