Respiration in Plants MCQ Quiz - Objective Question with Answer for Respiration in Plants - Download Free PDF

The correct answer is Zero.

Key Points

• The term glycolysis has originated from the Greek words, glycos for ''sugar'' and lysis for ''splitting''.
• The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof, and J. Parnas, and is often referred to as the EMP pathway.
• In anaerobic organisms, it is the only process in respiration.
• Glycolysis occurs in the cytoplasm of the cell and is present in all living organisms.
• In this process, glucose undergoes partial oxidation to form two molecules of pyruvic acid.

​Explanation:

• The glycolysis is a common pathway for aerobic and anaerobic respiration and no oxygen O₂ is consumed during this process.
• It is a universal pathway that occurs in every living organism be it be aerobic or anaerobic.
• Therefore, the number of oxygen molecules required during glycolysis of one glucose molecule is ''Zero''

Additional Information 

• It involves a series of 10 biochemical reactions where 1 molecule of glucose is degraded to 2 molecules of pyruvic acid.
• Each step is governed by some enzyme.
• In plants, this glucose is derived from sucrose, which is the end product of photosynthesis, or from storage carbohydrates.
• Sucrose is converted into glucose and fructose by the enzyme, invertase, and these two monosaccharides readily enter the glycolytic pathway.
• Glucose and fructose are phosphorylated to give rise to glucose-6- phosphate by the activity of the enzyme hexokinase.
• This phosphorylated form of glucose then isomerizes to produce fructose-6- phosphate.
• Subsequent steps of the metabolism of glucose and fructose are the same.
• In glycolysis, a chain of ten reactions, under the control of different enzymes, takes place to produce pyruvate from glucose

The correct answer is glucose.

Key Points

• The breakdown of glucose into pyruvate within a cell's cytoplasm is known as glycolysis.
• During aerobic conditions, pyruvate can diffuse into mitochondria where it joins the citric acid cycle and produces reducing equivalents in the form of NADH and FADH2.
• The electron transport chain then receives these reducing equivalents, which results in the creation of 32 ATP per molecule of glucose.
• Because the electron transport chain requires oxygen as the final electron acceptor, inadequate tissue oxygenation inhibits the process of oxidative phosphorylation.
• Under anaerobic conditions, pyruvate has a different fate.
• Instead of entering mitochondria, the cytosolic enzyme lactate dehydrogenase converts pyruvate to lactate.
• The regeneration of NAD+ from NADH is also made possible by this process.
• An oxidizing cofactor called NAD+ is required to keep the flow of glucose through glycolysis going.
• Glycolysis produces 2 ATP per glucose molecule, and thus provides a direct means of producing energy in the absence of oxygen.
• This process of breaking down glucose in the absence of oxygen is aptly named anaerobic glycolysis.

Additional Information

• Lactic acid:
  • Lactic acid is mainly produced in muscle cells and red blood cells.
  • It forms when the body breaks down carbohydrates to use for energy when oxygen levels are low. 
• Fructose:
  • Fructose is a type of sugar known as a monosaccharide.
• Citric acid:
  • Citric acid is a weak acid that is found naturally in all citrus fruits.

The correct answer is more than 1.

Hint

Respiratory substrate & Respiratory Quotient (RQ) 

• The respiratory substrate is broken down to release energy in the process of respiration. Aerobic and anaerobic respiration are the main two types of respiration that occur in the presence or absence of molecular oxygen. Glucose is the most common respiratory substrate present in plants.
• During aerobic respiration, O₂ is consumed and CO₂ is released.
• "The ratio of the volume of CO₂ evolved to the volume of O₂ consumed in respiration is called the Respiratory Quotient (RQ) or Respiratory Ratio."
• Respirometer is an instrument used for measuring the rate of respiration as well as R.Q. 

RQ Value is calculated using the given formula : 

The respiratory quotient depends upon the type of respiratory substrate used during respiration.

Explanation:

RQ of Organic acids (More than 1)

•    Organic acids like - Malic acid (Refer below reaction), Tartaric acid, Oxalic acid are rich in O₂ and require less O₂  for their oxidation, so when the organic acids are oxidized in respiration, the value of R.Q. is greater than one. The reaction & RQ is given below : 

​C₄H₆O₅ (Malic acid) + 3O₂  → 4CO₂ + 3H₂O + Energy

Important Points

Significance of RQ:

•   Helps in determining the type of respiration being performed.
• Determine the nature of the respiratory substrate that oxidized the transformation of the substrate and the biochemical mechanism of respiration.
• Knowing the metabolic rate.
• Determination of various pathological conditions like acidosis, alkalosis, etc.  

Additional Information

1. RQ of Succulent plants  [Zero]

• In succulent plants like - Bryophyllum, Opuntia, etc., stomata remain open during the nighttime. So, at night when oxygen is absorbed, the carbohydrates are partially oxidized to organic acids without the formation of CO₂. So, the value of R.Q. remains zero. 
• During the day, the value of RQ remains zero because the CO₂ released during respiration is used up as a substrate for photosynthesis

​2C6H12O6 (Glucose) + 3O2  → 3C₄H₆O₅ (Malic acid) + 3H2O + Energy

      2. RQ of Carbohydrates [1]

• When carbohydrates are used as substrate and are completely oxidized, the RQ will be 1, because equal amounts of CO₂ and O₂ are evolved and consumed, respectively.

​ C₆H₁₂O₆ + 6O2  (Glucose) → 6CO₂ + 6H2O + Energy

     3. RQ of Fats [Less than 1]

• Fats need more amount of O₂ for their oxidation as compared to other substrates. Fats are usually present in seeds as storage food in plants.
• Fats need more amount of O₂ for their oxidation as compared to other substrates.
• R.Q. value is less than one or unity in the aerobic respiration of fats.

​2C5 H98O6 (Tripalmitin)+ 145O2  → 102CO2 + 98H2O + Energy

 (Less than 1)

     4. RQ of Proteins & their derivatives [Less than 1]

• Proteins are building blocks of the living body and are made up of amino acids. 
• When the cells are going to starvation, then proteins act as a respiratory substrate.
• When proteins are respiratory substrates the ratio would be about 0.9.
• Protein structures vary with changes in amino acid sequence.
•  So, the value of R.Q. also varies from 0.8 - 0.9 depending upon the structure of different amino acids.

​2C3H₇O₂ N(Alanine)+ 6O2  → CO(NH₂)₂  (Urea) + 5CO2 + 5H2O + Energy

     5. RQ of Aerobic respiration [More than 1]

• In aerobic respiration, when respiratory substrate is fat or protein, R.Q is less than 1.
• When carbohydrate is the substrate, R.Q is 1.

Mistake Points

• Please note that the correct answer is "b, c₁, c, a, a₃", which is not given in the options.
• So, the nearest possible option has been marked correct and the correct explanation has been provided in the following solution.

Concept-

• Aerobic respiration is the complete oxidation of food with the use of food.

C₆H₁₂O₆ + 6 O₂ + 6 H₂O → 6 CO₂ + 12 H₂O + Energy

• Steps of aerobic respiration- Glycolysis, Krebs cycle, ETS.

Explanation-

• The metabolic pathway through which the electron passes from one carrier to another is called the electron transport system (ETS).
• It is present in the inner mitochondrial membrane. 
• Cytochromes are the proteins that help in electrons transfer.

Hence the correct sequence is Cyt b, c₁, c, a, a₃.

Note- You can easily get the answer from the above diagram.

Additional Information

• Molecular oxygen act as the final electron acceptor.
• Oxygen act as the final H2 acceptor. \

The correct answer is Both A and R are true and R is the correct explanation of A.

Concept:

• Glycolysis is a step in respiration that occurs in aerobic and anaerobic processes. 
• It occurs in the cytoplasm of the cell and is present in all living organisms.
• During the process of glycolysis, glucose undergoes partial oxidation to form two molecules of pyruvic acid.

Explanation:

• Glycolysis is a chain of ten reactions that takes place under the control of different enzymes. 
• During the initial phase of glycolysis, two molecules of ATP are used and during the later phase, two molecules of NADH and four molecules of ATP are produced.
• ATP is utilised at two steps: first in the conversion of glucose into glucose 6-phosphate and second in the conversion of fructose 6-phosphate to fructose 1, 6-bisphosphate.
• So overall, during the process of glycolysis two molecules of pyruvic acid, two molecules of ATP, and two molecules of NADH are produced.
• Pyruvic acid is the key product of glycolysis, which can have many metabolic fates. 
• Under aerobic conditions, it forms Acetyl CoA + CO₂, which is converted to CO₂ + H₂O after the citric acid cycle. 

Fig: Steps of glycolysis

Explanation:

• Pyruvate or pyruvic acid, which is formed by the glycolytic catabolism of carbohydrates in the cytosol, after it enters the mitochondrial matrix undergoes oxidative decarboxylation by a complex set of reactions catalyzed by pyruvic dehydrogenase.
• The reactions catalyzed by pyruvic dehydrogenase require the participation of several coenzymes, including NAD⁺ and Coenzyme A. This process is called Link reaction or gateway reaction.
• During this process, two molecules of NADH are produced from the metabolism of two molecules of pyruvic acid (produced from one glucose molecule during glycolysis)
• The acetyl CoA then enters a cyclic pathway, the citric acid cycle more commonly called Krebs’ cycle after the scientist Hans Krebs who first elucidated it.

• Thus, Pyruvic acid before combining with oxaloacetic acid of the citric acid cycle becomes Acetyl CoA​

Additional Information

• Under anaerobic conditions, the pyruvic acid undergoes partial oxidation to form lactic acid. This process is catalyzed by the enzyme lactate dehydrogenase
• During the Kreb's cycle, Acetyl CoA condenses with Oxaloacetic acid to form Citric acid. This Citric acid is then converted into Cis Aconitic acid in the presence of enzyme Aconitase.

The correct answer is ii; i; iii; iv

Concept:

• The complete oxidation of glucose during aerobic respiration involves several key metabolic pathways: glycolysis, the link reaction (pyruvate to acetyl CoA), the citric acid cycle (Krebs cycle), and the electron transport chain.

Explanation:

• Dihydroxyacetone phosphate → Glyceraldehyde-3-phosphate: This occurs during glycolysis
• Pyruvate → Acetyl CoA : This is the link reaction connecting glycolysis to the citric acid cycle
• Oxaloacetate → Citrate: This occurs during the citric acid cycle, the first step after Acetyl CoA enters the cycle
• Fumarate → Malate: This occurs later in the citric acid cycle

Therefore, the correct order is ii; i; iii; iv

The correct answer is A - II, B - IV, C - III, D - I 

Explanation:

A. Oxidative decarboxylation: This process involves the conversion of pyruvate to acetyl-CoA with the release of CO_2.The key enzyme involved in this process is pyruvate dehydrogenase.
B. Glycolysis: This is also known as the Embden-Meyerhof-Parnas (EMP) pathway, where glucose is converted to pyruvate.
C. Oxidative phosphorylation: This involves the electron transport chain (ETS) and chemiosmosis to produce ATP.
D. Tricarboxylic acid cycle (TCA cycle): Also known as the citric acid cycle or Krebs cycle, one of the key enzymes is citrate synthase.

Concept:

• Glycolysis was given by Gustav Embden, Otto Meyerhof, and J. Parnas, and is often referred to as the EMP pathway. 

• Glycolysis is a step in respiration that occurs in aerobic and anaerobic processes.
• It occurs in the cytoplasm of the cell and is present in all living organisms.
• During the process of glycolysis, glucose undergoes partial oxidation to form two molecules of pyruvic acid.

Explanation:

Option 1: 

• Phosphoglucomutase is an enzyme that transfers a phosphate group in D-glucose monomer from 1-to 6 positions of carbon in a forward direction (changes glucose 1-phosphate to glucose-6 phosphate).
• Therefore, this is an incorrect option.​

Option 2: 

• Phosphoglucoisomerase catalyzes the conversion of glucose- 6- phosphate to fructose -6 -phosphate.
• Therefore, this is an incorrect option.​

Option 3:

• In the process of glycolysis, the first step involves the phosphorylation of glucose/fructose, which results in the formation of Glucose-6-phosphate.
• The reaction is catalyzed with the help of the enzyme hexokinase in the presence of an Mg⁺² ion. The reaction is:
• Glucose(6C) + ATP → Glucose-6-phosphate + ADP
• Therefore, this is the correct answer.​

Option 4: 

• Phosphorylase is an enzyme that catalyzes the addition of phosphate groups from inorganic phosphate to an acceptor.
• Therefore, this is an incorrect option.

​ 

Concept:

• Cellular respiration can be defined as the metabolic process by which complex organic substances are broken down into simple products. 
• During this process, energy is released that is stored in energy-carrying biomolecules called ATP. This energy is later utilized to carry out other metabolic activities.
• In eukaryotic cells, mitochondria play an important role in ATP synthesis.
• The enzymes required for ATP synthesis are present in the mitochondria.
• However, the generation of ATP also takes place in certain processes without involving mitochondria such as in glycolysis.

Explanation:

Option 1: Krebs cycle - INCORRECT

• ​Krebs cycle also known as the TCA cycle is part of aerobic respiration.
• It provides energy to cells in the form of ATP.
• It takes place in the matrix of mitochondria.

Option 2: Electron Transport Chain - INCORRECT

• Electron Transport Chain is the third step during aerobic respiration and involves the formation of the water molecule and ATP.
• ETS takes place in the inner mitochondrial membrane.
• NADH₂ and FADH₂ produced during the initial steps of aerobic respiration - glycolysis, connecting link reaction, and Kreb's cycle- are oxidized in ETC with the help of various electron carriers and enzymes.

Option 3: Substrate-level Phosphorylation - CORRECT

• ​Substrate-level Phosphorylation is a chemical reaction in which ATP is synthesized by direct transfer of phosphate group from an intermediate molecule to ADP.
• Substrate-level Phosphorylation is seen during the process of glycolysis.
• Glycolysis is the first step in both aerobic and anaerobic respiration.
• It takes place in the cytoplasm without the use of oxygen.
• During glycolysis 2 ATP molecules are produced.
• These ATP molecules are formed without the involvement of mitochondria.

Option 4: Photorespiration - INCORRECT

• ​Photorespiration occurs in photosynthetic plants.
• Photorespiration can be defined as a light-dependent process in which the photosynthetic organs of a plant utilize oxygen and release carbon dioxide.
• Photorespiration is considered to be a wasteful process. This is because 25% of photosynthetically fixed carbon dioxide is lost in this process.
• It takes place in several organelles - chloroplast, peroxisome and mitochondria.
• At the end of the photorespiration CO₂ and ammonia are released. No ATP is produced in this process.

So the correct answer is option 3 (Substrate-level phosphorylation).