Kreb's cycle

Options

A. Liberates a minor part of energy during respiration
B. Is operative in photorespiration
C. Reactions are independent of oxygen supply
D. Is a link between carbohydrate and nitrogen metabolism

Answer

### Step-by-Step Solution for Kreb's Cycle

1. **Definition of Krebs Cycle**: The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, is a series of chemical reactions that occur in aerobic organisms. It is crucial for the release of stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.

2. **Energy Liberation**: The primary function of the Krebs cycle is to liberate energy. During the cycle, high-energy electron carriers such as NADH and FADH2 are produced. These carriers are essential for the electron transport chain, where most of the ATP is generated.

3. **Oxygen Requirement**: Although the Krebs cycle does not directly use oxygen, it is dependent on it indirectly. The cycle produces NADH and FADH2, which require oxygen for their oxidation in the electron transport chain. If oxygen is not available, the Krebs cycle will halt due to a lack of these electron carriers.

4. **Relation to Metabolism**: The Krebs cycle serves as a link between various metabolic pathways, particularly carbohydrate, fat, and protein metabolism. However, it is more specifically linked to the metabolism of acetyl-CoA and does not directly link carbohydrate and nitrogen metabolism.

5. **Evaluation of Options**:
- **Option A**: "Liberates a minor part of energy during respiration." - This is correct as the Krebs cycle does release energy.
- **Option B**: "It's operative in photorespiration." - This is incorrect; the Krebs cycle is part of aerobic respiration, not photorespiration.
- **Option C**: "Reactions are independent of oxygen supply." - This is incorrect; while the cycle does not require oxygen directly, it is dependent on it for the regeneration of NAD and FAD.
- **Option D**: "It's a link between carbohydrate and nitrogen metabolism." - This is incorrect; the Krebs cycle primarily links to carbohydrate and fat metabolism, not directly to nitrogen metabolism.

6. **Conclusion**: The correct answer is **Option A**, which states that the Krebs cycle liberates a minor part of energy during respiration.