Question

Consider the following statements with respect to respiration. (i) Glycolysis occurs in the cytoplasm of the cell. (ii) Aerobic respiration takes place within the mitochondria. (iii) Electron transport system is present in the outer mitochondrial membrane. (iv) \(\mathrm{C}_{51} \mathrm{H}_{98} \mathrm{O}_{6}\) is the chemical formula of tripalmitin, a fatty acid. (v) Respiratory quotient \(=\frac{\text { Volume of } \mathrm{O}_{2} \text { evolved }}{\text { Volume of } \mathrm{CO}_{2} \text { consumed }}\) Of the above statements (a) (i), (ii) and (iv) are correct (b) (ii), (iii) and (iv) are correct (c) (iii), (iv) and (v) are correct (d) (ii), (iv) and (v) are correct.

Short answer

(i), (ii), and (iv) are correct, making option (a) the correct answer.

Step-by-step solution

Evaluate Statement (i)

Assess the validity of statement (i) which states that glycolysis occurs in the cytoplasm of the cell. It is a well-known fact in cell biology that glycolysis, the process of breaking down glucose into pyruvate, takes place in the cytoplasm of cells. Therefore, statement (i) is correct.

Evaluate Statement (ii)

Examine statement (ii) which indicates that aerobic respiration takes place within the mitochondria. Aerobic respiration, which includes the Krebs cycle and oxidative phosphorylation, indeed occurs in the mitochondria of eukaryotic cells. Hence, statement (ii) is also correct.

Evaluate Statement (iii)

Assess the accuracy of statement (iii) about the electron transport system (ETS) being present in the outer mitochondrial membrane. The ETS is actually part of the inner mitochondrial membrane, not the outer membrane. Therefore, statement (iii) is incorrect.

Evaluate Statement (iv)

Validate statement (iv) which says that the chemical formula of tripalmitin, a common fat, is \(\mathrm{C}_{51} \mathrm{H}_{98} \mathrm{O}_{6}\). Tripalmitin is indeed a triglyceride made up of three palmitic acid molecules and one glycerol molecule, its formula is \(\mathrm{C}_{51} \mathrm{H}_{98} \mathrm{O}_{6}\), meaning statement (iv) is correct.

Evaluate Statement (v)

Review statement (v) which defines the respiratory quotient (RQ) as the volume of \(\mathrm{O}_{2}\) evolved over the volume of \(\mathrm{CO}_{2}\) consumed. However, this definition has its terms reversed; the RQ is actually the volume of \(\mathrm{CO}_{2}\) produced divided by the volume of \(\mathrm{O}_{2}\) consumed, making statement (v) incorrect.

Identify Correct Statements

Based on the evaluations, we have determined that statements (i), (ii), and (iv) are correct. By looking at the options provided, we can conclude that the correct answer is option (a), which lists (i), (ii), and (iv) as correct.

Key concepts

Glycolysis

Glycolysis is a series of reactions that are fundamental to cellular respiration. It takes place in the cytoplasm, the fluid that fills the cell, and serves as the initial stage of both aerobic (with oxygen) and anaerobic (without oxygen) respiration. During glycolysis, a single molecule of glucose, which is a six-carbon sugar, is broken down into two molecules of pyruvate, which are three-carbon compounds.

Throughout this process, small amounts of energy are captured in the form of ATP (Adenosine Triphosphate), which is the primary energy currency of the cell, and NADH, which is used later in the respiration process to generate more ATP. It is important to note that glycolysis does not require oxygen to occur, which makes it an anaerobic process.

Here are the main outcomes of glycolysis:

• Conversion of glucose to pyruvate
• Production of 2 ATP molecules (net gain)
• Reduction of NAD+ to NADH

Mitochondria

The mitochondria are known as the powerhouses of the cell, a term that underscores their role in energy production. They are specialized organelles within eukaryotic cells where aerobic respiration takes place. These are the steps of cellular respiration that require oxygen. The mitochondria have a unique double membrane structure, featuring an outer membrane that encloses the organelle and an highly folded inner membrane that provides surface area for the electron transport system.

Within the mitochondria, pyruvate from glycolysis is processed through a cycle known as the Krebs cycle or Citric Acid Cycle to produce more NADH and another energy carrier, FADH2. This process takes place in the mitochondrial matrix, the innermost compartment filled with a gel-like substance.

Functions of the mitochondria include:

• Production of ATP via the Krebs cycle and oxidative phosphorylation
• Regulation of cellular metabolism
• Playing a role in the initiation of programmed cell death (apoptosis)

Electron Transport System

The electron transport system (ETS), also known as the electron transport chain, is a sequence of protein complexes and other molecules embedded in the inner mitochondrial membrane. Contrary to what might be misunderstood from certain descriptions, it is not located in the outer membrane. The role of the ETS is crucial for cellular respiration. It is the final stage of aerobic respiration where the majority of ATP is produced.

As electrons are passed along the chain from molecule to molecule, a process called chemiosmosis occurs, whereby protons are pumped from the mitochondrial matrix into the intermembrane space. This creates a proton gradient that drives the synthesis of ATP by ATP synthase. Finally, oxygen acts as the terminal electron acceptor, combining with protons to form water.

The ETS involves several key components:

• The four complexes (I, II, III, IV) involved in electron transfer
• The mobile electron carriers, ubiquinone and cytochrome c
• ATP synthase, the enzyme that synthesizes ATP
• Oxygen, the final electron acceptor that helps form water

Without the ETS, the energy captured in the form of NADH and FADH2 during glycolysis and the Krebs cycle could not be effectively utilized to produce ATP.