Match List I with List II: List I i. Glycolysis ii. ETS iii. Accumulation of protons iv. Krebs' cycle List II a. Inner mitochondrial membrane b. Mitochondrial matrix c. Cytoplasm d. Intermembrane space Choose the correct answer from the options given below:

i – c, ii – a, iii – d, iv – b

i – a, ii – d, iii – c, iv – b

i – d, ii – b, iii – a, iv – c

i – b, ii – c, iii – d, iv – a

Aerobic Respiration

ஏரோபிக் சுவாசம்

NCERT Class 11 · Respiration in Plants · 1 NEET question

Most students confuse aerobic respiration with simple breathing. Oxygen is not just an input; it is the final electron acceptor in the Electron Transport System. Without it, the entire mitochondrial machinery halts instantly.

The idea

Aerobic respiration is the complete oxidation of organic substances in the presence of oxygen. This process occurs within the mitochondria of eukaryotic cells. It yields CO2, water, and a high volume of ATP. The pathway involves Glycolysis, the TCA cycle, and the Electron Transport System.

Why it matters

It is the most efficient way for complex organisms to extract maximum energy from respiratory substrates to support high metabolic demands.

NEET lens

NEET examiners test the location of these reactions and the net ATP yield. Memorize the stoichiometry of the TCA cycle and the specific complexes in the ETS. Do not confuse the mitochondrial matrix reactions with those occurring on the inner membrane.

Clinical significance

Cyanide poisoning is a lethal failure of this process. It binds to Cytochrome c oxidase, blocking the final step of aerobic respiration. This prevents ATP synthesis, leading to rapid cellular death and systemic organ failure.

Introduction

Aerobic respiration is the complete oxidation of glucose to CO₂ and H₂O in the presence of O₂, producing a maximum of ~36-38 ATP per glucose via glycolysis, pyruvate oxidation, Krebs cycle, and oxidative phosphorylation.

Core concept

Overall equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ~36-38 ATP. Four stages: (1) Glycolysis (cytoplasm): glucose → 2 pyruvate, 2 ATP + 2 NADH. (2) Pyruvate oxidation (mitochondrial matrix): 2 pyruvate → 2 acetyl-CoA + 2 CO₂ + 2 NADH. (3) Krebs cycle (matrix): 2 acetyl-CoA → 4 CO₂ + 6 NADH + 2 FADH₂ + 2 ATP. (4) ETC + oxidative phosphorylation (inner membrane): 10 NADH + 2 FADH₂ → ~34 ATP.

Go deeper

Why aerobic > anaerobic: glucose has 686 kcal/mol of chemical energy. Aerobic respiration captures ~277 kcal (~40% efficiency) as ATP. Anaerobic only produces 2 ATP (~14 kcal, ~2% efficiency). The difference is the ETC harnessing 90% of the available energy from NADH/FADH₂.

From Class 10

After glycolysis, if oxygen is available, cells extract far more energy from pyruvate. Aerobic respiration uses oxygen to completely break down glucose.