Question

Two cultures of a facultative anaerobe are grown under identical conditions, except that one was exposed to oxygen and the other was completely deprived of oxygen. What differences would you expect to see between the dry weights of the cultures? Why?

Short answer

The culture exposed to oxygen is expected to have a greater dry weight than the culture deprived of oxygen because facultative anaerobes utilize oxygen for the more efficient process of aerobic respiration, resulting in a larger total biomass.

Step-by-step solution

Understand Facultative Anaerobe Cultures

First, it is important to understand what a facultative anaerobe is. Facultative anaerobes are organisms which can survive in both oxygen-rich and oxygen-poor environments. They generate ATP by aerobic respiration when oxygen is present, but can switch to fermentation or anaerobic respiration when oxygen is absent.

Analyze the Role of Oxygen in Cellular Respiration

Next, analyze the role of oxygen in the process of cellular respiration. Aerobic respiration (respiration in the presence of oxygen) produces significantly more ATP than either fermentation or anaerobic respiration. Therefore, a culture exposed to oxygen would theoretically produce more ATP than one deprived of oxygen.

Predict the Differences in Dry Weights

Based on the above points, it can be predicted that the culture exposed to oxygen will have a greater dry weight than the culture deprived of oxygen. This is because aerobic respiration is a more efficient energy production process and can support greater cell growth and multiplication, leading to a higher overall biomass in the culture.

Key concepts

Cellular Respiration

Think of cellular respiration as a power plant within the cells of living organisms, operating to convert nutrients into energy. This intricate process involves breaking down glucose and other food molecules in the presence of oxygen to generate adenosine triphosphate (ATP), the energy currency of the cell. The stages of cellular respiration include glycolysis, the Krebs cycle, and oxidative phosphorylation.

Facultative anaerobes are particularly interesting because they can switch between oxygen-dependent and oxygen-independent energy production methods depending on their environment. This adaptability allows them to survive in varied conditions where oxygen availability fluctuates, showcasing the versatility of cellular respiration pathways.

Aerobic Respiration

Aerobic respiration is like a marathon runner using oxygen efficiently to go the distance. This process uses oxygen to completely break down glucose into carbon dioxide and water, releasing a substantial amount of ATP in the process. It is the preferred method of energy production for many cells because it yields more ATP compared to other forms of respiration.

In a facultative anaerobe culture exposed to oxygen, aerobic respiration would dominate. This high-efficiency system results in tremendous growth and biomass accumulation, represented by a greater dry weight, as the organism harnesses the maximum energy from its nutrients.

Anaerobic Respiration

When oxygen is not on the guest list, cells turn to anaerobic respiration. It's like a sprint, producing energy quickly but in smaller amounts compared to the marathon of aerobic respiration. This process does not use oxygen and instead relies on alternative electron acceptors to oxidize NADH back to NAD+, necessary for glycolysis to continue.

Anaerobic respiration in facultative anaerobes allows them to survive in oxygen-poor environments, but with less ATP yield. As such, a culture deprived of oxygen would have less energy for growth, leading to a lower dry weight compared to its oxygen-blessed counterpart.

Fermentation

Fermentation is the cellular equivalent of a backup generator—when the main power supply (oxygen) is out, fermentation kicks in. Unlike aerobic and anaerobic respiration, fermentation does not involve an electron transport chain. Instead, it regenerates NAD+ by directly reducing pyruvate or derivatives of it.

This process allows organisms to continue producing ATP through glycolysis but yields far less energy. Fermentation in the oxygen-deprived facultative anaerobe culture results in minimal ATP production, which translates into a smaller increase in dry weight as the cell's growth capacity is limited by available energy.

ATP Production

The common thread linking cellular respiration, aerobic and anaerobic processes, and fermentation is ATP production. ATP acts as a pocket-sized energy packet that cells use to power nearly all their activities. In environments with ample oxygen, ATP production soars due to the efficiency of aerobic respiration. Without oxygen, cells resort to anaerobic respiration or fermentation, both of which generate ATP but are less efficient.

The culture of facultative anaerobes exposed to oxygen would be a powerhouse of ATP production, supporting robust growth. On the other hand, the culture lacking oxygen leans on less productive methods, resulting in a lower yield of ATP and consequently, a lower dry weight. Thus, ATP production is a critical component in understanding the differences between the two cultures' growth.