Question

question 27
mixed acid fermentation
a occurs in all bacteria
b produces several different acids plus co₂ and h₂ gases
c also produces ethanol
d is seen in streptococcus and lactobacillus
e produces butyric acid

Explanation:

Mixed acid fermentation is a type of fermentation where bacteria produce multiple acids (such as lactic acid, acetic acid, formic acid) along with \(CO_2\) and \(H_2\) gases.

• Option A: Not all bacteria undergo mixed - acid fermentation. For example, some bacteria may undergo ethanol fermentation or butyric acid fermentation.
• Option C: Ethanol is not a major product of mixed - acid fermentation. Ethanol is more characteristic of yeast fermentation (alcoholic fermentation) or some bacterial fermentations like Zymomonas mobilis.
• Option D: Streptococcus and Lactobacillus are more known for homolactic or heterolactic fermentation (producing mainly lactic acid or lactic acid along with some other products like ethanol and \(CO_2\) in heterolactic case), not mixed - acid fermentation.
• Option E: Butyric acid is produced in butyric acid fermentation, not in mixed - acid fermentation.

Answer:

B. produces several different acids plus \(CO_2\) and \(H_2\) gases