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Q1. The process common to both aerobic and anaerobic organisms is  

• Glyoxylate cycle  
• Glycolysis  
• Krebs cycle  
• TCA cycle  

Solution

Glycolysis is a process in which glucose is broken down to pyruvic acid without the help of an external electron acceptor such as oxygen. It occurs in the cell cytoplasm and so is common to both aerobic and anaerobic organisms.   

Q2. The aerobic respiratory pathway is appropriately termed as  

• Catabolic  
• Parabolic  
• Amphibolic  
• Anabolic  

Solution

The amphibolic pathway is a pathway which acts as a catabolic pathway for respiratory substrates and also functions as an anabolic pathway for the synthesis of various intermediary metabolic products and secondary metabolites. The TCA or Krebs cycle acts as an amphibolic pathway because it is involved in the breakdown as well as synthesis of biomolecules.  

Q3. The end-product of oxidative phosphorylation is

• NADH
• Oxygen
• ADP
• ATP + H₂O

Solution

The aerobic breakdown of one glucose molecule yields 14 H₂O and 36 ATP molecules.

Q4. The terminal cytochrome of the respiratory chain which donates electrons to oxygen is

• cyt b
• cyt c
• cyt a₁
• cyt a₃

Solution

The respiratory assembly contains electron carriers such as cytochromes. The correct sequence of electron carrier/acceptor in ATP synthesis is cyt-b, cyt-c1, cyt-c, cyt-a and cyt-a₃. Cyt-a₃ is the terminal cytochrome as it possesses two copper centres which help in the transfer of electrons to oxygen.

Q5. The site of glycolysis is

• Cytoplasm
• Chloroplast
• Mitochondrial matrix
• Mitochondrial inner membrane

Solution

Glycolysis is a process in which glucose is broken down to pyruvic acid without the help of an external electron acceptor such as oxygen. It occurs in the cell cytoplasm.

Q6. Which of the following is the key intermediate compound linking glycolysis to the Krebs cycle?

• NADH
• ATP
• Acetyl CoA
• Malic acid

Solution

Pyruvic acid formed during glycolysis undergoes oxidative decarboxylation to form acetyl CoA. This 2-carbon acetyl CoA is the entrant molecule in the Krebs cycle and the receptor molecule is 4-carbon oxaloacetic acid.

Q7. The respiratory quotient (RQ) for fatty acid is

• >1
• <1
• 1
• 0

Solution

In fats, a large amount of O₂ is used to combine with H₂, so the output of CO₂ is less and RQ is only 0.70.

Q8. Energy equivalent of NADH is how many number of ATP molecules?

• 2
• 3
• 38
• 6

Solution

Each NADH molecule theoretically yields 3 ATP molecules during chemiosmosis. However, in some tissues, NADH requires more energy to cross the mitochondrial membrane and some of its potential is lost.

Q9. Life without air would be

• Reductional
• Free from oxidative damage
• Impossible
• Anaerobic

Solution

Anaerobic is the complete absence of molecular oxygen. So, life without air would be anaerobic. At the time of origin of life, the atmosphere of the Earth was deficient in free oxygen atoms. So, the primitive atmosphere was reducing in nature.

Q10. End-products of fermentation are  

• ATP  
• Ethanol + CO₂ + ATP  
• Ethyl alcohol + CO₂ + H₂O + ATP  
• Pyruvic acid + CO₂  

Solution

Fermentation is a metabolic process which converts sugar to acids, gases and/or alcohol in the complete absence of oxygen. The overall equation for fermentation is as follows:      

Q11. The TCA cycle is named after

• Embden
• Hans Krebs
• Melvin Calvin
• Robert Emerson

Solution

The TCA cycle, also known as the Krebs cycle or tricarboxylic acid cycle, has been named after the German biochemist Sir Hans Krebs who discovered the cycle in 1937 in England.

Q12. In which of the following do the two names refer to one and the same thing?

• Tricarboxylic acid cycle and urea cycle
• Krebs cycle and Calvin cycle
• Tricarboxylic acid cycle and citric acid cycle
• Citric acid cycle and Calvin cycle

Solution

The Krebs cycle is also called the citric acid cycle because of the formation of citric acid in the first step of this cycle. It is also referred to as the TCA cycle because many of the intermediate compounds formed in the cycle have three carboxyl groups. 

Q13. Which of the following is not correct about the Krebs cycle?

• It is also called the citric acid cycle.
• The intermediate compound which links glycolysis with the Krebs cycle is malic acid.
• It occurs in mitochondria.
• It starts with a six-carbon compound.

Solution

The Krebs cycle is also called the citric acid cycle after one of its participating compounds, citrate. It takes place in the mitochondrial matrix and begins with a six-carbon compound, citric acid. The intermediate compound which links glycolysis with the Krebs cycle is pyruvic acid which undergoes oxidative decarboxylation and forms active acetate.

Q14. In the Krebs cycle, FAD participates as an electron acceptor during the conversion of

• Succinyl CoA to succinic acid
• α-Ketoglutarate to succinyl CoA
• Succinic acid to fumaric acid
• Fumaric acid to malic acid

Solution

During the oxidation of succinic acid to fumaric acid, electrons and H+ ions are taken up by FAD, which gets reduced to FADH₂.

Q15. Oxidative phosphorylation refers to

• Anaerobic production of ATP
• Citric acid cycle production of ATP
• Production of ATP by chemiosmosis
• Alcoholic fermentation

Solution

According to the chemiosmotic coupling hypothesis of oxidative phosphorylation, adenosine triphosphate (ATP) is formed because of a proton gradient formed across the inner membrane.

Q16. The site of respiration in bacteria is

• Episome
• Ribosome
• Mesosome
• Microsome

Solution

The cytoplasmic membrane of bacteria invaginates into the cytoplasm at certain places in the form of tubules called mesosomes. Enzymes found on their surfaces are associated with respiration.

Q17. Which of the following is essential for the conversion of pyruvic acid to acetyl CoA?

• LAA
• NAD
• TPP
• ATP

Solution

Pyruvic acid enters the mitochondrial matrix, undergoes oxidative decarboxylation and forms acetyl CoA by a series of reactions catalysed by the multienzyme complex. The reaction requires participation of the enzyme pyruvate dehydrogenase and several coenzymes including NAD⁺, coenzyme A, thiamine pyrophosphate (TPP) and lipoic acid.

Q18. The ultimate electron acceptor of respiration in aerobic organisms is

• Cytochrome
• Oxygen
• Hydrogen
• Glucose

Solution

In aerobic organisms, the final electron acceptor of respiration is oxygen. Molecular oxygen is a strong oxidising agent, and therefore, an excellent electron acceptor.

Q19. EMP can produce a total of  

• 6 ATP  
• 8 ATP  
• 24 ATP  
• 38 ATP  

Solution

The EMP pathway produces a total of 8 ATP molecules, of which 2 ATP are consumed in the process. So, the net gain of energy is 6 ATP.  

Q20. The overall goal of glycolysis, Krebs cycle and electron transport system is the formation of  

• ATP in one large oxidation reaction  
• Sugars  
• Nucleic acids  
• ATP in small stepwise units  

Solution

Glycolysis, the Krebs cycle and the electron transport system all yield ATP which is the main energy currency of the cell. During oxidation of respiratory substrates within a cell, the energy contained in them is released in a series of slow stepwise reactions controlled by respiratory enzymes.  

Q21. Which of the following does not function as an electron carrier?

• Cytochrome c
• Cytochrome a
• Cytochrome a₃
• H₂0

Solution

An electron carrier is a molecule capable of accepting electrons from another molecule and then donates these electrons to another during the process of electron transport. As the electrons are transferred from one electron carrier to another, their energy level decreases and the energy is released. Cytochromes and quinines are some examples of electron carriers.

Q22. Oxidative phosphorylation involves simultaneous oxidation and phosphorylation to finally form

• Pyruvate
• NADP
• DPN
• ATP

Solution

Oxidative phosphorylation is the process in which ATP is formed as the electrons are transferred from NADH or FADH₂ to O₂ by a series of electron carriers, located in the inner membrane of the mitochondria.

Q23. Oxidative phosphorylation is the production of

• ATP during photosynthesis
• NADPH during photosynthesis
• ATP during respiration
• NADH during respiration

Solution

Oxidative phosphorylation involves the production of energy-rich ATP molecules by energy liberated during the oxidation of reduced coenzymes produced during respiration.

Q24. The connecting link between glycolysis and the Krebs cycle is

• Oxaloacetate
• PEP
• Pyruvate
• Acetyl CoA

Solution

In glycolysis, one molecule of glucose is broken down to two molecules of pyruvic acid. Before entering the Krebs cycle, pyruvic acid is carboxylated oxidatively to produce acetyl CoA, NADPH and CO₂ with the help of the enzyme complex pyruvate dehydrogenase. Here, acetyl CoA acts as a connecting link between glycolysis, Krebs cycle and carbohydrate and fat metabolism.

Q25. The Krebs cycle occurs in

• Mitochondria
• Cytoplasm
• Chloroplast
• Ribosomes

Solution

The Krebs cycle occurs inside the matrix of mitochondria.

Q26. The end products of aerobic respiration are

• Sugar and oxygen
• Water and energy
• Carbon dioxide, water and energy
• Carbon dioxide and energy

Solution

Aerobic respiration is an enzyme-mediated energy liberating catabolic process which involves the step-wise oxidative breakdown of organic substrate into CO₂ and water with oxygen acting as a terminal oxidant.

Q27. The apparatus to measure the rate of respiration and RQ is

• Auxanometer
• Potometer
• Respirometer
• Manometer

Solution

A respirometer is an instrument used to measure the rate of respiration and the respiratory quotient.

Q28. Mitochondria are called the powerhouses of the cell. Which of the following observations support this statement?

• Mitochondria synthesise ATP.
• Mitochondria have a double membrane.
• The enzymes of the Krebs cycle and the cytochromes are found in mitochondria.
• Mitochondria are found in almost all plant and animal cells.

Solution

Mitochondria are called the powerhouses of the cell because a major part of cellular respiration occurs there, thereby generating a maximum amount of ATP. This ATP provides energy for several vital biological functions.

Q29. Oxidative phosphorylation involves simultaneous oxidation and phosphorylation to finally form

• Pyruvate
• NADP
• DPN
• ATP

Solution

Oxidative phosphorylation involves the synthesis of energy-rich ATP from ADP and inorganic phosphate (phosphorylation), which is connected with the oxidation of reduced coenzymes produced during cellular respiration.

Q30. End-products of aerobic respiration are

• Sugar and oxygen
• Water and energy
• Carbon dioxide, water and energy
• Carbon dioxide and energy

Solution

Aerobic respiration involves the stepwise breakdown of respiratory substrates to CO₂ and H₂O in the presence of oxygen. It is an enzymatically controlled process which involves the release of energy in the form of ATP.

Q31. All enzymes of the TCA cycle are located in the mitochondrial matrix except one which is located in the inner mitochondrial membrane in eukaryotes and in the cytosol in prokaryotes. This enzyme is

• Lactate dehydrogenase
• Isocitrate dehydrogenase
• Malate dehydrogenase
• Succinate dehydrogenase

Solution

Succinate dehydrogenase is present on the inner membrane of mitochondria and catalyses the oxidation of succinate to fumarate.

Q32. Which of the following is the respiratory substrate in floating respiration?  

• Carbohydrates  
• Proteins  
• Fats  
• Organic acids  

Solution

When carbohydrates are oxidised during respiration, it is called floating respiration. If carbohydrates are used up and its shortage becomes acute, other protoplasmic substrates such as fats, organic acids and proteins are oxidised to obtain energy. It is called protoplasmic respiration.  

Q33. Anaerobic respiration in muscles gives rise to  

• C₃H₆O₃  
• CH₃COCOOH  
• C₂H₅OH  
• CH₃COOH  

Solution

Intense physical exercise results in an increased oxygen demand for the body. The muscle cells undergo anaerobic respiration and produce lactic acid. C₃H₆O₃ is lactic acid, CH₃COCOOH is pyruvic acid, C₂H₅OH is ethyl alcohol and CH₃COOH is acetic acid.  

Q34. The overall goal of glycolysis, Krebs cycle and the electron transport system is the formation of

• ATP in small stepwise units
• ATP in one large oxidation reaction
• Sugars
• Nucleic acids

Solution

Glycolysis, Krebs cycle and electron transport system are meant for ATP synthesis in different steps.

Q35. Pyruvic acid, the key product of glycolysis, can have many metabolic fates. Under aerobic conditions, it forms  

• Lactic acid  
• CO₂ + H₂O  
• Acetyl CoA + CO₂  
• CO₂  

Solution

Under aerobic conditions, pyruvic acid enters the mitochondrial matrix, undergoes oxidative decarboxylation and forms active acetate by a series of reactions catalysed by a multienzyme complex.      

Q36. Which of the following plant parts can respire even in the absence of oxygen?  

• Seeds  
• Roots  
• Stems  
• Leaves  

Solution

Certain tissues of higher plants can carry out the breakdown of glucose even in the absence of oxygen and conserve a small amount of energy. Some plant seeds when immersed in water during germination can carry out respiration even in the absence of oxygen.  

Q37. End-product of citric acid/Krebs cycle is

• Citric acid
• Lactic acid
• Pyruvic acid
• CO₂ + H₂O

Solution

Two molecules of pyruvic acid which enter the Krebs cycle are completely degraded to form 2 molecules of ATP, 8 molecules of NADH₂, 2 molecules of FADH₂, CO₂ and H₂O.

Q38. Incomplete oxidation of glucose into pyruvic acid with several intermediate steps is known as

• Glyoxylate cycle
• Glycolysis
• Krebs cycle
• TCA cycle

Solution

Glycolysis involves partial oxidation of glucose into pyruvic acid through a series of ten enzyme-mediated reactions. It occurs in cell cytoplasm. 

Q39. When fats are the respiratory substrate, the value of RQ would be

• Approx. 0.7
• Approx. 1.0
• More than 1.0
• None of the above

Solution

When fats are the respiratory substrates, they are hydrolysed to glycerol and fatty acids. The complete oxidation of glycerol yields an RQ of approx. 0.86. As fatty acids are deficient in O₂, they require more O₂ for oxidation as compared to CO₂. Therefore, O₂ absorption is more and CO₂ liberation is less, and the RQ becomes less than 1.

Q40. At a temperature above 35°C,

• Rate of photosynthesis will decline earlier than that of respiration
• Rate of respiration will decline earlier than that of photosynthesis
• There is no fixed pattern
• Both decline simultaneously