Question

A scientist is studying the respiration reactions carried out by a certain bacterium. Which of these would indicate that the respiration reactions occurring are anaerobic?

Answer 1

Lack of oxygen, presence of alternative electron acceptors, or production of fermentation products indicate anaerobic respiration.

Here are some indications that the respiration reactions occurring in a bacterium are anaerobic:

1. Absence of oxygen: This is the most obvious indication. If the bacterium is not exposed to oxygen, it will not be able to carry out aerobic respiration.
2. Presence of alternative electron acceptors: In the absence of oxygen, some bacteria can use other molecules as electron acceptors in their respiration reactions. These alternative electron acceptors can include nitrate, sulfate, or fumarate.
3. Production of fermentation products: Fermentation is a type of anaerobic respiration that produces organic waste products, such as lactate, ethanol, or carbon dioxide. If the bacterium is producing these products, it is a strong indication that it is carrying out anaerobic respiration.
4. Lack of a cytochrome oxidase enzyme: Cytochrome oxidase is an enzyme that is essential for aerobic respiration. If the bacterium does not have this enzyme, it will not be able to carry out aerobic respiration.
5. Growth in an oxygen-free environment: Some bacteria are obligate anaerobes, which means that they can only grow in the absence of oxygen. If the bacterium can grow in an oxygen-free environment, it is a strong indication that it is an anaerobe.

Here are some specific examples of bacteria that carry out anaerobic respiration:

• Lactic acid bacteria: These bacteria are responsible for the fermentation of milk into yogurt and cheese. They produce lactate as a fermentation product.
• Clostridium botulinum: This bacterium is responsible for botulism, a serious foodborne illness. It produces botulinum toxin, which is one of the deadliest toxins known.
• Desulfovibrio desulfuricans: This bacterium is responsible for the reduction of sulfate to sulfide in the environment. It produces hydrogen sulfide as a waste product.

By looking for these clues, scientists can determine whether or not a bacterium is carrying out anaerobic respiration.