Anaerobic respiration Questions in English

(D) $Statement-I$ is incorrect because skeletal muscles primarily derive energy through aerobic respiration under normal conditions. Anaerobic respiration occurs only during intense activity when oxygen supply is insufficient.
$Statement-II$ is correct because during vigorous exercise,the demand for oxygen exceeds the supply,leading to anaerobic glycolysis. This results in the accumulation of lactic acid in muscle fibres,which causes muscle fatigue.

(A) In alcohol fermentation,pyruvic acid is first converted into acetaldehyde and $CO_2$.
Subsequently,acetaldehyde acts as the final hydrogen acceptor.
It is reduced by $NADH + H^+$ to form ethanol,while $NAD^+$ is regenerated for glycolysis.

(C) In lactic acid fermentation, glucose $(C_6H_{12}O_6)$ first undergoes glycolysis to produce $2$ molecules of pyruvic acid along with $2 \ NADH + H^+$ and $2 \ ATP$.
Therefore, the first step is $C_6H_{12}O_6 \rightarrow 2 \ \text{Pyruvic acid} + 2 \ NADH + H^+$.
In the second step, pyruvic acid is reduced to lactic acid by the enzyme lactate dehydrogenase.
During this reduction, $NADH + H^+$ is oxidized back to $NAD^+$.
The reaction is: $2 \ \text{Pyruvic acid} + 2 \ NADH + H^+ \rightarrow 2 \ \text{Lactic acid} + 2 \ NAD^+$.
Comparing this with the given equation $C_6H_{12}O_6 \rightarrow A + B \rightarrow \text{Lactic acid} + C$, we identify:
$A = \text{Pyruvic acid}$
$B = 2 \ NADH + H^+$
$C = 2 \ NAD^+$
Thus, option $C$ represents the correct sequence.

(A) In the absence of oxygen,the pyruvic acid produced during glycolysis is reduced to lactic acid in animal cells and some bacteria. This process is a type of anaerobic respiration known as fermentation. During this process,$NADH + H^+$ is oxidized back to $NAD^+$,which is essential for the continuation of glycolysis.

(C) During anaerobic respiration,the breakdown of one glucose molecule produces a net gain of $2$ $ATP$ molecules.
This occurs because,during glycolysis,a total of $4$ $ATP$ molecules are produced,but $2$ $ATP$ molecules are consumed in the preparatory phase,resulting in a net gain of $2$ $ATP$ molecules.
Since anaerobic respiration does not involve the electron transport chain or oxidative phosphorylation,no additional $ATP$ molecules are generated beyond those produced during glycolysis.
Therefore,the number of $ATP$ molecules generated by the breakdown of $20$ glucose molecules is calculated as: $20 \text{ glucose molecules} \times 2 \text{ } ATP \text{ molecules/glucose} = 40 \text{ } ATP \text{ molecules}$.
Thus,the correct answer is $40$ $ATP$ molecules.

(A) In anaerobic respiration (specifically in alcoholic fermentation),the enzyme pyruvate decarboxylase catalyzes the conversion of pyruvate into acetaldehyde and carbon dioxide.
This enzyme requires thiamine pyrophosphate $(TPP)$ as a coenzyme and a divalent metal ion as a cofactor.
The specific metal ion required as a cofactor for pyruvate decarboxylase is $Mg^{2+}$ (magnesium ion).
Therefore,the correct option is $A$.

(C) In the anaerobic respiration pathway in yeast,pyruvate is first converted into acetaldehyde and $CO_2$ by the enzyme pyruvate decarboxylase.
Then,acetaldehyde is reduced to ethanol by the enzyme alcohol dehydrogenase,using $NADH$ as a reducing agent.
Looking at the provided pathway diagram:
$1$. Pyruvate is converted to $C$ $(CO_2)$ and $B$ (Acetaldehyde).
$2$. Acetaldehyde $(B)$ is then converted to $A$ (Ethanol).
Therefore,the correct labels are $A$-Ethanol,$B$-Acetaldehyde,and $C-CO_2$.

(A) Alcoholic fermentation.
The equation provided represents the process of alcoholic fermentation,where glucose $(C_6H_{12}O_6)$ is converted into ethanol $(2C_2H_5OH)$,carbon dioxide $(2CO_2)$,and a small amount of $ATP$ $(2ATP)$.
This is an anaerobic process that occurs in yeast and some bacteria,where ethanol and carbon dioxide are produced as byproducts.

(C) The correct answer is $C$.
During fermentation,whether it is lactic acid fermentation or alcoholic fermentation,only $2$ $ATP$ molecules are produced per molecule of glucose.
This is because fermentation is an anaerobic process,which only includes glycolysis.
Glycolysis results in a net gain of $2$ $ATP$ molecules,as the subsequent steps of fermentation do not produce any additional $ATP$.

(B) neither $O_2$ is used,nor $CO_2$ is liberated.
During lactic acid fermentation,oxygen is not consumed,and carbon dioxide is not produced.
This is an anaerobic process where glucose is converted into lactic acid without the involvement of oxygen or the release of carbon dioxide.
The chemical equation is:
$C_6H_{12}O_6 \longrightarrow 2C_3H_6O_3 + 2ATP$