Penicillin production relies on fungal metabolism using sugar as the primary energy source Steps: - Identify that penicillin is produced by Penicillium fungi via fermentation, requiring nutrients for growth and secondary metabolite production. - Recall that the fungus uses a carbon source like glucose to generate energy and precursors for antibiotic synthesis. - Note that in large-scale fermenters, the medium includes sugar as the key substrate to sustain high-yield production. - Eliminate options not central to the biosynthetic pathway: CO2 is a byproduct, oxygen aids aeration but isn't the main substance, and mineral ions are supplementary. Why D is correct: - Sugar (e.g., glucose) serves as the carbon and energy source in the fermentation medium, directly fueling the fungal metabolism needed for penicillin biosynthesis. Why the others are wrong: - A. Carbon dioxide is produced during respiration, not required as an input for penicillin production. - B. Mineral ions support general growth but are not the primary substance for antibiotic synthesis. - C. Oxygen is necessary for aerobic conditions but functions as an environmental factor, not a consumed substrate like …