Use the following choices to answer questions 7–10.
a. E. coli growing in glucose broth at 35℃ with O₂ for 5 days
b. E. coli growing in glucose broth at 35℃ without O₂ for 5 days
c. both a and b
d. neither a nor b


Which culture produces the most lactic acid?

Verified step by step guidance

1. Understand the metabolic pathways involved: E. coli can undergo aerobic respiration in the presence of O₂ and fermentation in the absence of O₂.
2. Identify the conditions for each scenario: (a) is aerobic with O₂, and (b) is anaerobic without O₂.
3. Recall that lactic acid is a product of fermentation, not aerobic respiration.
4. Determine which condition (a or b) would lead to fermentation: E. coli will ferment glucose to lactic acid in the absence of O₂.
5. Conclude that the culture growing without O₂ (b) will produce the most lactic acid.

Key Concepts

Lactic Acid Fermentation

Lactic acid fermentation is an anaerobic process where glucose is converted into lactic acid by certain bacteria, including E. coli, when oxygen is scarce. This process is crucial for energy production in environments lacking oxygen, leading to the accumulation of lactic acid as a byproduct. Understanding this concept helps in predicting which growth conditions favor lactic acid production.

Aerobic vs. Anaerobic Metabolism

Aerobic metabolism occurs in the presence of oxygen and typically yields more energy (ATP) from glucose compared to anaerobic metabolism, which occurs without oxygen. E. coli can switch between these two metabolic pathways, affecting the types and amounts of byproducts produced, including lactic acid. Recognizing the differences between these metabolic processes is essential for determining the conditions that lead to lactic acid production.

Effect of Oxygen on Metabolite Production

The presence or absence of oxygen significantly influences the metabolic pathways utilized by microorganisms. In the case of E. coli, oxygen availability can shift the fermentation process towards either lactic acid production or complete oxidation of glucose to carbon dioxide and water. This concept is vital for understanding how different growth conditions impact the overall yield of lactic acid in cultures.