Important Questions Class 11 Biology Chapter 12 Respiration in Plants 2026–27

Respiration in Plants explains how plant cells break down food molecules to release energy in the form of ATP.
For CBSE Class 11 Biology, Important Questions Class 11 Biology Chapter 12 help revise glycolysis, Krebs cycle, ETS, RQ and amphibolic pathways.

Respiration in Plants is Chapter 12 in the updated NCERT Class 11 Biology textbook for 2026–27. It explains how plants break down food molecules inside cells to release usable energy. The chapter covers glycolysis, fermentation, aerobic respiration, Krebs cycle, electron transport system, oxidative phosphorylation, respiratory balance sheet, amphibolic pathway and respiratory quotient.

Use these Important Questions Class 11 Biology Chapter 12 to revise definitions, pathways, equations, comparisons, ATP-yield logic and long-answer concepts. Start with respiration and ATP, then practise glycolysis, fermentation, aerobic respiration, ETS, oxidative phosphorylation, respiratory balance sheet and RQ values.

Key Takeaways

• Respiration: It breaks C-C bonds of complex organic molecules through oxidation to release energy.
• ATP: It acts as the energy currency of the cell.
• Glycolysis: It occurs in the cytoplasm and converts glucose into pyruvic acid.
• Aerobic respiration: It can theoretically yield 38 ATP from one glucose molecule.

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Very Short Answer Questions for Important Questions Class 11 Biology Chapter 12

Respiration in Plants begins with terms such as ATP, respiratory substrates, glycolysis and RQ. These answers help revise NCERT Class 11 Biology Chapter 12 before pathway-based questions.

Q1. What is respiration?

Respiration is the breaking of C-C bonds of complex organic molecules through oxidation inside cells.

This process releases energy, which is trapped as ATP. Carbon skeletons formed during respiration can also be used for biosynthesis.

Q2. What are respiratory substrates?

Respiratory substrates are compounds that are oxidised during respiration to release energy.

Carbohydrates are usually used as respiratory substrates. Proteins, fats and organic acids may also be used under certain conditions.

Q3. Name the most common respiratory substrate.

Glucose is the most common respiratory substrate.

It is generally produced from carbohydrates and enters the respiratory pathway through glycolysis.

Q4. What is ATP called?

ATP is called the energy currency of the cell.

Energy released during respiration is trapped in ATP and used whenever the cell needs energy.

Q5. Where does glycolysis occur?

Glycolysis occurs in the cytoplasm of the cell.

It is present in all living organisms and does not directly require oxygen.

Q6. What is the full form of EMP pathway?

EMP pathway stands for Embden-Meyerhof-Parnas pathway.

It is another name for glycolysis because Embden, Meyerhof and Parnas described its scheme.

Q7. What is the end product of glycolysis?

The end product of glycolysis is pyruvic acid.

One molecule of glucose is partially oxidised to form two molecules of pyruvic acid.

Q8. What is respiratory quotient?

Respiratory quotient is the ratio of the volume of carbon dioxide evolved to the volume of oxygen consumed during respiration.

It depends on the type of respiratory substrate used.

Objective Questions Class 11 Biology Chapter 12

Objective questions from Respiration in Plants test exact NCERT terms, pathway locations and basic reactions. They cover MCQs, fill in the blanks, true or false and matching formats.

Q9. Choose the correct The energy currency of the cell is ______.

1. a) DNA
   b) ATP
   c) NADH
   d) Pyruvate
2. b) ATP.

ATP stores energy released during respiration and supplies it for cellular activities.

Q10. Choose the correct Glycolysis occurs in the ______.

1. a) cytoplasm
   b) chloroplast
   c) nucleus
   d) vacuole
2. a) cytoplasm.

Glycolysis occurs in the cytoplasm and converts glucose into pyruvic acid.

Q11. Choose the correct Krebs cycle occurs in the ______.

1. a) cytoplasm
   b) mitochondrial matrix
   c) thylakoid membrane
   d) cell wall
2. b) mitochondrial matrix.

In eukaryotic cells, the Krebs cycle takes place in the matrix of mitochondria.

Q12. Choose the correct Oxygen acts as the final ______ acceptor in aerobic respiration.

1. a) carbon
   b) nitrogen
   c) hydrogen
   d) phosphate
2. c) hydrogen.

Oxygen removes hydrogen from the system and helps drive aerobic respiration.

Q13. Fill in the blank: Glucose is partially oxidised during glycolysis to form two molecules of ______.

pyruvic acid.

Pyruvic acid is the key product of glycolysis and can enter different pathways.

Q14. Fill in the blank: The ratio of the volume of CO2 evolved to the volume of O2 consumed is called ______.

respiratory quotient.

Respiratory quotient is also called respiratory ratio.

Q15. True or False: Plants have specialised respiratory organs like animals.

False.

Plants do not have specialised respiratory organs. They use stomata and lenticels for gaseous exchange.

Q16. Match the following: Glycolysis, Krebs cycle, ETS and fermentation.

Glycolysis occurs in the cytoplasm, Krebs cycle occurs in the mitochondrial matrix, ETS occurs on the inner mitochondrial membrane, and fermentation occurs under anaerobic conditions.

This matching checks the location and condition of major respiratory processes.

Short Answer Questions Class 11 Biology Chapter 12

Short Answer Questions from Respiration in Plants usually ask students to explain pathways, ATP formation and differences. Use NCERT terms such as glycolysis, pyruvic acid, acetyl CoA, ETS and oxidative phosphorylation clearly.

Q17. Why do plants not need specialised respiratory organs?

Plants do not need specialised respiratory organs because each plant part takes care of its own gas exchange.

There is very little transport of gases from one plant part to another.

Plants also have lower gas exchange demands than animals. Stomata, lenticels and intercellular spaces help gases diffuse easily.

Q18. Why is stepwise release of energy important in respiration?

Stepwise release of energy is important because it allows energy to be trapped as ATP.

If glucose released all its energy in one step, most of it would be lost as heat.

Stepwise enzyme-controlled reactions make respiration efficient. They also allow better control of the pathway.

Q19. What happens to glucose during glycolysis?

During glycolysis, glucose undergoes partial oxidation to form two molecules of pyruvic acid.

ATP is used in the early steps, and ATP and NADH are formed later.

The net gain from glycolysis is two ATP molecules and two NADH molecules per glucose molecule.

Q20. What are the major fates of pyruvic acid?

Pyruvic acid can enter lactic acid fermentation, alcoholic fermentation or aerobic respiration.

The fate depends on oxygen availability and the type of cell.

Under anaerobic conditions, it forms lactic acid or ethanol and carbon dioxide. Under aerobic conditions, it enters mitochondria for complete oxidation.

Q21. What is fermentation?

Fermentation is the incomplete oxidation of glucose under anaerobic conditions.

In alcoholic fermentation, pyruvic acid forms ethanol and carbon dioxide. In lactic acid fermentation, pyruvic acid forms lactic acid.

Fermentation releases less than seven per cent of the energy in glucose.

Q22. What is oxidative decarboxylation of pyruvate?

Oxidative decarboxylation of pyruvate is the conversion of pyruvic acid into acetyl CoA.

It occurs in the mitochondrial matrix and is catalysed by pyruvate dehydrogenase.

During this reaction, carbon dioxide is released and NADH is formed. Acetyl CoA then enters the Krebs cycle.

Q23. What is the role of F0-F1 particles in ATP synthesis?

F0-F1 particles form the ATP synthase complex during oxidative phosphorylation.

F0 is embedded in the inner mitochondrial membrane and forms a proton channel.

F1 is the headpiece where ATP is synthesised from ADP and inorganic phosphate. Proton movement through F0 drives ATP formation at F1.

Q24. Why is oxygen essential in aerobic respiration?

Oxygen is essential because it acts as the final hydrogen acceptor in aerobic respiration.

It helps remove hydrogen from the system and allows electron transport to continue.

Without oxygen, ETS cannot operate properly. This stops efficient ATP production through oxidative phosphorylation.

Long Answer Questions Class 11 Biology Chapter 12

Long Answer Questions from Respiration in Plants need stepwise explanation and correct pathway sequence. Strong answers connect glycolysis, Krebs cycle, ETS, ATP calculation, amphibolic nature and RQ values.

Q25. Explain glycolysis with its main steps.

Glycolysis is the breakdown of glucose into two molecules of pyruvic acid.

It occurs in the cytoplasm and is also called the EMP pathway.

In the first phase, glucose is phosphorylated using ATP. It forms glucose-6-phosphate and then fructose-6-phosphate.

Another ATP is used to form fructose-1,6-bisphosphate. Fructose-1,6-bisphosphate then splits into two triose phosphates.

These triose phosphates are converted through enzyme-controlled steps into phosphoenolpyruvate and finally pyruvic acid.

In glycolysis, two ATP are used and four ATP are formed. The net gain is two ATP and two NADH molecules.

Q26. Differentiate between fermentation and aerobic respiration.

Fermentation is an anaerobic process, while aerobic respiration occurs in the presence of oxygen.

Fermentation causes only partial breakdown of glucose. Aerobic respiration completely oxidises glucose to carbon dioxide and water.

Fermentation gives a net gain of only two ATP per glucose molecule. Aerobic respiration produces many more ATP molecules because it uses Krebs cycle and ETS.

Fermentation produces ethanol and carbon dioxide or lactic acid. Aerobic respiration produces carbon dioxide, water and a large amount of energy.

Q27. Describe the Krebs cycle with an overall view.

Krebs cycle is a cyclic pathway that operates in the mitochondrial matrix.

It is also called the citric acid cycle or tricarboxylic acid cycle.

The cycle begins when acetyl CoA combines with oxaloacetic acid and water to form citric acid. Citric acid is then converted through a series of reactions.

During the cycle, carbon dioxide is released, NADH and FADH2 are formed, and one GTP or ATP is produced. Oxaloacetic acid is regenerated so the cycle can continue.

The Krebs cycle completes the oxidation of acetyl CoA and provides reduced coenzymes for the electron transport system.

Q28. Explain the electron transport system and oxidative phosphorylation.

The electron transport system is a chain of electron carriers present on the inner mitochondrial membrane.

It transfers electrons from NADH and FADH2 to oxygen through a series of carriers.

Electrons from NADH enter through Complex I, while electrons from FADH2 enter through Complex II.

They pass to ubiquinone, cytochrome complex, cytochrome c and Complex IV.

The energy released during electron transport helps pump protons across the inner mitochondrial membrane. Their return through ATP synthase produces ATP.

This ATP synthesis linked to oxidation-reduction reactions is called oxidative phosphorylation.

Q29. Why is the respiratory balance sheet only a theoretical exercise?

The respiratory balance sheet is theoretical because it is based on several assumptions.

It assumes that glycolysis, Krebs cycle and ETS occur in a strict sequence.

It also assumes that NADH from glycolysis enters mitochondria for oxidative phosphorylation. It assumes that no pathway intermediates are used for other compounds.

It further assumes that only glucose is being respired. In living cells, pathways work together and intermediates enter or leave as needed.

Under theoretical assumptions, aerobic respiration of one glucose can yield 38 ATP.

Q30. Define respiratory quotient and explain its values for carbohydrates and fats.

Respiratory quotient is the ratio of the volume of carbon dioxide evolved to the volume of oxygen consumed during respiration.

It depends on the respiratory substrate used by the cell.

For carbohydrates, RQ is 1 because equal volumes of carbon dioxide and oxygen are exchanged. For example, complete oxidation of glucose uses six molecules of oxygen and releases six molecules of carbon dioxide.

For fats, RQ is less than 1 because fats require more oxygen for oxidation. For proteins, RQ is about 0.9.

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