Amphibolic Pathway Questions in English

(B) Palmitic acid $(C_{16}H_{32}O_2)$ undergoes $\beta$-oxidation to produce $8$ molecules of Acetyl-CoA,$7$ $FADH_2$,and $7$ $NADH$.
Each Acetyl-CoA enters the Krebs cycle to produce $3$ $NADH$,$1$ $FADH_2$,and $1$ $ATP$ (or $GTP$).
For $8$ Acetyl-CoA,the total yield is $24$ $NADH$,$8$ $FADH_2$,and $8$ $ATP$.
Adding the products from $\beta$-oxidation ($7$ $FADH_2$ and $7$ $NADH$),the total yield is $31$ $NADH$,$15$ $FADH_2$,and $8$ $ATP$.
Using standard conversion factors ($1$ $NADH = 2.5$ $ATP$ and $1$ $FADH_2 = 1.5$ $ATP$): $31 \times 2.5 = 77.5$ $ATP$ and $15 \times 1.5 = 22.5$ $ATP$.
Total $ATP = 77.5 + 22.5 + 8 = 108$ $ATP$.
However,considering the older convention ($1$ $NADH = 3$ $ATP$ and $1$ $FADH_2 = 2$ $ATP$): $31 \times 3 = 93$ $ATP$ and $15 \times 2 = 30$ $ATP$.
Total gross $ATP = 93 + 30 + 8 = 131$ $ATP$.
Since $2$ $ATP$ equivalents are consumed for the activation of fatty acid into Acyl-CoA,the net gain is $131 - 2 = 129$ $ATP$.

(C) The Assertion is correct: Fats are broken down by lipases into fatty acids and glycerol.
The Reason is incorrect: Glycerol is converted into $DHAP$ (Dihydroxyacetone phosphate),which then enters the glycolytic pathway. It does not enter through serine formation.
Therefore,the correct option is $C$.

(C) The $TCA$ cycle is considered an amphibolic pathway because it involves both catabolic and anabolic processes.
Catabolic reactions involve the breakdown of molecules to produce energy,while anabolic reactions use the intermediates of the $TCA$ cycle (such as $\alpha$-ketoglutarate,succinyl-$CoA$,and oxaloacetate) to synthesize other important biomolecules like amino acids,chlorophyll,and fatty acids.
Since the intermediates are used in both catabolic and anabolic reactions,the statement in the Reason that they are used in 'catabolic reactions only' is incorrect.
Therefore,the Assertion is correct,but the Reason is incorrect.

(C) The $Cori$ cycle,also known as the lactic acid cycle,describes the metabolic pathway in which lactate produced by anaerobic glycolysis in the muscles is transported to the liver.
In the liver,lactate is converted back to glucose through gluconeogenesis.
This glucose is then released back into the blood and returned to the muscles to be used as an energy source.
Therefore,the $Cori$ cycle involves both the liver and the muscles,with the blood acting as the transport medium between these two organs.

(C) $Xylem$ is responsible for the upward conduction of water and dissolved mineral salts from the roots to the aerial parts of the plant. It also transports some organic nitrogen and hormones.
$Phloem$ is responsible for the translocation of organic substances (mainly sucrose) synthesized in the leaves to other parts of the plant.

(D) Respiratory substrates are the organic compounds that are oxidized during the process of respiration to release energy.
Carbohydrates are the most common respiratory substrates.
However,proteins,fats (lipids),and organic acids can also be used as respiratory substrates under certain conditions,such as when carbohydrates are exhausted.
Therefore,all the given options are correct.

(D) Proteins are first degraded by proteases into amino acids.
These amino acids are then deaminated to form various intermediates of the respiratory pathway.
Depending on the structure of the amino acid,they can enter the respiratory pathway at different stages,such as pyruvic acid,acetyl $CoA$,or intermediates of the Krebs cycle (like $\alpha$-ketoglutarate).
Among the given options,pyruvic acid is a common entry point for amino acids after deamination.

(B) Fatty acids are first broken down into glycerol and fatty acids.
The glycerol is converted into $DHAP$ and enters the respiratory pathway.
The fatty acids are broken down into acetyl $CoA$ through the process of $\beta$-oxidation.
Thus,fatty acids enter the respiratory pathway as acetyl $CoA$.

(A) Glycerol is a derivative of fatty acids and is converted into $DHAP$ (Dihydroxyacetone phosphate) during the breakdown of fats.
$DHAP$ is an intermediate of glycolysis.
Therefore,glycerol enters the respiratory pathway at the level of $DHAP$.

(A) The provided figure illustrates the amphibolic pathway of cellular respiration,where both catabolic and anabolic processes occur.
$1$. Proteins are broken down into $P$,which are amino acids.
$2$. Fats are broken down into fatty acids and glycerol. Fatty acids are converted into $Q$,which is Acetyl $CoA$.
$3$. Carbohydrates are broken down into monosaccharides (like glucose),which enter glycolysis to form pyruvate,which is then converted into Acetyl $CoA$.
$4$. Acetyl $CoA$ $(Q)$ enters the $R$,which is the Krebs cycle ($TCA$ cycle),to produce $CO_2$ and $H_2O$.
Therefore,$P$ is amino acids,$Q$ is Acetyl $CoA$,and $R$ is the Krebs cycle.

(B) Respiration involves the breakdown of complex organic molecules like glucose into simpler substances like $CO_2$ and $H_2O$ to release energy.
Since this process involves the degradation or breakdown of molecules,it is classified as a catabolic process.
While respiration is often called an amphibolic pathway because it involves both catabolic and anabolic reactions (e.g.,synthesis of precursors),the primary act of breaking down respiratory substrates is catabolic.

(A) Statement $I$ is correct: The oxidation of respiratory substrates occurs in a stepwise manner rather than a single-step combustion. This controlled release of energy allows the cell to capture a larger proportion of energy in the form of $ATP$ rather than losing it as heat.
Statement $II$ is correct: Because respiration is a stepwise process involving various intermediates (like $Pyruvic$ acid,$Acetyl-CoA$,etc.),these intermediates can be diverted from the respiratory pathway to synthesize other biomolecules like amino acids or fatty acids. This makes respiration an amphibolic pathway.
Therefore,both statements are correct.

(A) Statement $I$ is correct: The Krebs cycle (Tricarboxylic Acid cycle) is considered an amphibolic pathway because it involves both catabolic reactions (breakdown of acetyl $CoA$ to $CO_2$) and anabolic reactions (synthesis of precursors for amino acids,fatty acids,etc.).
Statement $II$ is correct: During the Krebs cycle,the acetyl group of acetyl $CoA$ undergoes stepwise oxidation,releasing $CO_2$ and generating reduced coenzymes ($NADH$ and $FADH_2$) and $ATP$ (or $GTP$).
Therefore,both statements are correct.

(A) Acetyl-Co-$A$ is a $2C$ compound formed during the respiratory breakdown of fats and carbohydrates.
Succinate and Oxaloacetate $(OAA)$ are $4C$ compounds.
Pyruvic acid is a $3C$ compound formed during glycolysis.