Question

Which out of the following statements is incorrect? (a) The breakdown product of glucose which enters into mitochondrion during aerobic respiration is pyruvic acid generated in the cytosol. (b) When the electrons pass from one carrier to another via complex I to IV in the electron transport chain, they are coupled to ATP synthase (complex \(V\) ) for the production of ATP from ADP and Pi.(c) The ratio of volume of \(\mathrm{O}_{2}\) consumed in \(\mathrm{res}_{0}\) the volume of \(\mathrm{CO}_{2}\) evolved is called as the quotient (RQ). (d) Compensation point is the point reached when the rate of photosynthesis is equal of respiration.

Short answer

Statement (b) is incorrect as electrons transfer through complexes I-IV is not directly coupled to ATP synthase for ATP production.

Step-by-step solution

Verify Statement (a)

Analyze the accuracy of the statement about the breakdown of glucose. Pyruvic acid is indeed produced in the cytosol as a result of glycolysis, and during aerobic respiration, it enters the mitochondrion. This statement appears to be correct.

Verify Statement (b)

Examine the information about the electron transport chain. Electrons do pass from one carrier to another through complexes I to IV, but they are not directly coupled to ATP synthase for ATP production. Instead, the energy released from the electron transfer is used to create a proton gradient, which then drives ATP synthase to produce ATP from ADP and Pi. The statement, as written, is inaccurate and misleading.

Verify Statement (c)

Assess the claim regarding the respiratory quotient (RQ). The RQ is indeed the ratio of the volume of \(\mathrm{O}_{2}\) consumed to the volume of \(\mathrm{CO}_{2}\) evolved. This statement is correct.

Verify Statement (d)

Evaluate the definition of the compensation point. The compensation point is when the rate of photosynthesis equals the rate of respiration; this is true, so the statement is correct.

Key concepts

Glycolysis

Glycolysis is the first step in the process of aerobic respiration, a sequence that cells use to turn food into energy. It occurs in the cytoplasm and involves the breakdown of glucose, a six-carbon sugar, into two three-carbon molecules called pyruvate. This process does not require oxygen; hence, it also occurs during anaerobic respiration.

Throughout the glycolysis pathway, two main phases take place: the energy investment phase and the energy payoff phase. Initially, the cell uses ATP to phosphorylate glucose and its derivatives. This investment activates the glucose molecule for subsequent breakdown. By the end, a net gain of two ATP molecules and two NADH molecules is produced. These ATP and NADH molecules serve as an energy source and electron carriers for the following stages of respiration.

The two pyruvate molecules generated can either proceed to the mitochondrion for aerobic respiration if oxygen is present or be used in fermentation processes in the absence of oxygen.

Electron Transport Chain

The electron transport chain (ETC) is the final series of reactions in the aerobic respiration pathway and takes place in the inner mitochondrial membrane. It is composed of a series of electron carriers organized in four protein complexes (I to IV) and associated mobile carriers.

As electrons are passed along the ETC from one complex to the next, energy is released and used to pump protons (H+ ions) from the mitochondrial matrix into the intermembrane space, creating a proton gradient. This process is called chemiosmosis and is vital for ATP production. The energy from the gradient is harnessed by ATP synthase (complex V) to convert ADP and inorganic phosphate (Pi) into ATP. Therefore, the ETC does not directly produce ATP; rather, it creates the conditions necessary for ATP synthase to generate ATP.

The final electron acceptor in the chain is oxygen, which combines with electrons and protons to form water. This is why the entire process requires oxygen and is known as aerobic respiration.

Respiratory Quotient (RQ)

The respiratory quotient (RQ) is the ratio between the volume of carbon dioxide (CO2) given off and the volume of oxygen (O2) consumed by an organism during respiration. It is an important indicator of metabolic activity and the types of substrates being used for energy.

RQ values vary depending on the respiratory substrate. For carbohydrates, the RQ is typically around 1, because the amount of oxygen used is roughly equal to the carbon dioxide produced. For lipids, the RQ is closer to 0.7 as more oxygen is needed to metabolize fats than is released as CO2. In proteins, the RQ is about 0.8. Knowing the RQ can help scientists and medical professionals understand whether a subject is primarily burning fats, carbohydrates, or proteins.

It's also a useful measure in medical settings to assess patient metabolic rates and respiratory health. The analysis of RQ can therefore provide insights into energy metabolism and overall physiological condition.

Compensation Point in Photosynthesis

The compensation point in photosynthesis refers to the light intensity at which the rate of photosynthesis is exactly balanced by the rate of respiration. At this point, the concentration of carbon dioxide uptake (for photosynthesis) and carbon dioxide release (due to respiration) is the same, meaning no net gas exchange occurs.

This concept is essential in plant physiology, indicating the minimal light conditions under which a plant can survive without either growing or losing biomass. The compensation point varies among plant species, with shade-tolerant plants having a lower compensation point than those adapted to full sunlight.

Understanding the compensation point is vital for optimizing growing conditions in agriculture and horticulture, as well as in ecological studies assessing plant distribution and the potential impact of changes in light availability due to factors like climate change or deforestation.