Anaerobic respiration Questions in English

(C) During intense physical activities like a hurdle race,the demand for $ATP$ in the leg muscles exceeds the rate at which oxygen can be supplied for aerobic respiration.
As a result,the muscle cells shift to anaerobic respiration (lactic acid fermentation).
In this process,pyruvate is converted into lactate (lactic acid).
The accumulation of lactate in the muscle tissues leads to muscle fatigue and pain.

(A) Anaerobic respiration is the process of cellular respiration that occurs in the absence of oxygen $(O_2)$.
It is primarily observed in lower organisms such as bacteria and fungi (e.g.,yeast).
In these organisms,glucose is incompletely oxidized to produce ethanol and $CO_2$ or lactic acid,yielding a small amount of energy.

(B) Alcoholic fermentation is a biological process in which sugars such as glucose, fructose, and sucrose are converted into cellular energy and thereby produce ethanol and carbon dioxide as metabolic waste products.
This process is catalyzed by the enzyme complex known as $Zymase$, which is naturally found in yeast $(Saccharomyces \text{ } cerevisiae)$.

(C) During exercise,when the supply of $O_{2}$ is inadequate for cellular respiration in muscle cells,the cells undergo anaerobic respiration. In this process,pyruvic acid is reduced to lactic acid by the enzyme lactate dehydrogenase,using $NADH + H^+$ as a reducing agent.

(A) Fermentation is an anaerobic process that results in the partial breakdown of glucose into products like ethanol or lactic acid.
In contrast,aerobic respiration involves the complete oxidation of glucose into $CO_{2}$ and $H_{2}O$.

(A) In anaerobic respiration,certain bacteria perform lactic acid fermentation. In this process,pyruvic acid is reduced to lactic acid by the enzyme lactate dehydrogenase,using $NADH + H^+$ as the electron donor.

(A) During the fermentation of a glucose molecule,the process begins with glycolysis,which produces $2$ molecules of pyruvic acid,$2$ $NADH$,and a net gain of $2$ $ATP$ molecules.
In anaerobic conditions (fermentation),these pyruvic acid molecules are converted into ethanol and $CO_{2}$ (in alcoholic fermentation) or lactic acid (in lactic acid fermentation).
Since the $NADH$ produced during glycolysis is consumed to reduce pyruvic acid,no additional $ATP$ is generated during the fermentation steps.
Therefore,the net gain remains $2$ $ATP$ molecules per glucose molecule.
The overall reaction for alcoholic fermentation is: $C_{6}H_{12}O_{6} + 2ADP + 2Pi \rightarrow 2C_{2}H_{5}OH + 2CO_{2} + 2ATP$.

(B) In the absence of oxygen,yeast performs anaerobic respiration,also known as fermentation.
During this process,glucose is incompletely broken down into ethanol and carbon dioxide,releasing a small amount of energy.
The chemical equation for this process is:
$C_{6}H_{12}O_{6} \xrightarrow{\text{Zymase}} 2C_{2}H_{5}OH + 2CO_{2} + \text{Energy}$
Thus,the end-products are ethanol $(C_{2}H_{5}OH)$,carbon dioxide $(CO_{2})$,and energy.

(A) Louis Pasteur observed that yeast cells grew rapidly in air but used little sugar and produced little carbon dioxide and ethanol.
Under anaerobic conditions,they grew slower but used more sugar and produced more carbon dioxide and ethanol.
This phenomenon of inhibition of the breakdown of carbohydrates and the production of ethanol in the presence of oxygen is known as the Pasteur effect.
Biochemically,the Pasteur effect is an allosteric inhibition of the phosphofructokinase enzyme in the presence of oxygen.

(A) In anaerobic respiration (fermentation),the process of glycolysis occurs,which yields a net gain of $2$ $ATP$ molecules per molecule of glucose.
Since $4$ molecules of glucose undergo anaerobic respiration,the total net gain of $ATP$ is calculated as $4 \times 2 = 8$ $ATP$ molecules.
Therefore,the correct answer is $8$ $ATP$.

(A) Lactic acid fermentation is a type of anaerobic respiration.
In this process,pyruvic acid produced during glycolysis is reduced by $NADH$ to form lactic acid.
This reaction is catalyzed by the enzyme lactate dehydrogenase.
This process occurs in some bacteria and in animal muscle cells during intense exercise when oxygen supply is limited.

(B) In fermentation,the oxidation of $NADH$ to $NAD^+$ occurs at a slow rate.
This is because fermentation is an anaerobic process where the electron transport chain is absent,unlike aerobic respiration where $NADH$ is oxidized very rapidly.

(B) In anaerobic respiration,which occurs in the absence of $O_{2}$,the process involves glycolysis followed by fermentation.
Glycolysis is the initial step where glucose is broken down into pyruvic acid.
In fermentation,the incomplete oxidation of glucose occurs,where pyruvic acid is converted into products like $CO_{2}$ and ethanol or lactic acid,without the involvement of the $TCA$ cycle or oxidative phosphorylation.

(D) In anaerobic respiration (fermentation),the $2$ $NADH + H^{+}$ molecules produced during glycolysis are consumed to reduce pyruvate to either ethanol or lactic acid.
Specifically,the $NADH + H^{+}$ acts as a reducing agent to convert pyruvate into the final fermentation products.
Therefore,these $NADH + H^{+}$ molecules do not enter the electron transport chain to produce $ATP$ and are instead utilized in the reduction process,resulting in no net gain of $ATP$ from them.

(B) Anaerobic respiration is a process that occurs in the absence of oxygen. In this process,the entire sequence of reactions,including glycolysis and the subsequent fermentation steps,takes place exclusively in the cytoplasm of the cell. Unlike aerobic respiration,it does not involve the mitochondria.

(D) Anaerobic respiration (fermentation) is the process of breaking down glucose in the absence of oxygen.
In many organisms like yeast,pyruvic acid is converted into ethyl alcohol $(C_2H_5OH)$ and $CO_2$ through alcoholic fermentation.
In some bacteria and animal muscle cells,pyruvic acid is converted into lactic acid $(C_3H_6O_3)$ through lactic acid fermentation.
Therefore,the products of anaerobic respiration can be ethyl alcohol and $CO_2$,or lactic acid,depending on the organism and the type of fermentation occurring.

(C) Anaerobic respiration is a type of cellular respiration that occurs in the absence of oxygen.
In many microorganisms like yeast,the end product is ethyl alcohol $(C_2H_5OH)$ and $CO_2$.
In animal muscle cells during strenuous exercise,the end product is lactic acid $(C_3H_6O_3)$.
Among the given options,lactic acid is a recognized end product of anaerobic respiration.

(B) In ethyl alcohol fermentation,the process begins after glycolysis,where pyruvic acid is produced.
The first step involves the conversion of pyruvic acid $(CH_3COCOOH)$ into acetaldehyde $(CH_3CHO)$ and carbon dioxide $(CO_2)$.
This reaction is catalyzed by the enzyme pyruvic acid decarboxylase.
Since a molecule of carbon dioxide is removed from the pyruvic acid,this process is known as decarboxylation.
The reaction is: $2CH_3COCOOH \xrightarrow{\text{pyruvic acid decarboxylase}} 2CH_3CHO + 2CO_2$.

(C) During vigorous exercise,the demand for $O_2$ increases significantly. When the supply of $O_2$ becomes insufficient to meet the energy requirements of the muscle cells,they switch to an anaerobic metabolic pathway. In this process,glucose is broken down into lactic acid,which accumulates in the muscles and causes fatigue and cramps.

(B) In the glycolytic pathway,$3$-phosphoglyceric acid is converted into $2$-phosphoglycerate,which then forms Phosphoenol pyruvate $(PEP)$ before being converted into Pyruvate.
In the anaerobic respiration pathway (fermentation),Pyruvate is converted into Ethyl alcohol (ethanol) and $CO_2$ in yeast,or Lactic acid in muscles. The step involving the conversion of $NADH + H^+$ to $NAD^+$ indicates the reduction of Pyruvate to Ethyl alcohol.
Therefore,$(i)$ is Phosphoenol pyruvate and $(ii)$ is Ethyl alcohol.

(D) Fermentation is an anaerobic process involving the partial breakdown of glucose into ethanol or lactic acid. Option $A$ is correct as it is a partial breakdown. Option $B$ is correct as glycolysis yields a net of $2ATP$. Option $C$ is correct because the regeneration of $NAD^+$ is slow in fermentation compared to the rapid oxidation in the electron transport system. Option $D$ is incorrect because the Electron Transport System $(ETS)$ and the Krebs cycle are components of aerobic respiration,not fermentation.

(B) Ethyl alcohol fermentation occurs in two main steps.
In the first step,pyruvic acid $(CH_3COCOOH)$ is converted into acetaldehyde $(CH_3CHO)$ and carbon dioxide $(CO_2)$ by the enzyme pyruvate decarboxylase.
This process involves the removal of a carbon dioxide molecule from the pyruvate,which is known as decarboxylation.
Therefore,the first step of ethyl alcohol fermentation requires decarboxylation.

(A) In fermentation,the oxidation of $NADH$ to $NAD^+$ is a slow process compared to aerobic respiration. This is essential to regenerate $NAD^+$ so that glycolysis can continue in the absence of oxygen. Specifically,in lactic acid fermentation,$NADH$ is oxidized to $NAD^+$ while reducing pyruvate to lactic acid.

(C) In the presence of $O_2$,$NADH_2$ undergoes oxidative phosphorylation in the $ETS$ to produce $ATP$.
However,in the absence of $O_2$ (anaerobic conditions),$NADH_2$ is utilized to reduce pyruvate or acetaldehyde into products like lactic acid or ethanol.
Therefore,it acts as a reducing agent by donating electrons/hydrogen to the substrate.

(A) The Pasteur effect is the phenomenon where the rate of glycolysis (sugar breakdown) is inhibited or slowed down by the presence of $O_2$ in cells that are typically performing anaerobic respiration.
This occurs because,in the presence of oxygen,cells switch from fermentation to the more efficient aerobic respiration,which produces more $ATP$ per molecule of glucose,thereby reducing the need for high rates of sugar consumption.

(C) In alcoholic fermentation,glucose is incompletely oxidized into ethanol and $CO_2$.
The energy released during this process is very low compared to aerobic respiration.
The net gain is only $2$ $ATP$ molecules per glucose molecule.
This amount of energy represents less than $7 \%$ of the total energy stored in glucose,as most of the energy remains trapped in the chemical bonds of the ethanol produced.

(C) In aerobic respiration,glucose is completely oxidized to $CO _{2}$ and $H _{2}O$.
In alcoholic fermentation (a type of anaerobic respiration),glucose is converted into ethanol and $CO _{2}$.
In lactic acid fermentation,glucose is converted into lactic acid without the release of $CO _{2}$.
Therefore,$CO _{2}$ is not released during lactic acid fermentation.

(B) Mature mammalian erythrocytes $(RBCs)$ lack cell organelles,including mitochondria and the nucleus. Since mitochondria are the sites of aerobic respiration,their absence forces mature $RBCs$ to rely exclusively on anaerobic respiration to generate $ATP$.

(A) During strenuous exercise,the oxygen supply to the muscle cells becomes insufficient for aerobic respiration. Under these anaerobic conditions,the muscle cells break down stored glycogen into lactic acid through the process of glycolysis followed by fermentation. This process is part of the Cori cycle,where muscle glycogen is converted into lactic acid,which is then transported to the liver to be converted back into glucose or glycogen.

(C) In the liver,$80\%$ of the lactic acid produced during anaerobic muscle contraction is converted back into glycogen through a process known as gluconeogenesis.
This entire metabolic pathway,which involves the cycling of lactate between the muscles and the liver,is known as the 'Cori cycle' (or lactic acid cycle).

(D) The primitive atmosphere of the Earth was reducing in nature and lacked free molecular oxygen $(O_2)$.
Since oxygen was absent,the first living organisms must have been anaerobic,relying on anaerobic respiration to derive energy from organic molecules.
Aerobic respiration evolved only after the accumulation of free oxygen in the atmosphere,which was primarily produced by photosynthetic cyanobacteria.

(B) In humans,during intense physical exercise,the demand for $O_{2}$ exceeds the supply,leading to a deficit. Under these anaerobic conditions,pyruvic acid is converted into lactic acid by the enzyme lactate dehydrogenase.
$(b)$ In yeast,anaerobic respiration (fermentation) occurs in the complete absence of $O_{2}$. Pyruvic acid is converted into $CO_{2}$ and ethanol through the action of enzymes pyruvic acid decarboxylase and alcohol dehydrogenase.

(C) In lactic acid fermentation,glucose is incompletely oxidized into lactic acid.
This process is anaerobic and yields only $2$ molecules of $ATP$ per molecule of glucose.
Since the total energy available in one molecule of glucose is much higher (equivalent to $36-38$ $ATP$ in aerobic respiration),the energy released during fermentation is very low.
Specifically,less than $7\%$ of the energy present in glucose is released as $ATP$ during this process.

(A) In human skeletal muscle cells,during intense exercise when oxygen supply is limited,anaerobic respiration (lactic acid fermentation) occurs,producing $P -$ Lactic acid.
In yeast cells,anaerobic respiration (alcoholic fermentation) occurs,which produces $Q -$ Ethanol and $CO_2$ as byproducts.
Therefore,the correct match is $P -$ Lactic acid and $Q -$ Ethanol,$CO_2$.

(B) During vigorous exercise, the demand for $ATP$ in muscle cells increases significantly.
When the oxygen supply becomes insufficient to meet this demand, the muscle cells shift from aerobic respiration to anaerobic respiration.
Specifically, they undergo $Lactic$ $acid$ $fermentation$, where pyruvate is converted into lactic acid by the enzyme lactate dehydrogenase.
This process allows the cells to regenerate $NAD^+$ to continue glycolysis and produce a small amount of $ATP$ in the absence of oxygen.

(A) Fermentation is an anaerobic process where glucose is incompletely oxidized into ethanol and carbon dioxide.
In this process,the energy trapped in the chemical bonds of glucose is not fully released as $ATP$.
Only a small fraction of the energy present in glucose is released during fermentation.
Specifically,less than $7 \%$ of the energy in glucose is released and not all of it is trapped as high-energy bonds of $ATP$.

(D) In the given pathway of anaerobic respiration:
$1$. Glucose is converted into $3$-phosphoglyceric acid and then into Phosphoenolpyruvic acid.
$2$. Phosphoenolpyruvic acid is converted into $P$ (Pyruvic acid).
$3$. Pyruvic acid is then converted into $Q$ (Acetaldehyde) by the removal of $CO_2$.
$4$. Finally,Acetaldehyde is reduced to $R$ (Ethanol) using $NADH + H^+$.
Therefore,$P$ is Pyruvic acid,$Q$ is Acetaldehyde,and $R$ is Ethanol. However,looking at the options provided,the sequence $P$ = Pyruvic acid,$Q$ = Acetaldehyde (often simplified in diagrams),and $R$ = Ethanol matches the logic of alcoholic fermentation. Among the given choices,option $D$ is the most appropriate representation of the sequence of products in anaerobic pathways.

(B) In alcoholic fermentation,glucose is first broken down into two molecules of pyruvate through the process of glycolysis.
Glycolysis yields a net gain of $2$ $ATP$ molecules and $2$ $NADH$ molecules.
During the subsequent fermentation steps,pyruvate is converted into ethanol and carbon dioxide.
Since no additional $ATP$ is produced during the conversion of pyruvate to ethanol,the total net gain of $ATP$ from the entire process of alcoholic fermentation is $2$ $ATP$ molecules.

(B) Lactic acid fermentation is an anaerobic process occurring in certain bacteria and muscle cells.
In this process,glucose is first broken down into two molecules of pyruvic acid through glycolysis,which yields a net gain of $2$ $ATP$ molecules.
The pyruvic acid is then converted into lactic acid by the enzyme lactate dehydrogenase,using $NADH$ produced during glycolysis.
Since no additional $ATP$ is generated during the conversion of pyruvic acid to lactic acid,the net gain of $ATP$ remains $2$ per glucose molecule.

(A) The given reaction is the conversion of pyruvate into acetaldehyde and carbon dioxide,which is a key step in alcoholic fermentation.
This reaction is catalyzed by the enzyme $Pyruvate \ decarboxylase$.
In this process,the carboxyl group $(-COOH)$ is removed from the pyruvate molecule,releasing $CO_2$.

(B) The given reaction is the reduction of acetaldehyde $(CH_3CHO)$ to ethanol $(CH_3CH_2OH)$ using $NADH_2$ as a reducing agent.
This reaction occurs during alcoholic fermentation in yeast.
The enzyme that catalyzes the reduction of acetaldehyde to ethanol by transferring hydrogen from $NADH_2$ is Alcohol dehydrogenase.
Therefore,the correct option is $B$.

(A) The given reaction represents the reduction of pyruvate $(CH_3COCOOH)$ to lactic acid $(CH_3CHOHCOOH)$ in the presence of $NADH_2$.
This process is known as lactic acid fermentation.
The enzyme responsible for catalyzing the reduction of pyruvate to lactate is $Lactate \text{ } dehydrogenase$.
Therefore, the correct option is $A$.

(C) In anaerobic respiration (fermentation),glucose undergoes glycolysis in the cytoplasm,which produces $2$ molecules of pyruvate,$2$ molecules of $NADH + H^+$,and a net gain of $2$ $ATP$ molecules.
Since there is no oxygen available,the $NADH + H^+$ is used to reduce pyruvate into ethanol or lactic acid,and no further $ATP$ is generated through the electron transport chain.
Therefore,the net gain of $ATP$ molecules from one molecule of glucose in anaerobic respiration is $2$ $ATP$.

(C) In anaerobic respiration (fermentation),glucose undergoes glycolysis in the cytoplasm.
Glycolysis produces a net gain of $2$ $ATP$ molecules per glucose molecule.
Since anaerobic respiration does not involve the electron transport chain or the Krebs cycle,no additional $ATP$ is produced.
Therefore,the net gain of $ATP$ in anaerobic respiration is $2$ $ATP$ molecules.

(C) In animal cells,when oxygen is limited or absent,glycogen undergoes anaerobic respiration (glycolysis followed by lactic acid fermentation).
Glycogen is first broken down into glucose units.
Glucose is then converted into pyruvate via glycolysis.
In the absence of oxygen,pyruvate is reduced to lactic acid by the enzyme lactate dehydrogenase.
Therefore,the end product of anaerobic respiration in animal cells is lactic acid.

(B) Fermentation is an anaerobic process where glucose is partially oxidized to produce energy.
In alcoholic fermentation,glucose is converted into ethanol and $CO_2$.
During this process,$NADH$ is oxidized back to $NAD^{+}$ to allow glycolysis to continue.
$FAD^{+}$ is a coenzyme involved in the Krebs cycle (aerobic respiration) and the electron transport chain,not in the fermentation pathway.
Therefore,$FAD^{+}$ is not a product of fermentation.

(C) In anaerobic respiration (fermentation),pyruvic acid is converted into ethyl alcohol and $CO_2$ in two steps:
$1$. Pyruvic acid is first decarboxylated to acetaldehyde by the enzyme $Pyruvate \ decarboxylase$.
$2$. Acetaldehyde is then reduced to ethyl alcohol by the enzyme $Alcohol \ dehydrogenase$ using $NADH + H^+$ as a reducing agent.
Therefore,both decarboxylase and dehydrogenase enzymes are required for this conversion.

(C) Anaerobic respiration involves the breakdown of glucose into ethanol or lactic acid without the use of oxygen. In this process,both glycolysis (the breakdown of glucose to pyruvate) and the subsequent fermentation steps occur entirely within the cytoplasm of the cell. Unlike aerobic respiration,it does not involve the mitochondria.

(C) Lactic acid fermentation is an anaerobic process that occurs in animal muscle cells during intense physical activity.
When the demand for energy $(ATP)$ exceeds the supply of oxygen $(O_2)$ provided by the circulatory system,the muscle cells shift from aerobic respiration to anaerobic respiration.
In this process,pyruvic acid is reduced to lactic acid by the enzyme lactate dehydrogenase,using $NADH$ as a reducing agent.
Therefore,this fermentation occurs specifically due to a poor supply of $O_2$.

(C) During strenuous exercise,the demand for $O_2$ in muscle cells exceeds the supply.
Under these anaerobic conditions,the muscle cells perform lactic acid fermentation.
In this process,pyruvic acid is reduced to lactic acid by the enzyme lactate dehydrogenase.
The accumulation of lactic acid in the muscle fibres causes fatigue and muscle cramps.