Q.183 Zoology ⭐ 360° Option Elimination Active

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NEET 2021 Zoology Question 183 Solution

Topic: Breathing and Exchange of Gases · Official NTA Booklet Code M1

Question

The partial pressures (in mm Hg) of oxygen (O2) and carbon dioxide (CO2) at alveoli (the site of diffusion) are:

(1)pO2=104 and pCO2=40
(2)pO2=40 and pCO2=45
(3)pO2=95 and pCO2=40
(4)pO2=159 and pCO2=0.3

✓

Verified Against NTA Final Answer Key

Option (1) : pO2=104 and pCO2=40

📚 Breathing and Exchange of Gases Easy

📋 Given Parameters & Problem Setup

Site of Diffusion Pulmonary Alveoli

Target Gases Oxygen (O₂) and Carbon Dioxide (CO₂)

Units mm Hg

Question Objective Identify exact standard partial pressures pO₂ and pCO₂

⚡

The 30-Second Exam Hall Shortcut: ⚡ "Alveolar Pressures: 104 and 40 mm Hg"

⏱️ Save ~20 seconds

In pulmonary alveoli, the partial pressure of oxygen is 104 mm Hg and carbon dioxide is 40 mm Hg. This creates the exact steep gradient needed to oxygenate deoxygenated venous blood (pO₂ = 40, pCO₂ = 45)! Mark Option (1) instantly.

1 Recall NCERT Table of Partial Pressures: - Atmosphere:

pO_2 = 159

pCO_2 = 0.3

- Alveoli:

pO_2 = 104

pCO_2 = 40

- Deoxygenated blood:

pO_2 = 40

pCO_2 = 45

- Oxygenated blood:

pO_2 = 95

pCO_2 = 40

- Tissues:

pO_2 = 40

pCO_2 = 45

2 Identify Alveoli values:

pO_2 = 104\text{ mm Hg}

and

pCO_2 = 40\text{ mm Hg}

3 Select Option (1).

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Breathing and Exchange of Gases (Exchange of Gases: Partial pressures of oxygen and carbon dioxide at alveoli are pO2 = 104 mm Hg and pCO2 = 40 mm Hg).

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Partial Pressure Gradients Across Respiratory Compartments

Gas exchange across the alveolar-capillary respiratory membrane proceeds purely by simple passive diffusion governed by partial pressure gradients, gas solubility, and membrane thickness: - Atmospheric Air: $pO_2 = 159\text{ mm Hg}$ , $pCO_2 = 0.3\text{ mm Hg}$ . - Alveoli: $pO_2 = \mathbf{104\text{ mm Hg}}$ , $pCO_2 = \mathbf{40\text{ mm Hg}}$ . - Deoxygenated Blood (Pulmonary Artery): $pO_2 = 40\text{ mm Hg}$ , $pCO_2 = 45\text{ mm Hg}$ . - Oxygenated Blood (Pulmonary Vein / Systemic Arteries): $pO_2 = 95\text{ mm Hg}$ , $pCO_2 = 40\text{ mm Hg}$ . - Tissues: $pO_2 = 40\text{ mm Hg}$ , $pCO_2 = 45\text{ mm Hg}$ .

\text{Alveoli} \implies \begin{cases} \mathbf{pO_2} & = 104\text{ mm Hg} \\[3pt] \mathbf{pCO_2} & = 40\text{ mm Hg} \end{cases}

Step 2

Analysis of Diffusion Direction

- For $O_2$ : Gradient is from alveoli ( $104\text{ mm Hg}$ ) to deoxygenated capillary blood ( $40\text{ mm Hg}$ ), driving rapid influx of oxygen into blood. - For $CO_2$ : Gradient is from blood ( $45\text{ mm Hg}$ ) to alveoli ( $40\text{ mm Hg}$ ), driving excretion of carbon dioxide into alveolar air.

⭐

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 1

✓ 100% Correct

Verdict & Scientific Reason:

Correct. Perfectly matches canonical alveolar partial pressures.

💡

Why this is airtight: None. Candidate accurately remembers the standard gas values.

2 2

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. These are the partial pressures of deoxygenated blood and tissues, not alveoli.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing alveolar values with venous blood or tissue values.

3 3

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. These are the partial pressures of oxygenated systemic arterial blood.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing alveolar pO2 (104) with arterial blood pO2 (95) after physiological shunting.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. These are the partial pressures of dry ambient atmospheric air.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing ambient atmospheric air with humidified alveolar gas mixture.

⚠️

NTA Trap Alert: Alveoli (104) vs Arterial Blood (95) vs Atmospheric (159) Trap

NTA includes all 4 standard compartments in the options: Option 1 is Alveoli (104/40), Option 2 is Venous/Tissue (40/45), Option 3 is Arterial blood (95/40), and Option 4 is Atmospheric air (159/0.3).

🛡️ How to avoid the -1 mark: Commit the numerical pair to memory: Alveoli = 104 and 40.

📖

Core NEET Syllabus Standard

NEET / NCERT Biology · Breathing and Exchange of Gases Standard Benchmark

Core Scientific Principle Tested:

"Partial pressures of O2 and CO2 at alveoli are 104 mm Hg and 40 mm Hg respectively."

Syllabus Focus: Exchange of Gases

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2021 Zoology Question 183 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Alveolar Pressures: 104 and 40 mm Hg"

Step-by-Step Rigorous Workflow & Mathematical Proof

Partial Pressure Gradients Across Respiratory Compartments

Analysis of Diffusion Direction

360° Option Elimination Engine Key Feature

NTA Trap Alert: Alveoli (104) vs Arterial Blood (95) vs Atmospheric (159) Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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