Photosynthesis MCQ Quiz - Objective Question with Answer for Photosynthesis - Download Free PDF

The correct answer is Pheophytin - Plastoquinone A - Plastoquinone B - Cytochrome b₆f complex - Plastocyanin

Concept:

• The light-dependent reactions of photosynthesis occur in the thylakoid membranes of chloroplasts in plants. These reactions involve two photosystems: Photosystem II (P680) and Photosystem I (P700).
• The electron transport chain (ETC) facilitates the transfer of electrons from P680 in Photosystem II to P700 in Photosystem I, producing ATP and NADPH in the process.
  • Pheophytin: The primary electron acceptor in Photosystem II (P680). It receives excited electrons from chlorophyll molecules in P680.
  • Plastoquinone A: Pheophytin transfers electrons to Plastoquinone A, a mobile electron carrier within the thylakoid membrane.
  • Plastoquinone B: Electrons are transferred from Plastoquinone A to Plastoquinone B. These molecules shuttle electrons to the next complex in the chain.
  • Cytochrome b6f Complex: This protein complex accepts electrons from Plastoquinone B and uses the energy to pump protons (H⁺) into the thylakoid lumen, contributing to the proton gradient needed for ATP synthesis.
  • Plastocyanin: A mobile copper-containing protein that transfers electrons from the Cytochrome b6f Complex to Photosystem I (P700), completing the chain.

The correct answer is A and D

Concept:

• The Triose-Phosphate Translocator (TPT) and Xylulose 5-Phosphate Translocator (XPT) are crucial transporters in plants that facilitate the exchange of metabolites between the chloroplast and cytosol.
• The TPT primarily exports triose phosphate (e.g., glyceraldehyde-3-phosphate) from the chloroplast to the cytosol during photosynthesis in exchange for inorganic phosphate (Pi).
• The XPT is responsible for the transport of pentose phosphates, including xylulose 5-phosphate, between the chloroplast and cytosol, which are essential intermediates in the pentose phosphate pathway and Calvin-Benson cycle.
• If both TPT and XPT are inhibited, the metabolites they normally transport will accumulate in the chloroplast, as they cannot be exported to the cytosol.

Explanation:

• Triose phosphate accumulation in the chloroplast: When the Triose-Phosphate Translocator (TPT) is inhibited, triose phosphate (e.g., glyceraldehyde-3-phosphate) cannot be exported to the cytosol. As a result, it accumulates in the chloroplast. This aligns with assumption A.
• Xylulose 5-phosphate accumulation in the chloroplast: XPT is primarily involved in retrieving pentose phosphates, including xylulose 5 phosphate, from the extraplastidial space and making them available to the plastids. If XPT is inhibited, xylulose 5-phosphate would accumulate more in the cytosol because it cannot be efficiently transported into the chloroplast. This aligns with assumption D.

Therefore, the correct combination of assumptions is A and D.

The correct answer is A and D

Concept:

• RuBisCO (Ribulose-1,5-bisphosphate carboxylase-oxygenase) is a critical enzyme in the Calvin cycle, which occurs in the chloroplasts of photosynthetic organisms. It catalyzes two competing reactions: carboxylation and oxygenation of ribulose-1,5-bisphosphate (RuBP).
• Carboxylation leads to the production of 3-phosphoglycerate (3-PGA), which is used in the synthesis of carbohydrates, while oxygenation generates 3-PGA and 2-phosphoglycolate, a metabolically wasteful product.
• The catalytic mechanism of RuBisCO involves multiple steps, including enolization, carbon-carbon bond cleavage, and the addition of either CO₂ (carboxylation) or O₂ (oxygenation).

Explanation:

Statement A: "The first step of catalysis is enolization of RuBP."

• This is correct. The initial step in the catalytic cycle of RuBisCO involves the enolization of RuBP. During this step, RuBP is converted into an enediol intermediate, which is essential for the subsequent addition of CO₂ or O₂.

Statement B: "The carbon-carbon bond between C3 and C4 of RuBP is cleaved."

• This is incorrect. In both carboxylation and oxygenation reactions catalyzed by RuBisCO, the bond between the C2 and C3 (not C3 and C4) carbon atoms of RuBP is broken during the reaction, resulting in the formation of two smaller molecules.

Statement C: "Carboxylase activity produces only one molecule of 3-phosphoglycerate."

• This is incorrect. The carboxylase activity of RuBisCO produces two molecules of 3-phosphoglycerate (3-PGA) when CO₂ is added to RuBP. 

Statement D: "Oxygenase activity produces one molecule of 3-phosphoglycerate and one molecule of 2-phosphoglycolate."

• This is correct. When RuBisCO acts as an oxygenase, it adds O₂ to RuBP, producing one molecule of 3-phosphoglycerate (3-PGA) and one molecule of 2-phosphoglycolate. The latter is a metabolically wasteful product that requires energy to recycle.

Fig:  RuBP conversion by Rubisco through the carboxylase (a) and the oxygenase (b) reactions.

• Following RuBP (1) enolization, the 2,3-enol(ate) intermediate (2) may react with CO2 (a) or O2 (b) co-substrates. The carboxylase reaction produces the 2-carboxy-3-keto-arabinitol 1,5-bisphosphate intermediate (3) undergoing protonation to the 2-carboxylic acid before hydration. The C2-C3-scission reaction in C3-gemdiolate (5) is described occurring in a concerted mechanism upon P1 protonation through a Grotthuss mechanism, producing two molecules of 3-phospho-D-glycerate (3PGA, 6). The oxygenase reaction produces 3-phospho-D-glycerate (3PGA, 6) and 2-phosphoglycolate (2PG, 7). 

The correct option is: 2

Explanation:

• Chlorophyll absorbs light most efficiently in the blue (around 430–450 nm) and red (around 640–680 nm) regions of the light spectrum. These wavelengths are used in photosynthesis to drive the conversion of light energy into chemical energy.
• Green light (around 500–570 nm) is largely reflected by chlorophyll, which is why plants appear green to the human eye. Chlorophyll absorbs very little green light.
• Yellow (around 570–590 nm) and infrared (700 nm and above) light are not absorbed as efficiently by chlorophyll for photosynthesis. Infrared light has lower energy and does not contribute significantly to the photosynthetic process.
• Chlorophyll's absorption of blue and red light is essential for the light-dependent reactions of photosynthesis. In these reactions, light energy is used to produce ATP and NADPH, which are then used in the light-independent reactions (Calvin cycle) to fix carbon into glucose.

The correct answer is A, B and D

Explanation:

A. Expression of the plastid-localized Glutamine Synthetase (GS) gene is upregulated by light.

• Correct. Glutamine Synthetase (GS) is an important enzyme in nitrogen assimilation, and its expression is known to be regulated by light.
•  Light plays a critical role in photosynthesis, providing energy through the production of ATP and NADPH. These energy molecules are essential for many biosynthetic pathways, including the synthesis of amino acids.
• The increased activity of photosynthesis under light conditions provides more ATP and reduced carbon, which can be linked to the upregulation of genes encoding for GS. Hence, light positively influences the expression of the plastid-localized GS gene.

B. Darkness promotes the expression of Asparagine Synthetase (AS) gene.

• Correct. Asparagine Synthetase (AS) is involved in nitrogen storage and transport. Its expression tends to be upregulated in the dark when carbon fixation via photosynthesis is halted.
• In the absence of light (darkness), photosynthetic activity ceases, reducing the availability of ATP and NADPH.
• Under these conditions, plants need to manage and store nitrogen efficiently. The upregulation of AS in darkness allows for the storage of nitrogen in the form of asparagine, facilitating this management.
• Thus, darkness acts as a signal to increase the expression of the AS gene to adapt to the reduced availability of energy and carbon from photosynthesis.

C. Expression of GS is inhibited by sucrose while that of AS is upregulated by sucrose.

• Incorrect. Glutamine Synthetase (GS) plays a key role in the assimilation of ammonium by converting it into glutamine.
  The regulation of GS is critically dependent on nitrogen status rather than directly on sucrose levels. Sucrose acts more as a carbon source and signal that impacts overall plant metabolism rather than specifically inhibiting GS expression.Glutamine Synthetase (GS) plays a key role in the assimilation of ammonium by converting it into glutamine. The regulation of GS is critically dependent on nitrogen status rather than directly on sucrose levels. Sucrose acts more as a carbon source and signal that impacts overall plant metabolism rather than specifically inhibiting GS expression.
• Asparagine Synthetase (AS) converts aspartate and glutamine into asparagine, which serves as a nitrogen transport and storage compound. The expression of AS can be influenced by the carbon/nitrogen balance in plants. High carbon availability (e.g., from sucrose) can signal the need to store nitrogen during periods when carbon is abundant, which might promote AS expression.
• While sucrose can play a role in signaling pathways that impact various aspects of plant metabolism, the direct inhibition of GS by sucrose and upregulation of AS specifically by sucrose is not evident.

D. Asparagine is a more efficient carbon source than glutamine.

• Correct. Asparagine is a molecule that can be transported and stored more efficiently in plants compared to glutamine.
• It contains a higher nitrogen-to-carbon ratio, making it a suitable molecule for long-term nitrogen storage and transport.
• As a carbon source, asparagine's structure allows it to release its carbon more effectively during metabolic processes, providing a steady supply of carbon skeletons for various biosynthetic pathways.

Conclusion: The correct statements are A, B, and D. ​

Explanation:

Whenever a ray of light falls on a substance, then either it reflects the light or absorbs it.

The color which is reflected by the substance appears to be its color to the human eye. All other colors are absorbed by the substance and are not visible to the eye.

Hence, when a plant with green leaves is kept in a dark room with only green light on, then it will reflect all the green light and appears brighter than the surrounding.

∴ The plant will appear brighter than the surroundings.

The correct answer is Option 4 i.e. Reduction and regeneration

Key Points

• The Calvin cycle is a step in the photosynthetic process that converts atmospheric CO₂ into sugar phosphates for use in a broader metabolism that supports the growth and development of plants.
• In the stroma of plant cell chloroplasts, the Calvin cycle occurs.
• There are eleven enzymes involved in this cycle, which has three stages: 

1. Carboxylation - carried out by the Rubisco enzyme (ribulose-1,5-bisphosphate carboxylase oxygenase)
2. Reduction - of the C3 acids produced during the carboxylation reaction (the stage of sugar formation)
3. Regeneration - of ribulose-1,5-bisphosphate (RUBP), which is the CO₂-acceptor molecule of Rubisco enzyme.

Explanation:

• Reduction and regeneration are the two stages where ATP is consumed as shown in the figure above,
• Thus option 4 is the correct option and other mentioned options are false.

The correct answer is occurs in stroma of bundle sheath chloroplasts.

Concept:

• C4 plants have a unique mechanism to efficiently fix carbon dioxide (CO₂) and minimize photorespiration.
• The Calvin cycle is a set of biochemical redox reactions that occur in the stroma of chloroplasts in photosynthetic organisms.
• In C4 plants, the Calvin cycle is spatially separated from the initial CO₂ fixation.

Explanation:

• Option 1: occurs in stroma of bundle sheath chloroplasts: This is the correct answer. In C4 plants, the Calvin cycle takes place in the stroma of bundle sheath chloroplasts. This spatial separation allows C4 plants to efficiently fix CO₂ and minimize photorespiration.
• Option 2: occurs in grana of bundle sheath chloroplasts: This is incorrect. The Calvin cycle does not occur in the grana; it takes place in the stroma. The grana are involved in the light-dependent reactions of photosynthesis.
• Option 3: occurs in mesophyll of chloroplasts: This is incorrect. In C4 plants, the initial CO₂ fixation occurs in the mesophyll cells, but the Calvin cycle takes place in the bundle sheath cells.
• Option 4: does not occur as CO₂ is fixed mainly by PEP and no CO₂ is left for Calvin cycle: This is incorrect. While it is true that CO₂ is initially fixed by phosphoenolpyruvate (PEP) in the mesophyll cells, the CO₂ is then transported to the bundle sheath cells where it enters the Calvin cycle.

• Thylakoids are membrane-bound compartments inside chloroplasts that contain chlorophyll and other pigments necessary for the light-dependent reactions of photosynthesis.
• The light-dependent reactions occurring in the thylakoids produce ATP and NADPH, which are forms of assimilatory power needed for the Calvin cycle (light-independent reactions) to synthesize sugars.
• The Calvin cycle occurs in the stroma of the chloroplast and requires specific enzymes to convert CO₂ and water into glucose.
• When thylakoids are isolated and placed in an illuminated culture with CO₂ and water, the absence of these enzymes in the stroma prevents the synthesis of sugar, even though the thylakoids can still produce ATP and NADPH.

• Thylakoids are capable of performing light-dependent reactions to produce ATP and NADPH, which are essential for assimilatory power. Thus, the non-formation of assimilatory power is not the reason for the lack of sugar production.

• The thylakoids contain chlorophyll and other pigments necessary for capturing light energy. Therefore, light trapping is not absent in isolated thylakoids.

• Photosystem I and Photosystem II are both present in the thylakoid membranes and work together to produce ATP and NADPH during the light-dependent reactions. Thus, their nonlinking is not the issue.

The correct answer is A, B and D

Explanation:

A. Expression of the plastid-localized Glutamine Synthetase (GS) gene is upregulated by light.

• Correct. Glutamine Synthetase (GS) is an important enzyme in nitrogen assimilation, and its expression is known to be regulated by light.
•  Light plays a critical role in photosynthesis, providing energy through the production of ATP and NADPH. These energy molecules are essential for many biosynthetic pathways, including the synthesis of amino acids.
• The increased activity of photosynthesis under light conditions provides more ATP and reduced carbon, which can be linked to the upregulation of genes encoding for GS. Hence, light positively influences the expression of the plastid-localized GS gene.

B. Darkness promotes the expression of Asparagine Synthetase (AS) gene.

• Correct. Asparagine Synthetase (AS) is involved in nitrogen storage and transport. Its expression tends to be upregulated in the dark when carbon fixation via photosynthesis is halted.
• In the absence of light (darkness), photosynthetic activity ceases, reducing the availability of ATP and NADPH.
• Under these conditions, plants need to manage and store nitrogen efficiently. The upregulation of AS in darkness allows for the storage of nitrogen in the form of asparagine, facilitating this management.
• Thus, darkness acts as a signal to increase the expression of the AS gene to adapt to the reduced availability of energy and carbon from photosynthesis.

C. Expression of GS is inhibited by sucrose while that of AS is upregulated by sucrose.

• Incorrect. Glutamine Synthetase (GS) plays a key role in the assimilation of ammonium by converting it into glutamine.
  The regulation of GS is critically dependent on nitrogen status rather than directly on sucrose levels. Sucrose acts more as a carbon source and signal that impacts overall plant metabolism rather than specifically inhibiting GS expression.Glutamine Synthetase (GS) plays a key role in the assimilation of ammonium by converting it into glutamine. The regulation of GS is critically dependent on nitrogen status rather than directly on sucrose levels. Sucrose acts more as a carbon source and signal that impacts overall plant metabolism rather than specifically inhibiting GS expression.
• Asparagine Synthetase (AS) converts aspartate and glutamine into asparagine, which serves as a nitrogen transport and storage compound. The expression of AS can be influenced by the carbon/nitrogen balance in plants. High carbon availability (e.g., from sucrose) can signal the need to store nitrogen during periods when carbon is abundant, which might promote AS expression.
• While sucrose can play a role in signaling pathways that impact various aspects of plant metabolism, the direct inhibition of GS by sucrose and upregulation of AS specifically by sucrose is not evident.

D. Asparagine is a more efficient carbon source than glutamine.

• Correct. Asparagine is a molecule that can be transported and stored more efficiently in plants compared to glutamine.
• It contains a higher nitrogen-to-carbon ratio, making it a suitable molecule for long-term nitrogen storage and transport.
• As a carbon source, asparagine's structure allows it to release its carbon more effectively during metabolic processes, providing a steady supply of carbon skeletons for various biosynthetic pathways.

Conclusion: The correct statements are A, B, and D. ​

The correct answer is Option 3 i.e.A - chlorophyll b B - chlorophyll a C  - carotenoid

Concept:

• Grana are the disc-shaped plates present in the chloroplast.
• They contain chlorophyll and carotenoid molecules.
• Commonly four main pigments are present in higher plants:

1. Chlorophyll a - 
   • It is a blue pigment with the molecule formula C₅₅H₇₂O₅N₄Mg.
   • It has a porphyrin head and a phytol tail.
   • The Porphyrin head contains Mg in the centre.
   • The head region contains alternate single and double bonds because of which transfer of energy takes via resonance.
2. Chlorophyll b - 
   • It is yellowish-green pigment, with molecule formula C₅₅H₇₀O₆N₄Mg.
   • Chlorophyll a and chlorophyll b absorb red and blue light particularly and transmit green light, hence, plants appear green in colour. 
3. Carotenes - 
   • They are orange colour pigments with the molecular formula C₄₀H₅₆.
4. Xanthophylls - 
   • It is a yellow coloured pigment, with the molecular formula C₄₀H₅₆O₂.
   • Carotenes and xanthophylls together are called carotenoids. In the visible spectrum, carotenoids absorb light that is not absorbed by chlorophylls.
   • Carotenoids also protect the chlorophylls from photooxidation and damage by sunlight. 

Explanation:

• Pigments absorb light of various wavelengths. 
• Chlorophylls absorb blue and red light from the visible spectrum between 400 nm to 700nm. 
• This 400-700nm absorption spectrum is called photosynthetic active radiation (PAR).
• The graph showing the absorption of light at different radiation/wavelengths is called the absorption spectrum. 
• Chlorophyll a shows maximum absorption at wavelengths of 430-470 nm (blue) and 660-670 nm (red). 
• In the graph we can see that B have an absorption maximum at wavelength about 430-470 nm (blue) and 660-670 nm (red), hence, "B" is "chlorophyll a".
• Chlorophyll b shows maximum absorption at wavelengths of 450-450nm and 640-650 nm.
• In the graph, we can see that A has an absorption maximum at wavelength about 450-450nm (blue)and 640-650 nm (red), hence, "A" is "chlorophyll b".
• Carotenoids show maximum absorption at wavelengths of 450 and 475 nm.
• In the graph, we can see that C has an absorption maximum at wavelengths about 450 and 475 nm, hence, "C" is "carotenoids".

Hence, the correct answer is Option 3. 

The correct answer is Option 4 i.e.NAPDH is produced during carbon reactions by the enzymes present in stroma. 

Concept: 

• The light reaction is the first phase of photosynthesis in plants. 
• It takes place in the grand of the chloroplast.
• It is called light reaction because light energy is essential to carry out this reaction of photosynthesis. 
• It is a photochemical reaction.
• It includes absorption of the light by PS-I and PS-II;  photolysis of water to generate electrons, hydrogen ions and oxygen; and generation of high-energy molecules called ATP and NAPDH2. 
• In this reaction, light energy is converted to chemical energy. 

Explanation:

Option 1:

• The light reaction takes place in the thylakoid membrane because large protein complexes that are involved in light reaction are transmembrane and integral membrane proteins and they are present on the thylakoid membrane. 
• Hence, this is the incorrect option. 

Option 2: 

• During light reactions, ATP and NADPH2 are produced.
• Hence, ATP and NADPH2 are produced in the thylakoid membrane but they enter the stroma of the chloroplast. 
• Hence this is the incorrect option. 

Option 3: 

• The thylakoid lumen refers to a continuous aqueous phase that is enclosed by the thylakoid membrane. 
• Hence, this is the incorrect option. 

Option 4: 

• NADPH is produced during the light reaction of photosynthesis. 
• NADPH is produced in the stroma of chloroplast and it is produced when NADP receives 4 electrons from PS-I and four hydrogen ions from the water to produce a reduced co-enzyme called NADPH2. 
• Hence, this is the correct option. 

Hence, the correct answer is Option 4.  

The correct answer is Option 4 i.e. B.C and D

Concept:

• According to the Z-scheme, water (to the left) loses its electrons before being given to P680's lower (non-excited) oxidized state.
• P680 is excited to become P680* upon photon absorption, and P680* then "jumps" to a more actively reducing species.
• With proton pumping, P680* contributes one electron to the quinone-cytochrome bf chain.
• P700 is changed to P700* by the donation of an electron from cytochrome bf to PSI.
• This electron is transported to NADP together with other electrons to create NADPH.
• In cyclic electron flow, this electron may also return to cytochrome bf.​

Important Points

Statement A:- INCORRECT

• P680, the reaction center of photosystem II, releases an electron that travels upward and decreases pheophytin, a non-magnesium chlorophyll molecule.
• Plastoquinone accepts electrons from pheophytin and needs two electrons for full reduction.

Statement B:- CORRECT

• Plastocyanin quickly donates an electron to the P700 reaction center, which is electron-deficient.
• Before reaching ferredoxin, the P700 electron travels via a number of electron carriers in photosystem I.

Statement C:- CORRECT

• Oxygen is released as a byproduct of both light and dark operations. Photosynthetic organisms (photoautotrophs) utilize light energy to create ATP and reduced electron carriers (NADPH).
• The three by-products of photosynthesis are ATP, NADPH, and O₂.

Statement D:- CORRECT

• To begin photosynthesis, a photon interacts with photosystem II's antenna pigments.
• The energy is transferred to the electron transport chain, which then pumps hydrogen ions into the interior of the thylakoid (the lumen) from the reaction center that houses chlorophyll a.
• A significant concentration of hydrogen ions is created by this action.

Therefore, the correct answer is B, C, and D.

The correct answer is QB

Concept:

• Photosynthesis is a process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll.
• It involves two main stages: the light-dependent reactions (or light reactions) and the Calvin cycle (or light-independent reactions).
• During the light reactions, two photosystems (Photosystem I and Photosystem II) play crucial roles in the electron transport chain, leading to the production of ATP and NADPH.
• Herbicides like dichlorophenyldimethylurea (DCMU) and paraquat can affect this electron flow, thus blocking photosynthesis.

Explanation:

DCMU (Dichloro Phenyl Dimethyl Urea) is a herbicide. Two derivative of urea (monuron and divron) and triazine herbicide bind to Q_B binding site of D1 protein in photosystem II. The herbicide interferes with the binding of plastoquinone to the same site and thus, blocks the transfer of electron to plastoquinone.

• P680: This is the reaction center chlorophyll molecule of Photosystem II (PSII) that absorbs light and becomes excited to initiate the electron transport chain. DCMU does not directly prevent the reduction of P680.
• Q_A: Q_A is the primary quinone electron acceptor in PSII. It accepts an electron from the excited P680 and passes it to Q_B. DCMU does not block the reduction of Q_A directly but rather inhibits a step further down the chain.
• PQ (Plastoquinone): PQ refers to a pool of molecules that Q_A and Q_B use to shuttle electrons from PSII to the cytochrome b₆f complex. DCMU does not act at this step but blocks the transfer before it reaches PQ.
• Q_B: Q_B is the secondary quinone electron acceptor in PSII. After Q_A passes the electron to Q_B, Q_B becomes reduced to Q_B^-. When both electrons are accepted, Q_BH₂ (plastoquinol) is formed, which then dissociates from PSII and enters the pool of PQ. DCMU specifically binds to the Q_B site on the D1 protein of PSII, preventing it from accepting electrons from Q_A. This blockage stops the electron flow from Q_A to Q_B, thus inhibiting the reduction of QB.

The correct answer is Option 3 i.e.Complex III

Explanation-

• Antimycin A, a naturally occurring antibiotic, acts by binding to the cytochrome b of the enzyme complex III (also known as the cytochrome bc1 complex).
• Complex III is a crucial component of the electron transport chain located in the inner mitochondrial membrane.
• It plays a role in transferring electrons from ubiquinol to cytochrome c, facilitating the transfer of electrons to the next complex (Complex IV) in the chain.
• Antimycin A specifically inhibits the function of Complex III by blocking the transfer of electrons, disrupting the normal flow of electrons through the respiratory chain.

Additional Information

• The Electron Transport Chain (ETC) is a series of protein complexes located in the inner mitochondrial membrane (in eukaryotes) or the plasma membrane (in prokaryotes).
• The ETC plays a crucial role in the production of adenosine triphosphate (ATP) through oxidative phosphorylation.
• Several inhibitors can interfere with the functioning of the ETC, disrupting the normal flow of electrons and affecting ATP production. Here are some commonly used inhibitors:

Rotenone:

• Target: Complex I (NADH dehydrogenase)
• Mode of Action: Inhibits the transfer of electrons from NADH to ubiquinone in Complex I.

Antimycin A:

• Target: Complex III (cytochrome bc1 complex or ubiquinol-cytochrome c reductase)
• Mode of Action: Blocks the transfer of electrons from ubiquinol to cytochrome c in Complex III.

Cyanide (CN-) and Carbon Monoxide (CO):

• Target: Complex IV (cytochrome c oxidase)
• Mode of Action: Inhibit the activity of cytochrome c oxidase, preventing the final step of electron transfer to oxygen.

Azide (N₃^-):

• Target: Complex IV (cytochrome c oxidase)
• Mode of Action: Similar to cyanide, azide inhibits the activity of cytochrome c oxidase.

Oligomycin:

• Target: ATP synthase (Complex V)
• Mode of Action: Inhibits the synthesis of ATP by blocking the proton channel in ATP synthase, preventing the flow of protons required for ATP production.

Uncoupling Agents (e.g., 2,4-Dinitrophenol - DNP):

• Target: Inner mitochondrial membrane
• Mode of Action: Disrupts the coupling of electron transport and ATP synthesis by creating a proton leak across the inner mitochondrial membrane.