Question

Kreb's Cycle is

• A. Endothermic and oxidation
• B. Exothermic and reduction
• C. Endothermic and reduction
• D. Exothermic and oxidation

Hint:

Although the Krebs Cycle is classified under cellular respiration as an ______exothermic oxidation______ pathway, it is also termed ______amphibolic______ because some of its intermediate compounds (such as $\alpha$-ketoglutarate and succinyl-CoA) are withdrawn to synthesize amino acids and chlorophyll (anabolism).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The Krebs Cycle (also known as the Citric Acid Cycle or Tricarboxylic Acid Cycle) is the central metabolic pathway of aerobic respiration occurring inside the mitochondrial matrix.
It is responsible for harvesting energy from organic molecules.

Step 2: Detailed Explanation:
Let us analyze the thermodynamic and chemical nature of the Krebs Cycle:
1. ______Thermodynamic Nature (Exothermic/Exergonic):______
The primary purpose of the Krebs cycle is to break chemical bonds in acetyl-CoA to harvest energy.
The overall cycle releases free energy, which is used to directly synthesize GTP/ATP and reduce coenzymes.
Because it releases energy rather than absorbing it, the process is thermodynamically ______exothermic______ (exergonic).
2. ______Chemical Nature (Oxidation):______
The carbon atoms entering the cycle as acetyl-CoA are stepwise oxidized into two molecules of carbon dioxide ($CO_2$).
During these cyclic steps, high-energy electrons are stripped from the carbon substrates and transferred to electron carriers, converting $NAD^+$ to $NADH + H^+$ and $FAD$ to $FADH_2$.
Since the organic substrates undergo a loss of electrons and hydrogen atoms, the chemical process is strictly an ______oxidation______ pathway.
Thus, the Krebs cycle is classified as an exothermic and oxidation process.

Step 3: Final Answer:
Krebs Cycle is an exothermic and oxidation process, which corresponds to option (D).