Question 1: Differentiate between
(a) Respiration and Combustion
Answer: Respiration is a type of combustion. But while combustion is an uncontrolled process, respiration is controlled with high precision. Respiration takes place inside the cells of living beings, while combustion can take place anywhere.
(b) Glycolysis and Krebs’ cycle
Answer: Breakdown of glucose into pyruvic acid is called glycolysis, while further processing of pyruvic acid through aerobic route is called Krebs’ cycle. Glycolysis happens in all living beings, while Krebs’ cycle happens in aerobes only. Glycolysis happens in cytoplasm, while Krebs’ cycle happens in mitochondria.
(c) Aerobic respiration and Fermentation
Answer: Anaerobic respiration is also called fermentation. Ethanol and lactic acid are the major products of fermentation.
Question 2: What are respiratory substrates? Name the most common respiratory substrate.
Answer: A compound which is oxidized during respiration is called respiratory substrate. Glucose is the most common respiratory substrate.
Question 3: Give the schematic representation of glycolysis?
Answer: Refer to the chapter notes
Question 4: What are the main steps in aerobic respiration? Where does it take place?
Answer: Aerobic respiration takes place within the mitochondria. Following are the main steps in aerobic respiration:
- Stepwise removal of all the hydrogen atoms leads to complete oxidation of pyruvate. This leaves three molecules of CO2. This step takes place in the matrix of mitochondria.
- Electrons removed from hydrogen atoms are passed on to molecular O2. This happens with simultaneous synthesis of ATP. This step takes place in the inner membrane of mitochondria.
- Pyruvate enters the mitochondira matrix and undergoes oxidative decarboxylation. This involves a complex set of reactions which are catalysed by pyruvic dehydrogenase.
Question 5: Give the schematic representation of an overall view of Krebs’ cycle.
Answer: Refer to chapter notes
Question 6: Explain ETS.
Answer: The metabolic pathway through which the electron passes from one carrier to another, is called the electron transport system (ETS). This pathway is present in the inner mitochondrial membrane.
- Electrons from NADH (produced in the mitochondria matrix) are oxidized by an NADH dehydrogenase (Complex I). After that, electrons are transferred to ubiquinone which is located within the inner membrane.
- Ubiquinone also receives reducing equivalents via FADH2 (Complex II). FADH2 is generated during oxidation of succinate in the citric acid cycle.
- The reduced ubiquinone (ubiquinol) is then oxidised with the transfer of electrons to cytochrome c via cytochrome bc1 complex (complex III).
- Cytochrome c is a small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for transfer of electrons between complex III and IV.
- Complex IV refers to cytochrome c oxidase complex containing cytochromes a and a3, and two copper centres.
- 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). This coupling is necessary for the production of ATP from ADP and inorganic phosphate. The nature of the electron donor decides the number of ATP molecules synthesized.
Question 7: Distinguish between the following:
(a) Aerobic respiration and Anaerobic respiration
Answer: Aerobic respiration needs oxygen, while anaerobic respiration does not need oxygen. There is complete oxidation of glucose in aerobic respiration, while it is incomplete in anaerobic respiration. Lactic acid and ethanol are the main products of anaerobic respiration, while carbon dioxide is the end product of aerobic respiration.
(b) Glycolysis and Fermentation
Answer: Breakdown of glucose into pyruvic acid is called glycolysis, while further processing of pyruvic acid in anaerobes is called fermentation.
(c) Glycolysis and Citric acid Cycle
Answer: Breakdown of glucose into pyruvic acid is called glycolysis, while further processing of pyruvic acid through aerobic route is called Citric acid cycle. Glycolysis happens in all living beings, while Citric acid cycle happens in aerobes only. Glycolysis happens in cytoplasm, while Citric acid cycle happens in mitochondria.
Question 8: What are the assumptions made during the calculation of net gain of ATP?
Answer: The calculations for respiratory balance sheet are based on some assumptions which are as follows:
There is a sequential and orderly pathway in which one substrate makes the next substrate. Glycolysis, TCA cycle and ETS pathway follow one after another.
NADH is synthesized in glycolysis and is transferred into the mitochondria. The NADH undergoes oxidative phosphorylation within the mitochondria.
None of the intermediates in the pathway are utilised to synthesise any other compound.
Glucose is the only substrate undergoing respiration. No other alternative substrates are entering in the pathway at any stage.
Question 9: Discuss “The respiratory pathway is an amphibolic pathway.”
Answer: Respiratory process involves both catabolism and anabolism; because breakdown and synthesis of substrates are involved. Hence, respiratory pathway is considered as an amphibolic pathway rather than a catabolic one.
Question 10: Define RQ. What is its value for fats?
Answer: The ratio of the volume of CO2 evolved to the volume of O2 consumed during respiration is called the respiratory quotient (RQ) or respiratory ratio. The RQ for carbohydrates is 1. The RQ for fat and protein is less than 1.
Respiratory Quotient = Volume of CO2 ÷ Volume of O2 consumed
Reaction for respiration of fat:
2(C51H98O6 + 145O2 → 102CO2 + 98H2O
RQ of Fat = 102CO2 ÷ 145O2 = 0.7
Question 11: What is oxidative phosphorylation?
Answer: During photophosphorylation, light energy is utilised for the production of proton gradient. But in respiration, the energy of oxidation-reduction is utilised for the production of proton gradient. Hence, this process is called oxidative phosphorylation.
Question 12: What is the significance of step-wise release of energy in respiration?
Answer: The energy produced during respiration is also used for synthesizing other molecules. To ensure the adequate supply of energy for synthesis of different molecules; plants catabolise the glucose molecule in such a way that not all the liberated energy goes out as heat. Glucose is oxidized in several small steps. Some steps are large enough to ensure that the released energy can be coupled with ATP synthesis.