Question

Strains of Lactobacilli are used to make cheese because they ferment. If a bacterium uses fermentation as its only source of metabolism, it will grow: a. at the same rate in either the absence or presence of oxygen. b. only under anaerobic conditions since fermentation is an anaerobic process. c. much faster if oxygen is available for aerobic respiration. d. best in the absence of oxygen because the bacterium is an anaerobe.

Answer 1

A bacterium that only uses fermentation for metabolism will grow best in the absence of oxygen, as it is likely an anaerobe. Lactobacilli strains used in cheese production are obligate anaerobes and perform lactic acid fermentation, in which milk sugars are turned into lactic acid.

Step-by-step explanation:

If a bacterium uses fermentation as its only source of metabolism, it will grow best in the absence of oxygen because the bacterium is an anaerobe. The correct answer to the question is d. best in the absence of oxygen because the bacterium is an anaerobe. Strains of Lactobacilli, which are used in making cheese, are lactic acid bacteria that perform lactic acid fermentation. This is a process that converts pyruvate and NADH into lactic acid and NAD+, allowing glycolysis to continue in the absence of oxygen.

Lactic acid bacteria such as Lactobacillus and Streptococcus are involved in the production of foods like yogurt and cheese by fermenting milk sugars into lactic acid. This acidification causes the milk to curdle and form cheese. It's important to note that obligate anaerobes, like some fermentation-using bacteria, are poisoned by oxygen, so they grow only under anaerobic conditions.

Furthermore, many prokaryotes are facultatively anaerobic, meaning they can switch between aerobic respiration and fermentation based on oxygen availability. However, in the case of obligate anaerobes and when fermentation is the sole metabolism, the presence of oxygen is detrimental to their growth.