Respiratory Balance Sheet: Assumptions, Efficiency, and Respiratory Quotient
A respiratory balance sheet summarizes the total ATP yield from complete oxidation of one glucose molecule through glycolysis, Krebs cycle, and electron transport chain. It shows how ATP is produced directly and indirectly from NADH and FADH₂, highlighting the efficiency of aerobic respiration. This concept is essential for NEET and Class 11 Biology as it integrates all stages of cellular respiration into a single energy accounting system.
This Story also Contains
- What Is a Respiratory Balance Sheet?
- Overview of Cellular Respiration Steps
- ATP Yield in Each Step
- NADH And FADH2 Contribution
- ATP Summary Calculation
- Why ATP Yield Varies (27, 30, 32, 36, 38)?
- Significance of the Respiratory Balance Sheet
- Respiratory Quotient NEET MCQs (With Answers & Explanations)
- Recommended video on "Respiratory Balance Sheet"
What Is a Respiratory Balance Sheet?
A respiratory balance sheet is a summary of the input and products of cellular respiration including the amount of ATP produced and used up, together with its relation to main metabolic intermediates. Much of the importance attached to a respiratory balance sheet should deal with the efficiency and the regulation involved in cellular respiration—the process whereby cells convert glucose and oxygen into energy, carbon dioxide, and water. Cellular respiration comprises the processes of glycolysis, the citric acid cycle, and oxidative phosphorylation—all examples of biochemical pathways that support energy production in the cell.
Overview of Cellular Respiration Steps
In cell respiration, glucose and oxygen is converted into ATP, carbon dioxide, and water. It is a very important process for the survival of aerobic organisms because it yields all the required energy for several other cellular activities.
Glycolysis
Glycolysis takes place in the cytoplasm. It breaks one glucose molecule into two pyruvate molecules. The process directly yields 2 ATP molecules while generating 2 NADH molecules.
Krebs Cycle
Krebs cycle occurs in the mitochondrial matrix, where each pyruvate undergoes conversion to Acetyl-CoA and enters the Krebs cycle. The cycle happens twice per every glucose molecule to produce 6 NADH and 2 FADH₂, along with 2 net ATPs.
ETC & Oxidative Phosphorylation
It is located in the mitochondrial inner membrane. NADH and FADH₂ are oxidized, electrons donate their energy in the production of ATP through the process of chemiosmosis
ATP Yield in Each Step
ATP is the main energy equivalent or, in other words, the energy currency of the cell and is always required to drive every biochemical reaction or activity of the cell which makes life possible.
Glycolysis
Direct ATP: 2
NADH: 2 (5 ATP)
Total: 7 ATP
Link Reaction + Krebs Cycle
ATP: 2
NADH: 6 (15 ATP)
FADH2: 2 (3 ATP)
Total: 20 ATP
NADH And FADH2 Contribution
Each NADH molecule can produce approximately 2.5 ATPs in the ETC. Each FADH₂ molecule can produce approximately 1.5 ATPs in the ETC.
Calculation of ATP Contribution
From Glycolysis: 2 NADH × 2.5 ATP/NADH = 5 ATP
From Krebs Cycle: 6 NADH × 2.5 ATP/NADH = 15 ATP
From Krebs Cycle: 2 FADH₂ × 1.5 ATP/FADH₂ = 3 ATP
ATP Summary Calculation
Direct ATP production:
Glycolysis: 2 ATP
Krebs Cycle: 2 ATP
Total Direct ATP: 4 ATP
ATP from NADH: 8 NADH × 2.5 ATP/NADH = 20 ATP
ATP from FADH₂: 2 FADH₂ × 1.5 ATP/FADH₂ = 3 ATP
Total ATP yield per glucose molecule:
Direct ATP + ATP from NADH + ATP from FADH₂ = 4 ATP + 20 ATP + 3 ATP = 27 ATP
Why ATP Yield Varies (27, 30, 32, 36, 38)?
The ATP yield varies because:
Shuttle system used
Mitochondrial membrane leakiness
Proton pumping efficiency
Tissue specific variation
Significance of the Respiratory Balance Sheet
The significance of the respiratory balance sheet is:
Academic Importance
It shows how efficiently cells convert glucose to ATP by comparing theoretical and actual ATP outputs.
It ties together glycolysis, Krebs cycle, and oxidative phosphorylation into one unified energy overview.
Biological Significance
The balance sheet helps estimate total ATP generation and energy availability under different physiological conditions.
Different tissues modify steps of the balance sheet (e.g., shuttle systems), affecting their net ATP yield.
Changes in ATP yield reflect how metabolism adjusts during fasting, exercise, or nutrient shifts.
Respiratory Quotient NEET MCQs (With Answers & Explanations)
Important topics for NEET are:
ATP yield in each step
Significance of respiratory sheet balance
Practice Questions for NEET
Q1. Which of the following respiratory parameters is NOT included in the Respiratory Balance Sheet?
Respiratory rate
Tidal volume
Alveolar ventilation
Serum sodium levels
Correct answer: 4) Serum sodium levels
Explanation:
Serum sodium levels are NOT included in the Respiratory Balance Sheet. The Respiratory Balance Sheet is a tool used to evaluate the effectiveness of respiratory function, and it includes various respiratory parameters such as respiratory rate, tidal volume, alveolar ventilation, oxygen delivery, carbon dioxide elimination, and acid-base balance. The balance between oxygen delivery and carbon dioxide elimination is crucial for maintaining normal acid-base balance and avoiding respiratory acidosis or alkalosis. Other electrolyte levels such as serum potassium and bicarbonate may also be affected by respiratory imbalances, but they are not included in the Respiratory Balance Sheet.
Hence, the correct answer is option 4) Serum sodium levels
Q2. Which of the following is a potential consequence of an imbalance in the Respiratory Balance Sheet?
Hyperventilation
Acidosis
Hyperkalemia
Hypoglycemia
Correct answer: 2) Acidosis
Explanation:
A potential consequence of an imbalance in the Respiratory Balance Sheet is acidosis. This can occur when there is an excess of carbon dioxide in the blood, leading to a decrease in blood pH. Acidosis can have serious consequences on various body functions and systems, such as impaired neurological function, decreased cardiac output, and altered metabolic processes. It is important to maintain a balance between oxygen delivery and carbon dioxide elimination to prevent such imbalances.
Hence, the correct answer is option 2) Acidosis.
Q3. Number of ATP molecules produced via electron transport chain is
25
8
34
31
Correct answer: 3) 34
Explanation:
In the Electron Transport Chain (ETC), energy from high-energy molecules such as NADH and FADH2 is used to produce ATP through a process called oxidative phosphorylation. For every NADH2 molecule, approximately 3 ATPs are generated, and for every FADH2 molecule, about 2 ATPs are produced. However, your statement seems to indicate a different distribution. If we consider the correct ATP yield, NADH contributes around 2.5-3 ATPs and FADH2 contributes around 1.5-2 ATPs in eukaryotes, accounting for a total of about 30 ATPs from NADH and 4 ATPs from FADH2, a summing up to approximately 34 ATPs (or more depending on conditions).
Hence, the correct answer is option 3) 34.
Also Read:
Recommended video on "Respiratory Balance Sheet"
Frequently Asked Questions (FAQs)
A balance sheet would provide details on the following: • Amount of ATP produced in each of the three phases: glycolysis, Krebs cycle, and electron transport chain. • Contribution of the reduced co-enzymes NADH and FADH₂ as electron carriers in terms of ATP produced. Total ATP yield by adding direct ATP production to ATP produced from electron carriers.
Oxygen is important in ETC because the latter cannot take place without oxygen being the last electron acceptor; the reasons for this are explained below.
Electron Transfer: During the mechanism of ETC, the transfer of electrons from one electron carrier to another occurs down their electrochemical gradient in a series of protein complexes within the inner mitochondrial membrane.
Proton Gradient: Electron transport drives the pumping of protons—H⁺ ions—across the membrane, ultimately forming a proton gradient that will drive ATP generation.
Role of Oxygen: At the end of the ETC, oxygen picks up those electrons and joins with H⁺ to form water, H₂O. Without oxygen, this chain cannot continue because the electrons would back up, thus ending the processes of proton pumping and ATP synthesis.
Prevention of Electron Buildup: Oxygen, on getting reduced, prevents the back buildup of electrons. It thereby allows the smooth flow and proper functioning of the ETC.
Aerobic Respiration:
Oxygen Requirement: Requires oxygen
ATP Yield: High yield of ATP (~ 27 ATP per glucose molecule)
Process: The process involves glycolysis, Krebs cycle, and electron transport chain (ETC)
By-products: Carbon dioxide CO₂ and water H₂O.
Anaerobic Respiration:
Oxygen Requirement: No oxygen is required.
ATP Yield: Low yield of ATP, approximately 2 ATP per glucose molecule.
Process: It involves glycolysis succeeded by fermentation.
Products:
In animal Systems: Lactic acid is formed.
In Yeast Systems: Ethanol and carbon dioxide are formed.
This would be the case for mitochondrial health. In that case, the key factors would be:
Mitochondrial Efficiency: Healthy mitochondria go through the complete cycles of Krebs and the electron transport chain, hence producing ATP optimally.
Oxidative Stress: If mitochondria are damaged, more ROS will be produced, which possibly inactivate ETC components and thus decrease yields of ATP.
Mitochondrial DNA: Its mutation or damage leads to impairment in the expression of critical proteins involved in the process of ATP synthesis.
Supply of Nutrients: The supply of nutrients to the mitochondria at an appropriate level is essential for energy production. Poor nutrition negatively impacts mitochondrial function.