Part 3 – Productivity in Ecosystems
Part 3 – Productivity in Ecosystems (GPP, NPP, Secondary Productivity, Ecological Efficiency)
(25 MCQs with answers and detailed explanations, NCERT Class 12 + NEET UG level)
Q1.
Primary productivity of an ecosystem refers to:
a) Energy fixed by producers in a unit area per unit time
b) Energy used by herbivores
c) Total biomass of consumers
d) Decomposition rate
Answer: a) Energy fixed by producers in a unit area per unit time
Explanation:
- (a) Correct → Producers capture solar energy → biomass formed.
- (b) Secondary productivity.
- (c) Not productivity.
- (d) Decomposition is different.
Q2.
Gross primary productivity (GPP) is:
a) Total photosynthetic production including energy used in respiration
b) Energy available to herbivores
c) Energy left after respiration
d) Only chemical energy stored in detritus
Answer: a) Total photosynthetic production including energy used in respiration
Explanation:
- (a) Correct → GPP = total fixation before losses.
- (b) That’s NPP.
- (c) Wrong → NPP is after respiration.
- (d) Detritus → decomposition, not GPP.
Q3.
Net primary productivity (NPP) is defined as:
a) GPP – respiration losses (R)
b) GPP + respiration losses
c) Total plant biomass + decomposers
d) GPP × 10%
Answer: a) GPP – respiration losses (R)
Explanation:
- (a) Correct → NPP = energy available to consumers.
- (b) Wrong.
- (c) Not a definition.
- (d) 10% law refers to energy transfer, not NPP.
Q4.
Which is available for consumption by herbivores?
a) GPP
b) NPP
c) Secondary productivity
d) Respiration
Answer: b) NPP
Explanation:
NPP = GPP – R → available to next trophic level.
Q5.
Secondary productivity refers to:
a) Energy captured by producers
b) Rate of biomass formation by consumers
c) Decomposition rate of detritus
d) Rate of nutrient cycling
Answer: b) Rate of biomass formation by consumers
Explanation:
- (a) Producers → primary productivity.
- (b) Correct → Secondary productivity by heterotrophs.
- (c) Wrong.
- (d) Wrong.
Q6.
Which biome has the highest annual NPP?
a) Desert
b) Tropical rainforest
c) Tundra
d) Open ocean
Answer: b) Tropical rainforest
Explanation:
Warm, moist → maximum productivity.
Q7.
Which biome has the lowest annual NPP?
a) Grassland
b) Desert
c) Tropical rainforest
d) Wetland
Answer: b) Desert
Explanation:
Water scarcity → lowest productivity.
Q8.
Which ecosystem contributes maximum to Earth’s total productivity due to its vast area?
a) Tropical rainforest
b) Oceans
c) Wetlands
d) Grasslands
Answer: b) Oceans
Explanation:
Per unit productivity is low, but area vast → maximum global share.
Q9.
Rate of energy storage in plant tissues that is not used in respiration is called:
a) Gross primary productivity
b) Net primary productivity
c) Secondary productivity
d) Tertiary productivity
Answer: b) Net primary productivity
Explanation:
NPP = GPP – R.
Q10.
Which formula is correct?
a) NPP = GPP + R
b) NPP = GPP – R
c) GPP = NPP – R
d) R = GPP + NPP
Answer: b) NPP = GPP – R
Explanation:
Standard formula from NCERT.
Q11.
Which ecosystem has the highest productivity per unit area?
a) Coral reefs
b) Open ocean
c) Grassland
d) Desert
Answer: a) Coral reefs
Explanation:
Though small in area, coral reefs have very high per unit productivity.
Q12.
Which of the following is NOT true for NPP?
a) Represents plant biomass available to herbivores
b) Is equal to GPP minus plant respiration
c) Is always higher than GPP
d) Varies with ecosystems
Answer: c) Is always higher than GPP
Explanation:
NPP < GPP always, since respiration loss is subtracted.
Q13.
Ecological efficiency refers to:
a) Efficiency of light absorption
b) Percentage of energy transferred from one trophic level to next
c) Efficiency of respiration
d) Efficiency of decomposition
Answer: b) Percentage of energy transferred from one trophic level to next
Explanation:
Typically ~10% transfer efficiency (Lindeman’s law).
Q14.
Who gave the “10% law of energy transfer”?
a) Darwin
b) Lindeman
c) Odum
d) Malthus
Answer: b) Lindeman
Explanation:
Raymond Lindeman (1942) → 10% energy law.
Q15.
Productivity in an ecosystem is measured in terms of:
a) Energy per unit area per unit time
b) Total biomass only
c) Number of organisms per unit area
d) Rate of nutrient cycling
Answer: a) Energy per unit area per unit time
Explanation:
Measured in kcal/m²/yr or g/m²/yr.
Q16.
Which of the following contributes directly to secondary productivity?
a) Photosynthesis
b) Herbivory
c) Decomposition
d) Respiration
Answer: b) Herbivory
Explanation:
Consumers build biomass from plant/animal food.
Q17.
Which factor does NOT influence primary productivity?
a) Temperature
b) Water availability
c) Nutrient availability
d) Color of flowers
Answer: d) Color of flowers
Explanation:
Productivity depends on abiotic conditions, not flower color.
Q18.
Which ecosystem has inverted biomass pyramid but still high productivity?
a) Grassland
b) Tropical rainforest
c) Ocean
d) Desert
Answer: c) Ocean
Explanation:
Phytoplankton biomass small, but high turnover rate → high productivity.
Q19.
Which of the following ecosystems shows maximum secondary productivity?
a) Agricultural fields
b) Forests
c) Coral reefs
d) Desert
Answer: a) Agricultural fields
Explanation:
High crop biomass → herbivores and livestock productivity.
Q20.
Total plant biomass produced per year in an ecosystem is:
a) Primary productivity
b) Gross productivity
c) Net productivity
d) Standing crop
Answer: d) Standing crop
Explanation:
Standing crop = total living biomass at a given time.
Q21.
Which of the following is measured in kcal/m²/year?
a) Productivity
b) Standing crop
c) Population density
d) Species richness
Answer: a) Productivity
Explanation:
Expressed in energy per unit area per year.
Q22.
In which ecosystem is productivity mainly nutrient-limited?
a) Tropical rainforest
b) Ocean
c) Desert
d) Grassland
Answer: b) Ocean
Explanation:
Light is abundant, but nutrients (N, P, Fe) limit productivity.
Q23.
Which factor contributes most to high productivity of wetlands?
a) High nutrient availability
b) Low water levels
c) Cold temperatures
d) Scarcity of producers
Answer: a) High nutrient availability
Explanation:
Wetlands are nutrient-rich, leading to high NPP.
Q24.
Which of the following statements is FALSE?
a) NPP is always less than GPP
b) Productivity is measured as rate
c) Secondary productivity refers to consumers
d) Oceans have highest per unit productivity
Answer: d) Oceans have highest per unit productivity
Explanation:
Coral reefs and rainforests have highest per unit productivity; oceans contribute most total due to area.
Q25.
What is the approximate global average NPP of the biosphere?
a) 10 kcal/m²/yr
b) 170 billion tons dry weight/yr
c) 10 billion tons dry weight/yr
d) 1 billion tons dry weight/yr
Answer: b) 170 billion tons dry weight/yr
Explanation:
As per NCERT → Earth’s biosphere NPP ≈ 170 billion tons dry organic matter annually.
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