Question

Two cultures of a facultative anaerobe are grown in the same type of medium, but one is exposed to air and the other is maintained under anaerobic conditions. Which of the two cultures will contain more cells at the end of a week? Why?

Short answer

The culture exposed to air will contain more cells at the end of a week because facultative anaerobes can undergo a more efficient cellular respiration process in the presence of oxygen.

Step-by-step solution

Understanding the Organism Type

A facultative anaerobe refers to an organism that makes ATP by aerobic respiration if oxygen is present but is also capable of switching to fermentation or anaerobic respiration if oxygen is absent. This means it can efficiently grow under both aerobic and anaerobic environments.

Analyzing the Conditions

The condition that is exposed to air (oxygen) would imply an aerobic environment while the other one maintained under anaerobic condition offers a non-oxygen environment.

Predicting the Outcome

Given the nature of facultative anaerobes, they can survive in both conditions. However, the process of aerobic respiration is more efficient in producing ATP than anaerobic respiration or fermentation. Thus, in the presence of oxygen, these organisms prefer to undergo aerobic respiration.

Final Conclusion

Given the efficiency of energy production, the culture exposed to air (oxygen) will likely contain more cells at the end of a week, as the facultative anaerobe can generate more ATP (and thus support higher growth rates) in this condition.

Key concepts

Aerobic Respiration

Aerobic respiration is a cellular process that takes place in the presence of oxygen. It is one of the most efficient ways for cells to produce energy. Facultative anaerobes, when oxygen is available, will use this process to maximize their energy yield. During aerobic respiration, glucose is broken down and converted into carbon dioxide and water. This process occurs in the mitochondria of cells, utilizing oxygen to help extract the maximum amount of energy from the glucose molecule.

The reason aerobic respiration is so effective is due to the number of ATP molecules it generates. Producing roughly 36 to 38 ATP from one molecule of glucose, aerobic respiration provides much more energy than anaerobic processes. This abundance of ATP allows facultative anaerobes to grow and reproduce rapidly when oxygen is present, leading to more cells in cultures exposed to air.

Anaerobic Conditions

Anaerobic conditions refer to environments without oxygen. Facultative anaerobes are versatile because they can grow in both the presence and absence of oxygen, but their mode of energy production changes in these conditions. When oxygen is not available, these organisms switch to anaerobic respiration or fermentation.

In anaerobic metabolism, facultative anaerobes metabolize substrates inefficiently, producing less ATP. These processes include glycolysis followed by fermentation or anaerobic respiratory chains. Common byproducts can include lactic acid or ethanol, depending on the organism and specific conditions. Due to less energy being produced in these conditions, growth rates are significantly slower compared to aerobic environments, resulting in fewer cells in cultures that were maintained anaerobically.

ATP Production

ATP, or Adenosine Triphosphate, is essentially the energy currency of the cell. It powers various cellular activities, from muscle contractions to nerve impulse propagation. For facultative anaerobes, the primary concern is energy efficiency. These organisms aim to produce as much ATP as possible from the substrates they metabolize.

Under aerobic conditions, the production of ATP is maximized, thanks to the presence of oxygen which allows the complete oxidation of glucose. However, when oxygen is unavailable, facultative anaerobes rely on less efficient pathways. These pathways reduce the number of ATP molecules generated (often as few as 2 ATP per glucose via fermentation), which reduces the energy available for cell division and growth.

Ultimately, the efficiency in ATP production is what dictates the growth potential. In the presence of oxygen, more ATP means more energy for growth, leading to higher cell counts in cultures grown under aerobic conditions.