Question

The common phase between aerobic and anaerobic respiration is called (a) Tricarboxylic acid cycle (b) Oxidative phosphorylation (c) Embden, Meyerhoff, Parnas cycle (d) Kreb's cycle

Short answer

The common phase between aerobic and anaerobic respiration is the Embden, Meyerhoff, Parnas cycle (c)

Step-by-step solution

Understand each term

Aerobic respiration occurs in the presence of oxygen while anaerobic respiration occurs in the absence of oxygen. (a) The Tricarboxylic acid cycle, also known as the citric acid cycle or the Krebs cycle, is a series of chemical reactions used by all aerobic organisms to release stored energy from carbohydrates, fats, and proteins. (b) Oxidative phosphorylation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing the energy stored in the molecular bonds. This process occurs in mitochondria and it's usually responsive to the body's needs for ATP (adenosine triphosphate), hence, is in the pathway of aerobic respiration. (c) The Embden-Meyerhoff-Parnas (EMP) pathway is the sequence of reactions that converts glucose into pyruvate with the concomitant production of a relatively small amount of ATP, this pathway is also known as Glycolysis. (d) As mentioned above, the Kreb’s cycle is another name for the Tricarboxylic acid cycle.

Identify the common phase

Among these reactions, the Embden-Meyerhoff-Parnas cycle, or rather Glycolysis, occurs in both aerobic and anaerobic respiration, because it occurs outside the mitochondria and does not require oxygen. After glycolysis, the resultant products can be further broken down by either aerobic or anaerobic respiration, depending on the availability of oxygen.

Key concepts

Aerobic Respiration

Aerobic respiration is a type of cellular respiration that occurs in the presence of oxygen. It is a multi-step process primarily used by living organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. After glycolysis splits glucose into pyruvate, aerobic respiration continues in the mitochondria. Here, pyruvate is further broken down through the Tricarboxylic Acid Cycle (TCA).
Aerobic respiration is highly efficient, yielding a substantial amount of ATP compared to anaerobic pathways. This efficiency is due to its ability to fully oxidize glucose molecules, capturing a greater amount of energy.
Aerobic respiration not only produces more ATP but also contributes to cellular respiration by producing carbon dioxide and water as its main by-products.

Anaerobic Respiration

Anaerobic respiration is a type of respiration that takes place without the presence of oxygen. While aerobic respiration continues with the Tricarboxylic Acid Cycle, anaerobic respiration transforms the pyruvate from glycolysis into either lactate or ethanol, along with carbon dioxide.
This process does not produce as much ATP as aerobic respiration, but it allows organisms to generate energy quickly under low-oxygen conditions. Anaerobic pathways are crucial in environments where oxygen is scarce or in tissues that might require rapid bursts of energy.

• Lactic Acid Fermentation - Converts pyruvate into lactic acid.
• Alcoholic Fermentation - Turns pyruvate into ethanol and carbon dioxide.

In humans, anaerobic respiration is often experienced during intense exercise, where oxygen supply does not meet the demand.

Embden-Meyerhoff-Parnas Pathway

The Embden-Meyerhoff-Parnas Pathway, more commonly known as Glycolysis, is the first step of cellular respiration universal to both aerobic and anaerobic respiration. This pathway involves the metabolic breakdown of glucose into pyruvate, generating a small yield of ATP and also releasing NADH.
This process occurs in the cytoplasm of the cell and does not require oxygen, which makes it fundamental for both types of respiration.

• Begins with a glucose molecule and ends with two molecules of pyruvate.
• Nets two molecules of ATP and two molecules of NADH per molecule of glucose.

The key significance of glycolysis is its role in allowing cells to release some energy quickly before entering more energy-efficient aerobic pathways or continuing with anaerobic respiration.

Tricarboxylic Acid Cycle

The Tricarboxylic Acid Cycle (TCA), also known as the Krebs Cycle or Citric Acid Cycle, is a crucial part of aerobic respiration that takes place in the mitochondria. It processes pyruvate further, following glycolysis, and plays a major role in energy production.
Through a series of enzyme-catalyzed reactions, the TCA cycle fully oxidizes the acetyl-CoA derived from pyruvate into carbon dioxide. Along this journey, it produces NADH and FADH₂, which are key electron carriers used in oxidative phosphorylation to generate ATP.

• Completes the energy-harvesting phase of aerobic respiration after glycolysis.
• Releases high-energy electrons captured by NADH and FADH₂.

The cycle is integral in energy metabolism and also provides intermediates for biosynthetic processes, underlining its importance in cellular respiration.