ETS Questions in English

(A) The $ATP$ synthase enzyme consists of two major components,$F_o$ and $F_1$.
The $F_o$ component is an integral membrane protein complex that forms a channel through which protons $(H^+)$ cross the inner mitochondrial membrane from the intermembrane space into the matrix.
The movement of protons through this $F_o$ channel provides the energy required for the $F_1$ head piece to catalyze the synthesis of $ATP$ from $ADP$ and inorganic phosphate $(Pi)$.
Therefore,protons first pass through the $F_o$ part.

(B) Oxidative phosphorylation is the process by which $ATP$ is synthesized using the energy released during the electron transport system $(ETS)$.
In the inner mitochondrial membrane, $Complex$ $V$ is known as $ATP$ synthase.
This complex consists of two major components: $F_0$ and $F_1$.
$F_0$ is an integral membrane protein complex that forms a channel through which protons cross the inner membrane.
$F_1$ is a peripheral membrane protein complex that contains the site for $ATP$ synthesis from $ADP$ and inorganic phosphate $(Pi)$.

(B) In the mitochondrial electron transport system $(ETS)$,$CoQ$ (Coenzyme $Q$ or Ubiquinone) and $Cyt$ $c$ (Cytochrome $c$) act as mobile electron carriers.
$CoQ$ is a lipid-soluble carrier that moves within the inner mitochondrial membrane,while $Cyt$ $c$ is a small protein attached to the outer surface of the inner membrane that acts as a mobile carrier for electrons between Complex $III$ and Complex $IV$.

(A) The incorrect statement is $A$. Complex $I$ ($NADH$ dehydrogenase) specifically accepts electrons and protons from $NADH$ only,not from $FADH_2$. $FADH_2$ donates its electrons to Complex $II$ (Succinate dehydrogenase). Therefore,the statement that Complex $I$ accepts from both $NADH$ and $FADH_2$ is scientifically incorrect.

(A) The cytochrome $c$ oxidase complex (Complex $IV$) receives electrons from cytochrome $c$,not directly from ubiquinone. Ubiquinone transfers electrons to Complex $III$ (cytochrome $bc_1$ complex),which then transfers them to cytochrome $c$,and finally to Complex $IV$. Therefore,the statement that it receives electrons directly from ubiquinone is false.

(A) $2,4-DNP$ $(2,4-Dinitrophenol)$ acts as an uncoupling agent because it is a lipid-soluble proton ionophore.
It facilitates the movement of protons $(H^+)$ across the inner mitochondrial membrane,bypassing the $ATP$ synthase enzyme.
As a result,the proton gradient is dissipated,which prevents the synthesis of $ATP$ while allowing electron transport to continue.
Thus,both the Assertion and Reason are correct,and the lipid solubility of $DNP$ is the reason it can act as an uncoupler.

(C) In the Electron Transport System $(ETS)$,electrons move from a carrier with a lower redox potential to a carrier with a higher redox potential.
This movement releases energy,which is used to pump protons across the membrane,creating a proton gradient.
Because the electrons move towards a more positive (higher) redox potential,the process is described as a 'downhill' journey in terms of energy levels.
Therefore,the Assertion is correct because the movement is energetically favorable (downhill),but the Reason is incorrect because electrons actually move from low to high redox potential,not high to low.

(A) Cytochrome $c$ is a small protein attached to the outer surface of the inner mitochondrial membrane.
It acts as a mobile electron carrier for electron transfer between Complex $III$ (cytochrome $bc_1$ complex) and Complex $IV$ (cytochrome $c$ oxidase).
Since it is loosely associated with the membrane surface and not embedded within the lipid bilayer,it is classified as a peripheral membrane protein.
It is located on the side of the inner mitochondrial membrane that faces the intermembrane space (perimitochondrial space).
Therefore,both the Assertion and the Reason are correct,and the Reason provides the correct explanation for the Assertion.

(B) Oxygen $(O_{2})$ is utilised by living organisms indirectly during the oxidation of nutrients like glucose. It acts as the final electron acceptor in the electron transport chain $(ETC)$ located in the inner mitochondrial membrane,where it combines with electrons and protons to form water $(H_{2}O)$.

(B) The correct answer is $B$.
In the Electron Transport Chain $(ETC)$,the oxidation of one molecule of $NADH+H^{+}$ results in the production of $3$ $ATP$ molecules,while the oxidation of one molecule of $FADH_{2}$ results in the production of $2$ $ATP$ molecules.
Option $B$ states the reverse,making it incorrect.
Oxygen acts as the final electron acceptor at the end of the $ETC$ (terminal stage).
Complex $V$ ($ATP$ synthase) is responsible for the synthesis of $ATP$ using the proton gradient.
The proton gradient is generated by the energy released during oxidation-reduction reactions in the $ETC$.

(A) $F_{0}-F_{1}$ particles are located in the inner mitochondrial membrane. They take part in the synthesis of $ATP$,which is the energy currency of the cell.
The energy released during the electron transport system is utilized in synthesizing $ATP$ with the help of $ATP$ synthase (Complex $V$).
This complex consists of two major components,$F_{0}$ and $F_{1}$.
The $F_{1}$ headpiece is a peripheral membrane protein complex and contains the site for the synthesis of $ATP$ from $ADP$ and inorganic phosphate $(ADP + Pi \rightarrow ATP)$.
$F_{0}$ is an integral membrane protein complex that forms the channel through which protons cross the inner membrane.
The passage of protons through the channel is coupled to the catalytic site of the $F_{1}$ component for the production of $ATP$.
For each $ATP$ produced,$2 H^{+}$ ions pass through $F_{0}$ from the intermembrane space to the matrix down the electrochemical proton gradient.

(D) Cytochromes are iron-containing hemoproteins that act as electron carriers in electron transport chains.
They are found in the thylakoid membranes of the grana in chloroplasts (during photosynthesis),the inner mitochondrial membrane (during cellular respiration),and the plasma membrane of prokaryotes (mesosomes).
Therefore,all the given options are correct locations for cytochromes.

(A) During the process of oxidative phosphorylation in mitochondria,the electron transport chain $(ETC)$ complexes pump protons $(H^+)$ from the mitochondrial matrix into the intermembrane space. This creates a high concentration of protons in the intermembrane space compared to the matrix,establishing a proton gradient (electrochemical gradient) across the inner mitochondrial membrane. Therefore,the gradient is established from the matrix to the intermembrane space.

(D) $F_0$ and $F_1$ are the two main components of the $ATP$ synthase enzyme complex.
$F_0$ is an integral membrane protein complex that forms a transmembrane channel through which protons cross the membrane.
$F_1$ is a peripheral membrane protein complex that projects into the matrix or stroma and contains the site for $ATP$ synthesis from $ADP$ and inorganic phosphate $(Pi)$.

(B) Oxidative phosphorylation is the process in which $ATP$ is synthesized during the electron transport system $(ETS)$.
This process occurs in the inner mitochondrial membrane,where the electron transport chain complexes and $ATP$ synthase are located.
During this process,electrons are transferred from $NADH$ and $FADH_2$ to oxygen,and the energy released is used to pump protons across the membrane,creating a proton gradient that drives $ATP$ synthesis.

(A) In the electron transport system $(ETS)$ of oxidative phosphorylation,electrons are passed through a series of complexes.
At the end of the chain,the final electron acceptor is oxygen $(O_2)$.
Oxygen accepts the electrons and combines with protons $(H^+)$ to form water $(H_2O)$.
This process is essential for maintaining the flow of electrons through the transport chain.

(C) During oxidative phosphorylation,the electron transport system $(ETS)$ facilitates the synthesis of $ATP$ through chemiosmosis.
One molecule of $NADH + H^+$ donates electrons to Complex $I$,which leads to the pumping of protons across the inner mitochondrial membrane,resulting in the production of $3$ $ATP$ molecules.
One molecule of $FADH_2$ donates electrons to Complex $II$,bypassing Complex $I$,which results in the pumping of fewer protons and the production of $2$ $ATP$ molecules.
Therefore,the correct sequence is $3$ $ATP$ from $NADH + H^+$ and $2$ $ATP$ from $FADH_2$.

(D) In the Electron Transport System $(ETS)$,the complexes are primarily composed of proteins.
Specifically,cytochromes (which are heme-containing proteins) and iron-sulfur proteins act as essential electron carriers.
These proteins facilitate the transfer of electrons from $NADH$ and $FADH_2$ to oxygen,which is the final electron acceptor.
Therefore,proteins are the primary molecules that function as electron carriers in the $ETS$.

(C) The Electron Transport System $(ETS)$ in mitochondria consists of five major complexes:
$1$. Complex-$I$ is $NADH$ dehydrogenase.
$2$. Complex-$II$ is Succinate dehydrogenase ($FADH_2$ dehydrogenase).
$3$. Complex-$III$ is Cytochrome $bc_1$ complex.
$4$. Complex-$IV$ is Cytochrome $c$ oxidase complex.
$5$. Complex-$V$ is $ATP$ synthase.
Matching these with the given columns:
$P$ (Complex-$I$) matches with $V$ ($NADH$ dehydrogenase).
$Q$ (Complex-$II$) matches with $IV$ ($FADH_2$ dehydrogenase).
$R$ (Complex-$III$) matches with $II$ (Cytochrome $bc_1$ complex).
$S$ (Complex-$IV$) matches with $I$ (Cytochrome $c$ oxidase complex).
$T$ (Complex-$V$) matches with $III$ ($ATP$ synthase).
Therefore, the correct sequence is $(P-V), (Q-IV), (R-II), (S-I), (T-III)$.

(A) In the Electron Transport System $(ETS)$,$FADH_2$ is oxidized by Complex-$II$ (Succinate dehydrogenase).
Electrons from $FADH_2$ are transferred to ubiquinone $(Q)$ via Complex-$II$.
Since $FADH_2$ enters the $ETS$ at Complex-$II$,it bypasses Complex-$I$ ($NADH$ dehydrogenase).
Therefore,electrons from $FADH_2$ do not pass through Complex-$I$.

(B) In the Electron Transport System $(ETS)$,$NADH + H^+$ is oxidized by $NADH$ dehydrogenase,which is $Complex-I$.
Electrons from $NADH$ are transferred to $Ubiquinone$ $(UQ)$ via $Complex-I$.
$Complex-II$ ($Succinate$ dehydrogenase) is specifically involved in the oxidation of $FADH_2$,not $NADH$.
Therefore,electrons derived from $NADH$ do not pass through $Complex-II$.

(A) The diagram represents the Electron Transport System $(ETS)$ located in the inner mitochondrial membrane.
$P$ represents the matrix,where the $NADH$ and $FADH_2$ are oxidized and protons are released.
$Q$ represents the inner mitochondrial membrane,which contains the protein complexes $(I, II, III, IV)$ and $ATP$ synthase.
$R$ represents the intermembrane space,where protons are pumped to create a proton gradient.

(B) During the process of oxidative phosphorylation in mitochondria,the electron transport system $(ETS)$ is located in the inner mitochondrial membrane. As electrons pass through the complexes,energy is released,which is used to pump protons $(H^+)$ from the mitochondrial matrix into the intermembrane space. This creates a high concentration of protons in the intermembrane space compared to the matrix,establishing a proton gradient. Therefore,the proton gradient is established from the matrix to the intermembrane space.

(A) The $ATP$ synthase complex consists of two major components: $F_0$ and $F_1$.
$F_0$ is an integral membrane protein complex that acts as a channel for protons $(H^+)$ to cross the inner mitochondrial membrane.
$F_1$ is a peripheral membrane protein complex that contains the site for $ATP$ synthesis.
According to the chemiosmotic hypothesis,the movement of $2 H^+$ ions from the intermembrane space to the mitochondrial matrix through the $F_0-F_1$ complex provides enough energy to catalyze the phosphorylation of one $ADP$ molecule into one $ATP$ molecule.
Therefore,the passage of $2 H^+$ ions results in the production of $1$ $ATP$ molecule.

(D) In the Electron Transport System $(ETS)$,mobile electron carriers are essential for transferring electrons between fixed protein complexes.
$1$. Ubiquinone $(UQ)$ is a lipid-soluble mobile carrier that transfers electrons from Complex $I$ and Complex $II$ to Complex $III$ in the mitochondrial inner membrane.
$2$. Plastoquinone $(PQ)$ is a mobile carrier in the thylakoid membrane of chloroplasts that transfers electrons from Photosystem $II$ to the Cytochrome $b_6f$ complex.
$3$. Cytochrome $c$ $(Cyt\,c)$ is a small,water-soluble protein that acts as a mobile carrier,transferring electrons from Complex $III$ to Complex $IV$ in the mitochondria.
Since all three are mobile electron carriers,the correct answer is $D$.

(B) The figure shows the $F_0-F_1$ particle ($ATP$ synthase) located in the mitochondrial inner membrane.
$ATP$ synthesis occurs through chemiosmosis,which is driven by a proton gradient.
Protons $(H^+)$ flow from the intermembrane space (outside) into the mitochondrial matrix (inside) through the $F_0$ channel of the $ATP$ synthase complex.
This flow of protons provides the energy required for the phosphorylation of $ADP$ to $ATP$ in the $F_1$ headpiece.
Therefore,$P$ represents the flow of protons $(H^+)$.

(D) The $ATP$ synthase enzyme complex consists of two major components,$F_0$ and $F_1$.
$F_0$ is an integral membrane protein complex that forms a channel through which protons cross the inner mitochondrial membrane.
The $F_1$ headpiece is a peripheral membrane protein complex that protrudes into the mitochondrial matrix.
When protons flow through the $F_0$ channel into the matrix,the energy released is used by the $F_1$ subunit to catalyze the phosphorylation of $ADP$ to $ATP$ $(ADP + Pi \rightarrow ATP)$.
Therefore,the synthesis of $ATP$ occurs at the $F_1$ subunit.

(C) In the process of oxidative phosphorylation,$ATP$ synthase consists of two major components: $F_0$ and $F_1$.
$F_0$ is an integral membrane protein complex that forms a channel through which protons $(H^+)$ cross the inner mitochondrial membrane.
$F_1$ is a peripheral membrane protein complex that projects into the matrix and contains the site for $ATP$ synthesis.
Protons accumulate in the intermembrane space due to the electron transport chain,creating a proton gradient.
These protons flow back into the matrix through the $F_0$ channel,which provides the energy for $F_1$ to catalyze the synthesis of $ATP$ from $ADP$ and inorganic phosphate $(Pi)$.
Therefore,the path of $H^+$ is: Intermembrane space $\rightarrow F_0 \rightarrow$ Matrix.

(A) In the mitochondrial electron transport system,the $F_1$ subunit of $ATP$ synthase is a peripheral membrane protein complex.
It is located on the matrix side of the inner mitochondrial membrane.
In contrast,$F_0$ is an integral membrane protein complex that acts as a proton channel.
Complex-$I$ and Complex-$II$ are also integral membrane protein complexes embedded within the inner mitochondrial membrane.

(B) Complex $II$ of the mitochondrial electron transport chain is $\text{Succinate dehydrogenase}$.
It is a membrane-bound enzyme that catalyzes the oxidation of succinate to fumarate in the citric acid cycle, while simultaneously reducing $FAD$ to $FADH_2$, which then transfers electrons to the electron transport chain.

(B) Complex $IV$,also known as cytochrome $c$ oxidase,is the final protein complex in the electron transport chain.
It contains two heme groups ($a$ and $a_3$) and two copper centers ($Cu_A$ and $Cu_B$).
The $Cu_A$ center receives electrons from cytochrome $c$,while the $Cu_B$ center,along with heme $a_3$,forms the active site where oxygen is reduced to water.

(C) In the electron transport system $(ETS)$ located in the inner mitochondrial membrane,the complexes are organized as follows:
$1$. Complex-$I$: $NADH$ dehydrogenase.
$2$. Complex-$II$: Succinate dehydrogenase.
$3$. Complex-$III$: Cytochrome $bc_1$ complex.
$4$. Complex-$IV$: Cytochrome-$c$ oxidase complex (containing cytochromes $a$ and $a_3$ and two copper centers).
$5$. Complex-$V$: $ATP$ synthase.
Therefore,Complex-$I$ is $NADH$ dehydrogenase and Complex-$IV$ is the cytochrome-$c$ oxidase complex.

(D) The Cytochrome $C$ oxidase complex is known as Complex $IV$ in the electron transport system $(ETS)$.
It contains two cytochromes,$a$ and $a_3$,and two copper centers ($Cu_A$ and $Cu_B$).
These components work together to transfer electrons from cytochrome $c$ to molecular oxygen,reducing it to water.

(D) In the Electron Transport System $(\text{ETS})$,ubiquinone (also known as Coenzyme $Q$) acts as a mobile electron carrier within the inner mitochondrial membrane.
It receives reducing equivalents (electrons) from two main sources:
$1$. From $\text{Complex } I$ ($\text{NADH}$ dehydrogenase) via the oxidation of $\text{NADH}$.
$2$. From $\text{Complex } II$ (Succinate dehydrogenase) via the oxidation of succinate to fumarate.
Since $\text{Complex } II$ is one of the primary donors of electrons to ubiquinone,the correct option is $\text{Complex } II$.

(D) In the Electron Transport System $(ETS)$,Complex $\text{V}$ is $ATP$ synthase,which is responsible for the synthesis of $ATP$ from $ADP$ and inorganic phosphate using the proton gradient.
Complex $\text{III}$ (Cytochrome $bc_1$ complex) and Complex $\text{IV}$ (Cytochrome $c$ oxidase) are linked by Cytochrome $c$,which acts as a mobile electron carrier.
Therefore,the statement that Complex $\text{V}$ transfers electrons between Complex $\text{III}$ and $\text{IV}$ is incorrect.

(B) The Electron Transport System $(ETS)$ is a series of protein complexes and electron carrier molecules located in the inner mitochondrial membrane.
These complexes are embedded within the folds of the inner membrane,which are known as cristae.
The $ETS$ facilitates the transfer of electrons from $NADH$ and $FADH_2$ to oxygen,creating a proton gradient that drives the synthesis of $ATP$ via oxidative phosphorylation.

(C) Complex-$IV$ of the electron transport system $(ETS)$ is known as cytochrome-$c$ oxidase.
It contains cytochromes $a$ and $a_3$,and two copper centres.
Cytochrome-$c$ is a small protein that acts as a mobile electron carrier between complex-$III$ and complex-$IV$.
Therefore,cytochrome-$c$ is not a component of complex-$IV$ itself.

(B) In the electron transport system $(ETS)$ of aerobic respiration,the electrons are passed through a series of complexes.
At the end of this chain,molecular oxygen $(O_2)$ acts as the final or ultimate electron acceptor.
It combines with electrons and protons to form water $(H_2O)$,which is essential for the continuation of the process.

(B) The correct matching is as follows:
$i.$ $FADH_2$ is oxidized by Complex $II$ (Succinate dehydrogenase).
$ii.$ Ubiquinol $(QH_2)$ transfers electrons to Complex $III$ (Cytochrome $bc_1$ complex).
$iii.$ $NADH + H^{+}$ is oxidized by Complex $I$ ($NADH$ dehydrogenase).
$iv.$ Cytochrome $C$ transfers electrons to Complex $IV$ (Cytochrome $c$ oxidase).
Thus, the correct sequence is $i-c, ii-a, iii-d, iv-b$.

(D) Complex $IV$,also known as cytochrome $c$ oxidase,is the mitochondrial complex that donates electrons to molecular oxygen during the Electron Transport Chain $(ETC)$.
It is the final complex in the $ETC$ and plays a crucial role in transferring electrons to oxygen to form water $(H_2O)$.

(B) The net gain of $ATP$ by the complete oxidation of $1$ glucose molecule is $38$ $ATP$ molecules.
Out of these,$4$ $ATP$ molecules are produced via substrate-level phosphorylation (during glycolysis and the Krebs cycle).
The remaining $34$ $ATP$ molecules are generated through oxidative phosphorylation via the Electron Transport System $(ETS)$.

(A) The Electron Transport System $(ETS)$ is a series of protein complexes and electron carriers embedded in the inner mitochondrial membrane.
These complexes ($Complex$ $I$ to $IV$) and $ATP$ synthase ($Complex$ $V$) facilitate the transfer of electrons from $NADH$ and $FADH_2$ to oxygen,creating a proton gradient that drives $ATP$ synthesis.
Therefore,the inner mitochondrial membrane is the site where these enzymes are organized.

(C) Statement-$I$ is incorrect because Cytochrome $c$ is an iron-containing protein, not copper-containing.
Statement-$II$ is incorrect because Cytochrome $c$ acts as a mobile electron carrier that transfers electrons specifically between Complex-$III$ and Complex-$IV$, not between Complex-$I$, $II$, and $IV$.

(A) $NADH + H^+$ is oxidized by $NADH$ dehydrogenase (complex $I$).
Complex $IV$ is known as cytochrome $c$ oxidase,which contains cytochromes $a$ and $a_3$ along with two copper centers.
Therefore,complex $I$ is $NADH$ dehydrogenase and complex $IV$ is cytochrome $c$ oxidase.

(D) Ubiquinone (also known as Coenzyme $Q$) is a lipid-soluble electron carrier in the electron transport chain $(ETC)$ of mitochondria.
It exists in three redox states: fully oxidized (ubiquinone),semi-reduced (semiquinone),and fully reduced (ubiquinol).
Ubiquinol is the fully reduced form of ubiquinone,which carries two electrons and two protons $(H^+)$ during the process of cellular respiration.

(B) $Statement-I$ is correct: The Electron Transport System $(ETS)$ releases energy in a stepwise manner to ensure that the energy is captured efficiently in the form of $ATP$ and to prevent the sudden release of energy which could damage the cell.
$Statement-II$ is correct: During the final step of $ETS$, oxygen acts as the final electron acceptor and combines with protons and electrons to form water molecules $(H_2O)$.

(A) Statement-$I$ is correct: During the Electron Transport System $(ETS)$,the reduced co-enzymes $NADH + H^+$ and $FADH_2$ are oxidized to regenerate $NAD^+$ and $FAD^+$,which are then reused in the earlier stages of respiration (Glycolysis and Krebs cycle).
Statement-$II$ is correct: The primary function of the $ETS$ is to facilitate oxidative phosphorylation,where the energy released from electron transfer is used to synthesize a large amount of $ATP$ molecules from $ADP$ and inorganic phosphate $(Pi)$.
Therefore,both statements are correct.

(D) In aerobic respiration,the complete oxidation of one glucose molecule yields $10$ $NADH$ and $2$ $FADH_2$ molecules.
Through the electron transport system $(ETS)$ and oxidative phosphorylation,each $NADH$ produces $3$ $ATP$ ($10 \times 3 = 30$ $ATP$) and each $FADH_2$ produces $2$ $ATP$ ($2 \times 2 = 4$ $ATP$).
Therefore,the total number of $ATP$ molecules produced specifically through oxidative phosphorylation is $30 + 4 = 34$ $ATP$.

(A) In the electron transport system $(ETS)$ of the mitochondrial inner membrane,electrons are transferred through a series of complexes.
Specifically,the sequence of electron carriers in the cytochrome chain is: Cyt. $b \rightarrow$ Cyt. $c_1 \rightarrow$ Cyt. $c \rightarrow$ Cyt. $a \rightarrow$ Cyt. $a_3$.
Complex $III$ contains Cyt. $b$ and Cyt. $c_1$,which transfers electrons to Cyt. $c$,and subsequently to Complex $IV$ (which contains Cyt. $a$ and Cyt. $a_3$).
Therefore,the correct sequence is Cyt. $b-c_1 \rightarrow$ Cyt. $c \rightarrow$ Cyt. $a \rightarrow$ Cyt. $a_3$.

(A) The Electron Transport Chain $(ETC)$ located in the inner mitochondrial membrane consists of several protein complexes and mobile electron carriers.
Key components include $NADH$ dehydrogenase (Complex $I$),Succinate dehydrogenase (Complex $II$),Cytochrome $bc_1$ complex (Complex $III$),and Cytochrome $c$ oxidase (Complex $IV$).
These complexes contain prosthetic groups and co-enzymes such as flavoproteins ($FMN$,$FAD$),iron-sulfur proteins,and cytochromes.
Dehydrogenases are enzymes that catalyze the removal of hydrogen atoms from substrates,and they often utilize flavoproteins as co-enzymes to facilitate electron transfer.
Therefore,the correct group consisting of components/co-enzymes involved in the $ETC$ is Cytochromes,dehydrogenases,and flavoproteins.