Respiration in Plants

Subtopic: Electron Transport Chain

• Cytochrome: Heme-containing protein involved in electron transport within mitochondria or chloroplasts.

• Electron Transport Chain (ETC): Series of protein complexes that transfer electrons to generate a proton gradient for ATP synthesis.

• Complex III: Also called cytochrome bc1 complex, transfers electrons from ubiquinol to cytochrome c.

• Complex IV: Also called cytochrome oxidase, transfers electrons to oxygen forming water.

• Mobile Carrier: Molecule that shuttles electrons between protein complexes in the ETC.

• Proton Gradient: Electrochemical gradient formed by movement of protons across a membrane during electron transport.

• ATP Synthesis: Production of ATP by ATP synthase utilizing proton gradient.

• Cytochrome c: Small soluble heme protein that transfers electrons between complex III and IV.

• Redox Reaction: Reaction involving transfer of electrons from one molecule to another.

• Oxidative Phosphorylation: ATP production coupled to electron transport in mitochondria.

• Heme Group: Iron-containing prosthetic group in cytochromes responsible for electron transfer.

Lead Question - 2022 (Abroad)

Identify the cytochrome which acts as a mobile carrier for the transfer of electrons between complex III and IV?

1. Cytochrome a

2. Cytochrome a3

3. Cytochrome b c1

4. Cytochrome c

Explanation: Cytochrome c is a small, soluble heme protein that acts as a mobile carrier transferring electrons from complex III (cytochrome bc1) to complex IV (cytochrome oxidase) in the mitochondrial electron transport chain. This step is essential for proton gradient formation and ATP synthesis. Answer: Cytochrome c. Answer: 4

Q1: Which complex in the ETC reduces oxygen to water?

1. Complex I

2. Complex II

3. Complex III

4. Complex IV

Explanation: Complex IV, also called cytochrome oxidase, accepts electrons from cytochrome c and reduces molecular oxygen to water. This step is the final electron transfer in the mitochondrial ETC and is crucial for maintaining the proton gradient required for ATP synthesis. Answer: Complex IV. Answer: 4

Q2: The primary function of cytochrome b c1 complex is:

1. Electron transfer from NADH to oxygen

2. Electron transfer from ubiquinol to cytochrome c

3. Proton pumping from matrix to cytosol

4. ATP synthesis

Explanation: Cytochrome bc1 complex (Complex III) transfers electrons from ubiquinol to cytochrome c while pumping protons across the inner mitochondrial membrane. This creates an electrochemical gradient utilized for ATP synthesis. Answer: Electron transfer from ubiquinol to cytochrome c. Answer: 2

Q3: Which cytochromes are part of Complex IV?

1. Cytochrome a and a3

2. Cytochrome b and c1

3. Cytochrome c only

4. Cytochrome a and c

Explanation: Complex IV contains cytochrome a and cytochrome a3 as electron carriers. They facilitate the final electron transfer to oxygen, forming water. Cytochrome c is the mobile carrier delivering electrons from Complex III to IV. Answer: Cytochrome a and a3. Answer: 1

Q4: Which of the following is soluble in the intermembrane space?

1. Cytochrome b

2. Cytochrome c

3. Cytochrome a

4. Ubiquinone

Explanation: Cytochrome c is a small, soluble protein in the intermembrane space of mitochondria. It acts as a mobile electron carrier between Complex III and Complex IV, facilitating electron transport while maintaining proton gradient formation for ATP synthesis. Answer: Cytochrome c. Answer: 2

Q5: Ubiquinone transfers electrons between which complexes?

1. Complex I and II to III

2. Complex III to IV

3. Complex IV to oxygen

4. Complex II to IV

Explanation: Ubiquinone (coenzyme Q) transfers electrons from Complex I and II to Complex III in the ETC. It is a lipid-soluble molecule embedded in the inner mitochondrial membrane and participates in proton pumping. Answer: Complex I and II to III. Answer: 1

Q6: What is the role of proton pumping in ETC?

1. Generate ATP directly

2. Create a proton gradient across inner membrane

3. Reduce oxygen to water

4. Transport electrons to cytochrome c

Explanation: Proton pumping by Complexes I, III, and IV generates an electrochemical proton gradient across the inner mitochondrial membrane. This proton motive force drives ATP synthesis via ATP synthase. It does not directly reduce oxygen or transport electrons. Answer: Create a proton gradient across inner membrane. Answer: 2

Q7: Assertion (A): Cytochrome c is water-soluble.
Reason (R): It acts as a mobile carrier in the intermembrane space.

1. A is correct but R is not correct

2. A is not correct but R is correct

3. Both A and R are correct and R explains A

4. Both A and R are correct but R does not explain A

Explanation: Cytochrome c is a small water-soluble protein located in the intermembrane space. It functions as a mobile electron carrier between Complex III and IV. Both assertion and reason are correct, and the reason explains why its solubility is important. Answer: Both A and R are correct and R explains A. Answer: 3

Q8: Match the complex with its main components:

1. Complex I    A. NADH dehydrogenase
2. Complex II    B. Succinate dehydrogenase
3. Complex III    C. Cytochrome b c1
4. Complex IV    D. Cytochrome a, a3

1. 1-A, 2-B, 3-C, 4-D

2. 1-B, 2-A, 3-D, 4-C

3. 1-C, 2-D, 3-A, 4-B

4. 1-D, 2-C, 3-B, 4-A

Explanation: Complex I contains NADH dehydrogenase, Complex II has succinate dehydrogenase, Complex III contains cytochrome bc1, and Complex IV contains cytochrome a and a3. This correct matching shows component distribution in mitochondrial ETC. Answer: 1-A, 2-B, 3-C, 4-D. Answer: 1

Q9: The final electron acceptor in mitochondrial ETC is _______.

1. NAD+

2. FAD

3. Oxygen

4. Water

Explanation: Oxygen acts as the final electron acceptor in the mitochondrial electron transport chain. It accepts electrons from Complex IV via cytochrome a and a3 and combines with protons to form water, completing oxidative phosphorylation. Answer: Oxygen. Answer: 3

Q10: Select correct statements about cytochrome c:

1. It is water-soluble

2. Transfers electrons from Complex III to IV

3. Contains heme group

4. Located in intermembrane space

Explanation: Cytochrome c is a water-soluble protein in the intermembrane

Subtopic: Electron Transport System (ETS)

• ETS Complex: Electron Transport System complexes in mitochondria facilitating oxidative phosphorylation.

• Complex I (NADH dehydrogenase): First complex accepting electrons from NADH.

• Complex II (Succinate dehydrogenase): Accepts electrons from FADH2 and passes to ubiquinone.

• Complex III (Cytochrome bc1): Transfers electrons from ubiquinol to cytochrome c, containing Cyt b and Cyt c1.

• Complex IV (Cytochrome oxidase): Transfers electrons to oxygen, contains Cyt a, a3 and copper centres.

• Ubiquinone: Mobile electron carrier between complexes I/II and III.

• Cytochrome c: Mobile protein transferring electrons from complex III to IV.

• Oxidative Phosphorylation: ATP synthesis coupled to electron transport in mitochondria.

• NADH: Reduced coenzyme donating electrons to complex I.

• FADH2: Reduced coenzyme donating electrons to complex II.

• Mitochondrial Respiration: Process generating ATP via ETS and chemiosmosis.

Lead Question - 2022 (Abroad)

Match List-I with List-II

List-I
(a) ETS complex-I
(b) ETS complex-II
(c) ETS complex-III
(d) ETS complex-IV

List-II
(i) Cyt b1 dehydrogenase
(ii) Cyt a, a3 and 2 copper centres
(iii) NADH dehydrogenase
(iv) Ubiquinone and FADH dehydrogenase

Choose the correct answer from the options given below:

1. (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)

2. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)

3. (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)

4. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)

Explanation: In mitochondria, ETS complex-I is NADH dehydrogenase, accepting electrons from NADH. Complex-II contains FADH and ubiquinone. Complex-III contains cytochrome b1, transferring electrons to cytochrome c. Complex-IV contains cytochrome a, a3 and copper centres, transferring electrons to oxygen. Correct matching: a-III, b-IV, c-I, d-II. Answer: 4

Q1: The primary function of ETS is:

1. Glycolysis

2. ATP synthesis

3. Protein synthesis

4. Lipid metabolism

Explanation: Electron Transport System transfers electrons through complexes I-IV to generate proton gradient, driving ATP synthesis via ATP synthase. It is central to aerobic respiration. Other options like glycolysis, protein synthesis, or lipid metabolism are not direct functions of ETS. Answer: ATP synthesis. Answer: 2

Q2: Electrons from FADH2 enter ETS through:

1. Complex I

2. Complex II

3. Complex III

4. Complex IV

Explanation: FADH2 donates electrons directly to complex II (succinate dehydrogenase). This bypasses complex I, producing fewer ATP molecules per FADH2 compared to NADH. Complex III and IV receive electrons downstream. Answer: Complex II. Answer: 2

Q3: Cytochrome c transfers electrons between:

1. Complex I to II

2. Complex II to IV

3. Complex III to IV

4. Complex I to III

Explanation: Cytochrome c is a mobile electron carrier transferring electrons from complex III (cytochrome bc1) to complex IV (cytochrome oxidase). It is not involved in transfers from complex I or II directly. Answer: Complex III to IV. Answer: 3

Q4: Ubiquinone is:

1. Protein carrier

2. Lipid-soluble electron carrier

3. Enzyme complex

4. ATP synthase subunit

Explanation: Ubiquinone (coenzyme Q) is lipid-soluble, carrying electrons from complexes I and II to complex III within the inner mitochondrial membrane. It is not a protein, enzyme complex, or ATP synthase component. Answer: Lipid-soluble electron carrier. Answer: 2

Q5: Complex IV contains which key prosthetic groups?

1. Cyt b, Fe-S

2. Cyt a, a3, Cu

3. FADH2, Ubiquinone

4. ATP, ADP

Explanation: Complex IV (cytochrome oxidase) contains cytochromes a and a3 and copper centers which transfer electrons to molecular oxygen forming water. FADH2, ubiquinone, or ATP/ADP are not prosthetic groups of complex IV. Answer: Cyt a, a3, Cu. Answer: 2

Q6: NADH dehydrogenase is also called:

1. Complex I

2. Complex II

3. Complex III

4. Complex IV

Explanation: NADH dehydrogenase is complex I of ETS, receiving electrons from NADH and passing them to ubiquinone. Complex II handles FADH2; III and IV are downstream electron carriers. Answer: Complex I. Answer: 1

Q7: Assertion (A): Complex II contributes to proton gradient.
Reason (R): Electrons from FADH2 enter complex II.

1. A is correct but R is not correct

2. A is not correct but R is correct

3. Both A and R are correct and R explains A

4. Both A and R are correct but R does not explain A

Explanation: Complex II transfers electrons from FADH2 to ubiquinone but does not pump protons across the membrane, thus contributing minimally to proton gradient. Assertion is incorrect, Reason is correct. Answer: A is not correct but R is correct. Answer: 2

Q8: Match ETS complexes with primary electron donor:

1. Complex I    A. FADH2
2. Complex II    B. NADH
3. Complex III    C. Ubiquinol
4. Complex IV    D. Cytochrome c

1. 1-B, 2-A, 3-C, 4-D

2. 1-A, 2-B, 3-D, 4-C

3. 1-B, 2-A, 3-D, 4-C

4. 1-C, 2-D, 3-A, 4-B

Explanation: Complex I receives electrons from NADH, complex II from FADH2, complex III from ubiquinol, and complex IV from cytochrome c. Matching is: 1-B, 2-A, 3-C, 4-D. Answer: 1

Q9: Final electron acceptor in ETS is ______.

1. NAD+

2. FAD

3. Oxygen

4. Ubiquinone

Explanation: In mitochondrial respiration, oxygen is the final electron acceptor, combining with electrons and protons to form water. NAD+, FAD, and ubiquinone are intermediate carriers. Answer: Oxygen. Answer: 3

Q10: Choose correct statements about ETS:

1. Complex I oxidizes NADH

2. Complex II oxidizes FADH2

3. Complex IV reduces oxygen

4. ETS directly synthesizes ATP without gradient

Explanation: ETS complexes oxidize NADH/FADH2 and reduce oxygen at complex IV. Proton gradient generated drives ATP synthesis indirectly via ATP synthase. Direct ATP synthesis without gradient is incorrect. Correct statements: 1, 2, 3. Answer: 1, 2, 3

Topic: Glycolysis
Subtopic: ATP Yield from Glucose

Keyword Definitions:

• ATP (Adenosine Triphosphate): Primary energy currency of the cell used in metabolic processes.

• Glucose: Six-carbon monosaccharide that is the starting molecule in glycolysis.

• Pyruvic acid (Pyruvate): Three-carbon molecule formed at the end of glycolysis from glucose.

• Glycolysis: Cytoplasmic pathway that breaks one molecule of glucose into two molecules of pyruvate, producing ATP.

• Net gain: Total ATP produced minus ATP consumed during glycolysis.

• NADH: Reduced electron carrier produced during glycolysis, used in oxidative phosphorylation.

• Substrate-level phosphorylation: Direct synthesis of ATP by transferring phosphate groups from intermediates to ADP.

• Energy investment phase: First phase of glycolysis consuming 2 ATP molecules.

• Energy payoff phase: Second phase of glycolysis producing 4 ATP molecules per glucose.

• Anaerobic conditions: Glycolysis occurs without oxygen, producing ATP and pyruvate or lactate.

Lead Question (2022)
What is the net gain of ATP when each molecule of glucose is converted to two molecules of pyruvic acid?
(1) Six
(2) Two
(3) Eight
(4) Four

Explanation:
During glycolysis, one glucose molecule is converted into two pyruvate molecules. Two ATP molecules are consumed initially, while four ATP molecules are produced later. Therefore, the net gain is 4 – 2 = 2 ATP molecules per glucose. Correct answer is (2).

1. Single Correct Answer MCQ:
Which of the following occurs in the cytoplasm of a cell?
(1) Krebs cycle
(2) Glycolysis
(3) Electron transport chain
(4) Oxidative phosphorylation

Explanation:
Glycolysis occurs in the cytoplasm, converting glucose to pyruvate and producing ATP. Krebs cycle and electron transport chain occur in mitochondria. Oxidative phosphorylation occurs at the inner mitochondrial membrane. Correct answer is (2).

2. Single Correct Answer MCQ:
During glycolysis, how many NADH molecules are produced per glucose?
(1) One
(2) Two
(3) Three
(4) Four

Explanation:
Each glucose molecule generates two molecules of NADH during glycolysis, which later enter the mitochondria for oxidative phosphorylation. Correct answer is (2).

3. Single Correct Answer MCQ:
Glycolysis is considered an anaerobic process because:
(1) It requires oxygen
(2) It occurs without oxygen
(3) It produces carbon dioxide
(4) It occurs in mitochondria

Explanation:
Glycolysis does not require oxygen and occurs in the cytoplasm. It can produce ATP under anaerobic conditions. Oxygen is required later in mitochondrial respiration. Correct answer is (2).

4. Single Correct Answer MCQ:
Which enzyme catalyzes the conversion of glucose to glucose-6-phosphate?
(1) Hexokinase
(2) Phosphofructokinase
(3) Pyruvate kinase
(4) Aldolase

Explanation:
Hexokinase catalyzes the first step of glycolysis, phosphorylating glucose to glucose-6-phosphate, using one ATP molecule. Other enzymes act in later steps. Correct answer is (1).

5. Single Correct Answer MCQ:
The net ATP gain by substrate-level phosphorylation in glycolysis per glucose is:
(1) 1
(2) 2
(3) 3
(4) 4

Explanation:
During glycolysis, 4 ATP molecules are produced by substrate-level phosphorylation, but 2 ATP are used in the energy investment phase. Net ATP gain is 4 – 2 = 2. Correct answer is (2).

6. Single Correct Answer MCQ:
Which glycolysis product can enter mitochondria for further energy extraction?
(1) NAD+
(2) Pyruvate
(3) ADP
(4) Glucose-6-phosphate

Explanation:
Pyruvate generated in glycolysis is transported into mitochondria for the Krebs cycle and oxidative phosphorylation. NAD+ and ADP are cofactors, and glucose-6-phosphate remains in the cytoplasm. Correct answer is (2).

7. Assertion-Reason MCQ:
Assertion (A): Glycolysis produces a net gain of 2 ATP per glucose.
Reason (R): Four ATP are produced and two ATP are consumed during glycolysis.
Options:
(1) Both A and R are correct, R explains A
(2) A correct, R incorrect
(3) A incorrect, R correct
(4) Both A and R incorrect

Explanation:
Glycolysis consumes 2 ATP and produces 4 ATP, giving a net gain of 2 ATP per glucose. Reason accurately explains the assertion. Correct answer is (1).

8. Matching Type MCQ:
Match glycolysis intermediates with ATP usage:
A. Glucose → Glucose-6-phosphate — 1. ATP consumed
B. Fructose-6-phosphate → Fructose-1,6-bisphosphate — 2. ATP consumed
C. 1,3-Bisphosphoglycerate → 3-Phosphoglycerate — 3. ATP produced
D. Phosphoenolpyruvate → Pyruvate — 4. ATP produced
Options:
(1) A–1, B–2, C–3, D–4
(2) A–2, B–1, C–4, D–3
(3) A–1, B–2, C–4, D–3
(4) A–3, B–4, C–1, D–2

Explanation:
ATP is consumed during phosphorylation steps (A–1, B–2) and produced during substrate-level phosphorylation (C–3, D–4). Correct answer is (1).

9. Fill in the Blanks MCQ:
The final product of glycolysis is ________, which can undergo fermentation or enter mitochondria.
(1) Lactate
(2) Pyruvate
(3) Acetyl-CoA
(4) Glucose-6-phosphate

Explanation:
Glycolysis ends with pyruvate. Under anaerobic conditions, pyruvate undergoes fermentation; under aerobic conditions, it enters mitochondria as acetyl-CoA. Lactate is a fermentation product, not direct glycolysis product. Correct answer is (2).

10. Choose the correct statements MCQ:
(a) Glycolysis occurs in cytoplasm
(b) Net ATP gain per glucose is 2
(c) Oxygen is required
(d) NADH is produced
Options:
(1) a, b, d only
(2) a, c only
(3) b, c, d only
(4) a, b, c, d

Explanation:
Glycolysis occurs in cytoplasm (a), produces net 2 ATP (b), and generates NADH (d). It does not require oxygen (c). Correct answer is (1).

Topic: Fermentation
Subtopic: Lactic Acid Fermentation

Keyword Definitions:

• Glucose: A simple sugar (C6H12O6) and primary energy source for cellular respiration.

• Lactic Acid Fermentation: Anaerobic conversion of glucose into lactic acid, yielding small amounts of energy.

• Anaerobic: Metabolic processes occurring without oxygen.

• ATP: Adenosine triphosphate, the energy currency of the cell.

• Glycolysis: First step in glucose breakdown, producing pyruvate and ATP.

• Energy Yield: Amount of usable chemical energy released during metabolic reactions.

Lead Question (2022)
What amount of energy is released from glucose during lactic acid fermentation?
(1) More than 18%
(2) About 10%
(3) Less than 7%
(4) Approximately 15%

Explanation:
During lactic acid fermentation, glucose is partially oxidized to lactic acid. Only a small fraction of energy stored in glucose is released as ATP, roughly 7%. Most energy remains in lactic acid molecules. Hence, the correct answer is (3).

1. Which step occurs first in lactic acid fermentation?
(1) Krebs cycle
(2) Glycolysis
(3) Electron transport chain
(4) Oxidative phosphorylation

Explanation:
Glycolysis is the initial step in lactic acid fermentation, breaking glucose into two molecules of pyruvate and generating ATP. Pyruvate is then reduced to lactic acid. Hence, the correct answer is (2).

2. The end product of lactic acid fermentation in muscles is:
(1) Ethanol
(2) Carbon dioxide
(3) Lactic acid
(4) Acetyl CoA

Explanation:
In anaerobic conditions, muscle cells convert pyruvate into lactic acid to regenerate NAD+, allowing glycolysis to continue producing ATP. Hence, the correct answer is (3).

3. Lactic acid fermentation occurs in:
(1) Yeast
(2) Animal muscles
(3) Plant roots
(4) Both (2) and (3)

Explanation:
Lactic acid fermentation occurs in animal muscles during oxygen deficit and in some plant tissues like waterlogged roots. Yeast performs alcoholic fermentation. Hence, the correct answer is (4).

4. NAD+ is regenerated during lactic acid fermentation by:
(1) Reducing pyruvate to lactate
(2) Oxidizing glucose
(3) ATP hydrolysis
(4) Electron transport chain

Explanation:
Pyruvate acts as an electron acceptor, converting NADH back to NAD+ while forming lactate. This ensures glycolysis continues under anaerobic conditions. Hence, the correct answer is (1).

5. The ATP yield per glucose in lactic acid fermentation is approximately:
(1) 2 ATP
(2) 30 ATP
(3) 36 ATP
(4) 0 ATP

Explanation:
Lactic acid fermentation generates only 2 ATP molecules per glucose via glycolysis. Most energy remains in lactic acid. Hence, the correct answer is (1).

6. Which enzyme catalyzes the conversion of pyruvate to lactate?
(1) Lactate dehydrogenase
(2) Pyruvate kinase
(3) Hexokinase
(4) Phosphofructokinase

Explanation:
Lactate dehydrogenase reduces pyruvate to lactate using NADH, regenerating NAD+ required for glycolysis. Hence, the correct answer is (1).

7. Assertion-Reason Type:
Assertion (A): Lactic acid fermentation releases little energy.
Reason (R): Pyruvate is not fully oxidized to CO2 and water.
(1) Both A and R are correct, and R explains A
(2) Both A and R are correct, but R does not explain A
(3) A is false but R is true
(4) Both A and R are false

Explanation:
In lactic acid fermentation, pyruvate is partially reduced to lactate, not fully oxidized, resulting in low energy release (~7% of glucose). Hence, both A and R are correct, and R explains A. Correct answer is (1).

8. Matching Type:
Match the organism with fermentation type:
A. Muscle cells — 1. Alcoholic
B. Yeast — 2. Lactic acid
C. Bacteria (Lactobacillus) — 2. Lactic acid
D. Plant root — 2. Lactic acid
Options:
(1) A–2, B–1, C–2, D–2
(2) A–1, B–2, C–1, D–2
(3) A–2, B–2, C–1, D–1
(4) A–1, B–1, C–2, D–2

Explanation:
Muscle cells, Lactobacillus, and some plant roots perform lactic acid fermentation, while yeast undergoes alcoholic fermentation. Correct answer is (1).

9. Fill in the Blanks:
During anaerobic glycolysis, _______ is converted to lactate.
(1) Glucose
(2) Pyruvate
(3) NADH
(4) Acetyl CoA

Explanation:
Pyruvate, formed from glucose via glycolysis, is reduced to lactate in anaerobic conditions to regenerate NAD+. Hence, the correct answer is (2).

10. Choose the Correct Statements:
(a) Lactic acid fermentation is anaerobic.
(b) It produces 2 ATP per glucose.
(c) It converts pyruvate fully to CO2 and H2O.
(d) NAD+ is regenerated during the process.
Options:
(1) (a), (b), (d) only
(2) (a) and (c) only
(3) (b) and (c) only
(4) All statements are correct

Explanation:
Lactic acid fermentation is anaerobic, yields 2 ATP per glucose, and regenerates NAD+. Pyruvate is not fully oxidized. Hence, statements (a), (b), and (d) are correct. Correct answer is (1).

Topic: Aerobic Respiration
Subtopic: Pyruvate Dehydrogenase Complex (PDC)

Keyword Definitions:

• Pyruvate dehydrogenase complex (PDC): Multienzyme complex converting pyruvate into acetyl-CoA for Krebs cycle.

• Aerobic respiration: Energy-yielding process using oxygen to oxidize glucose into CO2, generating ATP.

• Calcium (Ca2+): Cofactor that activates pyruvate dehydrogenase by stimulating phosphatase activity.

• Iron (Fe): Component of cytochromes in electron transport chain, not direct PDC cofactor.

• Cobalt (Co): Component of vitamin B12, not directly required for PDC function.

• Magnesium (Mg2+): Cofactor stabilizing ATP and enzyme-substrate complexes in PDC reactions.

• Acetyl-CoA: Product of pyruvate decarboxylation entering Krebs cycle.

• NAD+ and FAD: Electron carriers accepting electrons during pyruvate oxidation.

• Thiamine pyrophosphate (TPP): Vitamin B1-derived coenzyme essential for PDC decarboxylation of pyruvate.

• Lipoamide: Coenzyme that transfers acyl groups in PDC.

• Aerobic energy metabolism: Oxidation of pyruvate in mitochondria to produce ATP efficiently.

Lead Question - 2020 (COVID Reexam)

Pyruvate dehydrogenase activity during aerobic respiration requires :-

1. Calcium
2. Iron
3. Cobalt
4. Magnesium

Explanation: Pyruvate dehydrogenase is activated by calcium ions, which stimulate the dephosphorylation of its E1 component. Magnesium stabilizes ATP and enzyme interactions but calcium is essential for PDC regulation during aerobic respiration. Correct answer is option 1: Calcium. This ensures efficient pyruvate conversion to acetyl-CoA. (50 words)

Guessed Question 1. Single Correct Answer MCQ: Which cofactor activates pyruvate dehydrogenase in mitochondria?

1. Calcium
2. Iron
3. Magnesium
4. Cobalt

Explanation: Calcium ions activate pyruvate dehydrogenase by promoting dephosphorylation of the E1 enzyme. This activation occurs during high-energy demand in aerobic respiration. Correct answer is option 1: Calcium. It regulates flux from pyruvate to acetyl-CoA in mitochondria. (50 words)

Guessed Question 2. Single Correct Answer MCQ: Magnesium in PDC primarily:

1. Accepts electrons
2. Stabilizes ATP and enzyme complexes
3. Releases CO2
4. Activates phosphatase

Explanation: Magnesium stabilizes ATP and enzyme-substrate interactions within PDC, aiding proper enzymatic function. It does not directly activate pyruvate dehydrogenase. Correct answer is option 2: Stabilizes ATP and enzyme complexes. Mg2+ supports the catalytic efficiency of the complex during aerobic respiration. (50 words)

Guessed Question 3. Single Correct Answer MCQ: Product of PDC is:

1. Pyruvate
2. Acetyl-CoA
3. Lactate
4. Oxaloacetate

Explanation: Pyruvate dehydrogenase converts pyruvate into acetyl-CoA, which enters the Krebs cycle for aerobic energy production. Correct answer is option 2: Acetyl-CoA. This step links glycolysis and aerobic respiration efficiently. (50 words)

Guessed Question 4. Single Correct Answer MCQ: Vitamin-derived cofactor in PDC is:

1. Thiamine pyrophosphate
2. NAD+
3. FAD
4. Coenzyme A

Explanation: Thiamine pyrophosphate (TPP), derived from vitamin B1, is essential for the decarboxylation of pyruvate in PDC. Correct answer is option 1: Thiamine pyrophosphate. It participates directly in catalysis, forming hydroxyethyl-TPP intermediate. (50 words)

Guessed Question 5. Assertion-Reason MCQ:

Assertion (A): Pyruvate dehydrogenase requires calcium for activation.
Reason (R): Calcium stimulates phosphatase that dephosphorylates E1 component of PDC.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: Calcium activates pyruvate dehydrogenase by stimulating the phosphatase that removes inhibitory phosphate from the E1 component. Both assertion and reason are true, and R correctly explains A. Correct answer is option 1. This regulation ensures efficient acetyl-CoA production in aerobic respiration. (50 words)

Guessed Question 6. Matching Type MCQ:

Column I - PDC Component
(a) E1 (i) Pyruvate decarboxylation
(b) E2 (ii) Lipoamide-mediated acyl transfer
(c) E3 (iii) FAD-mediated oxidation
(d) Coenzyme A (iv) Accepts acetyl group
Options:
1. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
2. (a)-(ii), (b)-(iii), (c)-(i), (d)-(iv)
3. (a)-(i), (b)-(iii), (c)-(ii), (d)-(iv)
4. (a)-(iii), (b)-(ii), (c)-(i), (d)-(iv)

Explanation: E1 catalyzes pyruvate decarboxylation, E2 transfers acetyl group via lipoamide, E3 oxidizes lipoamide with FAD, and CoA accepts acetyl group to form acetyl-CoA. Correct answer is option 1. This coordinated mechanism ensures efficient pyruvate oxidation in aerobic respiration. (50 words)

Guessed Question 7. Fill in the blank:

Activation of pyruvate dehydrogenase requires _______ ions.

1. Magnesium
2. Calcium
3. Iron
4. Zinc

Explanation: Calcium ions activate pyruvate dehydrogenase by stimulating phosphatase-mediated dephosphorylation of E1 component. Correct answer is option 2: Calcium. This regulation ensures efficient flux from pyruvate to acetyl-CoA during aerobic respiration. (50 words)

Guessed Question 8. Single Correct Answer MCQ: PDC is located in:

1. Cytoplasm
2. Mitochondrial matrix
3. Chloroplast stroma
4. Nucleus

Explanation: Pyruvate dehydrogenase complex is located in the mitochondrial matrix, where it converts pyruvate to acetyl-CoA for Krebs cycle. Correct answer is option 2: Mitochondrial matrix. Matrix localization allows direct integration with aerobic respiration and NADH/FADH2 production. (50 words)

Guessed Question 9. Single Correct Answer MCQ: Essential cofactor for acyl group transfer in PDC is:

1. Lipoamide
2. NAD+
3. FAD
4. Coenzyme Q

Explanation: Lipoamide acts as swinging arm transferring the acetyl group from E2 active site to CoA. Correct answer is option 1: Lipoamide. This is critical for the enzymatic mechanism of pyruvate dehydrogenase complex during aerobic respiration. (50 words)

Guessed Question 10. Choose the correct statements MCQ:

(a) PDC converts pyruvate to acetyl-CoA
(b) Calcium activates PDC
(c) CoA accepts acetyl group
(d) Iron directly activates PDC
Options:
1. a, b, c
2. a, c, d
3. b, c, d
4. a, b, d

Explanation: PDC converts pyruvate to acetyl-CoA, calcium activates PDC, and CoA accepts the acetyl group. Iron is not a direct activator. Correct answer is option 1: a, b, c. These components ensure efficient aerobic pyruvate oxidation. (50 words)

Topic: Citric Acid Cycle
Subtopic: Substrate Level Phosphorylation

Keyword Definitions:

• Citric Acid Cycle: A series of enzyme-catalyzed reactions in mitochondria that oxidize acetyl-CoA to CO₂ while producing NADH, FADH₂, and ATP/GTP.

• Substrate Level Phosphorylation: Direct synthesis of ATP (or GTP) from ADP (or GDP) using energy released in a chemical reaction.

• Oxidative Phosphorylation: ATP synthesis driven by electron transport and proton gradient in mitochondria.

• NADH: Reduced form of nicotinamide adenine dinucleotide, a carrier of electrons and hydrogen ions.

• FADH₂: Reduced form of flavin adenine dinucleotide, another electron carrier in respiration.

• Succinyl-CoA: An intermediate of the citric acid cycle that generates GTP/ATP via substrate level phosphorylation.

Lead Question - 2020

The number of substrate level phosphorylations in one turn of citric acid cycle is :

(1) Two
(2) Three
(3) Zero
(4) One

Explanation: In one turn of the citric acid cycle, only one substrate level phosphorylation occurs during the conversion of succinyl-CoA to succinate, generating GTP or ATP. All other ATP molecules are produced later via oxidative phosphorylation. Hence, the correct answer is option (4).

Guessed Questions:

1) How many NADH molecules are formed in one turn of citric acid cycle?
(1) Two
(2) Three
(3) Four
(4) One

Explanation: In one turn of the citric acid cycle, three NADH molecules are produced at the steps catalyzed by isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase. These are later used in oxidative phosphorylation to generate ATP. Hence, the correct answer is option (2).

2) Which intermediate links glycolysis to citric acid cycle?
(1) Pyruvate
(2) Acetyl-CoA
(3) Citrate
(4) Oxaloacetate

Explanation: Pyruvate from glycolysis is converted into acetyl-CoA by the pyruvate dehydrogenase complex before entering the citric acid cycle. Thus, acetyl-CoA serves as the connecting link between glycolysis and citric acid cycle. Hence, the correct answer is option (2).

3) Assertion (A): FADH₂ is produced in the citric acid cycle.
Reason (R): It is formed during the oxidation of succinate to fumarate.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation of A
(3) A is true, R is false
(4) A is false, R is true

Explanation: In the citric acid cycle, FADH₂ is formed when succinate is oxidized to fumarate by succinate dehydrogenase. Both A and R are true, and R correctly explains A. Hence, the correct answer is option (1).

4) Which enzyme catalyzes the substrate level phosphorylation in citric acid cycle?
(1) Succinyl-CoA synthetase
(2) Malate dehydrogenase
(3) Citrate synthase
(4) Aconitase

Explanation: Succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to succinate with the simultaneous synthesis of ATP or GTP through substrate level phosphorylation. Hence, the correct answer is option (1).

5) Match the products with the corresponding reactions in the citric acid cycle:
(a) Isocitrate dehydrogenase (i) FADH₂
(b) α-ketoglutarate dehydrogenase (ii) NADH
(c) Succinate dehydrogenase (iii) NADH
(d) Malate dehydrogenase (iv) NADH
(1) a-(ii), b-(iii), c-(i), d-(iv)
(2) a-(i), b-(ii), c-(iii), d-(iv)
(3) a-(ii), b-(iv), c-(iii), d-(i)
(4) a-(iii), b-(ii), c-(i), d-(iv)

Explanation: Isocitrate dehydrogenase produces NADH, α-ketoglutarate dehydrogenase produces NADH, succinate dehydrogenase produces FADH₂, and malate dehydrogenase produces NADH. Hence, the correct answer is option (1).

6) Fill in the blank: In one complete oxidation of acetyl-CoA in citric acid cycle, ______ ATP equivalents are formed.
(1) 10
(2) 12
(3) 6
(4) 8

Explanation: Complete oxidation of one acetyl-CoA yields 3 NADH (9 ATP), 1 FADH₂ (2 ATP), and 1 GTP (1 ATP), totaling 12 ATP equivalents. Hence, the correct answer is option (2).

7) Which of the following statements are correct?
(i) Citric acid cycle occurs in cytoplasm
(ii) One FADH₂ is produced per turn
(iii) Three NADH molecules are produced per turn
(1) i and ii only
(2) ii and iii only
(3) i and iii only
(4) i, ii and iii

Explanation: The citric acid cycle occurs in the mitochondrial matrix, not in cytoplasm. Each turn produces one FADH₂ and three NADH molecules. Hence, statements ii and iii are correct. The correct answer is option (2).

8) Which reaction produces CO₂ in citric acid cycle?
(1) Isocitrate to α-ketoglutarate
(2) Succinyl-CoA to succinate
(3) Malate to oxaloacetate
(4) Citrate to isocitrate

Explanation: The decarboxylation of isocitrate to α-ketoglutarate by isocitrate dehydrogenase releases CO₂. Another CO₂ is released in the conversion of α-ketoglutarate to succinyl-CoA. Hence, option (1) is correct.

9) How many ATP equivalents are formed by complete oxidation of one glucose via glycolysis, citric acid cycle, and oxidative phosphorylation?
(1) 30
(2) 36
(3) 38
(4) 40

Explanation: One glucose yields about 36-38 ATP depending on shuttle systems used for NADH transport. Classical calculation gives 38 ATP: 2 from glycolysis, 2 from citric acid cycle, and 34 from oxidative phosphorylation. Hence, the correct answer is option (3).

10) Which coenzyme is required for the conversion of α-ketoglutarate to succinyl-CoA?
(1) Biotin
(2) Thiamine pyrophosphate (TPP)
(3) Pyridoxal phosphate
(4) Coenzyme Q

Explanation: The α-ketoglutarate dehydrogenase complex requires thiamine pyrophosphate (TPP), lipoic acid, FAD, NAD⁺, and CoA as cofactors. TPP plays a central role in this reaction. Hence, the correct answer is option (2).

Subtopic: Glycolysis

Keyword Definitions:

• Glucose: A six-carbon monosaccharide that serves as primary energy source.

• Glucose-6-phosphate: Phosphorylated form of glucose formed during the first step of glycolysis.

• Glycolysis: Metabolic pathway that breaks down glucose to pyruvate, generating ATP.

• Hexokinase: Enzyme that catalyzes phosphorylation of glucose to glucose-6-phosphate.

• Aldolase: Enzyme in glycolysis that splits fructose-1,6-bisphosphate into two three-carbon molecules.

• Phosphofructokinase: Key regulatory enzyme of glycolysis catalyzing phosphorylation of fructose-6-phosphate.

• Enolase: Enzyme that converts 2-phosphoglycerate to phosphoenolpyruvate in glycolysis.

Lead Question (2019):

Conversion of glucose to glucose-6-phosphate, the first irreversible reaction of glycolysis, is catalyzed by:
(1) Aldolase
(2) Hexokinase
(3) Enolase
(4) Phosphofructokinase

Explanation: Correct answer is (2). Hexokinase catalyzes the phosphorylation of glucose to glucose-6-phosphate, the first irreversible step in glycolysis. This reaction traps glucose inside the cell and primes it for further breakdown, ensuring energy extraction and regulation of the glycolytic pathway efficiently.

1) Single Correct Answer MCQ:
Which enzyme catalyzes the formation of fructose-1,6-bisphosphate in glycolysis?
(1) Hexokinase
(2) Phosphofructokinase
(3) Aldolase
(4) Enolase

Explanation: Correct answer is (2). Phosphofructokinase catalyzes phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate, a key irreversible regulatory step in glycolysis controlling pathway flux.

2) Single Correct Answer MCQ:
Which enzyme splits fructose-1,6-bisphosphate into two three-carbon molecules?
(1) Aldolase
(2) Hexokinase
(3) Enolase
(4) Phosphofructokinase

Explanation: Correct answer is (1). Aldolase cleaves fructose-1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate during glycolysis, facilitating energy extraction from glucose.

3) Single Correct Answer MCQ:
Which glycolytic enzyme converts 2-phosphoglycerate to phosphoenolpyruvate?
(1) Aldolase
(2) Hexokinase
(3) Enolase
(4) Phosphofructokinase

Explanation: Correct answer is (3). Enolase catalyzes the dehydration of 2-phosphoglycerate to phosphoenolpyruvate, producing a high-energy intermediate necessary for ATP generation in glycolysis.

4) Single Correct Answer MCQ:
Hexokinase requires which cofactor for activity?
(1) NAD+
(2) ATP
(3) FAD
(4) GTP

Explanation: Correct answer is (2). Hexokinase uses ATP to phosphorylate glucose to glucose-6-phosphate. ATP provides the phosphate group, and this step is irreversible, committing glucose to metabolism within the cell.

5) Single Correct Answer MCQ:
Which step of glycolysis is irreversible?
(1) Glucose to glucose-6-phosphate
(2) Fructose-6-phosphate to fructose-1,6-bisphosphate
(3) Phosphoenolpyruvate to pyruvate
(4) All of the above

Explanation: Correct answer is (4). The irreversible steps of glycolysis are catalyzed by hexokinase, phosphofructokinase, and pyruvate kinase, ensuring directional flow and regulation of the pathway.

6) Single Correct Answer MCQ:
The main purpose of glucose phosphorylation in glycolysis is:
(1) ATP production
(2) Trapping glucose inside cell
(3) Reducing NAD+
(4) Forming pyruvate directly

Explanation: Correct answer is (2). Phosphorylation of glucose to glucose-6-phosphate prevents it from diffusing out of the cell and prepares it for further metabolism in glycolysis.

7) Assertion-Reason MCQ:
Assertion (A): Hexokinase catalyzes the first step of glycolysis.
Reason (R): Hexokinase generates glucose-6-phosphate from glucose using ATP.
Options:
(1) A true, R true, R correct explanation
(2) A true, R true, R not correct explanation
(3) A true, R false
(4) A false, R true

Explanation: Correct answer is (1). The assertion is true; hexokinase catalyzes the first irreversible step. The reason is also correct, describing ATP-dependent formation of glucose-6-phosphate.

8) Matching Type MCQ:
Match the enzyme with its glycolytic function:
(a) Hexokinase - (i) Splits fructose-1,6-bisphosphate
(b) Aldolase - (ii) Phosphorylates glucose
(c) Phosphofructokinase - (iii) Phosphorylates fructose-6-phosphate
(d) Enolase - (iv) Converts 2-phosphoglycerate to phosphoenolpyruvate
Options:
(1) a-ii, b-i, c-iii, d-iv
(2) a-i, b-ii, c-iii, d-iv
(3) a-iii, b-i, c-ii, d-iv
(4) a-ii, b-iii, c-i, d-iv

Explanation: Correct answer is (1). Hexokinase phosphorylates glucose, aldolase cleaves fructose-1,6-bisphosphate, phosphofructokinase phosphorylates fructose-6-phosphate, and enolase dehydrates 2-phosphoglycerate to phosphoenolpyruvate.

9) Fill in the Blanks MCQ:
The first irreversible step of glycolysis is catalyzed by ________.
(1) Hexokinase
(2) Phosphofructokinase
(3) Aldolase
(4) Enolase

Explanation: Correct answer is (1). Hexokinase catalyzes phosphorylation of glucose to glucose-6-phosphate, the first irreversible step in glycolysis ensuring glucose is committed to metabolism.

10) Choose the correct statements MCQ:
(1) Hexokinase catalyzes first glycolytic step
(2) Aldolase splits fructose-1,6-bisphosphate
(3) Enolase forms phosphoenolpyruvate
(4) Phosphofructokinase phosphorylates glucose</

Subtopic: Respiratory Quotient

Keyword Definitions:

• Respiratory Quotient (RQ): Ratio of CO₂ produced to O₂ consumed during respiration.

• Tripalmitin: A triglyceride consisting of three palmitic acid molecules, a lipid.

• Carbohydrate RQ: Typically 1, as equal O₂ is consumed and CO₂ released.

• Lipid RQ: Usually 0.7, less CO₂ produced per O₂ consumed due to high H content.

• Protein RQ: Approximately 0.8, intermediate between carbohydrate and lipid values.

Lead Question (September 2019):

Respiratory Quotient (RQ) value of tripalmitin is:
(1) 0.9
(2) 0.7
(3) 0.07
(4) 0.09

Explanation: The correct answer is (2) 0.7. Tripalmitin is a lipid, and the RQ of lipids is typically 0.7, indicating less CO₂ produced per unit O₂ consumed. NEET UG tests understanding of RQ values for carbohydrates, fats, and proteins, which helps determine the type of substrate utilized in respiration.

1) RQ of carbohydrate is:
(1) 1
(2) 0.7
(3) 0.8
(4) 0.9

Explanation: The correct answer is (1) 1. Carbohydrates produce equal CO₂ per O₂ consumed. NEET UG tests recognition of RQ values to identify the type of nutrient metabolized during respiration.

2) Protein RQ is approximately:
(1) 0.7
(2) 0.8
(3) 1
(4) 0.9

Explanation: The correct answer is (2) 0.8. Proteins yield intermediate CO₂ per O₂ consumed. NEET UG emphasizes the distinction of RQ values among macronutrients for metabolism questions.

3) High RQ (>1) indicates:
(1) Lipid metabolism
(2) Protein metabolism
(3) Excess carbohydrate metabolism
(4) Starvation

Explanation: The correct answer is (3) Excess carbohydrate metabolism. When carbohydrates are metabolized in surplus, RQ can exceed 1. NEET UG often tests interpretation of RQ in physiological and clinical contexts.

4) RQ indicates:
(1) Oxygen consumption only
(2) Carbon dioxide production only
(3) Ratio of CO₂ produced to O₂ consumed
(4) Energy expenditure

Explanation: The correct answer is (3). RQ = CO₂ produced / O₂ consumed. NEET UG tests students’ ability to calculate or interpret respiratory quotient to determine substrate utilization.

5) Tripalmitin is classified as:
(1) Carbohydrate
(2) Protein
(3) Lipid
(4) Nucleic acid

Explanation: The correct answer is (3) Lipid. Tripalmitin is a triglyceride composed of palmitic acid molecules. NEET UG tests chemical classification and its link to RQ values.

6) RQ value is used to determine:
(1) Type of substrate oxidized
(2) Respiratory rate
(3) Blood oxygen levels
(4) ATP production rate

Explanation: The correct answer is (1) Type of substrate oxidized. RQ varies with carbohydrates, fats, and proteins, allowing assessment of which nutrient is metabolized. NEET UG often uses RQ to interpret energy source during metabolism.

7) Assertion-Reason Type:
Assertion (A): Lipid metabolism has RQ = 0.7.
Reason (R): Lipids produce less CO₂ per O₂ consumed due to high hydrogen content.
(1) A true, R true, R correct explanation
(2) A true, R true, R not explanation
(3) A true, R false
(4) A false, R true

Explanation: The correct answer is (1). Lipids, such as tripalmitin, have RQ = 0.7 because their oxidation consumes more oxygen relative to CO₂ released, due to high hydrogen content. NEET UG tests understanding of chemical basis of RQ.

8) Matching Type:
Match substrate with approximate RQ:
(a) Carbohydrate - (i) 0.7
(b) Lipid - (ii) 1
(c) Protein - (iii) 0.8
Options:
(1) a-ii, b-i, c-iii
(2) a-i, b-ii, c-iii
(3) a-iii, b-i, c-ii
(4) a-i, b-iii, c-ii

Explanation: The correct answer is (1). Carbohydrate – 1, Lipid – 0.7, Protein – 0.8. NEET UG often tests students’ ability to correlate substrate type with RQ for energy metabolism analysis.

9) Fill in the Blanks:
The RQ value of tripalmitin, a lipid, is ______.
(1) 0.7
(2) 0.8
(3) 1
(4) 0.9

Explanation: The correct answer is (1) 0.7. Tripalmitin is a triglyceride; oxidation produces less CO₂ per O₂ consumed, giving an RQ of 0.7. NEET UG questions often require students to calculate or recall RQ values for different macronutrients.

10) Choose the correct statements:
(1) Carbohydrate RQ = 1
(2) Lipid RQ = 0.7
(3) Protein RQ = 0.8
(4) Tripalmitin RQ = 0.09
Options:
(1) 1, 2, 3
(2) 2 and 4
(3) 1 and 4
(4) All of the above

Explanation: The correct answer is (1) 1, 2, 3. RQ values correctly reflect substrate metabolism: carbohydrate 1, lipid 0.7, protein 0.8. Tripalmitin has RQ = 0.7, not 0.09. NEET UG tests interpretation of RQ in metabolic studies.

Topic: Stomata Types

Subtopic: Grass Leaf Stomata

Keyword Definitions:

• Stomata: Pores in the epidermis of leaves and stems for gas exchange.

• Grass leaf: Monocot leaf with parallel venation, often having specialized stomata.

• Dumb-bell shaped stomata: Stomata with elongated guard cells and central pore, typical of grasses.

• Barrel shaped stomata: Common in dicots, kidney-shaped guard cells.

• Gas exchange: Process of CO2 uptake and O2 release during photosynthesis.

• Guard cells: Cells surrounding stomatal pore controlling opening and closing.

Lead Question (2018):

Stomata in grass leaf are:

(A) Barrel shaped

(B) Dumb-bell shaped

(C) Rectangular

(D) Kidney shaped

Explanation:

The correct answer is (B) Dumb-bell shaped. Grass, being a monocot, has dumb-bell shaped stomata with narrow ends and central pore, which allow efficient opening and closing. Barrel or kidney-shaped stomata are typically found in dicots. This structure helps in water conservation and gas exchange in grasses.

1. The main function of stomata is:

(A) Photosynthesis

(B) Gas exchange

(C) Transport of water

(D) Nutrient absorption

Explanation:

The correct answer is (B) Gas exchange. Stomata allow CO2 uptake for photosynthesis and O2 release. While stomata influence transpiration and water balance, their primary function is gas exchange, not nutrient absorption or direct photosynthesis.

2. Guard cells of grass stomata contain:

(A) Chloroplasts

(B) No chloroplasts

(C) Only mitochondria

(D) Only vacuoles

Explanation:

The correct answer is (A) Chloroplasts. Guard cells in grass have chloroplasts that help in sensing light and producing ATP for stomatal opening. They are metabolically active and contribute to opening and closing mechanisms.

3. Monocot stomata differ from dicot stomata in being:

(A) Kidney-shaped

(B) Dumb-bell shaped

(C) Circular

(D) Irregular

Explanation:

The correct answer is (B) Dumb-bell shaped. Monocots like grasses have dumb-bell shaped stomata for efficient opening. Dicots usually have kidney or barrel-shaped stomata. This adaptation helps monocots conserve water and respond rapidly to environmental changes.

4. Stomatal opening is regulated by:

(A) Light and potassium ions

(B) CO2 only

(C) Temperature only

(D) Oxygen only

Explanation:

The correct answer is (A) Light and potassium ions. Light triggers photosynthesis in guard cells, leading to K+ ion accumulation, osmotic water influx, and stomatal opening. CO2, temperature, and humidity also influence stomata, but K+ ions and light are primary regulators.

5. In which plant type are dumb-bell shaped stomata common?

(A) Dicots

(B) Monocots

(C) Gymnosperms

(D) Ferns

Explanation:

The correct answer is (B) Monocots. Dumb-bell shaped stomata are characteristic of monocot leaves such as grasses, aiding in rapid opening and closing. Dicots and gymnosperms have kidney or barrel-shaped stomata.

6. Stomatal density is generally higher on:

(A) Upper epidermis

(B) Lower epidermis

(C) Both equally

(D) Stem only

Explanation:

The correct answer is (B) Lower epidermis. Most leaves have higher stomatal density on the lower epidermis to minimize water loss while allowing gas exchange. Upper epidermis may have fewer stomata or none.

7. Assertion-Reason Question:

Assertion (A): Grass stomata are dumb-bell shaped.

Reason (R): This shape allows efficient opening and closing.

(A) Both A and R true, R explains A

(B) Both A and R true, R does not explain A

(C) A true, R false

(D) A false, R true

Explanation:

Correct answer is (A). The dumb-bell shape of guard cells in grasses enables rapid and efficient opening and closing of stomata, conserving water while ensuring adequate gas exchange. Both assertion and reason are true, with the reason explaining the assertion.

8. Matching Type Question:

Match stomatal types with plant examples:

(i) Dumb-bell shaped – (a) Grass

(ii) Kidney-shaped – (b) Sunflower

(iii) Barrel-shaped – (c) Bean

(iv) Circular – (d) Some algae

(A) i-a, ii-b, iii-c, iv-d

(B) i-b, ii-a, iii-d, iv-c

(C) i-c, ii-d, iii-b, iv-a

(D) i-d, ii-c, iii-a, iv-b

Explanation:

Correct answer is (A). Dumb-bell shaped stomata occur in grasses, kidney-shaped in sunflower, barrel-shaped in beans, and circular in some algae. Matching highlights structural diversity in stomata across plant groups.

9. Fill in the Blanks:

Stomata in monocots like grass are ______ and help in ______.

(A) Barrel-shaped, photosynthesis

(B) Dumb-bell shaped, efficient gas exchange

(C) Kidney-shaped, water storage

(D) Rectangular, transpiration only

Explanation:

Correct answer is (B) Dumb-bell shaped, efficient gas exchange. Grass stomata are dumb-bell shaped, allowing rapid opening and closing for gas exchange and water conservation. Barrel-shaped and kidney-shaped stomata are common in dicots.

10. Choose the correct statements:

(A) Grass stomata are dumb-bell shaped

(B) Stomata allow gas exchange

(C) Guard cells contain chloroplasts

(D) Monocots have kidney-shaped stomata

Options:

(1) A, B, C

(2) A, C, D

(3) B, C, D

(4) A, B, D

Explanation:

Correct answer is (1) A, B, C. Grass stomata are dumb-bell shaped, facilitate gas exchange, and guard cells contain chloroplasts. Monocots do not have kidney-shaped stomata, which are typical of dicots.

Topic: Electron Transport and Redox Reactions

Subtopic: Role of NAD+ in Energy Metabolism

Keyword Definitions:

• NAD+: Nicotinamide adenine dinucleotide, a coenzyme that functions as an electron carrier in redox reactions.

• Cellular respiration: Metabolic process converting glucose into ATP with the help of oxygen and electron carriers.

• Electron carrier: Molecule that transfers electrons between biochemical reactions in metabolism.

• Anaerobic respiration: Energy-producing process occurring without oxygen, using alternative electron acceptors.

• ATP synthesis: Production of adenosine triphosphate, the cellular energy currency, through substrate-level or oxidative phosphorylation.

Lead Question (2018):

What is the role of NAD+ in cellular respiration?

(A) It is the final electron acceptor for anaerobic respiration

(B) It functions as an enzyme

(C) It is a nucleotide source for ATP synthesis

(D) It functions as an electron carrier

Explanation:

The correct answer is (D) It functions as an electron carrier. NAD+ accepts electrons and hydrogen ions during glycolysis and the Krebs cycle, forming NADH. It transports these electrons to the electron transport chain, facilitating ATP production. It does not act as an enzyme, nucleotide source, or final electron acceptor in anaerobic respiration.

1. During glycolysis, NAD+ is reduced to:

(A) NADH

(B) FADH2

(C) ATP

(D) ADP

Explanation:

The correct answer is (A) NADH. NAD+ accepts electrons and hydrogen ions from glucose intermediates to form NADH. NADH later donates electrons to the electron transport chain to generate ATP. FADH2, ATP, or ADP are not formed directly from NAD+ in glycolysis.

2. In aerobic respiration, NADH transfers electrons to:

(A) Oxygen directly

(B) Electron transport chain

(C) Pyruvate

(D) Glucose

Explanation:

The correct answer is (B) Electron transport chain. NADH carries electrons from glycolysis and Krebs cycle to the mitochondrial electron transport chain, where they ultimately reduce oxygen to water. This electron transfer drives ATP synthesis. NADH does not transfer electrons directly to pyruvate or glucose.

3. Which process regenerates NAD+ under anaerobic conditions?

(A) Glycolysis

(B) Fermentation

(C) Krebs cycle

(D) Electron transport chain

Explanation:

The correct answer is (B) Fermentation. Fermentation regenerates NAD+ by oxidizing NADH while converting pyruvate to lactate or ethanol, allowing glycolysis to continue. In aerobic respiration, NAD+ is regenerated in the electron transport chain, but under anaerobic conditions, fermentation is essential for NAD+ availability.

4. NAD+ is classified as a:

(A) Coenzyme

(B) Enzyme

(C) Substrate

(D) Hormone

Explanation:

The correct answer is (A) Coenzyme. NAD+ is a non-protein coenzyme that assists enzymes in redox reactions by accepting and donating electrons. It is not an enzyme, substrate, or hormone, but a crucial electron carrier in energy metabolism.

5. NADH contributes to ATP production by:

(A) Directly forming ATP

(B) Donating electrons to electron transport chain

(C) Acting as a substrate for glycolysis

(D) Binding oxygen

Explanation:

The correct answer is (B) Donating electrons to electron transport chain. NADH transfers electrons to complexes in the mitochondrial electron transport chain, generating a proton gradient that drives ATP synthesis via oxidative phosphorylation. NADH does not directly form ATP, act as glycolysis substrate, or bind oxygen.

6. Which vitamin is a precursor of NAD+?

(A) Niacin (Vitamin B3)

(B) Riboflavin (Vitamin B2)

(C) Thiamine (Vitamin B1)

(D) Pantothenic acid (Vitamin B5)

Explanation:

The correct answer is (A) Niacin (Vitamin B3). Niacin is converted into NAD+ and NADP+, essential electron carriers in cellular respiration. Riboflavin forms FAD/FMN, thiamine forms TPP, and pantothenic acid forms CoA, but only niacin is the precursor for NAD+.

7. Assertion-Reason Question:

Assertion (A): NAD+ is essential for glycolysis and Krebs cycle.

Reason (R): NAD+ accepts electrons and is reduced to NADH.

(A) Both A and R true, R explains A

(B) Both A and R true, R does not explain A

(C) A true, R false

(D) A false, R true

Explanation:

Correct answer is (A). NAD+ is required in glycolysis and Krebs cycle to accept electrons, forming NADH. This reduction is essential for continued metabolic flux and ATP generation. Both assertion and reason are true, and the reason correctly explains the assertion.

8. Matching Type Question:

Match the molecule with its function:

(i) NAD+ – (a) Electron carrier

(ii) FAD – (b) Electron carrier

(iii) ADP – (c) Substrate for ATP formation

(iv) Oxygen – (d) Final electron acceptor

(A) i-a, ii-b, iii-c, iv-d

(B) i-b, ii-a, iii-d, iv-c

(C) i-c, ii-d, iii-a, iv-b

(D) i-a, ii-d, iii-b, iv-c

Explanation:

Correct answer is (A). NAD+ and FAD function as electron carriers, ADP serves as substrate for ATP synthesis, and oxygen is the final electron acceptor in the electron transport chain. Matching reinforces understanding of roles of molecules in cellular respiration.

9. Fill in the Blanks:

NAD+ functions as a ______ by accepting electrons and forming ______.

(A) Enzyme, NADH

(B) Electron carrier, NADH

(C) Nucleotide source, ATP

(D) Oxygen carrier, NADH

Explanation:

Correct answer is (B) Electron carrier, NADH. NAD+ accepts electrons and hydrogen ions, forming NADH, which transports electrons to the electron transport chain, facilitating ATP production. It is not an enzyme, nucleotide source, or oxygen carrier.

10. Choose the correct statements:

(A) NAD+ is reduced to NADH during glycolysis and Krebs cycle

(B) NAD+ acts as a coenzyme

(C) NADH donates electrons to electron transport chain

(D) NAD+ directly forms ATP

Options:

(1) A, B, C

(2) A, B, D

(3) B, C, D

(4) A, C, D

Explanation:

Correct answer is (1) A, B, C. NAD+ is reduced to NADH, acts as coenzyme, and NADH donates electrons to electron transport chain for ATP synthesis. NAD+ does not directly produce ATP. Understanding NAD+ role is essential for NEET UG questions on cellular respiration.

Subtopic: Glycolysis and Mitochondrial Function

Keyword Definitions:

• Oxidative phosphorylation: Process in mitochondria generating ATP using electron transport chain and chemiosmosis.

• Mitochondrial matrix: Innermost compartment of mitochondria containing enzymes for TCA cycle.

• Glycolysis: Cytosolic pathway that converts glucose into pyruvate with net ATP production.

• NAD: Nicotinamide adenine dinucleotide, electron carrier involved in redox reactions.

• TCA cycle: Tricarboxylic acid cycle, central pathway of aerobic respiration producing energy intermediates.

• Cytosol: Fluid portion of cytoplasm where glycolysis and other metabolic reactions occur.

Lead Question - 2018

Which of these statements is incorrect :

(A) Oxidative phosphorylation takes place in outer mitochondrial membrane

(B) Enzymes of TCA cycle are present in mitochondrial matrix

(C) Glycolysis operates as long as it is supplied with NAD that can pick up hydrogen atoms

(D) Glycolysis occurs in cytosol

Explanation:

Answer is (A). Oxidative phosphorylation occurs on the inner mitochondrial membrane, not the outer membrane. This membrane contains electron transport chain complexes and ATP synthase, facilitating proton gradient-driven ATP synthesis. TCA enzymes reside in the matrix, and glycolysis functions in the cytosol, dependent on NAD availability for hydrogen acceptance.

Guessed Questions for NEET UG:

1) Single Correct: Site of TCA cycle enzymes:

(A) Cytosol

(B) Mitochondrial matrix

(C) Inner mitochondrial membrane

(D) Outer mitochondrial membrane

Explanation:

Answer is (B). TCA cycle enzymes are located in the mitochondrial matrix, where acetyl-CoA oxidation produces NADH, FADH2, and GTP for energy metabolism.

2) Single Correct: Electron transport chain is embedded in:

(A) Cytosol

(B) Inner mitochondrial membrane

(C) Outer mitochondrial membrane

(D) Mitochondrial matrix

Explanation:

Answer is (B). The inner mitochondrial membrane houses the electron transport chain, creating a proton gradient for ATP synthesis during oxidative phosphorylation.

3) Single Correct: Glycolysis produces ATP in:

(A) Mitochondrial matrix

(B) Cytosol

(C) Golgi apparatus

(D) Endoplasmic reticulum

Explanation:

Answer is (B). Glycolysis occurs in cytosol, breaking glucose into pyruvate and producing a net of 2 ATP and 2 NADH per glucose molecule.

4) Assertion-Reason:

Assertion: NAD is essential for glycolysis.

Reason: It accepts electrons from glucose intermediates to maintain pathway flux.

(A) Both true, Reason correct

(B) Both true, Reason incorrect

(C) Assertion true, Reason false

(D) Both false

Explanation:

Answer is (A). NAD acts as an electron acceptor in glycolysis. Without NAD, glycolytic intermediates cannot be oxidized, halting ATP production.

5) Single Correct: Main purpose of oxidative phosphorylation:

(A) Produce pyruvate

(B) Generate ATP

(C) Reduce NAD

(D) Oxidize glucose in cytosol

Explanation:

Answer is (B). Oxidative phosphorylation generates ATP by utilizing the proton gradient formed by electron transport through inner mitochondrial membrane complexes.

6) Single Correct: NADH donates electrons to:

(A) TCA cycle enzymes

(B) Glycolytic enzymes

(C) Electron transport chain

(D) ATP synthase

Explanation:

Answer is (C). NADH produced in glycolysis and TCA cycle donates electrons to the electron transport chain, driving proton pumping and ATP synthesis.

7) Matching Type:

Column I | Column II

a. Glycolysis | i. Cytosol

b. TCA cycle | ii. Mitochondrial matrix

c. Oxidative phosphorylation | iii. Inner mitochondrial membrane

(A) a-i, b-ii, c-iii

(B) a-ii, b-i, c-iii

(C) a-iii, b-ii, c-i

(D) a-i, b-iii, c-ii

Explanation:

Answer is (A). Glycolysis occurs in cytosol, TCA in matrix, and oxidative phosphorylation on inner membrane of mitochondria.

8) Fill in the Blank:

Glycolysis can continue as long as sufficient ______ is available to accept electrons.

(A) FAD

(B) ATP

(C) NAD

(D) Oxygen

Explanation:

Answer is (C). NAD acts as an electron acceptor in glycolysis, regenerating NAD+ is critical for maintaining continuous ATP production.

9) Choose the correct statements:

(i) Oxidative phosphorylation occurs in inner mitochondrial membrane.

(ii) TCA enzymes are in cytosol.

(iii) Glycolysis is cytosolic and NAD-dependent.

(A) i and iii only

(B) i and ii only

(C) ii and iii only

(D) i, ii, iii

Explanation:

Answer is (A). Oxidative phosphorylation occurs on inner membrane (i), glycolysis is cytosolic and requires NAD (iii). TCA enzymes are in mitochondrial matrix, not cytosol.

10) Clinical-type: In mitochondrial disorders affecting inner membrane, which process is directly impaired?

(A) Glycolysis

(B) TCA cycle

(C) Oxidative phosphorylation

(D) Gluconeogenesis

Explanation:

Answer is (C). Inner membrane defects impair electron transport chain and ATP production, reducing oxidative phosphorylation efficiency, while glycolysis in cytosol remains functional.

Chapter: Cellular Respiration

Topic: Krebs Cycle / Citric Acid Cycle

Subtopic: Steps and Energy Yield of Krebs Cycle

Keyword Definitions:

• Krebs Cycle – Series of chemical reactions generating energy via oxidation of acetyl-CoA.

• Acetyl-CoA – Two-carbon molecule entering Krebs cycle from pyruvate decarboxylation.

• Citric Acid – Six-carbon compound formed in first step of Krebs cycle.

• NAD+ – Nicotinamide adenine dinucleotide, electron carrier reduced to NADH.

• FAD – Flavin adenine dinucleotide, electron carrier reduced to FADH2.

• GTP – Guanosine triphosphate, energy-carrying molecule similar to ATP.

• Succinyl CoA – Four-carbon intermediate in Krebs cycle.

• Succinic Acid – Four-carbon molecule formed from succinyl CoA.

• Oxidative Phosphorylation – ATP synthesis using electron transport chain and chemiosmosis.

• Pyruvic Acid – End product of glycolysis converted into acetyl-CoA.

Lead Question – 2017:

Which statement is wrong for Krebs’ cycle ?

(A) The cycle starts with condensation of acetyl group (acetylCoA) with pyruvic acid to yield citric acid

(B) There are three points in the cycle where NAD+ is reduced to NADH + H+

(C) There is one point in the cycle where FAD+ is reduced to FADH2

(D) During conversion of succinyl CoA to succinic acid, a molecule of GTP is synthesised

Explanation:

Statement (A) is incorrect. The cycle begins with condensation of acetyl-CoA with oxaloacetate to form citric acid, not pyruvic acid. Three NAD+ reductions, one FAD reduction, and GTP formation during succinyl-CoA conversion are correct. This ensures energy capture from the acetyl group oxidation. (Answer: A)

1) Single Correct Answer MCQ:

Which molecule condenses with acetyl-CoA to start Krebs cycle?

(A) Pyruvate

(B) Oxaloacetate

(C) Citrate

(D) Succinyl CoA

Explanation:

Krebs cycle begins with acetyl-CoA condensing with oxaloacetate to form citrate (citric acid). Pyruvate is first converted to acetyl-CoA, succinyl CoA is a later intermediate, and citrate is the product. (Answer: B)

2) Single Correct Answer MCQ:

How many NADH molecules are produced per acetyl-CoA in Krebs cycle?

(A) 1

(B) 2

(C) 3

(D) 4

Explanation:

Each acetyl-CoA oxidation produces three NADH molecules at different steps: isocitrate → α-ketoglutarate, α-ketoglutarate → succinyl-CoA, malate → oxaloacetate. NADH feeds electrons into the electron transport chain for ATP generation. (Answer: C)

3) Single Correct Answer MCQ:

Which intermediate produces GTP in Krebs cycle?

(A) Citrate

(B) α-Ketoglutarate

(C) Succinyl-CoA

(D) Fumarate

Explanation:

Conversion of succinyl-CoA to succinate produces one molecule of GTP via substrate-level phosphorylation. Citrate, α-ketoglutarate, and fumarate do not directly produce GTP. (Answer: C)

4) Single Correct Answer MCQ:

Which electron carrier is reduced to FADH2 in Krebs cycle?

(A) NAD+

(B) FAD

(C) Coenzyme A

(D) ADP

Explanation:

FAD is reduced to FADH2 during succinate → fumarate conversion. NAD+ is reduced to NADH at other steps. Coenzyme A and ADP are not electron carriers. FADH2 contributes electrons to the electron transport chain. (Answer: B)

5) Single Correct Answer MCQ:

During Krebs cycle, how many CO2 molecules are released per acetyl-CoA?

(A) 1

(B) 2

(C) 3

(D) 4

Explanation:

Each acetyl-CoA generates two CO2 molecules during oxidative decarboxylation: isocitrate → α-ketoglutarate and α-ketoglutarate → succinyl-CoA. These CO2 molecules represent complete carbon oxidation of acetyl group. (Answer: B)

6) Single Correct Answer MCQ:

Krebs cycle occurs in:

(A) Cytoplasm

(B) Mitochondrial matrix

(C) Golgi apparatus

(D) Endoplasmic reticulum

Explanation:

Krebs cycle enzymes are located in the mitochondrial matrix, enabling acetyl-CoA oxidation and NADH/FADH2 generation for oxidative phosphorylation. Cytoplasm hosts glycolysis; Golgi and ER are not involved in Krebs cycle. (Answer: B)

7) Assertion-Reason MCQ:

Assertion (A): GTP is synthesized in Krebs cycle.

Reason (R): Conversion of succinyl-CoA to succinate generates GTP via substrate-level phosphorylation.

(A) Both A and R true, R correct explanation

(B) Both A and R true, R not correct explanation

(C) A true, R false

(D) A false, R true

Explanation:

Both statements are correct. During succinyl-CoA → succinate, GTP is produced via substrate-level phosphorylation. This is the only step in Krebs cycle generating GTP directly. (Answer: A)

8) Matching Type MCQ:

Match step with product:

1. Isocitrate → α-Ketoglutarate – (i) CO2 + NADH

2. α-Ketoglutarate → Succinyl-CoA – (ii) CO2 + NADH

3. Succinate → Fumarate – (iii) FADH2

4. Succinyl-CoA → Succinate – (iv) GTP

Options:

(A) 1-i, 2-ii, 3-iii, 4-iv

(B) 1-ii, 2-i, 3-iv, 4-iii

(C) 1-i, 2-iii, 3-ii, 4-iv

(D) 1-iv, 2-iii, 3-i, 4-ii

Explanation:

Correct matching reflects biochemical events: NADH is formed at steps 1 & 2, FADH2 at succinate → fumarate, and GTP at succinyl-CoA → succinate. (Answer: A)

9) Fill in the Blanks MCQ:

During conversion of α-ketoglutarate to succinyl-CoA, ________ is released.

(A) CO2

(B) GTP

(C) FADH2

(D) Citrate

Explanation:

Oxidative decarboxylation of α-ketoglutarate releases CO2 and reduces NAD+ to NADH, forming succinyl-CoA. This is one of two CO2-generating steps in Krebs cycle. (Answer: A)

10) Choose the correct statements MCQ:

1. Three NADH and one FADH2 are produced per acetyl-CoA.

2. Two CO2 molecules are released per acetyl-CoA.

3. GTP is produced from succinyl-CoA.

4. Acetyl-CoA condenses with pyruvate to form citrate.

Options:

(A) 1, 2, 3

(B) 1, 2, 4

(C) 2, 3, 4

(D) 1, 3, 4

Explanation:

Statements 1, 2, 3 are correct. Statement 4 is wrong because acetyl-CoA condenses with oxaloacetate, not pyruvate. This clarifies the sequence and energy yield of Krebs cycle. (Answer: A)

Topic: Stomatal Physiology

Subtopic: Mechanism of Stomatal Opening

Keyword Definitions:

• Stomata – Small pores on leaf surface for gas exchange.

• Guard cells – Specialized cells surrounding stomatal pore, controlling its opening and closing.

• Turgidity – Pressure of water inside cells, causing swelling.

• Cellulose microfibrils – Structural components of cell wall influencing shape and flexibility.

• Aperture – The opening of the stomatal pore.

• Longitudinal orientation – Arrangement of microfibrils along the length of guard cells.

• Radial orientation – Microfibrils arranged perpendicular to guard cell length.

• Osmosis – Movement of water into guard cells affecting turgor pressure.

• Potassium ions – Ions involved in guard cell turgor regulation.

• Clinical relevance – Stomatal regulation affects plant water use, drought resistance.

Lead Question – 2017:

Which of the following facilitates opening of stomatal aperture?

(A) Longitudinal orientation of cellulose microfibrils in the cell wall of guard cells

(B) Contraction of outer wall of guard cells

(C) Decrease in turgidity of guard cells

(D) Radial orientation of cellulose microfibrils in the cell wall of guard cells

Explanation:

Stomatal opening occurs due to radial orientation of cellulose microfibrils in guard cells, allowing the cells to bow out when turgid. Water influx increases turgor pressure, causing radial expansion and opening the pore. Longitudinal microfibrils or decreased turgidity would not facilitate opening. (Answer: D)

1) Single Correct Answer MCQ:

Which ion accumulation triggers stomatal opening?

(A) Sodium

(B) Potassium

(C) Calcium

(D) Magnesium

Explanation:

Accumulation of potassium ions in guard cells lowers water potential, leading to water influx and increased turgor pressure, opening stomata. Sodium or calcium play secondary roles, but potassium is the primary driver for guard cell swelling. (Answer: B)

2) Single Correct Answer MCQ:

Stomatal closure is induced by:

(A) Light

(B) High CO2

(C) Potassium influx

(D) Radial microfibrils

Explanation:

Stomata close in response to high CO2 concentration or water stress. Loss of potassium from guard cells reduces turgor pressure, closing the pore. Light and radial microfibrils facilitate opening, not closure. (Answer: B)

3) Single Correct Answer MCQ:

Which hormone promotes stomatal closure?

(A) Auxin

(B) Abscisic acid

(C) Gibberellin

(D) Cytokinin

Explanation:

Abscisic acid (ABA) signals guard cells during drought, causing potassium efflux, reduced turgor, and stomatal closure. Auxins, gibberellins, and cytokinins generally promote growth, not closure. ABA is key for plant water conservation under stress. (Answer: B)

4) Single Correct Answer MCQ:

The swelling of guard cells is due to:

(A) Osmosis of water

(B) Photosynthesis

(C) Cell division

(D) Evaporation

Explanation:

Osmosis of water into guard cells increases turgor pressure, causing swelling and stomatal opening. Photosynthesis or cell division does not directly cause swelling, and evaporation reduces turgor rather than increasing it. (Answer: A)

5) Single Correct Answer MCQ:

Which cell wall feature allows bowing of guard cells?

(A) Radial microfibrils

(B) Longitudinal microfibrils

(C) Lignin deposits

(D) Pectin accumulation

Explanation:

Radial microfibrils permit guard cells to bow outward when turgid, widening the stomatal pore. Longitudinal microfibrils restrict bowing. Lignin or pectin provide rigidity but do not facilitate the dynamic opening mechanism. (Answer: A)

6) Single Correct Answer MCQ:

Which environmental factor increases stomatal opening?

(A) Darkness

(B) Light

(C) High CO2

(D) Drought

Explanation:

Light stimulates stomatal opening by activating proton pumps and potassium uptake, increasing turgor in guard cells. Darkness or drought induces closure, while high CO2 can signal partial closure. (Answer: B)

7) Assertion-Reason MCQ:

Assertion (A): Guard cells open when turgor increases.

Reason (R): Radial microfibrils in cell walls facilitate expansion.

(A) Both A and R true, R correct explanation

(B) Both A and R true, R not correct explanation

(C) A true, R false

(D) A false, R true

Explanation:

Both A and R are true. Increased turgor pressure causes guard cells to expand, and radial microfibrils direct the expansion outward, opening the stomatal pore. The orientation of microfibrils is the correct mechanism. (Answer: A)

8) Matching Type MCQ:

Match the term with its feature:

(A) Radial microfibrils – (i) Facilitate bowing of guard cells

(B) Longitudinal microfibrils – (ii) Restrict cell expansion

(C) Potassium influx – (iii) Increases turgor

(D) ABA – (iv) Induces closure

Options:

(A) A-i, B-ii, C-iii, D-iv

(B) A-ii, B-i, C-iv, D-iii

(C) A-i, B-iii, C-ii, D-iv

(D) A-iii, B-ii, C-i, D-iv

Explanation:

Correct matching: Radial microfibrils facilitate bowing, longitudinal restrict expansion, potassium influx increases turgor, ABA induces closure. This explains structural and hormonal regulation of stomatal aperture. (Answer: A)

9) Fill in the Blanks MCQ:

Stomatal opening is promoted by ________ turgor in guard cells.

(A) Increased

(B) Decreased

(C) No change

(D) Negative

Explanation:

Stomatal aperture is controlled by guard cell turgor. Increased turgor due to water influx causes guard cells to swell, bow outward, and open the stomatal pore, facilitating gas exchange. Decreased turgor leads to closure. (Answer: A)

10) Choose the correct statements MCQ:

1. Radial microfibrils facilitate stomatal opening.

2. Potassium ions accumulation in guard cells increases turgor.

3. Abscisic acid promotes stomatal opening.

4. Light stimulates stomatal opening.

Options:

(A) 1, 2, 3, 4

(B) 1, 2, 4

(C) 2, 3, 4

(D) 1, 3, 4

Explanation:

Statements 1, 2, and 4 are correct. Radial microfibrils allow bowing, potassium influx increases turgor, and light promotes opening. Abscisic acid induces closure, not opening. Knowledge of structural, ionic, and environmental factors is crucial for understanding stomatal physiology. (Answer: B)

Subtopic: Cellular Respiration

Keyword Definitions:

- Oxidative phosphorylation: ATP production using energy from electron transport chain.

- ATP: Adenosine triphosphate, primary energy currency of the cell.

- Substrate-level phosphorylation: Direct transfer of phosphate group to ADP from a substrate.

- Electron transport chain (ETC): Series of protein complexes in mitochondria transferring electrons to generate proton gradient.

- Mitochondria: Cell organelle where oxidative phosphorylation occurs.

- Proton gradient: Electrochemical gradient of H+ ions used to drive ATP synthesis.

- ADP: Adenosine diphosphate, precursor to ATP.

- ATP synthase: Enzyme that synthesizes ATP using proton motive force.

Lead Question - 2016 (Phase 2)

Oxidative phosphorylation is:

(1) formation of ATP by energy released from electrons removed during substrate oxidation

(2) formation of ATP by transfer of phosphate group from a substrate to ADP

(3) oxidation of phosphate group in ATP

(4) addition of phosphate group to ATP

Answer & Explanation:

Correct answer: formation of ATP by energy released from electrons removed during substrate oxidation. Oxidative phosphorylation occurs in mitochondria, where electrons from NADH and FADH2 pass through the electron transport chain, creating a proton gradient. ATP synthase uses this energy to phosphorylate ADP to ATP efficiently.

1. Where does oxidative phosphorylation occur?

(1) Cytoplasm

(2) Nucleus

(3) Mitochondrial matrix

(4) Mitochondrial inner membrane

Answer & Explanation:

Oxidative phosphorylation occurs in the inner mitochondrial membrane. Electrons pass through the electron transport chain complexes, generating a proton gradient across the membrane. ATP synthase uses this gradient to produce ATP. This process is essential for cellular energy production and efficient metabolism.

2. Assertion (A): Oxidative phosphorylation requires oxygen.

Reason (R): Oxygen acts as the final electron acceptor.

(1) Both A and R are true, and R is correct explanation of A

(2) Both A and R are true, but R is not correct explanation of A

(3) A is true, R is false

(4) A is false, R is true

Answer & Explanation:

Both A and R are true, and R is correct explanation of A. Oxygen accepts electrons at the end of the electron transport chain, forming water. Without oxygen, the electron transport chain would halt, preventing ATP production via oxidative phosphorylation.

3. Match the following:

A. Substrate-level phosphorylation - (i) Direct phosphate transfer

B. Oxidative phosphorylation - (ii) ATP via electron transport

C. Photophosphorylation - (iii) ATP via light energy

(1) A-i, B-ii, C-iii

(2) A-ii, B-i, C-iii

(3) A-iii, B-ii, C-i

(4) A-i, B-iii, C-ii

Answer & Explanation:

Correct answer: A-i, B-ii, C-iii. Substrate-level phosphorylation transfers phosphate directly to ADP. Oxidative phosphorylation generates ATP using energy from electrons in the ETC. Photophosphorylation occurs in chloroplasts during photosynthesis, using light energy to produce ATP.

4. Fill in the blank:

The enzyme that synthesizes ATP during oxidative phosphorylation is ________.

(1) Hexokinase

(2) Phosphofructokinase

(3) ATP synthase

(4) Pyruvate kinase

Answer & Explanation:

ATP synthase synthesizes ATP by utilizing the proton gradient generated across the mitochondrial inner membrane. Protons flow through ATP synthase, driving conformational changes that phosphorylate ADP to ATP, which is the primary energy currency for cellular functions.

5. Clinical-type Question:

Deficiency in oxidative phosphorylation may result in:

(1) Hypoglycemia

(2) Mitochondrial diseases

(3) Excess ATP

(4) Reduced glycolysis

Answer & Explanation:

Deficiency in oxidative phosphorylation impairs ATP production, leading to mitochondrial disorders, muscle weakness, neurological defects, and lactic acidosis. Cells rely on less efficient glycolysis, which cannot meet energy demands, highlighting the clinical significance of proper mitochondrial function.

6. Which molecules donate electrons for oxidative phosphorylation?

(1) Glucose

(2) NADH and FADH2

(3) Oxygen

(4) ADP

Answer & Explanation:

NADH and FADH2 donate electrons to the electron transport chain during oxidative phosphorylation. These electrons drive the formation of a proton gradient, which ATP synthase uses to produce ATP. Efficient electron donation is critical for cellular energy supply.

7. Which process is coupled to ATP synthesis in mitochondria?

(1) Glycolysis

(2) Citric acid cycle

(3) Electron transport chain

(4) Gluconeogenesis

Answer & Explanation:

The electron transport chain is coupled to ATP synthesis. Electron flow through the chain generates a proton gradient across the inner mitochondrial membrane, which ATP synthase uses to phosphorylate ADP, forming ATP efficiently in oxidative phosphorylation.

8. Choose the correct statements:

(a) Oxidative phosphorylation requires oxygen

(b) It occurs in cytoplasm

(c) It produces most ATP in cellular respiration

(d) Substrate-level phosphorylation produces more ATP

Answer & Explanation:

Correct statements are a and c. Oxidative phosphorylation occurs in mitochondria, requires oxygen, and produces the majority of ATP during cellular respiration. Substrate-level phosphorylation contributes less ATP and occurs in glycolysis and citric acid cycle.

9. Which process generates proton gradient for ATP synthesis?

(1) Glycolysis

(2) Citric acid cycle

(3) Electron transport chain

(4) Fermentation

Answer & Explanation:

Electron transport chain generates a proton gradient across the inner mitochondrial membrane. This gradient drives ATP synthase to phosphorylate ADP to ATP. Without this gradient, oxidative phosphorylation cannot occur, emphasizing the ETC's central role.

10. Why is oxidative phosphorylation clinically significant?

(1) It regulates blood sugar

(2) It produces most cellular ATP

(3) It synthesizes proteins

(4) It generates oxygen

Answer & Explanation:

Oxidative phosphorylation produces the majority of cellular ATP, essential for all energy-dependent processes. Dysfunction leads to mitochondrial disorders, neurodegeneration, and muscle weakness. Therapeutic interventions often target mitochondrial function to manage energy metabolism-related diseases.

Subtopic: Central Metabolic Pathways

Keyword Definitions:

• Acetyl CoA: Central metabolic intermediate in catabolism of carbohydrates, fats, and proteins.

• Glucose-6-phosphate: Phosphorylated glucose intermediate in glycolysis and gluconeogenesis.

• Fructose 1,6-bisphosphate: Glycolytic intermediate formed during breakdown of glucose.

• Pyruvic acid: End product of glycolysis, precursor to Acetyl CoA.

Lead Question - 2016 (Phase 2):

Which of the following biomolecules is common to respiration-mediated breakdown of fats, carbohydrates and proteins?

(1) Acetyl CoA

(2) Glucose-6-phosphate

(3) Fructose 1,6-bisphosphate

(4) Pyruvic acid

Explanation: Acetyl CoA is the key biomolecule common to the catabolism of fats, carbohydrates, and proteins. It serves as the central intermediate entering the Krebs cycle. Carbohydrates and proteins are converted to Acetyl CoA after glycolysis and deamination. Correct answer: (1) Acetyl CoA, essential for NEET UG metabolism.

1. Single Correct Answer MCQ:

What is the end product of glycolysis?

(1) Acetyl CoA

(2) Pyruvic acid

(3) Fructose 1,6-bisphosphate

(4) Glucose-6-phosphate

Explanation: The end product of glycolysis is pyruvic acid, formed after the breakdown of glucose. Pyruvic acid can be converted into Acetyl CoA for entry into the Krebs cycle. The correct answer is (2) Pyruvic acid, important for understanding cellular respiration in NEET UG.

2. Single Correct Answer MCQ:

Acetyl CoA enters which metabolic cycle?

(1) Glycolysis

(2) Pentose phosphate pathway

(3) Krebs cycle

(4) Calvin cycle

Explanation: Acetyl CoA enters the Krebs cycle (also known as the citric acid cycle), where it undergoes oxidation to generate ATP, NADH, and FADH2. This is central to aerobic respiration. Correct answer: (3) Krebs cycle, a vital concept in NEET UG metabolism.

3. Single Correct Answer MCQ:

Which process produces Acetyl CoA from fatty acids?

(1) Glycolysis

(2) Beta-oxidation

(3) Gluconeogenesis

(4) Fermentation

Explanation: Beta-oxidation is the process by which fatty acids are broken down in mitochondria to produce Acetyl CoA, which then enters the Krebs cycle for energy production. The correct answer is (2) Beta-oxidation, essential for NEET UG metabolism topics.

4. Single Correct Answer MCQ:

Which enzyme converts pyruvate to Acetyl CoA?

(1) Pyruvate kinase

(2) Pyruvate dehydrogenase complex

(3) Hexokinase

(4) Lactate dehydrogenase

Explanation: Pyruvate is converted to Acetyl CoA by the pyruvate dehydrogenase complex in the mitochondrial matrix. This step is critical for linking glycolysis to the Krebs cycle. Correct answer is (2) Pyruvate dehydrogenase complex, important for NEET UG metabolism understanding.

5. Single Correct Answer MCQ (Clinical-type):

Deficiency of pyruvate dehydrogenase complex leads to

(1) Hypoglycemia

(2) Lactic acidosis

(3) Hyperlipidemia

(4) Ketosis

Explanation: Deficiency of the pyruvate dehydrogenase complex causes accumulation of pyruvate, which is converted into lactate, resulting in lactic acidosis. This is a significant metabolic disorder important for clinical applications in NEET UG. Correct answer: (2) Lactic acidosis.

6. Single Correct Answer MCQ:

Which molecule is formed by combining acetyl group with coenzyme A?

(1) Pyruvic acid

(2) Acetyl CoA

(3) Fructose 1,6-bisphosphate

(4) Glucose-6-phosphate

Explanation: Acetyl CoA is formed by the combination of an acetyl group with coenzyme A, catalyzed by pyruvate dehydrogenase complex. This is central to energy metabolism. Correct answer: (2) Acetyl CoA, fundamental for NEET UG biochemistry.

7. Assertion-Reason MCQ:

Assertion (A): Acetyl CoA is a central metabolic intermediate.

Reason (R): It participates in the Krebs cycle to generate energy.

(1) Both A and R are true and R is correct explanation of A

(2) Both A and R are true but R is not correct explanation of A

(3) A is true but R is false

(4) A is false but R is true

Explanation: Both assertion and reason are true and the reason correctly explains the assertion. Acetyl CoA links carbohydrate, fat, and protein metabolism by feeding into the Krebs cycle, essential for energy production. Correct answer: (1) Both A and R are true and R is correct explanation of A.

8. Matching Type MCQ:

Match the biomolecule with its role:

A. Acetyl CoA

B. Pyruvic acid

C. Glucose-6-phosphate

D. Fructose 1,6-bisphosphate

1. Glycolysis intermediate

2. Central metabolic intermediate

3. Precursor to Acetyl CoA

4. Phosphorylated glucose derivative

Options:

(1) A-2, B-3, C-4, D-1

(2) A-1, B-2, C-3, D-4

(3) A-2, B-1, C-3, D-4

(4) A-3, B-1, C-2, D-4

Explanation: The correct match is A-2 (Acetyl CoA-central metabolic intermediate), B-3 (Pyruvic acid-precursor to Acetyl CoA), C-4 (Glucose-6-phosphate-phosphorylated glucose derivative), D-1 (Fructose 1,6-bisphosphate-glycolysis intermediate). Thus, the correct answer is (1) A-2, B-3, C-4, D-1.

9. Fill in the Blanks MCQ:

Acetyl CoA is produced from ______ during carbohydrate metabolism.

(1) Glucose

(2) Fatty acids

(3) Pyruvic acid

(4) Amino acids

Explanation: During carbohydrate metabolism, glucose is broken down by glycolysis into pyruvic acid, which is then converted to Acetyl CoA by pyruvate dehydrogenase. The correct answer is (3) Pyruvic acid, crucial for NEET UG metabolism concepts.

10. Choose the Correct Statements MCQ:

Select correct statements regarding Acetyl CoA:

(1) Produced from carbohydrates, fats, and proteins

(2) Enters the Krebs cycle

(3) Synthesized during fermentation

(4) Central to aerobic respiration

Options:

(1) 1, 2, and 4 only

(2) 1 and 3 only

(3) 2 and 4 only

(4) All statements are correct

Explanation: Statements 1, 2, and 4 are correct: Acetyl CoA is produced from carbs, fats, and proteins, enters the Krebs cycle, and is central to aerobic respiration. Fermentation does not synthesize Acetyl CoA. Correct answer is (1) 1, 2, and 4 only.

Chapter: Plant Physiology

Topic: Reproduction in Flowering Plants

Subtopic: Apomixis and Seed Formation

Keyword Definitions:

• Seed Formation: Process by which seeds are produced for plant reproduction.

• Fertilization: Fusion of male and female gametes to form a zygote.

• Sporulation: Formation of spores in plants, not related to seed formation without fertilization.

• Budding: Asexual reproduction by outgrowth of a part of the parent organism.

• Apomixis: Formation of seeds without fertilization, commonly in some flowering plants.

• Somatic Hybridization: Fusion of somatic cells from different species for hybrid production.

2016 (Phase 1)

Lead Question: Seed formation without fertilization in flowering plants involves the process of :

• (1) Sporulation

• (2) Budding

• (3) Somatic hybridization

• (4) Apomixis

Answer & Explanation: The correct answer is (4) Apomixis. Apomixis is a process where seeds develop without the fusion of gametes. This asexual reproduction mechanism is commonly observed in some flowering plants like dandelions and grasses, allowing them to produce progeny genetically identical to the parent plant without fertilization.

Keyword Definitions:

• Dandelion: A plant known for apomictic seed formation, producing seeds without fertilization.

Single Correct Answer MCQ: Apomixis leads to offspring that are:

• (1) Genetically varied

• (2) Genetically identical to the parent

• (3) Hybrid of two plants

• (4) Genetically different due to recombination

Answer & Explanation: The correct answer is (2). In apomixis, seeds develop without fertilization, resulting in progeny that are clones of the parent plant. This preserves desirable traits and provides advantages in agriculture by enabling consistent crop production without relying on cross-pollination or genetic recombination mechanisms.

Keyword Definitions:

• Genetically Identical: Offspring having the same genetic makeup as the parent due to asexual reproduction.

Single Correct Answer MCQ (Clinical Type): Apomixis is useful in agriculture because it helps in:

• (1) Increasing genetic diversity

• (2) Preserving superior crop varieties

• (3) Promoting random mutations

• (4) Enhancing pest resistance

Answer & Explanation: The correct answer is (2). Apomixis allows propagation of plants that retain desired genetic traits without the need for repeated hybridization. This ensures uniformity in crop yield and quality, especially important for traits like fruit size and disease resistance, improving agricultural efficiency and stability in production.

Keyword Definitions:

• Hybridization: Crossing of two different plant varieties to combine traits.

Single Correct Answer MCQ: The essential characteristic of apomixis is:

• (1) Requires pollen fertilization

• (2) Produces spores

• (3) Seed formation without fertilization

• (4) Formation of new plants by grafting

Answer & Explanation: The correct answer is (3). Apomixis is defined by the formation of seeds without fertilization, bypassing sexual reproduction mechanisms. The embryos develop directly from the maternal tissues, leading to clonal propagation, which is useful for maintaining genetic stability across plant generations in both wild and agricultural plants.

Keyword Definitions:

• Clonal Propagation: Reproduction producing genetically identical offspring from a single parent.

Assertion-Reason MCQ:

Assertion (A): Apomixis helps in the consistent propagation of crop varieties.

Reason (R): Because apomictic seeds are genetically identical to the parent plant.

• (1) Both A and R are true, and R is correct explanation of A

• (2) Both A and R are true, but R is not correct explanation of A

• (3) A is true, but R is false

• (4) A is false, but R is true

Answer & Explanation: The correct answer is (1). Apomixis leads to the formation of genetically identical seeds, preserving traits of superior plants across generations. This allows for predictable crop yields and quality without reliance on cross-pollination, enhancing efficiency and reducing variation in large-scale agriculture practices.

Keyword Definitions:

• Genetic Stability: Maintenance of identical genetic characteristics in progeny.

Matching Type MCQ: Match the term with its description:

A. Apomixis               1. Seed formation without fertilization

B. Sporulation            2. Formation of spores

C. Budding                3. New individual grows from parent body

D. Somatic Hybridization  4. Fusion of somatic cells from different species

• (1) A-1, B-2, C-3, D-4

• (2) A-3, B-1, C-4, D-2

• (3) A-4, B-3, C-2, D-1

• (4) A-2, B-4, C-1, D-3

Answer & Explanation: The correct answer is (1). Apomixis produces seeds without fertilization. Sporulation is spore formation. Budding forms new individuals from parent tissue. Somatic hybridization fuses somatic cells to create hybrids. These processes are essential biological mechanisms differentiating asexual and sexual reproduction pathways in plants and microorganisms.

Keyword Definitions:

• Somatic Cells: Body cells not involved in gamete production.

Fill in the Blanks / Completion MCQ: Apomictic seeds are formed from __________ cells of the parent plant.

• (1) Gametic

• (2) Somatic

• (3) Pollen

• (4) Sporogenous

Answer & Explanation: The correct answer is (2). In apomixis, seeds develop from somatic cells of the parent plant without the fusion of gametes. This enables clonal reproduction, producing offspring that are genetic copies of the parent. Apomixis ensures stability of desirable traits in agricultural crops.

Keyword Definitions:

• Somatic Cells: Non-reproductive cells forming the body of the plant or animal.

Choose the correct statements MCQ:

• 1. Apomixis occurs naturally in some plants.

• 2. Apomixis requires fertilization.

• 3. Apomixis helps in uniform crop production.

• 4. Apomixis results in genetically diverse offspring.

• (1) 1 and 3 only

• (2) 1, 2, and 3

• (3) 2 and 4 only

• (4) All statements are correct

Answer & Explanation: The correct answer is (1). Apomixis occurs naturally in plants like dandelions. It enables the production of genetically identical offspring without fertilization, ensuring uniform crop traits across generations. This method is exploited in agriculture for maintaining high-yield, disease-resistant crop varieties without the need for complex hybridization processes.

Topic: Plant Gas Exchange

Subtopic: Stomatal Function

Keyword Definitions:

• Stomatal Opening: Pores on leaf surfaces allowing gas exchange between plant and atmosphere.

• Photosynthesis: Process where plants use light energy to convert CO₂ and water into glucose and oxygen.

• Diffusion Coefficient: A measure of the rate at which molecules spread out from high to low concentration.

• Water Vapour: Gaseous form of water released by transpiration in plants.

• Carbon Dioxide: Essential gas absorbed by plants for photosynthesis.

2016 (Phase 1)

Lead Question: Water vapour comes out from the plant leaf through the stomatal opening. Through the same stomatal opening carbon dioxide diffuses into the plant during photosynthesis. Reason out the above statements using one of following options :

• (1) Both processes cannot happen simultaneously.

• (2) Both processes can happen together because the diffusion coefficient of water and CO₂ is different.

• (3) The above processes happen only during night time.

• (4) One process occurs during day time, and the other at night.

Answer & Explanation: The correct answer is (2). Both transpiration (water vapor loss) and CO₂ uptake happen simultaneously during daylight. The difference in diffusion coefficients allows water to exit rapidly while CO₂ enters slowly through the stomata. This mechanism supports photosynthesis while managing water loss effectively under sunlight conditions.

Keyword Definitions:

• Transpiration: Process where plants lose water vapor through stomata, aiding nutrient transport.

Single Correct Answer MCQ: Stomatal opening is regulated primarily by:

• (1) Temperature changes

• (2) Guard cells

• (3) Root pressure

• (4) Chlorophyll content

Answer & Explanation: The correct answer is (2). Guard cells flank the stomatal pore and control its opening or closing by changing turgor pressure. Light exposure causes guard cells to accumulate potassium ions, drawing water in and opening stomata, thus facilitating gas exchange crucial for photosynthesis.

Keyword Definitions:

• Guard Cells: Specialized cells that regulate the stomatal aperture based on environmental conditions.

Single Correct Answer MCQ (Clinical Type): Impaired stomatal function in crops can result in:

• (1) Increased CO₂ absorption

• (2) Reduced photosynthesis and drought susceptibility

• (3) Enhanced water retention without effects

• (4) Overproduction of glucose

Answer & Explanation: The correct answer is (2). Malfunctioning stomata hinder gas exchange, reducing photosynthesis and making plants prone to drought stress. This affects crop yield and resilience, leading to economic losses in agriculture, and necessitates breeding of varieties with optimized stomatal behavior for improved productivity.

Keyword Definitions:

• Drought Susceptibility: Reduced plant ability to survive low water availability.

Single Correct Answer MCQ: Stomata typically open during:

• (1) Night

• (2) Day

• (3) Both day and night equally

• (4) Only during rainfall

Answer & Explanation: The correct answer is (2). Stomata open during daylight to facilitate CO₂ uptake for photosynthesis while transpiring water. Light stimulates guard cells to accumulate ions, increasing turgor pressure and opening stomata. This balances the need for CO₂ with water conservation strategies in various environments.

Keyword Definitions:

• Turgor Pressure: Pressure exerted by water inside guard cells causing stomatal opening.

Assertion-Reason MCQ:

Assertion (A): Water vapor diffuses faster than carbon dioxide through stomata.

Reason (R): The diffusion coefficient of water vapor is greater than that of CO₂.

• (1) Both A and R are true, and R is correct explanation of A

• (2) Both A and R are true, but R is not correct explanation of A

• (3) A is true, but R is false

• (4) A is false, but R is true

Answer & Explanation: The correct answer is (1). Water vapor diffuses more rapidly than CO₂ because of its smaller molecular size and higher diffusion coefficient. This explains why transpiration occurs at a significant rate compared to CO₂ uptake, ensuring efficient physiological processes in plants.

Keyword Definitions:

• Diffusion Coefficient: Measure of rate of molecular movement through a medium.

Matching Type MCQ: Match the process with its primary role:

A. Transpiration           1. CO₂ entry for photosynthesis

B. Photosynthesis          2. Water vapor release cooling plant

C. Guard cell function     3. Regulation of stomatal aperture

• (1) A-2, B-1, C-3

• (2) A-1, B-2, C-3

• (3) A-3, B-1, C-2

• (4) A-2, B-3, C-1

Answer & Explanation: The correct answer is (1). Transpiration releases water vapor, aiding cooling and nutrient transport. Photosynthesis enables CO₂ uptake for energy production. Guard cells regulate stomatal aperture to balance gas exchange and water conservation. These interconnected processes sustain plant physiology and environmental adaptation.

Keyword Definitions:

• Photosynthesis: Conversion of light energy, CO₂, and water into glucose and oxygen.

Fill in the Blanks / Completion MCQ: During photosynthesis, carbon dioxide enters through __________.

• (1) Lenticels

• (2) Stomata

• (3) Xylem vessels

• (4) Phloem vessels

Answer & Explanation: The correct answer is (2). Carbon dioxide enters plant leaves through stomata, small pores controlled by guard cells. This gas is essential for photosynthesis, allowing plants to produce glucose and oxygen. The stomatal mechanism ensures efficient gas exchange while minimizing water loss under varying environmental conditions.

Keyword Definitions:

• Lenticels: Pores in woody stems aiding gas exchange.

Choose the correct statements MCQ:

• 1. Stomatal opening increases during high light intensity.

• 2. Transpiration provides cooling and nutrient transport.

• 3. Guard cells do not respond to environmental cues.

• 4. CO₂ and water vapor diffuse in opposite directions simultaneously.

• (1) 1, 2, and 4 only

• (2) 1 and 3 only

• (3) 2 and 3 only

• (4) All statements are correct

Answer & Explanation: The correct answer is (1). Stomata open in light to enable CO₂ uptake; transpiration aids nutrient flow and cooling. Guard cells respond actively to light, CO₂, and humidity. Water vapor exits and CO₂ enters simultaneously through stomata, a key feature supporting plant survival and photosynthesis efficiency.