Answer: Saccharomyces cerevisiae.
- A Lactobacillus
- B Aspergillus niger
- C Saccharomyces cerevisiae
- D Rhizobium
Correct answer: C. Saccharomyces cerevisiae
Explanation: Saccharomyces cerevisiae (bakers yeast) ferments sugars to produce CO<sub>2</sub> which causes bread to rise.
Sewage passes through physical removal (primary), then aerobic biological treatment where microbes form flocs that consume organic matter (secondary); the settled activated sludge is then digested anaerobically to produce biogas - a deliberate switch from aerobic to anaerobic conditions between stages.
Concept context
Microorganisms in food, medicine, sewage treatment, biocontrol, and biofertilizers