Q.69 Zoology ⭐ 360° Option Elimination Active

NEET 2020 Zoology Question 69 Solution

Topic: Ecosystem · Official NTA Booklet Code E1

Question

In relation to Gross primary productivity and Net primary productivity of an ecosystem, which one of the following statements is correct?

(1)Gross primary productivity is always less than net primary productivity.
(2)Gross primary productivity is always more than net primary productivity.
(3)Gross primary productivity and Net primary productivity are one and same.
(4)There is no relationship between Gross primary productivity and Net primary productivity.

✓

Verified Against NTA Final Answer Key

Option (2) : Gross primary productivity is always more than net primary productivity.

📚 Ecosystem Easy

📋 Given Parameters & Problem Setup

Ecological Concepts Gross Primary Productivity (GPP), Net Primary Productivity (NPP), Respiration Losses (R)

Biophysical Relationship NPP = GPP - R

⚡

The 30-Second Exam Hall Shortcut: ⚡ "NPP = GPP - R: GPP is ALWAYS MORE than NPP!"

⏱️ 20 seconds

Gross primary productivity (GPP) is the total rate of organic matter synthesis. A considerable portion is consumed in plant respiration (R). Net primary productivity is the remainder: $NPP = GPP - R$ . Since plants always respire ( $R > 0$ ), GPP is ALWAYS MORE than NPP! Mark Option (2) in 5 seconds.

1 Recall formula: NPP = GPP - R.

2 Total production = GPP; Respiration loss = R; Remaining available biomass = NPP.

3 Since R is always greater than 0, GPP must always exceed NPP.

4 Select Option (2) Gross primary productivity is always more than net primary productivity.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Ecosystem (Productivity: Gross vs Net Primary Productivity)

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Define Gross Primary Productivity (GPP)

Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis by all primary producers.

Step 2

Account for Respiration Losses (R)

Plants must continually utilize their synthesized organic compounds for their own cellular respiration (R) to support active transport, maintenance, and metabolic processes.

Step 3

Define Net Primary Productivity (NPP)

Net primary productivity is the biomass remaining after accounting for respiratory losses: $\text{NPP} = \text{GPP} - R$ This net biomass is what is available to herbivores and decomposers.

Step 4

Deduce Relative Magnitude

Because living autotrophs inevitably lose energy through respiration ( $R > 0$ ), Gross Primary Productivity is strictly and always greater than Net Primary Productivity.

⭐

360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 A

✗ Incorrect

Verdict & Scientific Reason:

Physically impossible; total synthesized energy (GPP) cannot be less than the net energy remaining after metabolic losses.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing Gross and Net definitions.

2 B

✓ 100% Correct

Verdict & Scientific Reason:

Factually and ecologically exact; GPP equals NPP plus respiratory losses, so GPP is always greater than NPP.

💡

Why this is airtight: None; fundamental ecological energy balance.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; they could only be equal if respiration were zero ( $R = 0$ ), which is biologically impossible in living organisms.

⚠️

Student Fallacy (Why candidates pick this trap): Ignoring respiratory losses in autotrophs.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; they are mathematically and biologically linked by the equation $\text{NPP} = \text{GPP} - R$ .

⚠️

Student Fallacy (Why candidates pick this trap): Dismissing the definitive physiological relationship.

⚠️

NTA Trap Alert: Accounting Analogy: Gross Salary vs Net Salary

Gross Salary (Total Earned) = GPP. Taxes (Cost of Living/Respiration) = R. Net Take-Home Salary = NPP. Gross is always greater than Net!

🛡️ How to avoid the -1 mark: Gross = Total before deduction; Net = Leftover after deduction. GPP > NPP always!

📖

Core NEET Syllabus Standard

Zoology · Ecosystem Standard Benchmark

Core Scientific Principle Tested:

Syllabus Focus: Gross Primary Productivity (GPP) vs Net Primary Productivity (NPP)

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Zoology Question 69 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "NPP = GPP - R: GPP is ALWAYS MORE than NPP!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Define Gross Primary Productivity (GPP)

Account for Respiration Losses (R)

Define Net Primary Productivity (NPP)

Deduce Relative Magnitude

360° Option Elimination Engine Key Feature

NTA Trap Alert: Accounting Analogy: Gross Salary vs Net Salary

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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