In the context of BOD testing, what does synthesis refer to?

• A. Bacteria release energy by respiration
• B. Bacteria take in BOD and make new cells
• C. Bacteria break down complex molecules to release energy
• D. Bacteria convert BOD into carbon dioxide

Answer: (B)

In BOD testing, synthesis means the microbes use the biodegradable material as building blocks to grow and form new cells. This is the biosynthetic, or anabolic, part of metabolism where carbon from the substrate is turned into cellular components like proteins, nucleic acids, and membranes to produce new biomass.

Oxygen is consumed not only for energy release during breaking down substrates (catabolism) but also because the growing cells require oxygen for various metabolic processes. The option about respiration or breaking down molecules to release energy describes these catabolic, energy-generating processes, not the creation of new cell material. The idea of simply converting BOD into carbon dioxide is also not accurate in this context, since BOD refers to the amount of oxygen needed to oxidize the organic matter, while synthesis specifically points to building new cells from that material.

So the best understanding is that bacteria take in BOD and make new cells.