Final answer:
Catabolic pathways use varied substrates to produce few products and alongside anabolic pathways, they maintain energy balance within cells.
Metabolic pathways are efficient, with anaplerotic reactions replenishing intermediates, contrary to the suggested wastefulness.
Therefore, the correct answer is: option "catabolic pathways use a wide variety of substrates to produce a small number of waste products.".
Step-by-step explanation:
The correct statement regarding metabolic pathways is that catabolic pathways use a wide variety of substrates to produce a small number of waste products. Metabolic pathways consist of anabolic and catabolic processes which are essential for maintaining the cell's energy balance.
Anabolic pathways require energy to synthesize larger molecules from smaller ones, while catabolic pathways generate energy by breaking down larger molecules into smaller ones. The statement that catabolic pathways are generally reductive is incorrect, as they are actually oxidative, breaking down molecules to release energy.
Also, NAD+ is utilized as an oxidizing agent in catabolic reactions to accept electrons, becoming NADH, whereas NADPH is used as a reducing agent in anabolic pathways to donate electrons.
Moreover, the idea that an amphiboic pathway is extremely wasteful because it operates as both anabolic and catabolic is incorrect.
These pathways are actually economical and efficient, providing a means to adapt metabolism to the cell's needs. The presence of anaplerotic reactions in metabolism illustrates its economy by replenishing intermediates in the pathway, rather than being wasteful.