The process of ATP synthesis through a combination of electrochemical and osmotic events is known as: [KMU-2024]
C
Oxidative phosphorylation
D
Oxidation of pyruvate to acetyl CoA
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:The synthesis of ATP driven by a proton gradient across a membrane is formally known as chemiosmosis.
Solution:- During cellular respiration, this chemiosmotic generation of ATP is coupled to the transfer of electrons from NADH/FADH2 to oxygen.
- Because it relies on oxygen as the final electron acceptor and involves a proton (osmotic) gradient, the entire combined process is called Oxidative phosphorylation.
Why other options are incorrect:- Glycolysis and fermentation generate ATP via substrate-level phosphorylation, which involves direct enzymatic transfer of a phosphate group, not an electrochemical gradient.
Which mechanism would be compromised in the absence of cytochrome complex during light reactions of photosynthesis? [NUMS-2024]
A
Reduction of reaction center chlorophyll
C
Oxidation of primary electron receptor
D
Establishment of proton gradient across thylakoid membrane
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The cytochrome complex sits between Photosystem II and Photosystem I and acts as a proton pump.
Solution:- As electrons move from PSII to PSI, they pass through the cytochrome \( b_6f \) complex.
- This complex uses the energy of the electrons to actively pump protons (\( H^+ \)) from the stroma into the thylakoid lumen.
- Without this complex, protons would not be pumped, heavily compromising the establishment of the proton gradient necessary for ATP synthesis.
Why other options are incorrect:- Photolysis of water is driven by PSII, upstream of the cytochrome complex.
During glycolysis, isomerization takes place in the form of: [NUMS-2024]
A
Dihydroxyacetone phosphate and 2-phosphoglcerate
B
G3P and fructose 6-phosphates
D
Fructose 6-phosphate and 3-phosphoglycerate
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Isomerases are enzymes that rearrange the atomic structure of a molecule without adding or removing atoms, converting it into its isomer.
Solution:- During glycolysis, two major classical isomerization reactions occur:
- 1. Glucose 6-phosphate is isomerized into Fructose 6-phosphate by phosphoglucose isomerase.
- 2. Dihydroxyacetone phosphate (DHAP) is isomerized into Glyceraldehyde 3-phosphate (G3P) by triose phosphate isomerase.
- Option B correctly pairs molecules that are products of these specific isomerization steps in the glycolytic pathway.
Why other options are incorrect:- PEP and pyruvate involve a kinase (phosphate transfer), not an isomerase.
- 3-phosphoglycerate and 2-phosphoglycerate involve a mutase, which is a subtype of isomerase, but the pairings in the other options incorrectly mix non-isomeric steps.
The production of energy is ____. [KMU-2024]
A
Faster in anaerobic respiration
B
Faster in aerobic respiration
C
Same in both types of respiration
D
Not associated with respiration
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Cellular respiration is responsible for the production of ATP, but the efficiency and overall rate of productive yield depend heavily on the presence of oxygen.
Solution:- Aerobic respiration fully oxidizes a glucose molecule, generating 36 to 38 ATP per molecule.
- Anaerobic respiration only yields 2 ATP per molecule.
- Because aerobic respiration rapidly generates such a massive, sustained yield of ATP through the electron transport chain, its overall functional "production of energy" is considered significantly higher and effectively faster at meeting large metabolic demands.
Why other options are incorrect:- While anaerobic glycolysis can rapidly produce ATP in short bursts (like in sprinting muscles), it cannot sustain high-volume energy production, leading to rapid energy depletion compared to aerobic pathways.
The pathway to the breakdown of glucose, carried out by micro-organisms, is called: [KMU-2024]
A
Lactic acid fermentation
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Microorganisms utilize specific anaerobic pathways to extract energy from glucose when oxygen is scarce.
Solution:- In specific microorganisms, most notably yeast, the anaerobic breakdown of glucose follows a specific pathway.
- After glycolysis, pyruvate is decarboxylated and reduced to form ethanol and \( CO_2 \).
- This entire process is classified as Alcoholic fermentation.
Why other options are incorrect:- Lactic acid fermentation primarily occurs in animal muscle cells and certain bacteria (like Lactobacilli), but standard microbiology/botany contexts highlight yeast's alcoholic fermentation as the classic micro-organism pathway for industrial/baking applications.
Which option is correct about a chlorophyll molecule? [UHS-2024]
A
Chemical formula \( C_{55}H_{70}O_{6}N_{4}Mg \)
B
Porphyrin ring with nitrogen in centre
C
Methyl group on second pyrrole ring
D
Aldehyde group on second pyrrole ring
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:There are different forms of chlorophyll (primarily
a and
b), each with a highly specific molecular formula and functional group.
Solution:- The chemical formula \( C_{55}H_{70}O_{6}N_{4}Mg \) is the exact molecular formula for Chlorophyll b.
- Since Chlorophyll b is definitively "a chlorophyll molecule," this statement is completely accurate.
Why other options are incorrect:- Option B: The center of the porphyrin ring contains Magnesium (\( Mg \)), not Nitrogen. The nitrogen atoms strictly coordinate the central Magnesium.
- Option C & D: These are specific differentiators. Chlorophyll a has a methyl group, and Chlorophyll b has an aldehyde group, but a general formula is universally true for its specific type.
In the journey of electrons from photosystem II to photosystem I plastocyanin is reduced by: [UHS-2024]
D
Primary electron acceptor of PSI
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:The thylakoid electron transport chain follows a strict, sequential order of electron carriers between the two photosystems.
Solution:- Electrons leave Photosystem II and are passed to Plastoquinone (PQ).
- Plastoquinone passes them to the Cytochrome \( b_6f \) complex.
- The Cytochrome complex then passes the electrons to Plastocyanin (PC).
- Because Plastocyanin receives (gains) these electrons from the Cytochrome complex, it is technically reduced by the Cytochrome complex.
Why other options are incorrect:- Plastoquinone passes electrons to cytochrome, not directly to plastocyanin.
- P700 and the primary acceptor of PSI are located after plastocyanin in the chain.
Enzyme NADP reductase is responsible for: [UHS-2024]
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Enzymes are generally named after the substrate they act upon and the specific type of chemical reaction they catalyze.
Solution:- NADP reductase is located at the very end of the non-cyclic electron transport chain.
- It takes two high-energy electrons from Ferredoxin and a proton (\( H^+ \)) from the stroma.
- It adds these to \( NADP^+ \). The addition of electrons is called reduction.
- Therefore, it is responsible for reducing \( NADP^+ \) to form NADPH.
Why other options are incorrect:- It does not oxidize \( NADP^+ \).
- Ferredoxin is what reduces the enzyme, not the other way around.
- P700 is reduced by plastocyanin.
The PS II during light reactions receives electrons from splitting: [UHS-2024]
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:When Photosystem II (P680) absorbs light and ejects electrons, it becomes a powerful oxidizing agent that must replace its lost electrons to continue functioning.
Solution:- To fill the "electron hole" created in the P680 reaction center, an associated enzyme complex carries out photolysis.
- Photolysis is the physical splitting of Water (\( H_2O \)) into protons, oxygen, and electrons.
- These extracted electrons are immediately fed into Photosystem II.
Why other options are incorrect:- Plastoquinone, Plastocyanin, and Ferredoxin are all downstream carriers in the electron transport chain; they receive electrons from the photosystems, rather than supplying them to PS II.
In Calvin cycle \( CO_2 \) reacts with RuBP to produce _. [UHS-2024]
C
6-Carbon unstable intermediate
D
1,3 bisphosphoglycerate
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:The very first step of the Calvin cycle is carbon fixation, catalyzed by the enzyme RuBisCO.
Solution:- A single molecule of \( CO_2 \) (1 carbon) is covalently attached to Ribulose-1,5-bisphosphate (RuBP) (5 carbons).
- This immediately produces a 6-carbon unstable intermediate compound.
- Because it is so highly unstable, this 6-carbon molecule instantly breaks in half to form two molecules of 3-phosphoglycerate (3-PGA).
Why other options are incorrect:- While 3-PGA is the first stable product, the direct initial reaction produces the transient 6-carbon intermediate.
Presence of PEP carboxylase in \( C_4 \) plants enable them to avoid photorespiration due to: [NUMS-2024]
A
Presence of enzyme in high concentration
C
PEP carboxylase being strictly carboxylase
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:\( C_4 \) plants have evolved a unique biochemical pump to ensure RuBisCO only ever interacts with \( CO_2 \), completely bypassing photorespiration.
Solution:- In mesophyll cells of \( C_4 \) plants, the initial carbon fixation is performed by PEP carboxylase, not RuBisCO.
- The key evolutionary advantage is that PEP carboxylase has absolutely no affinity for oxygen. It is strictly a carboxylase.
- It locks \( CO_2 \) into malate, safely shuttles it to the bundle-sheath cells, and floods RuBisCO with \( CO_2 \) so photorespiration cannot happen.
Why other options are incorrect:- \( C_4 \) plants definitely still possess RuBisCO (it operates in the bundle-sheath cells to run the Calvin cycle).
- Concentration and yield of the enzyme are irrelevant; its structural specificity (zero oxygenase activity) is the mechanism.
Fats and proteins can be used as respiratory fuel. Which of the following serves as common molecule produced through their catabolism? [NUMS-2024]
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Metabolic pathways are interconnected. Carbohydrates, lipids, and proteins can all feed into cellular respiration at various intersection points.
Solution:- When fats are broken down (beta-oxidation of fatty acids) and proteins are deaminated, they must enter the central respiratory pathway to generate ATP.
- The universal "crossroads" molecule that links the catabolism of carbohydrates, fats, and most amino acids directly into the Krebs cycle is Acetyl CoA.
Why other options are incorrect:- While some amino acids can form pyruvate, fatty acids cannot. Acetyl CoA is the exclusively common denominator.
- G3P is specific to glycolysis.
- Lactate is an end-product of anaerobic fermentation.
Which is the main event in electron transport chain? [UHS-2023]
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:The electron transport chain (ETC) is the final and most productive phase of cellular respiration.
Solution:- The primary purpose and main functional event of the ETC is to generate a proton gradient that drives the enzyme ATP synthase.
- This results in massive ATP synthesis via oxidative phosphorylation.
Why other options are incorrect:- Decarboxylation (removal of \( CO_2 \)) happens during the link reaction and Krebs cycle.
- Isomerisation and substitution are chemical reactions that occur heavily in glycolysis and the Krebs cycle, not the main event of the ETC.
Out of 36 ATPs, how many are produced in electron transport chain? [UHS-2023]
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: ATP accounting in cellular respiration.
Solution: Out of 36 net ATP generated per glucose molecule, 4 ATP are produced via substrate-level phosphorylation (2 in glycolysis, 2 in Krebs cycle). The remaining 32 ATP are derived via oxidative phosphorylation in the electron transport chain.
The major enzymes involved in transfer of phosphate group from ATP to Glucose is: [UHS-2023]
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Enzymes are strictly categorized based on the specific type of chemical reaction they catalyze.
Solution:- Enzymes that transfer a phosphate group from a high-energy molecule (like ATP) to a substrate are universally called Kinases (e.g., Hexokinase or Phosphofructokinase in glycolysis).
Why other options are incorrect:- Isomerases: rearrange atoms within a single molecule.
- Dehydrogenases: remove hydrogen atoms (involved in redox reactions).
- Decarboxylases: remove carboxyl groups, releasing \( CO_2 \).
The end product of glycolysis in anaerobic respiration is: [SZABMU-2023]
A
Ethanol and Carbon dioxide
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Glycolysis is a universal pathway that is identical regardless of whether oxygen is present or absent.
Solution:- The pathway of glycolysis specifically ends with the formation of two molecules of Pyruvate (pyruvic acid).
- What happens to the pyruvate afterward (e.g., turning into lactate or ethanol) is defined as the fermentation phase, which occurs after glycolysis.
Why other options are incorrect:- Ethanol and Lactate are end products of fermentation, not glycolysis itself.
- Acetyl CoA is formed during the transition reaction in aerobic environments.
The ATP formed in the preparatory phase of glycolysis is (are): [ETEA-2023]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Glycolysis is divided into an energy-investment (preparatory) phase and an energy-payoff phase.
Solution:- During the preparatory phase, the cell must spend energy to phosphorylate the glucose molecule, consuming 2 ATP.
- Because ATP is consumed and not generated during this phase, the number of ATP formed is exactly 0.
Why other options are incorrect:- 4 ATP are formed later in the payoff phase.
- 2 ATP represents the amount consumed, not formed.
Which of the following is used in baking? [UHS-2023]
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:The baking industry relies heavily on the metabolic byproducts of
Saccharomyces cerevisiae (baker's yeast).
Solution:- When mixed into dough, the environment rapidly becomes devoid of oxygen.
- The yeast shifts to anaerobic respiration (alcoholic fermentation) to survive.
- This process converts sugars into ethanol and \( CO_2 \). The trapped \( CO_2 \) bubbles cause the bread dough to rise.
Why other options are incorrect:- Aerobic respiration requires oxygen and does not produce the intense, rapid gas accumulation necessary for rising dough.
In alcoholic fermentation _ ATP molecules are produced from 1 glucose molecule. [ETEA-2023]
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Fermentation pathways allow glycolysis to continue in the absence of oxygen but do not produce additional ATP themselves.
Solution:- During alcoholic fermentation, the entire energy yield comes solely from the preceding glycolysis step.
- Glycolysis yields a net of 2 ATP per glucose molecule.
- The subsequent steps (converting pyruvate to ethanol) consume NADH but produce no further ATP.
Why other options are incorrect:- 32 and 36 ATP represent the massive energy yields of aerobic respiration, which utilizes the electron transport chain.
#20 of 56
ETEA-2023 Retake
What is the number of carbon atoms in pyruvic acid? [ETEA-2023 Retake]
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Glycolysis physically cleaves the carbon skeleton of glucose into two smaller, equal-sized molecules.
Solution:- Glucose starts as a 6-carbon molecule (\( C_6H_{12}O_6 \)).
- It is split directly in half during glycolysis.
- Therefore, each resulting molecule of pyruvic acid contains exactly 3 carbon atoms.
Why other options are incorrect:- 2-carbon compounds form after pyruvate is decarboxylated into Acetyl CoA.
- 4-carbon and 5-carbon compounds are intermediates in the Krebs cycle.
The final acceptor of both electrons and protons during light reactions of photosynthesis is: [SZABMU-2023]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Non-cyclic electron flow (the Z-scheme) in photosynthesis moves electrons from water ultimately to a carrier molecule that will be used in the dark reactions.
Solution:- Electrons travel from PSII, through the ETC, to PSI, and finally to the enzyme NADP reductase.
- Here, \( NADP^+ \) serves as the terminal electron acceptor.
- It simultaneously picks up protons (\( H^+ \)) from the stroma to form NADPH, taking both to the Calvin cycle.
Why other options are incorrect:- Plastoquinone (PQ), Plastocyanin (PC), and Ferredoxin (Fd) are intermediate carriers that simply pass electrons along, rather than holding them at the end of the chain.
When light falls on P700, which event is likely to occur? [NUMS-2023]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:P700 is the specialized pair of chlorophyll
a molecules at the reaction center of Photosystem I.
Solution:- When P700 absorbs photon energy (either directly or via antenna pigments), its electrons become highly excited.
- These excited electrons are physically ejected out of the molecule and transferred to a primary electron acceptor.
- Losing electrons chemically means that P700 becomes oxidized.
Why other options are incorrect:- Photolysis (splitting of water) is induced by P680 (Photosystem II), not P700.
- It loses electrons rather than accepting them initially (it accepts them later from the ETC to regenerate).
The only copper containing protein involved during light reactions of photosynthesis is: [SZABMU-2023]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The electron transport chain connecting Photosystem II to Photosystem I relies on specific metalloproteins to pass electrons.
Solution:- Plastocyanin is a small, water-soluble, blue-colored protein found in the thylakoid lumen.
- Its ability to carry electrons is strictly dependent on a single copper atom at its active site, which cycles between \( Cu^{2+} \) and \( Cu^+ \).
Why other options are incorrect:- Plastoquinone: is a lipid-soluble quinone, not a metalloprotein.
- Cytochrome: contains iron (heme).
- Ferredoxin: contains iron-sulfur clusters.
End product of Calvin cycle is: [SZABMU-2023]
B
1-3 bisphosphoglycerate
C
Glyceraldehyde 3 phosphate
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:The Calvin cycle builds sugar one carbon at a time and releases a specific 3-carbon intermediate.
Solution:- The direct, final carbohydrate product that exits the Calvin cycle is Glyceraldehyde 3-phosphate (G3P).
- For every 3 turns of the cycle, one G3P molecule leaves to be used by the plant to build glucose and other organic compounds.
Why other options are incorrect:- 3-phosphoglycerate and 1,3-bisphosphoglycerate are intermediates within the cycle.
- Glucose is assembled later outside the cycle in the cytoplasm using two G3P molecules.
Which are the end products of light reactions of photosynthesis? [NUMS-2023]
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:The sole purpose of the light-dependent reactions is to trap solar energy into usable chemical forms for the dark reactions.
Solution:- Light energy drives the phosphorylation of ADP to create ATP.
- Electrons from water are used to reduce \( NADP^+ \) to create NADPH.
- These two molecules (collectively called assimilatory power) are the crucial end products sent to the stroma.
Why other options are incorrect:- Glucose is produced in the light-independent reactions (Calvin cycle).
- Water is consumed (split via photolysis), not produced, during the light reactions.
Synthesis of ATP during photosynthesis takes place at the region: [NUMS-2023]
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:ATP synthesis requires an intact membrane to hold a proton gradient (chemiosmosis).
Solution:- In chloroplasts, protons are pumped into the lumen of the thylakoid.
- ATP synthase enzymes are physically embedded in the thylakoid membrane.
- As protons flow back out into the stroma, ATP is synthesized right at the membrane surface.
Why other options are incorrect:- Stroma: where ATP is consumed during the Calvin cycle, not where it is synthesized.
- Matrix: found in mitochondria, not chloroplasts.
Which of the following molecules are released after completion of light reaction and the utilized in the dark reaction of photosynthesis? [NUMS-2023]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:There is a strict biochemical link between the light-dependent thylakoid reactions and the light-independent stroma reactions.
Solution:- The light reactions generate energy-rich molecules.
- Specifically, ATP provides the chemical energy, and NADPH provides the reducing power (high-energy electrons).
- Both of these are released into the stroma where they are immediately utilized by the Calvin cycle (dark reaction) to fix \( CO_2 \) into sugars.
Why other options are incorrect:- \( ADP \) and \( NADP^+ \) are the depleted, low-energy forms that return to the light reactions to be recharged.
Light reaction occurs in the _ of chloroplast: [ETEA-2023]
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:The light reactions heavily depend on photosystems, which are large protein-pigment complexes requiring a specific membrane structure.
Solution:- These photosystems are densely packed into the thylakoid membranes.
- A stack of thylakoid membranes is called a granum.
- Therefore, the grana are the precise structural locations where light energy is absorbed and converted into chemical energy.
Why other options are incorrect:- The outer and inner membranes of the chloroplast simply serve as protective and selective boundaries.
- The stroma is the fluid site of the dark reactions.
#29 of 56
ETEA-2023 Retake
The carotenoids absorb light in the visible spectrum between _ and wavelengths. [ETEA-2023 Retake]
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Accessory pigments like carotenoids absorb wavelengths of light that chlorophyll cannot efficiently capture, broadening the plant's action spectrum.
Solution:- Carotenoids are yellow, orange, and red pigments.
- They primarily absorb light in the blue-green range of the spectrum.
- Based on the specific data from the curriculum notes, this blue-green absorption strongly occurs in the 500-600 nm range.
Why other options are incorrect:- 630-700 nm is the red range, which is strongly absorbed by chlorophyll, not carotenoids. (Note: The source document provides options C and D as identical 500-600nm, which corresponds to the correct range).
#30 of 56
ETEA-2023 Retake
In the non-cyclic electron transport of light reaction, the deficit of _ electrons occur in the chlorophyll, as it absorbs energy. [ETEA-2023 Retake]
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Non-cyclic photophosphorylation (Z-scheme) relies on a continuous flow of electrons from water, through the photosystems, to NADP+.
Solution:- When light strikes Photosystem II (P680), an excited pair of electrons is ejected.
- This creates a deficit of exactly 2 electrons in the chlorophyll a reaction center.
- To fill this hole, one molecule of water is split (photolysis) to provide exactly 2 replacement electrons.
Why other options are incorrect:- The biological mechanism of photolysis specifically yields 2 electrons per water molecule split, perfectly matching the 2-electron deficit in the activated photosystem.
During photosynthesis, \( CO_2 \) works as: [NUMS-2022]
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:During the Calvin cycle (light-independent reactions), carbon dioxide is reduced to form glyceraldehyde 3-phosphate (G3P).
Solution:- In the reduction phase of the Calvin cycle, \( CO_2 \) receives protons and electrons from \( NADPH \) (which is oxidized to \( NADP^+ \)).
- Because it accepts protons during this reduction, \( CO_2 \) acts as a proton acceptor.
Why other options are incorrect:- \( CO_2 \) does not donate protons or electrons.
- Water (\( H_2O \)), not \( CO_2 \), is the source of oxygen evolved during photosynthesis.
In the process of photosynthesis, water acts as: [NUMS-2022]
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:In the light-dependent reactions of photosynthesis, water undergoes photolysis to replace the electrons lost by Photosystem II.
Solution:- Light energy splits water into \( 2H^+ \), \( \frac{1}{2}O_2 \), and releases electrons.
- These electrons are donated to the oxidized chlorophyll molecules of the reaction center, making water the ultimate electron donor in non-cyclic photophosphorylation.
Why other options are incorrect:- Water donates protons (\( H^+ \)) to the thylakoid lumen rather than accepting them.
- \( NADPH \) acts as the direct reducer of \( CO_2 \), not water.
The range of visible light is from: [ETEA-2022]
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:The visible light spectrum is the segment of the electromagnetic spectrum that the human eye can view, and which drives photosynthesis.
Solution:- The accepted standard range of visible light is approximately 380 nm to 750 nm.
- Photosynthetic pigments specifically absorb various wavelengths within this exact spectrum to capture energy.
Why other options are incorrect:- Other ranges are either too narrow, omitting key red or violet wavelengths, or shift too far into the infrared or ultraviolet regions.
Which scientist among the following hypothesized that plant splits water to release oxygen as by-product? [ETEA-2022]
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:The origin of oxygen evolved during photosynthesis was a major historical question in biology, eventually traced back to water rather than carbon dioxide.
Solution:- In the 1930s, Cornelis van Niel hypothesized that plants split water (\( H_2O \)) as a source of hydrogen, releasing oxygen as a byproduct.
- He based this on his studies of photosynthetic bacteria that utilize hydrogen sulfide (\( H_2S \)) and release sulfur.
Why other options are incorrect:- Melvin Calvin discovered the light-independent carbon fixation pathway.
- Hans Krebs discovered the citric acid cycle in cellular respiration.
Maximum photosynthesis occurs when: [BUMHS-2022]
A
Blue light is given to the plant
B
Red light is given to the plant
C
Green light is given to the plant
D
Yellow light is given to the plant
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Photosynthetic pigments, particularly chlorophyll
a and
b, have specific absorption peaks that determine the rate of photosynthesis across different wavelengths.
Solution:- Chlorophyll absorbs blue and red light most effectively.
- While both drive high rates of photosynthesis, blue light is absorbed at a slightly higher maximum capacity by the combined action of chlorophylls and accessory pigments (carotenoids).
Why other options are incorrect:- Green and yellow light are mostly reflected or transmitted, leading to minimal photosynthetic activity.
What is the colour of chlorophyll 'b' molecule? [UHS-2022]
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Different types of chlorophyll have slight structural differences that shift their absorption spectra, resulting in different visible colors.
Solution:- Chlorophyll a appears blue-green.
- Chlorophyll b appears yellow-green.
- This difference allows plants to broaden the spectrum of light they can effectively absorb.
Why other options are incorrect:- Bluish-green is the characteristic color of chlorophyll a.
Magnesium is an important nutrient in plant for the formation of: [NUMS-2022]
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Chlorophyll is a complex organic molecule built around a central metallic ion.
Solution:- The core of the chlorophyll molecule consists of a porphyrin ring.
- Magnesium (\( Mg^{2+} \)) is located exactly in the center of this porphyrin ring.
- Without magnesium, the plant cannot synthesize chlorophyll, leading to chlorosis (yellowing of leaves).
Why other options are incorrect:- Proteins and enzymes primarily rely on nitrogen and sulfur.
- Lipids are primarily composed of carbon, hydrogen, and oxygen.
If oxygen is available, complete breakdown of glucose produces _ ATP molecules in prokaryotes. [NUMS-2022]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Cellular respiration yields ATP through substrate-level phosphorylation and oxidative phosphorylation.
Solution:- In prokaryotes, the complete breakdown of glucose yields a net of 38 ATP.
- However, during the preparatory phase of glycolysis, 2 ATP are consumed.
- Therefore, the total (gross) production of ATP molecules during the complete breakdown is 38 (net) + 2 (consumed) = 40 ATP.
Why other options are incorrect:- 38 is the net ATP yield in prokaryotes.
- 36 is the standard net ATP yield in eukaryotes (due to the cost of transporting NADH into the mitochondria).
What is the number of hydrogen atoms in the molecular formula of chlorophyll 'a'? [BUMHS-2022]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Chlorophyll
a is the primary photosynthetic pigment with a specific complex chemical formula.
Formula:$$ C_{55}H_{72}O_{5}N_{4}Mg $$
Solution:- Based on the molecular formula, chlorophyll a contains exactly 72 hydrogen atoms.
Why other options are incorrect:- 55 is the number of Carbon atoms.
- 70 is the number of hydrogen atoms in chlorophyll b (\( C_{55}H_{70}O_{6}N_{4}Mg \)).
Each carrier in electron transport chain is first and then . [UHS-2022]
A
Broken-down, regenerate
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The electron transport chain (ETC) is a series of consecutive redox (reduction-oxidation) reactions.
Solution:- When an electron carrier accepts an electron from the previous molecule, it gains a negative charge and becomes reduced.
- When it passes that electron to the next carrier in the chain, it loses the electron and becomes oxidized again.
- Thus, the sequence is always reduced, then oxidized.
Why other options are incorrect:- Starting with oxidized would mean it loses an electron before gaining one, which contradicts the chain flow. Carriers must first receive (reduce) before they can give (oxidize).
Electron transport chain explains: [UHS-2022]
D
Mechanism of ATP synthesis
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The ETC is fundamentally coupled to chemiosmosis, providing the energy required to synthesize ATP.
Solution:- As electrons move energetically downhill along the ETC, they release energy.
- This energy is used to pump protons across a membrane, creating an electrochemical gradient.
- The flow of protons back across the membrane through ATP synthase explains the primary mechanism of ATP synthesis.
Why other options are incorrect:- While the ETC is involved in photophosphorylation and the Z-scheme, its universal biological role (in both mitochondria and chloroplasts) is explaining the mechanism behind bulk ATP synthesis.
What are the products of light dependent reactions of photosynthesis? [NUMS-2022]
A
ATP, RuBP and reduced NAD
B
ATP, oxygen and reduced NADP
C
GP, oxygen and reduced NAD
D
GP, reduced NADP and RuBP
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:The light-dependent reactions convert solar energy into chemical energy, providing the necessary assimilatory power for the dark reactions.
Solution:- ATP is generated via photophosphorylation.
- Reduced NADP (NADPH) is generated when electrons from PSI reduce \( NADP^+ \).
- Oxygen (\( O_2 \)) is released as a byproduct from the photolysis of water.
Why other options are incorrect:- RuBP and GP (glycerate 3-phosphate) are components/products of the light-independent reactions (Calvin cycle).
- Reduced NAD (NADH) is produced in cellular respiration, not photosynthesis.
Each granum consists of _ thylakoids. [SZABMU-2022]
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Thylakoids are flattened membrane sacs inside the chloroplast that stack on top of each other to maximize light absorption.
Solution:- A stack of thylakoids is called a granum (plural: grana).
- A typical granum consists of a stack of 25 to 50 thylakoid sacs.
Why other options are incorrect:- The other numerical ranges over-estimate or under-estimate the standard biological average taught for granum structure.
The element whose electrons are excited during light reactions of photosynthesis is: [SZABMU-2022]
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Photosynthetic pigments must be able to absorb light energy and readily release high-energy electrons.
Solution:- The core of the chlorophyll molecule is a porphyrin ring containing a central Magnesium (\( Mg \)) atom.
- When sunlight hits chlorophyll, it is the electrons associated with this central magnesium atom and the alternating double bonds of the porphyrin ring that become highly excited and are expelled to a primary electron acceptor.
Why other options are incorrect:- Carbon, hydrogen, and nitrogen form the structural backbone of the ring, but magnesium plays the central role in electron excitation and release.
Light reaction of photosynthesis takes place in: [DUHS-2022]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The light-dependent reactions require a membrane to embed photosystems and establish a proton gradient.
Solution:- Photosystems (groups of pigment molecules) and the electron transport chain are physically embedded in the thylakoid membrane.
- Consequently, all light-driven reactions, including photolysis of water and ATP synthesis, take place on or across the thylakoid.
Why other options are incorrect:- Stroma: The fluid where light-independent reactions (Calvin cycle) occur.
- Cristae: The folds of the inner mitochondrial membrane (cellular respiration).
- Cisternae: Flattened sacs in the Golgi apparatus or ER.
End product of Calvin cycle is: [NUMS-2022]
B
1-3 bisphosphoglycerate
C
Glyceraldehyde 3-phosphate
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:The Calvin cycle synthesizes a 3-carbon sugar directly, which the plant then uses to synthesize larger carbohydrates.
Solution:- The actual carbohydrate product expelled by the Calvin cycle is Glyceraldehyde 3-phosphate (G3P).
- For every three molecules of \( CO_2 \) that enter the cycle, one molecule of G3P is released as a net product.
Why other options are incorrect:- Glucose: is synthesized later in the cytoplasm by combining two molecules of G3P. It is not the direct end product of the cycle itself.
- 3-phosphoglycerate & 1,3-bisphosphoglycerate: are intermediate compounds formed prior to the reduction phase of the cycle.
Light independent phase of photosynthesis involves: [SZABMU-2022]
A
Formation of energy rich carbohydrates
D
Production of reducing molecules
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:The light-independent phase (Calvin cycle) uses the assimilatory power generated by the light reactions to fix carbon.
Solution:- In this phase, \( CO_2 \) is incorporated into organic molecules.
- ATP and NADPH are consumed to reduce this carbon, leading to the formation of energy-rich carbohydrates (such as G3P).
Why other options are incorrect:- Hydrolysis of water, ATP generation, and production of reducing molecules (NADPH) strictly occur during the light-dependent reactions.
In which part of chloroplast the fixation of carbon dioxide results in the formation of sugars? [ETEA-2022]
D
Outer membrane of chloroplast
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Carbon fixation via the Calvin cycle requires a specific biochemical environment rich in specific enzymes (like RuBisCO).
Solution:- The Calvin cycle takes place in the stroma, which is the dense aqueous fluid surrounding the thylakoids inside the chloroplast.
- The stroma contains all the necessary soluble enzymes to catalyze the formation of sugars from \( CO_2 \).
Why other options are incorrect:- Grana and intergrana (thylakoid structures) are dedicated solely to capturing light and carrying out the light-dependent reactions.
The Calvin cycle is completed in _ stages. [ETEA-2022]
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:The Calvin cycle is conventionally divided into distinct functional phases.
Solution:- The cycle occurs in three primary stages:
- Stage 1: Carbon Fixation (attaching \( CO_2 \) to RuBP).
- Stage 2: Reduction (using ATP and NADPH to convert 3-PGA to G3P).
- Stage 3: Regeneration (re-arranging G3P to regenerate the starting RuBP molecule).
Why other options are incorrect:- Dividing the cycle into any other number of core phases does not align with standard biochemical consensus.
The enzyme which is used in Calvin cycle is: [DUHS-2022]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Carbon fixation requires an incredibly specific enzyme to attach inorganic \( CO_2 \) to an organic 5-carbon molecule.
Solution:- The critical enzyme that performs this initial carbon fixation is Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO).
- It is considered the most abundant protein on the planet.
Why other options are incorrect:- While reductases and isomerases are general classes of enzymes used throughout metabolism, RuBisCO is the defining, specific enzyme of the Calvin cycle.
What is the end product of glucose by yeast in anaerobic respiration? [UHS-2022]
D
Lactic acid and \( CO_2 \)
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:When oxygen is absent, yeast cells undergo alcoholic fermentation to regenerate \( NAD^+ \) so glycolysis can continue.
Solution:- In yeast, the pyruvic acid from glycolysis is first decarboxylated to form acetaldehyde, releasing Carbon Dioxide (\( CO_2 \)).
- The acetaldehyde is then reduced by NADH to form Ethanol.
Why other options are incorrect:- Oxygen is never a product of anaerobic respiration.
- Lactic acid is the end product of anaerobic respiration in animal muscle cells and certain bacteria, not yeast.
Which of the following is not a consequence of anaerobic respiration in human muscles cells? [UHS-2022]
B
High consumption of energy
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Anaerobic respiration (lactic acid fermentation) in human muscle cells is a temporary emergency measure that yields very little energy compared to aerobic respiration.
Solution:- Anaerobic respiration provides a very low energy yield (only 2 net ATP per glucose molecule), meaning it is highly inefficient.
- Therefore, "High consumption of energy" (implying a high energy output or high-efficiency state) is NOT a consequence of anaerobic pathways; rather, it is characterized by an energy deficit.
- The accumulation of lactic acid leads to tiredness, pain, and cramps.
Why other options are incorrect:- Cramps, pain, and tiredness are all direct physiological consequences of the lactic acid buildup during anaerobic exertion.
Which of the following is used in baking? [BUMHS-2022]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The baking of bread relies on the metabolic byproducts of yeast.
Solution:- In baking, yeast cells are trapped inside the dough where oxygen is rapidly depleted.
- The yeast undergoes anaerobic respiration (alcoholic fermentation), converting sugars into ethanol and \( CO_2 \) gas.
- The trapped \( CO_2 \) bubbles cause the dough to rise, giving bread its fluffy texture.
Why other options are incorrect:- Aerobic respiration does not produce the rapid burst of \( CO_2 \) gas in a trapped, oxygen-deprived dough environment necessary for rising.
Net ATP produced at the end of glycolysis: [DUHS-2022]
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Glycolysis includes an investment (preparatory) phase and a payoff phase.
Solution:- During the preparatory phase, the cell consumes 2 ATP to phosphorylate glucose.
- During the payoff phase, substrate-level phosphorylation produces a total of 4 ATP.
- The net gain is calculated as: 4 (produced) - 2 (invested) = 2 ATP.
Why other options are incorrect:- 4 ATP is the gross production, not the net.
- 6 and 3 ATP do not reflect the stoichiometry of glycolysis.
Pyruvic acid is acid of: [DUHS-2022]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Glycolysis is the splitting of a single sugar molecule into two smaller molecules.
Solution:- Glucose is a 6-carbon sugar.
- During glycolysis, it is ultimately split into two molecules of pyruvic acid.
- Therefore, each pyruvic acid molecule is a 3-carbon compound.
Why other options are incorrect:- 4-carbon compounds are typical in the Krebs cycle (e.g., oxaloacetate).
- 5-carbon compounds include RuBP (Calvin cycle) or alpha-ketoglutarate (Krebs cycle).
- 6-carbon compounds include glucose and citrate.
In aerobic respiration, glucose molecule is completely broken down into \( CO_2 \), \( H_2O \) and _. [ETEA-2022]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Aerobic cellular respiration maximizes the extraction of energy from a single glucose molecule.
Solution:- In eukaryotic cells, the complete oxidation of one glucose molecule yields a net total of roughly 36 ATP.
- This includes 2 net ATP from glycolysis, 2 from the Krebs cycle, and 32 from the electron transport chain.
Why other options are incorrect:- 2 ATP is the yield from anaerobic respiration (glycolysis only).
- 34 ATP represents just the typical output of the electron transport chain (or an intermediate estimate), not the complete net yield.
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