Final answer:
NADPH is not formed during the Krebs cycle; whereas CO2, FADH2, and NADH are all products of this cycle. NADPH is produced during photosynthesis and the pentose phosphate pathway. Option 4 is correct.
Step-by-step explanation:
The molecule that is not formed during the Krebs cycle (also known as the citric acid cycle or the tricarboxylic acid cycle) is NADPH. This cycle is a series of chemical reactions used by all aerobic organisms to generate energy. During the Krebs cycle, two molecules of CO2 are released, FADH2 is produced, and NADH is also generated by the oxidation of NAD+.
Regarding the formation of NADPH, it is produced during photosynthesis in plants (not during the Krebs cycle) and via the pentose phosphate pathway in both plants and animals. Hence, out of the options provided - CO2, FADH2, NADH, and NADPH - the answer is NADPH, as this is not a product of the Krebs cycle.
The molecule that is not formed during the Krebs cycle is NADPH. The Krebs cycle, also known as the citric acid cycle, produces several important molecules including CO₂, FADH₂, and NADH. These molecules play significant roles in cellular respiration and the production of ATP.