Biology Class 11 CBQ of Respiration in Plants (Crucial Mastery)

---

---

Competency-Based Questions CBQ of Respiration in Plants in Class 11 Biology on Respiration in Plants are designed to move students beyond rote memorization and into analytical reasoning. Respiration in plants is a fundamental process where glucose is broken down to release energy in the form of ATP, sustaining cellular activities. CBQs encourage learners to apply this knowledge in real-world contexts—such as explaining why seeds kept in airtight containers fail to germinate, or analysing how oxygen availability influences aerobic versus anaerobic pathways.

Instead of simply recalling the stages of glycolysis, Krebs cycle, and electron transport chain, students are prompted to evaluate how these processes interconnect and adapt under different conditions. For example, a CBQ may ask students to compare respiration in roots submerged in water with those in well-aerated soil, pushing them to reason about oxygen diffusion and energy yield.

These questions sharpen critical thinking, foster problem-solving, and highlight the dynamic nature of plant physiology. By engaging with CBQs, students not only master the biochemical steps but also appreciate respiration as a living, adaptive process essential for growth and survival. Thus, CBQs make the topic both intellectually rigorous and practically meaningful.

---

Section A: Multiple Choice Questions (MCQs)

1. In plant respiration, the primary role of oxygen is to:

1. Directly form ATP during glycolysis
2. Act as the final electron acceptor in the electron transport chain
3. Convert pyruvate into acetyl CoA
4. Catalyze the breakdown of glucose in the cytoplasm

---

2. Which of the following is NOT a product of the Krebs cycle?

1. ATP
2. NADH
3. FADH₂
4. Ethanol

---

3. The term “amphibolic pathway” in respiration refers to a pathway that:

1. Occurs only in anaerobic conditions
2. Involves both catabolic and anabolic reactions
3. Produces only ATP and water
4. Is exclusive to photosynthetic organisms

---

Section B: Diagram-Based MCQs

4. Refer to the glycolysis pathway. At which step is NADH + H⁺ first produced?

---

5. In the citric acid cycle diagram, which compound is regenerated to allow the cycle to continue?

---

6. Examine the electron transport system. Which complex directly receives electrons from FADH₂?

---

Section C: Data Analysis-Based MCQs

7. Given: One molecule of glucose yields 2 NADH during glycolysis, 2 NADH during pyruvate to acetyl CoA conversion, and 6 NADH + 2 FADH₂ during the Krebs cycle. If each NADH produces 3 ATP and each FADH₂ produces 2 ATP via oxidative phosphorylation, how many ATP are generated from these electron carriers alone (excluding substrate-level ATP)?

1. 30 ATP
2. 34 ATP
3. 36 ATP
4. 38 ATP

---

8. If a plant is respiring a fatty acid with an RQ of 0.7, what does this indicate about the substrate?

1. It is fully oxidized like glucose
2. It requires more oxygen per CO₂ released than carbohydrates
3. It produces more CO₂ than O₂ consumed
4. It is undergoing fermentation

---

9. In an experiment, a plant tissue showed an RQ of 0.9. Which substrate is likely being respired?

1. Carbohydrate
2. Fat
3. Protein
4. Organic acid

---

Section D: Case-Based MCQs

10. Case: A researcher is studying respiration in yeast cultures. One culture is given ample oxygen, while the other is kept in a sealed, anaerobic environment. After 24 hours, the anaerobic culture shows a much slower growth rate and a detectable smell of ethanol. The aerobic culture shows vigorous growth and no odor.

What best explains the difference in growth and metabolic products?

1. Both cultures perform Krebs cycle, but anaerobic yeast cannot use NADH.
2. Anaerobic yeast performs fermentation, yielding less ATP and producing ethanol, while aerobic yeast undergoes oxidative phosphorylation for more ATP.
3. Aerobic yeast uses lactic acid fermentation, while anaerobic yeast uses alcoholic fermentation.
4. Anaerobic yeast cannot perform glycolysis, so it uses fats as an alternative substrate.

---

11. Case: In a plant physiology lab, students compare respiration in green leaves vs. non-green potato tuber tissues. Both tissues are supplied with glucose and oxygen. The leaves show a higher rate of CO₂ release in the dark but produce O₂ in the light. The tubers consistently release CO₂.

Why do leaves show different gas exchange patterns under light and dark?

1. Leaves perform only respiration in the dark and only photosynthesis in the light.
2. In light, photosynthesis fixes CO₂, masking respiratory CO₂ release, while in dark, only respiration occurs.
3. Tubers lack mitochondria and perform only glycolysis.
4. Leaves have stomata open only in the light, limiting gas exchange in the dark.

---

12. Case: A farmer stores harvested potatoes in a cold, humid cellar to prevent sprouting and spoilage. Over time, he notices the potatoes become sweeter. Analysis shows an increase in sugar content and a decrease in starch.

What metabolic shift best explains this change?

1. The cold inhibits glycolysis, causing sugar accumulation.
2. Low temperature promotes starch synthesis from sugars.
3. Respiration continues at a low rate, converting starch to sugars via gluconeogenesis to maintain metabolic activity.
4. Fermentation produces ethanol and CO₂, breaking down starch into sugars.

---

Section E: Scenario-Based HOT MCQs with Tabular Data

13. Scenario: You are optimizing yeast fermentation for bioethanol production. The goal is to maximize ethanol yield while minimizing ATP use for cell growth. Below is the ATP and ethanol yield from different metabolic pathways in yeast:

Pathway	ATP per Glucose	Ethanol per Glucose
Alcoholic Fermentation	2 ATP	2 molecules
Aerobic Respiration	38 ATP	0 molecules
Mixed Mode (some O₂)	15 ATP	1 molecule

Which condition should you maintain for maximum ethanol production?

1. Fully aerobic — high ATP supports more yeast growth.
2. Fully anaerobic — no ATP waste, all carbon goes to ethanol.
3. Low oxygen — some ATP for maintenance but high ethanol yield.
4. Intermittent oxygen — balance between growth and ethanol.

---

14. Scenario: A plant physiologist is comparing respiratory substrates in germinating seeds. She measures O₂ consumed and CO₂ released for three substrates:

Substrate	O₂ consumed (mL)	CO₂ released (mL)
Glucose	60	60
Tripalmitin	145	102
Protein mix	90	81

Which substrate has the highest energy yield per mole of O₂ consumed, assuming complete oxidation?

1. Glucose — RQ = 1, efficient energy yield.
2. Tripalmitin — low RQ but high carbon content.
3. Protein mix — moderate RQ, good balance.
4. Cannot determine without ATP yield data.

---

15. Scenario: In a mitochondria study, researchers measure ATP synthesis with different electron donors. Data:

Electron Donor	ATP Produced	Pathway Step
NADH	3 ATP	Complex I → ETS
FADH₂	2 ATP	Complex II → ETS
Succinate	2 ATP	Directly to Complex II

If a mutation disables Complex I, which substrate will be least affected in ATP yield?

1. Pyruvate (produces NADH)
2. Succinate (produces FADH₂)
3. α-ketoglutarate (produces NADH)
4. Citrate (produces NADH)

---

Section F: Short Answer Questions

16. Define “respiratory quotient” (RQ). Why does the RQ value differ when fats are used as a respiratory substrate compared to carbohydrates?

17. Explain why the respiratory pathway is described as an “amphibolic pathway.” Provide one specific example of an anabolic and one catabolic process that use respiratory intermediates.

18 Describe two structural adaptations in plants that facilitate gaseous exchange for respiration, and explain why plants do not require specialized respiratory organs like animals.

---

Section G: Diagram-Based Questions.

19. Refer to Figure (Glycolysis). Identify and name the step where:

20. Refer to Figure (Electron Transport System). If Complex III is inhibited, explain the effect on:

---

Section h: Data Analysis-Based Questions

21. The table below shows the ATP yield from different stages of aerobic respiration per molecule of glucose:

Stage	ATP Yield (Net)
Glycolysis	2 ATP
Oxidative Decarboxylation	—
Krebs Cycle	2 ATP
Oxidative Phosphorylation	?

Given that 10 NADH and 2 FADH₂ are produced in total from one glucose molecule, calculate the total ATP yield from oxidative phosphorylation. What is the total net ATP from one glucose molecule under theoretical conditions?

---

22. A researcher measures the following gas exchanges in three different plant tissues over one hour:

Tissue Type	O₂ Consumed (ml)	CO₂ Released (ml)
A	24	24
B	50	35
C	30	27

Calculate the RQ for each tissue. Which tissue is most likely respiring proteins, and why?

---

23. In an experiment, yeast cells are grown in three different conditions:

Condition	Growth Rate	Ethanol Produced
1	High	None
2	Low	High
3	Moderate	Moderate

Explain the metabolic reasons behind the observed growth rates and ethanol production in each condition.

---

Section I: Case-Based Questions

24. Case: Controlled Atmosphere Apple Storage
A farmer stores apples in reduced oxygen atmospheres to slow ripening, but if oxygen drops too low, apples develop off-flavors and abnormal softening.

Sub-parts:

1. What specific metabolic pathway becomes dominant under extremely low oxygen conditions?
2. Name two specific compounds that might cause the off-flavor.
3. How does this metabolic shift explain the abnormal softening of apple tissue?
4. What would be the approximate RQ value when apples are in this spoiled state?
5. Suggest one physiological reason why apple cells switch to this less efficient pathway despite its drawbacks.

---

Section J: Scenario-Based HOT Questions with Tabular Data

25. Scenario: A plant researcher is comparing the efficiency of different respiratory substrates in germinating pea seeds. She measures the volume of O₂ consumed and CO₂ released:

Substrate	O₂ Consumed (μmol)	CO₂ Released (μmol)
Glucose	60	60
Oleic Acid	145	102
Alanine	90	72

Which substrate provides the most energy per mole of O₂ consumed, and why? Use RQ and energy yield logic to explain.

---

26. Scenario: In a lab, mitochondria are isolated and provided with different substrates. The rate of ATP synthesis is measured:

Substrate	ATP Produced/min	Enters Pathway at:
Pyruvate	100 units	Mitochondrial Matrix
Succinate	65 units	Krebs Cycle → Complex II
Malate	95 units	Krebs Cycle → NADH

If a toxin blocks Complex I of the ETS, which substrate’s ATP synthesis rate will be least affected? Explain using the electron entry points into the ETS.

---

Section K: Additional Passage-Based Questions

27. Passage 1

The complete oxidation of glucose in the presence of oxygen releases a large amount of energy stored in the substrate, producing CO₂ and H₂O. This process, known as aerobic respiration, involves glycolysis, the Krebs cycle, and the electron transport system. However, some organisms or tissues can function without oxygen by partially oxidizing glucose through fermentation, which yields far less energy.

1. State what is meant by “fermentation” in the context of respiration.
2. Yeast cells in an anaerobic environment produce ethanol and CO₂. Name the two enzymes involved in converting pyruvic acid to these products.
3. (i) What is the net gain of ATP molecules per glucose in fermentation?
   (ii) How does this compare to the theoretical ATP yield in aerobic respiration?

---

28. Passage 2

In aerobic respiration, pyruvate enters the mitochondria and is converted to acetyl CoA, which then enters the Krebs cycle. During this cycle, multiple redox reactions occur, generating NADH, FADH₂, and ATP. These reduced coenzymes then donate electrons to the electron transport system located on the inner mitochondrial membrane, leading to the synthesis of a large number of ATP molecules through oxidative phosphorylation.

1. State the role of oxygen in the electron transport system.

2. A mutation disrupts Complex I of the ETS. Will FADH₂ oxidation be directly affected? Justify briefly.

3. (i) How many molecules of NADH and FADH₂ are produced from one molecule of glucose in the Krebs cycle?
   (ii) What is the total ATP generated from these if all undergo oxidative phosphorylation?

---

Answer Key

1. B Act as the final electron acceptor in the electron transport chain
2. D Ethanol
3. B Involves both catabolic and anabolic reactions
4. B Conversion of PGAL to BPGA
5. B Oxaloacetic acid (OAA)
6. B Complex II
7. B (Glycolysis: 2 NADH → 6 ATP, Pyruvate→Acetyl CoA: 2 NADH → 6 ATP, Krebs: 6 NADH → 18 ATP + 2 FADH₂ → 4 ATP; Total = 34 ATP)
8. B It requires more oxygen per CO₂ released than carbohydrates
9. C Protein
10. B Anaerobic yeast performs fermentation, yielding less ATP and producing ethanol, while aerobic yeast undergoes oxidative phosphorylation for more ATP.
11. B In light, photosynthesis fixes CO₂, masking respiratory CO₂ release, while in dark, only respiration occurs.
12. C Respiration continues at a low rate, converting starch to sugars via gluconeogenesis to maintain metabolic activity.
13. B Fully anaerobic — no ATP waste, all carbon goes to ethanol.
14. A Glucose — RQ = 1, efficient energy yield. (Highest RQ indicates most energy per O₂)
15. B Succinate (produces FADH₂)

16.

1. RQ = CO₂ released\O₂ consumed
2. Carbohydrates: RQ ≈ 1.
3. Fats: RQ < 1 because fats require more oxygen for complete oxidation.

17.

• Amphibolic = both catabolic and anabolic.
• Catabolic: Oxidation of acetyl CoA in Krebs cycle.
• Anabolic: Acetyl CoA used in fatty acid synthesis.

18.

• Stomata in leaves, lenticels in stems.
• Plants rely on diffusion; every cell is close to the surface, so specialized organs aren’t needed.

19.

1. ATP is first consumed → Glucose → Glucose-6-phosphate (hexokinase).
2. NADH + H⁺ is first produced → Glyceraldehyde-3-phosphate → 1,3-bisphosphoglycerate.
3. A substrate-level phosphorylation occurs to synthesize ATP → 1,3-bisphosphoglycerate → 3-phosphoglycerate and phosphoenolpyruvate → pyruvate.

20.

1. Electron flow from NADH → Blocked beyond ubiquinone.
2. Proton gradient formation → Reduced.
3. ATP synthesis → Decreases due to reduced proton motive force.

21.

• NADH: 10 × 3 = 30 ATP.
• FADH₂: 2 × 2 = 4 ATP.
• Oxidative phosphorylation = 34 ATP.
• Net total = 38 ATP (theoretical).

22.

• Tissue A: RQ = 24/24 = 1 → Carbohydrates.
• Tissue B: RQ = 35/50 = 0.7 → Fat.
• Tissue C: RQ = 27/30 = 0.9 → Protein.
• Tissue C most likely respiring proteins (RQ = 0.9).

23.

• Condition 1: Aerobic → High growth, no ethanol.
• Condition 2: Anaerobic → Low growth, high ethanol.
• Condition 3: Low oxygen → Moderate growth, moderate ethanol.

24.

1. → Anaerobic fermentation.
2. → Ethanol, acetaldehyde.
3. → Accumulation of ethanol/organic acids damages cell walls.
4. → RQ > 1.
5. → Survival mechanism under low oxygen.

25.

Glucose provides the most energy per mole of O₂ consumed
Explanation:

To determine energy yield per mole of oxygen, we use the Respiratory Quotient (RQ):

RQ = VcO2 / VO2
Let’s calculate RQ for each substrate:

Substrate	CO₂ Released	O₂ Consumed	RQ = CO₂/O₂
Glucose	60	60	1.00
Oleic Acid	102	145	0.70
Alanine	72	90	0.80

• Higher RQ means more energy per mole of O₂ consumed, because carbohydrate oxidation is more oxygen-efficient.
• Glucose (RQ = 1.0) is a carbohydrate and yields ~21.1 kJ per liter of O₂.
• Oleic acid (RQ = 0.7) is a fat and yields ~19.6 kJ per liter of O₂.
• Alanine (RQ = 0.8) is a protein and yields ~20.1 kJ per liter of O₂.

Conclusion:

Glucose is the most efficient substrate in terms of energy yield per mole of oxygen consumed, due to its higher RQ and complete oxidation pathway.

26. → Succinate, because it enters via Complex II, bypassing Complex I.

27.

1. → Partial oxidation of glucose without oxygen.
2. → Pyruvate decarboxylase, alcohol dehydrogenase.
3. (i) → 2 ATP.
   (iI) → Aerobic = 38 ATP, much higher.

28.

1. – Oxygen = Final electron acceptor, forms water.

2. – FADH₂ oxidation not directly affected since it enters via Complex II.

3. (i) Krebs cycle: 6 NADH, 2 FADH₂. (iI) ATP = 22 (from oxidative phosphorylation).

---

Click here for any Help, Click here for any Suggestions.