Which molecule from glycolysis or the citric acid pathway serves as the building block for lipid synthesis?

Answer: Acetyl-CoA

Explanation:

Acetyl-CoA can be obtained from the pyruvate, the end product of aerobic glycolysis. Also, Acetyl-CoA is the one of the starting materials of citric acid cycle.

For lipid synthesis, biotin carries activated CO2 that is incorporated into acetyl-CoA to form Malonyl-CoA, which is then elongated to yield various lipids of different length.

Thus, Acetyl-CoA is the building block of lipid synthesis