ETS Questions in English

(D) 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 takes place in the inner mitochondrial membrane.
It is the final stage of cellular respiration,where the energy released during the electron transport chain is used to synthesize $ATP$ from $ADP$ and inorganic phosphate $(Pi)$.
Therefore,oxidative phosphorylation is a key component of aerobic respiration.

(B) The respiratory chain,also known as the Electron Transport System $(ETS)$,is located in the inner mitochondrial membrane.
It consists of several complexes and electron carriers.
Cytochrome $a_3$ is a component of Complex $IV$ (Cytochrome $c$ oxidase) in the mitochondrial electron transport chain.
It acts as the final electron acceptor in the chain,transferring electrons to oxygen to form water.
Cytochrome $f$,Plastocyanin,and Ferredoxin are components typically associated with the photosynthetic electron transport chain in chloroplasts,not the respiratory chain.

(B) In the Electron Transport System $(ETS)$ located in the inner mitochondrial membrane,electrons are passed through a series of complexes.
Oxygen acts as the final electron acceptor at the end of the chain.
It combines with electrons and protons $(H^+)$ to form water $(H_2O)$,a reaction catalyzed by the enzyme cytochrome $c$ oxidase (which contains cytochromes $a$ and $a_3$).

(D) In the Electron Transport System $(ETS)$, electrons are passed from one carrier to another via complexes $I$ to $IV$.
At the end of the chain, the enzyme $Cytochrome \, c \, oxidase$ (Complex $IV$) transfers electrons to oxygen.
Oxygen acts as the final electron acceptor and combines with protons $(H^+)$ from the matrix to form water $(H_2O)$.
Therefore, the formation of water occurs at the very end of the $ETS$ process.

(B) Cytochromes are iron-containing hemoproteins that act as electron carriers in both photosynthesis and cellular respiration.
In photosynthesis, they are part of the electron transport chain in the thylakoid membrane (e.g., $Cytochrome \, b_6f$ complex).
In cellular respiration, they are essential components of the electron transport system located in the inner mitochondrial membrane (e.g., $Cytochrome \, c$, $Cytochrome \, a$, $Cytochrome \, a_3$).

(D) Cytochromes are iron-containing hemoproteins that act as electron carriers in the Electron Transport System $(ETS)$ of mitochondria and chloroplasts.
They contain a heme group,which is a prosthetic group consisting of an iron atom coordinated within a porphyrin ring.
These proteins facilitate the transfer of electrons through redox reactions,where the iron atom oscillates between the ferrous $(Fe^{2+})$ and ferric $(Fe^{3+})$ states.
Therefore,they are classified as iron-containing proteins.

(C) The correct answer is $C$.
According to the chemiosmotic hypothesis,the synthesis of $ATP$ in both mitochondria and chloroplasts is driven by a proton $(H^{+})$ gradient across the membrane.
In mitochondria,this gradient is established across the inner mitochondrial membrane during the electron transport chain,creating a higher concentration of protons in the intermembrane space compared to the matrix.
This electrochemical gradient provides the energy required for $ATP$ synthase to phosphorylate $ADP$ into $ATP$.

(D) The energy of respiration is converted into heat.
In mammals,there are two types of adipose tissue: white and brown. 'Brown fat' cells contain a great many mitochondria,and brown adipose tissue is well supplied by blood capillaries. Brown adipose tissue produces a considerable amount of heat because lipids are respired there with little or no $ATP$ formation; most energy is released as heat. This heat is transported in the blood to the body organs.

(A) The correct option is $A$.
In the electron transport system $(ETS)$ located in the inner mitochondrial membrane:
$1$. Coenzyme $Q$ (ubiquinone),labeled as $A$,acts as a mobile electron carrier that transfers electrons from Complex $I$ ($NADH$ dehydrogenase) and Complex $II$ (succinate dehydrogenase) to Complex $III$ (cytochrome $bc_1$ complex).
$2$. Cytochrome $c$,labeled as $B$,is a small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for electrons between Complex $III$ and Complex $IV$ (cytochrome $c$ oxidase).