Anaerobic respiration Questions in English

(A) The early Earth's atmosphere was reducing in nature and lacked free molecular oxygen $(O_2)$.
As the first primitive life forms evolved in this environment,they relied on anaerobic processes to generate energy.
Therefore,the first type of respiration to arise was anaerobic respiration,which does not require oxygen.

(A) Fermentation is an anaerobic process where glucose (sugar) is incompletely oxidized into ethanol and carbon dioxide in the presence of enzymes like zymase, which are produced by yeast.
The chemical equation for alcoholic fermentation is: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{Energy}$.
Therefore, the end products of fermentation using sugar as a raw material are alcohol (ethanol) and $CO_2$.

(C) Anaerobic respiration is a process of cellular respiration that occurs in the absence of oxygen.
In eukaryotic cells,the process of glycolysis,which is the initial stage of both aerobic and anaerobic respiration,takes place in the cytoplasm.
Since anaerobic respiration (such as fermentation) relies on the products of glycolysis and does not involve the mitochondria,the entire process occurs within the cytoplasm of the cell.

(A) Fermentation is a type of anaerobic respiration where glucose is incompletely oxidized into products like ethanol or lactic acid. Since it occurs in the absence of oxygen and involves the partial breakdown of respiratory substrates,both $A$ and $B$ are technically correct descriptions. However,in the context of standard biology textbooks,fermentation is primarily defined as a form of anaerobic respiration. Therefore,$A$ is the most appropriate answer.

(B) In anaerobic respiration (fermentation),glucose is incompletely oxidized into ethanol and $CO_2$ (in yeast) or lactic acid (in muscles).
During this process,glycolysis occurs,which yields a net gain of $2$ $ATP$ molecules per glucose molecule.
Since the Krebs cycle and electron transport system do not occur in anaerobic respiration,no additional $ATP$ is produced.
Therefore,the total number of $ATP$ molecules produced is $2$.

(B) Yeast $(Saccharomyces)$ $\text{ } cerevisiae$ is a facultative anaerobe.
It is a unicellular fungus that can perform fermentation in the absence of $O_2$ to produce ethanol and $CO_2$.
This process is known as anaerobic respiration or alcoholic fermentation.
Therefore, yeast is the most common organism among the given options that can respire without $O_2$.

(B) The Pasteur effect is the inhibitory effect of oxygen on the process of fermentation (anaerobic respiration). When oxygen is introduced to an anaerobic culture,the rate of glucose consumption decreases significantly because the organism switches to the more efficient aerobic respiration pathway,which produces more $ATP$ per molecule of glucose.

(A) In alcoholic fermentation,glucose is broken down into two molecules of pyruvic acid through glycolysis,producing $NADH$.
In the subsequent steps,pyruvic acid is converted into acetaldehyde by the enzyme pyruvate decarboxylase.
Finally,acetaldehyde acts as the terminal electron acceptor,receiving electrons from $NADH$ (via the oxidation of triose phosphate intermediates) to be reduced into ethanol by the enzyme alcohol dehydrogenase.
Therefore,triose phosphate acts as the electron donor (indirectly via $NADH$) and acetaldehyde acts as the electron acceptor.

(C) Anaerobic respiration is a type of respiration that does not require oxygen. In eukaryotic cells,the process of glycolysis,which is the first step of both aerobic and anaerobic respiration,takes place in the cytoplasm. Since anaerobic respiration (such as fermentation) involves the breakdown of glucose into ethanol or lactic acid without entering the mitochondria,the entire process occurs within the cytoplasm.

(D) Fermentation is an anaerobic process where glucose is partially oxidized. In yeast,fermentation results in the production of ethanol $(C_2H_5OH)$ and carbon dioxide $(CO_2)$. Therefore,$C_2H_5OH$ is one of the primary end products of alcoholic fermentation.

(C) Anaerobic respiration is a type of cellular respiration that occurs in the absence of oxygen.
In many microorganisms like yeast, sugar (glucose) undergoes incomplete breakdown through fermentation.
The chemical equation for this process is: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{Energy}$.
As shown in the equation, the products formed are ethanol (alcohol) and carbon dioxide $(CO_2)$.
Therefore, the correct option is $C$.

(B) Fermentation is an anaerobic metabolic process that converts sugar into acids,gases,or alcohol in yeast,bacteria,and oxygen-starved muscle cells.
In this process,the oxidation of the substrate occurs without the involvement of an external electron acceptor,unlike aerobic respiration where oxygen acts as the final electron acceptor.
Therefore,the correct answer is $B$.

(C) Anaerobic respiration is a type of cellular respiration that occurs in the absence of oxygen $(O_2)$.
In this process,organic molecules like glucose are incompletely oxidized to produce energy.
Since seeds can undergo anaerobic respiration when oxygen is limited (e.g.,in waterlogged soil),the correct condition is the absence of $O_2$.

(B) In yeast, fermentation is an anaerobic process where glucose is converted into ethanol and carbon dioxide.
The chemical equation for the fermentation of glucose by yeast is:
$C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{Energy}$.
Here, $C_2H_5OH$ represents ethanol, which is the primary organic product of this process.
Therefore, the correct option is $B$.

(C) In anaerobic respiration (fermentation) in yeast, pyruvic acid is converted into ethyl alcohol and $CO_2$ through two main steps:
$1$. Pyruvic acid is first decarboxylated to acetaldehyde by the enzyme $pyruvate \text{ } decarboxylase$.
$2$. Acetaldehyde is then reduced to ethyl alcohol (ethanol) by the enzyme $alcohol \text{ } dehydrogenase$, using $NADH + H^+$ as a reducing agent.
Therefore, both $pyruvate \text{ } decarboxylase$ and $alcohol \text{ } dehydrogenase$ are involved in this process.

(D) In alcoholic fermentation,$Pyruvate$ is converted into $Ethanol$ and $CO_2$.
This process involves two main steps catalyzed by specific enzymes:
$1$. $Pyruvate$ is converted to $Acetaldehyde$ by the enzyme $Pyruvate$ $decarboxylase$.
$2$. $Acetaldehyde$ is then reduced to $Ethanol$ by the enzyme $Alcohol$ $dehydrogenase$.
Therefore,both $Pyruvate$ $decarboxylase$ and $Alcohol$ $dehydrogenase$ are involved in the process of alcoholic fermentation.

(D) Anaerobic respiration is a type of respiration that occurs in the absence of oxygen.
Among the given options,the tapeworm ($Taenia$ $solium$) is an endoparasite that lives in the intestine of its host.
Since the environment inside the intestine is largely devoid of oxygen,the tapeworm has adapted to perform anaerobic respiration to generate energy.
Earthworms,rabbits,and echinoderms are aerobic organisms that require oxygen for their metabolic processes.

(D) In anaerobic respiration (lactic acid fermentation),one molecule of glucose $(C_6H_{12}O_6)$ is broken down into two molecules of lactic acid $(C_3H_6O_3)$.
During glycolysis,which is the first step of this process,$2 \ ATP$ molecules are produced as a net gain.
Since no further $ATP$ is produced during the conversion of pyruvic acid to lactic acid,the net gain of the entire process is $2 \ ATP$.
None of the options provided ($1 \ ATP$ loss,$3 \ ATP$ loss,or $6 \ ATP$ loss) represent the actual energy yield or loss.
Therefore,the correct answer is 'None of these'.

(C) Fermentation is an anaerobic process where organic compounds are broken down by microorganisms.
It is not a universal process for all microorganisms.
For example,yeast ($Saccharomyces$ $cerevisiae$),which is a fungus,performs alcoholic fermentation.
Many bacteria,such as $Lactobacillus$,perform lactic acid fermentation.
However,many other bacteria and fungi are obligate aerobes and cannot perform fermentation.
Therefore,fermentation is carried out by only some fungi and some bacteria.

(B) Fermentation is a type of anaerobic respiration where glucose is incompletely broken down into ethanol and carbon dioxide in the absence of oxygen.
The chemical equation for alcoholic fermentation is: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$.
Option $A$ represents aerobic respiration.
Option $C$ and $D$ represent photosynthesis.
Therefore,option $B$ is the correct representation of fermentation.

(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 carried out by yeast and some bacteria.
The enzyme complex responsible for this conversion is known as $Zymase$.
$Zymase$ catalyzes the fermentation of sugar into ethanol and carbon dioxide.

(A) Anaerobic respiration,also known as fermentation,was first demonstrated by Louis Pasteur. He observed that yeast could ferment sugar in the absence of oxygen,a phenomenon he famously described as 'life without air'. Therefore,the correct option is $A$.

(B) Methanogens are a group of bacteria that produce methane $(CH_4)$ as a metabolic byproduct in anoxic (oxygen-free) conditions. These bacteria are strictly anaerobic,meaning they can only survive and perform respiration in the absence of oxygen. They are commonly found in the rumen of cattle and in anaerobic sludge during sewage treatment.

(D) The correct answer is $(d)$.
Anaerobic respiration or fermentation is of two main types: lactate fermentation and alcoholic (ethanol) fermentation.
In lactate fermentation,pyruvic acid produced during glycolysis is directly reduced by $NADH$ to form lactic acid. This process does not involve the decarboxylation step,and therefore,no $CO_2$ is released.
In contrast,alcoholic fermentation involves the conversion of pyruvate to acetaldehyde and then to ethanol,a process that releases $CO_2$.
Aerobic respiration in both plants and animals involves the Krebs cycle and the electron transport system,which release $CO_2$ as a byproduct.

(B) : Fermentation is an energy-releasing metabolic process in which organic substrates,such as carbohydrates,are oxidized without the involvement of an external electron acceptor.
In this process,an endogenous electron acceptor (usually an organic compound) is used.
This is in contrast to aerobic respiration,where electrons are transferred to an exogenous electron acceptor,such as oxygen,via an electron transport chain.

(D) Anaerobic respiration is a type of cellular respiration that occurs in the absence of oxygen.
In many microorganisms like yeast, glucose undergoes fermentation to produce ethanol (alcohol) and carbon dioxide $(CO_2)$.
The chemical equation for this process is: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{Energy}$.
Since oxygen is not utilized, the glucose molecule is not completely oxidized into $CO_2$ and water, leading to the formation of alcohol as a byproduct.

(B) In animal muscle cells,during anaerobic respiration (also known as lactic acid fermentation),glucose is broken down into lactic acid.
During this process,the glycolysis pathway occurs,which produces a net gain of $2$ $ATPs$ per glucose molecule.
Since anaerobic respiration does not involve the Krebs cycle or the electron transport chain,no additional $ATPs$ are generated beyond those produced in glycolysis.
Therefore,the total yield is $2$ $ATPs$.

(B) Alcoholic fermentation is a type of anaerobic respiration where glucose is converted into ethanol and $CO_2$ in the presence of enzymes like zymase.
This process is characteristic of yeast ($Saccharomyces$ $cerevisiae$) and some bacteria.
Endoparasites typically perform lactic acid fermentation,and animal muscles also undergo lactic acid fermentation under anaerobic conditions.
Therefore,the correct option is $B$.

(C) Fermentation is an anaerobic process where glucose is incompletely oxidized.
In this process,pyruvic acid is converted into $CO_2$ and ethanol (in yeast) or lactic acid (in muscles).
Since the breakdown of glucose is incomplete,the energy yield is significantly lower compared to aerobic respiration.
Therefore,the statement that 'Glucose is oxidised completely' is incorrect,as complete oxidation occurs only during aerobic respiration.

(B) Anaerobic respiration is a process of cellular respiration that occurs in the absence of oxygen.
In this process,glucose is not completely broken down into $CO_2$ and $H_2O$.
Instead,it undergoes incomplete oxidation,resulting in products like ethanol and $CO_2$ (in yeast) or lactic acid (in muscles).
Therefore,the correct answer is incomplete oxidation of glucose.

(C) The conversion of glucose into lactic acid is a form of anaerobic respiration or fermentation.
Metabolic pathways are broadly classified into two types: Anabolism and Catabolism.
Anabolism involves the synthesis of complex molecules from simpler ones,which requires energy.
Catabolism involves the breakdown of complex molecules into simpler ones,which releases energy.
Since the breakdown of glucose $(C_6H_{12}O_6)$ into lactic acid $(C_3H_6O_3)$ is a degradative process that releases energy,it is classified as a catabolic process.

(A) During intense physical exercise,when the oxygen supply to the muscle cells is insufficient,the cells undergo anaerobic respiration.
In this process,the $Pyruvic \ acid$ produced during glycolysis is reduced to $Lactic \ acid$ by the enzyme $Lactate \ dehydrogenase$.
This reaction also regenerates $NAD^+$ from $NADH$,allowing glycolysis to continue and providing a limited amount of $ATP$ for muscle contraction.
Therefore,the correct product formed in our muscles during anaerobic respiration is $Lactic \ acid$.

(C) Life as we know it on Earth is primarily dependent on aerobic respiration,which requires $O_2$ to efficiently produce $ATP$ through the electron transport chain. Without air (specifically $O_2$),the complex metabolic processes required to sustain multicellular life cannot occur. While some microorganisms are obligate anaerobes,for the vast majority of living organisms,life without air is impossible.

(D) In yeast, fermentation is an anaerobic process where glucose is incompletely oxidized in the absence of oxygen.
This process is catalyzed by enzymes like pyruvic acid decarboxylase and alcohol dehydrogenase.
The chemical reaction is: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{Energy}$.
Thus, the end products of fermentation in yeast are ethyl alcohol $(C_2H_5OH)$ and carbon dioxide $(CO_2)$.

(B) Fermentation is a type of anaerobic respiration that occurs in the absence of oxygen.
In this process,glucose is incompletely oxidized into various products depending on the organism.
Common products of fermentation include ethanol (alcohol),lactic acid,or other organic compounds like butyric acid.
Therefore,option $B$ is the correct answer.

(B) In alcoholic fermentation,glucose is broken down into pyruvic acid via glycolysis,producing $NADH + H^+$.
In the subsequent steps,pyruvic acid is converted into acetaldehyde,which then acts as the final electron acceptor.
Acetaldehyde accepts electrons from $NADH + H^+$ (which originated from the oxidation of triose phosphate during glycolysis) to form ethanol.
Thus,triose phosphate acts as the ultimate electron donor,and acetaldehyde acts as the electron acceptor.

(B) In the process of fermentation,organic compounds act as the final electron acceptors. Unlike aerobic respiration where oxygen is the external electron acceptor and gets reduced,in fermentation,the organic molecule (like pyruvate or acetaldehyde) accepts electrons from $NADH$ to regenerate $NAD^+$,without the molecule itself being oxidized in the process. This allows glycolysis to continue under anaerobic conditions.

(D) In aerobic respiration (both in plants and animals),glucose is completely oxidized to produce $CO_2$,$H_2O$,and energy.
In alcoholic fermentation,pyruvic acid is converted into ethanol and $CO_2$.
In lactic acid fermentation,pyruvic acid is reduced to lactic acid by the enzyme lactate dehydrogenase,and no $CO_2$ is released during this process.

(A) Alcoholic fermentation is an anaerobic process where glucose is converted into ethanol and carbon dioxide.
In the final step of this pathway,acetaldehyde is reduced to ethanol by the enzyme alcohol dehydrogenase.
During this specific reduction reaction,$NADH + H^+$ is oxidized back to $NAD^+$.
This regeneration of $NAD^+$ is crucial for the continuation of glycolysis.

(N/A) In fermentation by yeast,the incomplete oxidation of glucose is achieved under anaerobic conditions through a series of reactions where pyruvic acid is converted into $CO_{2}$ and ethanol.
$C_{6}H_{12}O_{6} \longrightarrow 2CH_{3}COCOOH \longrightarrow 2C_{2}H_{5}OH + 2CO_{2}$
The enzymes pyruvic acid decarboxylase and alcohol dehydrogenase catalyze these reactions.
Other organisms,such as certain bacteria,produce lactic acid from pyruvic acid.
In animal cells,such as muscles during intense exercise,when oxygen is inadequate for cellular respiration,pyruvic acid is reduced to lactic acid by the enzyme lactate dehydrogenase.
The reducing agent is $NADH + H^{+}$,which is reoxidized to $NAD^{+}$ in both processes. In both lactic acid and alcohol fermentation,very little energy is released.
Less than $7\%$ of the energy in glucose is released,and not all of it is trapped as high-energy bonds of $ATP$.
Furthermore,these processes can be hazardous to the cells.
In this pathway,a net gain of $2ATP$ molecules is achieved (as $4ATP$ are formed and $2ATP$ are consumed).
When the concentration of alcohol exceeds $13\%$,it becomes toxic to yeast,leading to its death.
In contrast,aerobic respiration in eukaryotes occurs within the mitochondria and requires $O_{2}$. This process leads to the complete oxidation of organic substances in the presence of oxygen,releasing $CO_{2}$,water,and a large amount of energy.

(A) During anaerobic respiration in muscle cells,glucose is broken down into lactic acid. This process occurs when oxygen supply is insufficient,such as during intense physical exercise. The reaction is: $C_6H_{12}O_6 \rightarrow 2C_3H_6O_3 + 2ATP$ (Lactic acid).

(C) The process where glucose is broken down into lactic acid is a type of anaerobic respiration known as fermentation. Specifically,in muscle cells or certain bacteria,glucose undergoes glycolysis to form pyruvate,which is then converted into lactic acid. While glycolysis is the initial step,the overall pathway leading to lactic acid is categorized as lactic acid fermentation.

(N/A) Although aerobic respiration is more efficient in producing $ATP$,anaerobic respiration serves as a vital survival mechanism under specific physiological conditions.
$1$. In human beings: During intense physical exercise,the demand for $ATP$ in muscle cells increases rapidly. The rate of oxygen supply via the circulatory system may become insufficient to meet this high demand. In such cases,muscle cells temporarily switch to anaerobic respiration (lactic acid fermentation) to generate $ATP$ quickly,allowing the muscles to continue functioning despite the oxygen deficit.
$2$. In angiosperms (plants): Under conditions like waterlogging or soil compaction,roots may experience oxygen deficiency (hypoxia). To survive these temporary anaerobic conditions,plant cells can perform anaerobic respiration (alcoholic fermentation) to maintain basic metabolic processes until oxygen levels are restored.

(B) Respiration does not always require $O_2$.
- Some living organisms survive in the absence of $O_2$ by performing anaerobic respiration.
- The first cells on Earth,such as early prokaryotic organisms,obtained energy through anaerobic processes or by breaking down inorganic substances.
- For example,in chemosynthetic bacteria (like sulphur bacteria),chemosynthesis occurs as follows: $12H_2S + 6CO_2 \rightarrow C_6H_{12}O_6 + 6H_2O + 12S \downarrow$.

(N/A) The symbols in the flow chart represent the steps of glycolysis and fermentation:
$a = \text{Glucose-6-phosphate}$
$b = \text{Phosphoenolpyruvate (PEP)}$
$c = \text{Ethanol}$
$d = \text{Lactic acid}$
Explanation: The process shown is glycolysis followed by anaerobic respiration (fermentation). Glycolysis is the breakdown of glucose into pyruvic acid, occurring in the cytoplasm. Under anaerobic conditions, pyruvic acid is converted into either ethanol and $CO_2$ (in yeast) or lactic acid (in muscle cells/bacteria).
Applications:
$1$. Brewing Industry: Used in the production of alcoholic beverages like wine and beer.
$2$. Baking Industry: Used in bread making where $CO_2$ released makes the dough rise.

(N/A) Due to continuous strenuous exercise,her muscles undergo anaerobic respiration because the oxygen supply is insufficient to meet the high energy demand. This leads to the accumulation of lactic acid in the skeletal muscles,causing muscle fatigue and pain.
$(b)$ Her breathing rate increases significantly from the normal resting rate. During exercise,the muscles require more $O_2$ for the production of $ATP$ through aerobic respiration. Therefore,the breathing rate increases to intake more $O_2$ from the atmosphere and to eliminate the excess $CO_2$ produced.

(A) When oxygen is present in limiting conditions,the breakdown of glucose or glycogen occurs via anaerobic respiration.
This process leads to the production of lactic acid in the muscle cells.
The accumulation of lactic acid increases the concentration of hydrogen ions,which causes the $pH$ of the muscles to become acidic.

(C) Under anaerobic conditions,such as during intense physical exercise,the oxygen supply to muscle cells becomes insufficient.
In these conditions,pyruvic acid is reduced by $NADH$ to form lactic acid.
This reaction is catalyzed by the enzyme lactate dehydrogenase.
This process allows for the regeneration of $NAD^+$ so that glycolysis can continue to produce a small amount of $ATP$.

(B) In anaerobic respiration,glucose is incompletely broken down in the absence of oxygen. In yeast,this process is known as fermentation,which results in the production of ethanol (alcohol) and carbon dioxide $(CO_2)$.