#1 of 53
SZABMU 2024
Permalink
Which of the following receives electrons from \( FADH_2 \) during oxidative phosphorylation in cristae of mitochondria?
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Electrons from different carriers enter the electron transport chain at different points based on their energy levels.
Solution:- While NADH delivers electrons to Complex I, \( FADH_2 \) possesses slightly less energy and bypasses Complex I entirely.
- \( FADH_2 \) donates its electrons directly to Complex II.
- From Complex II, the electrons are immediately passed to the mobile lipid carrier Coenzyme Q (Ubiquinone).
Why other options are incorrect:- Cytochromes a, b, and c are located further downstream in the electron transport chain and receive electrons only after they have passed through Coenzyme Q.
#2 of 53
SZABMU 2024
Permalink
What is the product formed at the end of the respiratory chain in inner membrane of mitochondria?
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:The electron transport chain ends when the depleted electrons are finally accepted by a terminal molecule.
Solution:- At the very end of the respiratory chain (Complex IV), electrons are passed to molecular Oxygen (\( O_2 \)).
- The oxygen atoms accept these electrons and combine with protons (\( H^+ \)) from the surrounding matrix.
- This chemical combination yields Water (\( H_2O \)) as the final metabolic product of the chain.
Why other options are incorrect:- Oxygen is the reactant (acceptor), not the product.
- \( CO_2 \) is produced earlier during the Krebs cycle and link reaction, not the ETC.
#3 of 53
SZABMU 2024
Permalink
The type of phosphorylation which involves the transfer of electrons from NADH to Coenzyme Q in the inner mitochondrial membrane is called:
B
Non-cyclic Phosphorylation
C
Oxidative Phosphorylation
D
Substrate level Phosphorylation
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Phosphorylation (the addition of a phosphate to ADP) is classified by the energy source driving the reaction.
Solution:- The transfer of electrons from NADH to Coenzyme Q is the first step of the mitochondrial electron transport chain.
- The energy released from this redox transfer pumps protons, creating a gradient that drives ATP synthase.
- Because this entire process is dependent on redox reactions ending with oxygen, it is termed Oxidative Phosphorylation.
Why other options are incorrect:- Cyclic and Non-cyclic phosphorylation are light-driven processes occurring in chloroplasts (photosynthesis).
- Substrate-level phosphorylation relies on direct enzyme transfer without an ETC.
#4 of 53
NUMS 2024
Permalink
Which mechanism would be compromised in the absence of cytochrome complex during light reactions of photosynthesis?
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.
#5 of 53
SZABMU 2024
Permalink
Which of the following steps of glycolysis does not involve ATP directly?
A
Conversion of Glucose to Glucose 6-phosphate
B
Conversion of Fructose 6-phosphate to Fructose 1,6-bisphosphate
C
Conversion of Glyceraldehyde 3-phosphate to 1,3- bisphosphoglycerate
D
Conversion of 1,3- bisphosphoglycerate to 3- phosphoglycerate
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Glycolysis features specific steps that either consume ATP (kinases) or produce ATP via substrate-level phosphorylation.
Solution:- Step A consumes 1 ATP (Hexokinase).
- Step B consumes 1 ATP (Phosphofructokinase).
- Step D produces 1 ATP (Phosphoglycerate kinase).
- Step C is an oxidation reaction catalyzed by GAPDH. It utilizes inorganic phosphate (Pi) from the cytosol and reduces \( NAD^+ \) to NADH. It does not directly involve ATP.
Why other options are incorrect:- Options A, B, and D all feature a direct physical interaction with ATP molecules.
#6 of 53
NUMS 2024
Permalink
During glycolysis, isomerization takes place in the form of:
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.
#7 of 53
SZABMU 2024
Permalink
The amount of energy present in bonds of glucose which is converted into ATP during anaerobic respiration is:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Anaerobic respiration is an incredibly inefficient method of extracting the total potential chemical energy locked within the bonds of a glucose molecule.
Solution:- The complete aerobic oxidation of glucose captures a large percentage of its energy (around 36-40%).
- However, during anaerobic respiration (fermentation), the glucose molecule is only partially broken down.
- As a result, only a net of 2 ATP is produced, meaning only about 2% of the total potential energy in glucose is actually converted into usable ATP. The rest remains locked in the toxic byproducts (ethanol or lactic acid).
Why other options are incorrect:- 4%, 10%, and 36% grossly overestimate the thermodynamic efficiency of fermentation.
#8 of 53
UHS 2024
Permalink
In Calvin cycle \( CO_2 \) reacts with RuBP to produce _.
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.
#9 of 53
SZABMU 2024
Permalink
The step of Calvin Cycle during which five molecules of Glyceraldehyde 3-phosphate (G3P) are converted in Ribulose 1,5-Phosphate by utilizing 3 molecules of ATP is:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:For a biochemical cycle to continuously run, its starting material must be remade at the end of every turn.
Solution:- The starting molecule of the Calvin cycle is RuBP.
- After the reduction phase, some G3P exits the cycle, but the majority (5 out of 6 molecules) remain.
- Through a complex series of ATP-dependent reactions, these five 3-carbon G3P molecules are rearranged to regenerate three 5-carbon RuBP molecules.
- This specific final phase is fundamentally called the Regeneration step.
Why other options are incorrect:- Fixation is the attachment of \( CO_2 \).
- Reduction uses ATP and NADPH to convert 3-PGA to G3P.
#10 of 53
SZABMU 2024
Permalink
Which of the following does not take place during cyclic phosphorylation of the light dependent reaction of photosynthesis?
C
Photoexcitation of electrons
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Cyclic photophosphorylation is an alternate pathway that only involves Photosystem I to generate extra ATP.
Solution:- In cyclic flow, electrons are excited in PSI, travel down the cytochrome complex (generating ATP), and return directly back to PSI.
- Because the electrons cycle in a closed loop, there is no electron deficit in PSI.
- Therefore, there is no need to split water to replace electrons. Photolysis of water absolutely does NOT occur in this pathway.
Why other options are incorrect:- Light absorption, photoexcitation of electrons, and ATP synthesis are the fundamental driving events of the cyclic pathway.
#11 of 53
SZABMU 2024 Reconduct
Permalink
Ubiquinone contains:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: Electron transport chain prosthetic groups and carriers.
Solution: Ubiquinone (Coenzyme Q) works closely with iron-sulfur clusters in mitochondrial Complex I and Complex II to transfer electrons down the respiratory chain.
#12 of 53
SZABMU 2024 Reconduct
Permalink
Chlorophyll and accessory pigments absorb light and transfer the energy, that initiates the light reactions. What is the order of energy transfer?
A
Chlorophyll b \(\rightarrow\) Carotenoids \(\rightarrow\) Chlorophyll a
B
Chlorophyll b \(\rightarrow\) Carotenoids \(\rightarrow\) Chlorophyll b
C
Chlorophyll a \(\rightarrow\) Chlorophyll b \(\rightarrow\) Carotenoids
D
Carotenoids \(\rightarrow\) Chlorophyll b \(\rightarrow\) Chlorophyll a
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The photosystem acts like a funnel, gathering light energy from a wide antenna complex and directing it inward to a central reaction center.
Solution:- Light is initially absorbed by the outermost accessory pigments (Carotenoids), which absorb broader wavelengths.
- They pass this excitation energy via resonance to Chlorophyll b.
- Chlorophyll b funnels the energy inward directly to the reaction center, which is exclusively composed of Chlorophyll a.
- Therefore, the correct inward vector is: Carotenoids \(\rightarrow\) Chlorophyll b \(\rightarrow\) Chlorophyll a.
Why other options are incorrect:- Energy always flows from accessory pigments towards the primary pigment (Chlorophyll a), never outward or in reverse.
#13 of 53
SZABMU 2024
Permalink
What is the concentration of \( CO_2 \) in air?
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Carbon dioxide is a crucial trace gas in the Earth's atmosphere, acting as the primary carbon source for global photosynthesis.
Solution:- Despite its massive biological importance, \( CO_2 \) makes up a tiny fraction of the standard atmospheric volume.
- The universally taught biological baseline for atmospheric \( CO_2 \) concentration is approximately 0.03% to 0.04% (which equates to 300-400 parts per million).
Why other options are incorrect:- Options A and C represent concentrations that are far too low (plants would suffocate and die).
- Option D (3-4%) is far too high and would be toxic to much of aerobic life while causing catastrophic global warming.
#14 of 53
SZABMU 2024
Permalink
What is the efficiency of \( CO_2 \) fixation in plants with photorespiration?
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Photorespiration is a wasteful process where RuBisCO accidentally binds to Oxygen instead of Carbon Dioxide, draining the plant's resources.
Solution:- In standard \( C_3 \) plants, when stomata close on hot days, \( O_2 \) builds up and outcompetes \( CO_2 \).
- This oxygenase activity can undercut the plant's photosynthetic output by roughly 25%.
- Consequently, the remaining operational efficiency of actual \( CO_2 \) fixation drops down to about 75%.
Why other options are incorrect:- 25% represents the amount of efficiency lost, not the amount retained.
- 20% and 45% do not align with standard physiological metrics for photorespiratory drag.
#15 of 53
NUMS 2024
Permalink
Presence of PEP carboxylase in \( C_4 \) plants enable them to avoid photorespiration due to:
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.
#16 of 53
NUMS 2024
Permalink
Fats and proteins can be used as respiratory fuel. Which of the following serves as common molecule produced through their catabolism?
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.
#17 of 53
UHS 2023
Permalink
Which is the main event in electron transport chain?
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.
#18 of 53
UHS 2023
Permalink
Out of 36 ATPs, how many are produced in electron transport chain?
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.
#19 of 53
UHS 2023
Permalink
The major enzymes involved in transfer of phosphate group from ATP to Glucose is:
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 \( CO_2 \).
#20 of 53
SZABMU 2023
Permalink
The end product of glycolysis in anaerobic respiration is:
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.
#21 of 53
ETEA 2023
Permalink
The ATP formed in the preparatory phase of glycolysis is (are):
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.
#22 of 53
ETEA 2023
Permalink
In alcoholic fermentation _ ATP molecules are produced from 1 glucose molecule.
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.
#23 of 53
SZABMU 2023
Permalink
The final acceptor of both electrons and protons during light reactions of photosynthesis is:
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.
#24 of 53
NUMS 2023
Permalink
When light falls on P700, which event is likely to occur?
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).
#25 of 53
SZABMU 2023
Permalink
The only copper containing protein involved during light reactions of photosynthesis is:
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.
#26 of 53
SZABMU 2023
Permalink
End product of Calvin cycle is:
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.
#27 of 53
NUMS 2023
Permalink
Which are the end products of light reactions of photosynthesis?
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.
#28 of 53
NUMS 2023
Permalink
Synthesis of ATP during photosynthesis takes place at the region:
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.
#29 of 53
NUMS 2023
Permalink
Which of the following molecules are released after completion of light reaction and the utilized in the dark reaction of photosynthesis?
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.
#30 of 53
ETEA 2023
Permalink
Light reaction occurs in the _ of chloroplast:
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.
#31 of 53
ETEA 2023 Retake
Permalink
The carotenoids absorb light in the visible spectrum between _ and wavelengths.
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).
#32 of 53
NUMS 2022
Permalink
During photosynthesis, \( CO_2 \) works as:
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.
#33 of 53
NUMS 2022
Permalink
In the process of photosynthesis, water acts as:
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.
#34 of 53
ETEA 2022
Permalink
The range of visible light is from:
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.
#35 of 53
ETEA 2022
Permalink
Which scientist among the following hypothesized that plant splits water to release oxygen as by-product?
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.
#36 of 53
BUMHS 2022
Permalink
Maximum photosynthesis occurs when:
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.
#37 of 53
UHS 2022
Permalink
What is the colour of chlorophyll 'b' molecule?
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.
#38 of 53
NUMS 2022
Permalink
Magnesium is an important nutrient in plant for the formation of:
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.
#39 of 53
NUMS 2022
Permalink
If oxygen is available, complete breakdown of glucose produces _ ATP molecules in prokaryotes.
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).
#40 of 53
UHS 2022
Permalink
Each carrier in electron transport chain is first and then .
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).
#41 of 53
NUMS 2022
Permalink
What are the products of light dependent reactions of photosynthesis?
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.
#42 of 53
SZABMU 2022
Permalink
Each granum consists of _ thylakoids.
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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.
#43 of 53
SZABMU 2022
Permalink
The element whose electrons are excited during light reactions of photosynthesis is:
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.
#44 of 53
DUHS 2022
Permalink
Light reaction of photosynthesis takes place in:
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.
#45 of 53
NUMS 2022
Permalink
End product of Calvin cycle is:
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.
#46 of 53
SZABMU 2022
Permalink
Light independent phase of photosynthesis involves:
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.
#47 of 53
ETEA 2022
Permalink
In which part of chloroplast the fixation of carbon dioxide results in the formation of sugars?
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.
#48 of 53
ETEA 2022
Permalink
The Calvin cycle is completed in _ stages.
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.
#49 of 53
DUHS 2022
Permalink
The enzyme which is used in Calvin cycle is:
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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.
#50 of 53
UHS 2022
Permalink
Which of the following is not a consequence of anaerobic respiration in human muscles cells?
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.
#51 of 53
DUHS 2022
Permalink
Net ATP produced at the end of glycolysis:
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.
#52 of 53
DUHS 2022
Permalink
Pyruvic acid is acid of:
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.
#53 of 53
ETEA 2022
Permalink
In aerobic respiration, glucose molecule is completely broken down into \( CO_2 \), \( H_2O \) and _.
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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