In which of the following processes, Bacteria is NOT used?

Concept: Microorganisms are not a single uniform group — bacteria, fungi, and protozoa each carry out distinct biological transformations. Whether a given process involves bacteria depends entirely on which specific microorganism drives the underlying chemical change in that process.

Application: Baking of bread, as commonly practiced and taught at this level, depends on baker's yeast (Saccharomyces cerevisiae), a fungus rather than a bacterium. Yeast ferments the sugars present in dough anaerobically, releasing carbon dioxide gas that gets trapped in the gluten network and makes the dough rise; this standard yeast-leavened process does not involve bacterial fermentation.

• Formation of curd: Lactobacillus bacteria convert lactose (milk sugar) into lactic acid, which curdles the milk protein casein — bacteria are directly responsible for this process.

• Fermentation of sugarcane juice: the standard example taught at this level is bacteria fermenting sugarcane juice into vinegar, so this process is treated as bacteria-driven here.

• Nitrogen fixation: Rhizobium bacteria living in the root nodules of leguminous plants convert atmospheric nitrogen into a usable form — again a bacterial process.

Cross-check: under the standard convention taught for this topic, baking of bread is the process carried out by a fungus (yeast) rather than a bacterium, while curd formation, sugarcane-juice fermentation, and nitrogen fixation are the bacterial actions taught alongside it. This is the convention behind the official CTET Paper 2 (December 2019) answer key, which keys baking of bread as the process where bacteria are not used.