Q.19 Botany ⭐ 360° Option Elimination Active

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NEET 2020 Botany Question 19 Solution

Topic: Breathing and Exchange of Gases · Official NTA Booklet Code E1

Question

Identify the wrong statement with reference to transport of oxygen.

(1)Binding of oxygen with haemoglobin is mainly related to partial pressure of O2.
(2)Partial pressure of CO2 can interfere with O2 binding with haemoglobin.
(3)Higher H+ conc. in alveoli favours the formation of oxyhaemoglobin.
(4)Low pCO2 in alveoli favours the formation of oxyhaemoglobin.

✓

Verified Against NTA Final Answer Key

Option (3) : Higher H+ conc. in alveoli favours the formation of oxyhaemoglobin.

📚 Breathing and Exchange of Gases Easy

📋 Given Parameters & Problem Setup

Physiological Process Transport of Oxygen / Oxyhaemoglobin Dynamics

Microenvironment Pulmonary Alveoli vs Systemic Tissues

Question Objective Identify the WRONG / incorrect statement

⚡

The 30-Second Exam Hall Shortcut: ⚡ "Alveoli Must Have LESS H⁺ (Higher pH) to Form Oxyhaemoglobin!"

⏱️ Save ~20 seconds

At the alveoli, loading oxygen requires high pO₂, low pCO₂, LESS H⁺ concentration (alkaline pH), and lower temperature. Higher H⁺ (acidity) shifts the curve to the RIGHT and promotes DISSOCIATION (Bohr effect). Statement (3) claims higher H⁺ favours formation — which is completely WRONG! Select Option (3).

1 Recall alveolar conditions for oxyhaemoglobin formation: High

pO_2

, low

pCO_2

, LESS

H^+

conc. (high pH), and lower temperature.

2 Recall Bohr effect: Elevated

[H^+]

(acidity) weakens oxygen binding and causes O₂ dissociation in tissues.

3 Analyze Statement (3): Claims "Higher H+ conc. in alveoli favours the formation" -> Blatantly false!

4 Option (3) is the wrong statement and therefore the correct answer.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Breathing and Exchange of Gases (Transport of Gases: In the alveoli, where there is high pO2, low pCO2, lesser H+ concentration and lower temperature, the factors are all favourable for the formation of oxyhaemoglobin, whereas in the tissues, low pO2, high pCO2, high H+ concentration and higher temperature exist, the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin).

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Allosteric Regulation of Oxygen-Haemoglobin Binding

The reversible oxygenation of haemoglobin to form oxyhaemoglobin ( $Hb(O_2)_4$ ) is governed by local allosteric modulators: - In Pulmonary Alveoli: Environmental conditions favor maximal oxygen saturation (leftward shift of dissociation curve): 1. High partial pressure of oxygen ( $pO_2 \approx 104\text{ mm Hg}$ ). 2. Low partial pressure of carbon dioxide ( $pCO_2 \approx 40\text{ mm Hg}$ ). 3. Lesser $H^+$ concentration (higher, slightly alkaline pH $\approx 7.4$ ). 4. Lower body temperature. - In Systemic Tissues: Cellular respiration generates $CO_2$ and lactic acid, creating: 1. Low $pO_2$ ( $40\text{ mm Hg}$ ). 2. High $pCO_2$ ( $45\text{ mm Hg}$ ). 3. High $H^+$ concentration (acidosis). 4. Elevated temperature. - High $[H^+]$ protonates key histidine residues on haemoglobin subunits, stabilizing the low-affinity deoxygenated T-state (Bohr effect) and promoting oxygen dissociation, never formation.

\text{Alveoli} \implies \begin{cases} \mathbf{\uparrow pO_2} & \\ \mathbf{\downarrow pCO_2} & \\ \mathbf{\downarrow [H^+]} & (\mathbf{Lesser\,H^+\,Concentration}) \\ \mathbf{\downarrow \text{Temp}} & \end{cases} \implies \mathbf{Favour\,Oxyhaemoglobin\,Formation}

Step 2

Statement Evaluation

Statement (3) asserts that "Higher H+ conc. in alveoli favours the formation of oxyhaemoglobin." This directly contradicts the Bohr effect and textbook facts; therefore, statement (3) is false and is the correct response.

⭐

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:

This is a true statement. pO2 is the primary determining factor governing cooperative oxygen binding.

⚠️

Student Fallacy (Why candidates pick this trap): Overlooking that pO2 is the principal driver of oxygen saturation.

2 B

✗ Incorrect

Verdict & Scientific Reason:

This is a true statement. Increased pCO2 decreases hemoglobin affinity for oxygen (Bohr effect).

⚠️

Student Fallacy (Why candidates pick this trap): Denying the competitive allosteric role of carbon dioxide.

3 C

✓ 100% Correct

Verdict & Scientific Reason:

Correct as the wrong statement. Lesser H+ concentration (not higher) in alveoli favours oxyhaemoglobin formation.

💡

Why this is airtight: None. Candidate accurately remembers that low H+ (high pH) is required at the alveoli.

4 D

✗ Incorrect

Verdict & Scientific Reason:

This is a true statement. Low pCO2 in alveoli shifts the curve to the left, promoting O2 loading.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing alveolar pCO2 with tissue pCO2.

⚠️

NTA Trap Alert: H⁺ Concentration vs pH Reciprocal Trap

Remember that higher $[H^+]$ means *lower pH* (acidic, which unloads oxygen). Lower $[H^+]$ means *higher pH* (alkaline, which loads oxygen in the alveoli). The prompt uses "Higher H+ conc." which causes oxygen release, not binding.

🛡️ How to avoid the -1 mark: Remember: Alveoli = Less H⁺ (Basic); Tissues = More H⁺ (Acidic).

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Core NEET Syllabus Standard

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

Core Scientific Principle Tested:

"Lesser H+ concentration (higher pH) in alveoli favours oxyhaemoglobin formation."

Syllabus Focus: Transport of Oxygen

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Botany Question 19 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Alveoli Must Have LESS H⁺ (Higher pH) to Form Oxyhaemoglobin!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Allosteric Regulation of Oxygen-Haemoglobin Binding

Statement Evaluation

360° Option Elimination Engine Key Feature

NTA Trap Alert: H⁺ Concentration vs pH Reciprocal Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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