Final answer:
An amphibolic pathway is A pathway that is both anabolic and catabolic, involved in both the synthesis and breakdown of molecules, with the citric acid cycle being a prime example. The option (D) is correct.
Step-by-step explanation:
An amphibolic pathway is best described as A pathway that is both anabolic and catabolic. This dual nature means that the pathway can simultaneously be involved in building up larger molecules from smaller ones (anabolism) which requires energy, and breaking down larger molecules into smaller ones (catabolism) which releases energy. The importance of such pathways is highlighted by the citric acid cycle (also known as the tricarboxylic acid cycle or TCA cycle) which has an amphibolic role in metabolism, functioning in both the oxidative degradation of macronutrients and the biosynthesis of essential molecules.
Unlike options A, B, and C, which either describe a pathway's environmental or cellular location, option D accurately describes the functional characteristics of a biochemical pathway. The statement that the pathway only occurs in the mitochondria is an oversimplification. While the mitochondria do house many steps of metabolic pathways, amphibolic pathways, such as the citric acid cycle, occur in both the mitochondria and cytosol of cells and are not restricted to mitochondrial boundaries. Therefore, option (D) is correct.