ETS Questions in English

(B) In the mitochondrial Electron Transport System $(ETS)$,electrons are transferred through a series of complexes.
Specifically,the sequence of cytochromes involved in the electron transport chain is $Cyt$ $b \rightarrow Cyt$ $c_1 \rightarrow Cyt$ $c \rightarrow Cyt$ $a \rightarrow Cyt$ $a_3$.
Therefore,the correct order among the given options is $Cyt$ $b, c, a, a_3$.

(C) Oxidative phosphorylation is the process in which $ATP$ is synthesized during the electron transport system $(ETS)$.
This process occurs in the inner mitochondrial membrane,specifically within the cristae (folds of the inner membrane).
The enzymes and electron carriers required for $ETS$ and oxidative phosphorylation are embedded in the inner mitochondrial membrane.
Therefore,the correct location is the cristae of the mitochondria.

(C) The Electron Transport System $(ETS)$ is located in the inner mitochondrial membrane.
These enzymes,organized into complexes ($I$ through $IV$) and $ATP$ synthase ($Complex$ $V$),are embedded within the inner membrane to facilitate the transfer of electrons and the synthesis of $ATP$ via oxidative phosphorylation.

(B) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain $(ETC)$.
They contain a heme group,which is a porphyrin ring with a central iron $(Fe)$ atom.
These proteins are essential for cellular respiration and photosynthesis.
Therefore,they are classified as $Fe$-containing porphyrin pigments.

(C) In both photosynthesis (photophosphorylation) and respiration (oxidative phosphorylation),$ATP$ synthesis is driven by the movement of electrons through an electron transport chain $(ETC)$.
As electrons move from a higher energy state to a lower energy state through various carriers (like cytochromes or ferredoxin),they release energy.
This released energy is used to pump protons $(H^+)$ across a membrane,creating a proton gradient.
The dissipation of this proton gradient through $ATP$ synthase provides the energy required to phosphorylate $ADP$ into $ATP$.
Therefore,the energy for $ATP$ synthesis is derived from the movement of electrons.

(D) In the electron transport system $(ETS)$ of aerobic respiration,the final complex is Complex $IV$,also known as cytochrome $c$ oxidase.
This complex contains cytochromes $a$ and $a_3$,along with two copper centers.
The cytochrome $a_3$ is the terminal component that transfers electrons directly to the final electron acceptor,which is oxygen $(O_2)$,to form water $(H_2O)$.

(B) Oxidative phosphorylation is the process in which $ATP$ is formed as a result of the transfer of electrons from $NADH$ or $FADH_2$ to $O_2$ by a series of electron carriers.
This process occurs in the inner mitochondrial membrane during cellular respiration.
In contrast,photophosphorylation is the process of $ATP$ synthesis in the chloroplast during photosynthesis.
Therefore,oxidative phosphorylation is specifically associated with the production of $ATP$ during respiration.

(A) In aerobic respiration,the complete oxidation of one glucose molecule yields $38$ $ATP$ molecules.
Out of these,$4$ $ATP$ are produced via substrate-level phosphorylation (two from glycolysis and two from the Krebs cycle).
The remaining $32$ $ATP$ molecules are generated through the Electron Transport System $(ETS)$ or Respiratory chain,where $NADH$ and $FADH_2$ are oxidized to produce $ATP$ via oxidative phosphorylation.

(B) Cyanide is a potent inhibitor of the electron transport chain $(ETC)$,specifically binding to cytochrome c oxidase (Complex $IV$).
This inhibition prevents the final step of aerobic respiration,where oxygen is reduced to water.
As a result,the proton gradient across the inner mitochondrial membrane cannot be maintained,and $ATP$ synthesis stops.
Since $ATP$ is essential for vital cellular processes,including the active transport of ions via the $Na^+ - K^+$ pump,the cessation of $ATP$ production leads to cell death and toxicity.

(D) Oxidative phosphorylation is the metabolic pathway in which cells use enzymes to oxidize nutrients,thereby releasing energy which is used to produce $ATP$.
In this process,the electron transport chain $(ETC)$ facilitates the transfer of electrons from $NADH$ and $FADH_2$ to oxygen.
The energy released during this electron transfer is used to pump protons across the inner mitochondrial membrane,creating an electrochemical gradient.
Finally,$ATP$ synthase utilizes this gradient to phosphorylate $ADP$ into $ATP$.
Therefore,the final product of this process is $ATP$.

(D) The complete oxidation of glucose involves several stages: Glycolysis,the Link reaction,the Krebs cycle,and the Electron Transport Chain $(ETC)$.
$1$. Glycolysis produces a net gain of $2 \ ATP$ molecules.
$2$. The Krebs cycle produces $2 \ GTP$ (which is equivalent to $2 \ ATP$) per glucose molecule.
$3$. The Electron Transport Chain $(ETC)$ is the final stage where the majority of $ATP$ is synthesized via oxidative phosphorylation.
$4$. During $ETC$,the oxidation of $NADH$ and $FADH_2$ provides the energy to pump protons,creating a gradient that drives $ATP$ synthase to produce approximately $28$ to $30 \ ATP$ molecules per glucose molecule.
Therefore,the maximum number of $ATP$ molecules is produced during the $ETC$.

(C) The chemiosmotic coupling hypothesis,proposed by Peter Mitchell,explains that $ATP$ synthesis in mitochondria occurs due to the electrochemical gradient of protons ($H^+$ ions).
$1$. During the electron transport chain,protons are pumped from the mitochondrial matrix into the intermembrane space.
$2$. This creates a high concentration of protons in the intermembrane space compared to the matrix,establishing a proton gradient (or proton-motive force) across the inner mitochondrial membrane.
$3$. Protons flow back into the matrix through the $F_0-F_1$ $ATP$ synthase complex.
$4$. This flow of protons provides the energy required for the phosphorylation of $ADP$ to form $ATP$.

(B) Oxidative phosphorylation is the process in which $ATP$ is synthesized from $ADP$ and inorganic phosphate $(Pi)$ using the energy released during the electron transport chain $(ETC)$.
In this process,electrons are removed from substrates (like $NADH$ and $FADH_2$) and passed through a series of electron carriers to oxygen.
The energy released during this electron transfer is used to pump protons across the inner mitochondrial membrane,creating a proton gradient.
The flow of protons back into the mitochondrial matrix through $ATP$ synthase drives the synthesis of $ATP$.

(D) $NAD^+$ (Nicotinamide Adenine Dinucleotide) acts as a coenzyme in cellular respiration.
Its primary role is to accept high-energy electrons and hydrogen ions during metabolic pathways such as glycolysis,the link reaction,and the Krebs cycle.
By accepting these electrons,it gets reduced to $NADH$.
This $NADH$ then transports these electrons to the electron transport system $(ETS)$ located in the inner mitochondrial membrane,where they are used to generate $ATP$.
Therefore,$NAD^+$ functions as an electron carrier.

(C) In the $ETS$ (Electron Transport System) or respiratory chain,there are several cytochromes including $b$,$c_1$,$c$,$a$,and $a_3$.
Cytochrome $a_3$ is the terminal cytochrome of the $ETS$.
It is responsible for donating electrons directly to $O_2$,which acts as the final electron acceptor.
This process leads to the reduction of $O_2$ and the formation of metabolic water.

(C) The respiratory electron transport system $(ETS)$ in plants is located in the inner mitochondrial membrane.
This system consists of a series of protein complexes $(Complexes I-IV)$ and electron carriers that facilitate the transfer of electrons from $NADH$ and $FADH_2$ to oxygen.
The energy released during this electron transport is used to pump protons from the matrix into the intermembrane space,creating a proton gradient that drives $ATP$ synthesis via $ATP$ synthase.

(N/A) $ETS$ or electron transport system is located in the inner mitochondrial membrane. It facilitates the release and utilization of energy stored in $NADH + H^+$ and $FADH_2$,which are formed during glycolysis and the citric acid cycle. $NADH + H^+$ is oxidized by $NADH$ dehydrogenase (complex $I$). The electrons generated are transferred to ubiquinone through $FMN$. Similarly,$FADH_2$ (complex $II$) generated during the citric acid cycle transfers its electrons to ubiquinone. The electrons from ubiquinone are received by cytochrome $bc_1$ (complex $III$) and further transferred to cytochrome $c$. Cytochrome $c$ acts as a mobile carrier between complex $III$ and the cytochrome $c$ oxidase complex,which contains cytochrome $a$ and $a_3$ along with copper centers (complex $IV$).
During the transfer of electrons through these complexes,the process is coupled with the synthesis of $ATP$ from $ADP$ and inorganic phosphate by the action of $ATP$ synthase (complex $V$). The amount of $ATP$ produced depends on the molecule being oxidized. Generally,the oxidation of one molecule of $NADH$ yields $3$ $ATP$ molecules,and the oxidation of one molecule of $FADH_2$ yields $2$ $ATP$ molecules.

(N/A) Oxidative phosphorylation is a process in which electrons are transferred from electron donors to oxygen,which acts as the final electron acceptor.
This process involves oxidation-reduction reactions that lead to the formation of a proton gradient across the inner mitochondrial membrane.
The main role in oxidative phosphorylation is played by the enzyme $ATP$ synthase (complex $V$).
This enzyme complex consists of $F_{0}$ and $F_{1}$ components.
The $F_{1}$ headpiece is a peripheral membrane protein complex and contains the site for $ATP$ synthesis from $ADP$ and inorganic phosphate.
The $F_{0}$ component is an integral membrane protein complex that acts as a channel for the movement of protons from the intermembrane space to the mitochondrial matrix.
For every two protons passing through the $F_{0}-F_{1}$ complex,the synthesis of one $ATP$ molecule takes place.

(N/A) The respiratory process releases and utilizes the energy stored in $NADH+H^{+}$ and $FADH_{2}$. This is accomplished when they are oxidized through the electron transport system,and the electrons are passed on to $O_{2}$,resulting in the formation of $H_{2}O$.
The metabolic pathway through which electrons pass from one carrier to another is called the electron transport system $(ETS)$.
It is located in the inner mitochondrial membrane.
Electrons from $NADH$ produced in the mitochondrial matrix during the citric acid cycle are oxidized by an $NADH$ dehydrogenase $(Complex-I)$.
Electrons are then transferred to ubiquinone located within the inner membrane.
Ubiquinone also receives reducing equivalents via $FADH_{2}$ $(Complex-II)$,which is generated during the oxidation of succinate in the citric acid cycle.
The reduced ubiquinone is then oxidized with the transfer of electrons to cytochrome $c$ via the cytochrome $bc_{1}$ complex $(Complex-III)$.
Cytochrome $c$ is a small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for the transfer of electrons between $Complex-III$ and $IV$.
$Complex-IV$ refers to the cytochrome $c$ oxidase complex containing cytochromes $a$ and $a_{3}$,and two copper centers.
$ATP$ formation in $ETS$:
When electrons pass from one carrier to another via $Complex-I$ to $IV$ in the electron transport chain,they are coupled to $ATP$ synthase $(Complex-V)$ for the production of $ATP$ from $ADP$ and inorganic phosphate.
The number of $ATP$ molecules synthesized depends on the nature of the electron donor.
Oxidation of one molecule of $NADH$ gives rise to $3$ molecules of $ATP$,while that of one molecule of $FADH_{2}$ produces $2$ molecules of $ATP$.
Although the aerobic process of respiration takes place only in the presence of oxygen,the role of oxygen is limited to the terminal stage of the process. Yet,the presence of oxygen is vital,since it drives the whole process by removing hydrogen from the system.
Oxygen acts as the final hydrogen acceptor (for the production of $H_{2}O$).
In respiration,the energy of oxidation-reduction is utilized for the same process. It is for this reason that the process is called oxidative phosphorylation.

(N/A) The respiratory process releases and utilizes energy stored in $NADH+H^{+}$ and $FADH_{2}$.
This is accomplished when they are oxidized through the electron transport system $(ETS)$,and electrons are passed to $O_{2}$,resulting in the formation of $H_{2}O$.
The metabolic pathway through which electrons pass from one carrier to another is called the electron transport system $(ETS)$,which is present in the inner mitochondrial membrane.
Electrons from $NADH$ produced in the mitochondrial matrix during the citric acid cycle are oxidized by $NADH$ dehydrogenase (Complex-$I$).
Electrons are then transferred to ubiquinone located within the inner membrane.
Ubiquinone also receives reducing equivalents via $FADH_{2}$ (Complex-$II$),which is generated during the oxidation of succinate in the citric acid cycle.
The reduced ubiquinone is then oxidized with the transfer of electrons to cytochrome $c$ via the cytochrome $bc_{1}$ complex (Complex-$III$).
Cytochrome $c$ is a small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for the transfer of electrons between Complex-$III$ and Complex-$IV$.
Complex-$IV$ refers to the cytochrome $c$ oxidase complex containing cytochromes $a$ and $a_{3}$,and two copper centers.
$ATP$ formation in $ETS$: When electrons pass from one carrier to another via Complex-$I$ to $IV$ in the electron transport chain,they are coupled to $ATP$ synthase (Complex-$V$) for the production of $ATP$ from $ADP$ and inorganic phosphate.
The number of $ATP$ molecules synthesized depends on the nature of the electron donor. Oxidation of one molecule of $NADH$ gives rise to $3$ molecules of $ATP$,while that of one molecule of $FADH_{2}$ produces $2$ molecules of $ATP$.
Although the aerobic process of respiration takes place only in the presence of oxygen,the role of oxygen is limited to the terminal stage of the process. Yet,the presence of oxygen is vital,since it drives the whole process by removing hydrogen from the system. Oxygen acts as the final hydrogen acceptor for the production of $H_{2}O$.
In respiration,the energy of oxidation-reduction is utilized for this process; hence,it is called oxidative phosphorylation.

(N/A) The chemiosmotic hypothesis explains how the energy released during the electron transport system is utilized to synthesize $ATP$ with the help of $ATP$ synthase (complex $V$).
The $ATP$ synthase complex consists of two major components: $F_{0}$ and $F_{1}$.
The $F_{1}$ headpiece is a peripheral membrane protein complex that contains the catalytic 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 a transmembrane channel through which protons $(H^{+})$ cross the inner mitochondrial membrane.
The passage of protons through this channel is coupled to the catalytic site of the $F_{1}$ component,which drives the production of $ATP$.
For each $ATP$ molecule produced,$2 H^{+}$ ions pass through the $F_{0}$ channel from the intermembrane space into the matrix,moving down the electrochemical proton gradient.
This flow of protons provides the necessary energy to drive the conformational changes in $ATP$ synthase,resulting in the synthesis of $ATP$.

(N/A) 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,moving down the electrochemical proton gradient.
Thus,$ATP$ is synthesized.

(N/A) In aerobic respiration, $O_{2}$ acts as the final electron acceptor in the Electron Transport System $(ETS)$.
Although the entire process of respiration involves glycolysis, the Krebs cycle, and the $ETS$, $O_{2}$ is specifically required at the very end of the $ETS$.
It combines with electrons and protons $(H^{+})$ to form water $(H_{2}O)$.
By removing electrons from the last cytochrome $(Cyt a_{3})$, $O_{2}$ allows the continuous flow of electrons through the $ETS$, which is essential for the generation of the proton gradient required for $ATP$ synthesis via oxidative phosphorylation.
Without $O_{2}$, the $ETS$ would stop, leading to the accumulation of reduced coenzymes ($NADH$ and $FADH_{2}$) and the cessation of $ATP$ production.

(A-ATP, B-F1 PARTICLE, C-PI, D-2H+, E-INNER MITOCHONDRIAL MEMBRANE) Based on the mechanism of oxidative phosphorylation in the mitochondria:
$A$ represents $ATP$,which is the final product of the reaction.
$B$ represents the $F_1$ particle (the catalytic head of the $ATP$ synthase enzyme).
$C$ represents the inorganic phosphate $(Pi)$ required for the phosphorylation of $ADP$ to $ATP$.
$D$ represents the flow of $2H^+$ ions from the intermembrane space into the matrix through the $F_0$ particle.
$E$ represents the inner mitochondrial membrane,where the $ATP$ synthase complex is embedded.

(N/A) The importance of $O_{2}$ in aerobic respiration is as follows:
$1$. Aerobic respiration begins with the glycolysis of glucose in the cytoplasm.
$2$. This is followed by the Krebs cycle,and finally,the Electron Transport System $(ETS)$ occurs in the inner mitochondrial membrane.
$3$. $O_{2}$ acts as the final electron acceptor in the $ETS$.
$4$. It accepts electrons and protons to form water $(H_{2}O)$.
$5$. If $O_{2}$ is absent,electrons cannot pass through the electron transport chain,preventing the formation of a proton gradient across the inner mitochondrial membrane.
$6$. Consequently,the proton pump stops,and $ATP$ synthesis via oxidative phosphorylation cannot occur. Thus,$O_{2}$ is essential for the completion of aerobic respiration.

(C) Cyanide acts as a potent metabolic poison. It binds to the iron atom in the heme group of the cytochrome $c$ oxidase enzyme (complex $IV$) in the mitochondrial electron transport chain. This binding is a classic example of non-competitive inhibition,which prevents the enzyme from transferring electrons to oxygen. Consequently,cellular respiration is halted,$ATP$ production ceases,and the organism dies due to the inability of cells to produce energy.

(A) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain. They play a crucial role in both cellular respiration (in the mitochondria) and photosynthesis (in the chloroplasts) by facilitating the transfer of electrons.

(A) The Electron Transport System $(ETS)$ is located in the inner mitochondrial membrane. During the citric acid cycle,$NADH$ is produced in the mitochondrial matrix. These electrons are oxidized by an $NADH$ dehydrogenase (Complex $I$) and are subsequently transferred to ubiquinone,which is located within the inner mitochondrial membrane.

(D) The respiratory chain,which is responsible for oxidative phosphorylation,is located in the inner mitochondrial membrane.
Photolysis and photophosphorylation occur in the chloroplasts during photosynthesis.
Carboxylation is a key step in the Calvin cycle,which also occurs in the chloroplasts.

(D) The chemiosmotic hypothesis for $ATP$ synthesis was proposed by Peter Mitchell in $1961$.
This mechanism explains how a proton gradient across the inner mitochondrial membrane drives the synthesis of $ATP$ via $ATP$ synthase.

(A) The electron transport chain $(ETC)$ occurs in the inner mitochondrial membrane and consists of various electron carriers such as flavins,ubiquinone,and cytochromes.
In aerobic respiration,electrons are passed through these carriers to the final electron acceptor.
The sequence of electron transport is:
$NADH + H^+ \rightarrow FMN \rightarrow Co-Q \rightarrow Cyt-b \rightarrow Cyt-c_1 \rightarrow Cyt-c \rightarrow Cyt-a \rightarrow Cyt-a_3 \rightarrow O_2$.
Oxygen $(O_2)$ acts as the final electron acceptor,where it combines with electrons and protons to form water $(H_2O)$.

(D) Respiratory poisons are substances that inhibit the process of cellular respiration by blocking the electron transport chain $(ETC)$.
$1$. Cyanides inhibit cytochrome $c$ oxidase (Complex $IV$) in the $ETC$.
$2$. Antimycin-$A$ inhibits the oxidation of ubiquinol by cytochrome $c$ reductase (Complex $III$).
$3$. Carbon monoxide binds to the iron in cytochrome $c$ oxidase,similar to cyanide,thereby blocking the electron flow.
Therefore,all the listed substances act as inhibitors of the electron transport chain.

(D) Cytochromes are small proteins (intrinsic membrane proteins) that contain a cofactor,haem,which holds an iron atom.
The iron carries electrons and cycles between $+2$ and $+3$ oxidation states.
These form a part of the electron transport chain in mitochondria and chloroplasts and act as electron transporters or electron acceptors in respiration and photosynthesis.

(A) The metabolic pathway through which electrons pass from one carrier to another is known as the Electron Transport System $(ETS)$.
This system is located in the inner mitochondrial membrane of eukaryotic cells.
It involves a series of protein complexes that facilitate the transfer of electrons,ultimately leading to the production of $ATP$ through oxidative phosphorylation.

(A) Chemiosmosis is the movement of ions across a semi-permeable membrane,down their electrochemical gradient.
In the context of cellular respiration,it refers to the generation of $ATP$ by the movement of hydrogen ions $(H^+)$ across the inner mitochondrial membrane.
The electron transport system creates a proton gradient by pumping protons from the mitochondrial matrix to the intermembrane space.
As these protons flow back into the matrix through the $ATP$ synthase enzyme,the energy released is used to phosphorylate $ADP$ into $ATP$.
This mechanism occurs in mitochondria,chloroplasts,and many bacteria.

(C) During the process of glycolysis,$NADH$ is produced in the cytoplasm.
This $NADH$ is then transported into the mitochondria to participate in the electron transport system.
Inside the mitochondria,it undergoes oxidative phosphorylation to produce $ATP$.

(B) In the electron transport chain $(ETC)$,the final step involves the transfer of electrons to oxygen.
Cytochrome $a_{3}$ (part of cytochrome $c$ oxidase complex) transfers electrons to molecular oxygen $(O_{2})$.
Oxygen acts as the terminal electron acceptor and combines with protons $(H^{+})$ to form water $(H_{2}O)$.
Therefore,molecular $O_{2}$ is the terminal electron acceptor in aerobic respiration.

(D) The complex $V$ of the $ETS$ of the mitochondrial membrane is $ATP$ synthase.
It consists of a head piece,a stalk,and a base piece.
The head piece is identified as the coupling factor $1$ $(F_{1})$,the stalk portion is necessary for binding to the inner mitochondrial membrane,and the base piece is isolated as $F_{0}$,which is embedded within the inner mitochondrial membrane.

(C) Most enzymes of the Krebs' cycle,fatty acid synthesis,and amino acid synthesis are located in the mitochondrial matrix.
However,Succinic dehydrogenase (a component of Complex $II$) and Cytochrome oxidase (a component of Complex $IV$ of the Electron Transport Chain) are specifically embedded within the inner mitochondrial membrane.

(B) The complete oxidation of glucose involves several stages.
In glycolysis,a net gain of $2$ $ATP$ molecules is achieved.
In the Krebs' cycle,$2$ $ATP$ (or $GTP$) molecules are produced directly.
The Electron Transport Chain $(ETC)$ is the final stage where the majority of $ATP$ is synthesized through oxidative phosphorylation.
Specifically,the oxidation of $NADH$ and $FADH_2$ produced in earlier stages yields approximately $34$ $ATP$ molecules.
Therefore,the greatest number of $ATP$ molecules is formed during the Electron transport chain.

(C) Oxidative phosphorylation refers to the synthesis of $ATP$ from $ADP$ and inorganic phosphate by chemiosmosis. It occurs with the help of energy obtained from the oxidation of reduced coenzymes ($NADH$ and $FADH_2$) produced during glycolysis and the citric acid cycle. This process takes place in the inner mitochondrial membrane.

(B) In the electron transport system $(ETS)$ of the inner mitochondrial membrane,electrons are transferred through a series of carriers. The correct sequence of cytochromes involved in the electron transport chain is $cyt-b \rightarrow cyt-c \rightarrow cyt-a \rightarrow cyt-a_{3}$. Therefore,the correct sequence is $cyt-b, c, a, a_{3}$.

(A) The primary purpose of the electron transport chain $(ETC)$ is to release and utilize the energy stored in $NADH + H^+$ and $FADH_2$. This is accomplished when these molecules are oxidized through the electron transport system,and the electrons are passed on to $O_2$,resulting in the formation of $H_2O$ and the regeneration of $NAD^+$ and $FAD$.

(A) Cyanide reacts with one of the proteins (cytochrome-$a_3$) in the electron transport system and prevents the transfer of electrons to oxygen.
This leads to the inhibition of $ATP$ formation through oxidative phosphorylation.
$ATP$ is required for the active transport of substances across the plasma membrane,in addition to other metabolic reactions.
Therefore,active transport is the process most likely to be affected by the lack of $ATP$.

(C) $ETS$ (Electron Transport System) occurs in the inner mitochondrial membrane of the mitochondria. This is where the complexes of the electron transport chain are located,facilitating the synthesis of $ATP$ through oxidative phosphorylation.

(C) The electron transport system $(ETS)$ in the inner mitochondrial membrane consists of four major protein complexes involved in the transfer of electrons:
$1$. Complex-$I$ ($NADH$ dehydrogenase)
$2$. Complex-$II$ (Succinate dehydrogenase)
$3$. Complex-$III$ (Cytochrome $bc_1$ complex)
$4$. Complex-$IV$ (Cytochrome $c$ oxidase)
Although $ATP$ synthase is often referred to as Complex-$V$,it is involved in oxidative phosphorylation ($ATP$ synthesis) rather than the electron transport chain itself. Therefore,$4$ complexes are primarily involved in the electron transport process.

(B) In the Electron Transport System $(ETS)$,electrons derived from $FADH_2$ are transferred to ubiquinone by Complex $II$ (succinate dehydrogenase). Complex $I$ receives electrons from $NADH$. Therefore,the correct complex is Complex $II$.

(C) In the Electron Transport System $(ETS)$,the final electron transfer to oxygen is mediated by Complex-$IV$.
Complex-$IV$ is also known as Cytochrome $c$ oxidase.
It contains two copper centers ($Cu_A$ and $Cu_B$) and two cytochromes,$Cyt$ $a$ and $Cyt$ $a_3$.
$Cyt$ $a_3$ is the specific component that directly reduces oxygen to water.

(D) In the electron transport system $(ETS)$,ubiquinone (coenzyme $Q$) acts as a mobile electron carrier.
It receives electrons from complex-$I$ ($NADH$ dehydrogenase) via $NADH + H^+$ and from complex-$II$ (succinate dehydrogenase) via $FADH_2$.
Therefore,ubiquinone receives reducing equivalents from both $NADH + H^+$ and $FADH_2$.

(B) $Cyt$ $c$ (Cytochrome $c$) is a small protein attached to the outer surface of the inner mitochondrial membrane and acts as a mobile electron carrier for the transfer of electrons between $Complex$ $III$ ($Cytochrome$ $bc_1$ complex) and $Complex$ $IV$ ($Cytochrome$ $c$ oxidase complex) in the electron transport system $(ETS)$.