Which of the following are the three-carbon molecules formed during respiration?

Correct option is C

The correct answer is (c) Lactic acid and pyruvate.
Explanation:

During respiration, particularly anaerobic respiration, the three-carbon molecules produced are pyruvate and lactic acid.
1. Pyruvate: Pyruvate is the end product of glycolysis, which is the first step of cellular respiration. In this process, one molecule of glucose (a 6-carbon molecule) is broken down into two molecules of pyruvate, each having 3 carbon atoms.
2. Lactic Acid: In anaerobic conditions (when oxygen is not available), pyruvate can be converted into lactic acid (also a 3-carbon molecule) through lactic acid fermentation. This process helps regenerate NAD⁺, allowing glycolysis to continue producing ATP without the need for oxygen.
Why the other options are incorrect: 

• Ethanol and lactic acid: Ethanol is produced in anaerobic respiration (fermentation) in yeast, but not directly in animal cells. Ethanol is a 2-carbon molecule, not a 3-carbon molecule.
  
•  Ethanol and malic acid: Malic acid is involved in the citric acid cycle (Krebs cycle), but it is not a direct product of glycolysis or fermentation.
  
•  Pyruvate and ethanol: While pyruvate is produced in glycolysis, ethanol is a product of fermentation in yeast, not in animal cells. Ethanol is a 2-carbon molecule, not a 3-carbon one.
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