Respiration in Plants – NEET Notes with MCQs & Concept Explanations
Class 11 NCERT Biology | Chapter 14 |

As we all know, plants use photosynthesis to produce their own food, but like animals, they also require respiration to discharge energy from that food.
The purpose of respiration in plants is to liberate ATP, the cell's energy currency, by breaking down glucose and other organic substances.

This chapter discusses:
respiration types (fermentation, anaerobic, and aerobic)
Substrates for respiration (proteins, lipids, and carbohydrates)
respiration steps (ETS, Krebs cycle, glycolysis)

Let's proceed gradually.

Respiratory Types

The process of aerobic respiration
total breakdown of glucose when O₂ is present.
Final products: ATP (36–38 ATP) + CO₂ + H₂O.

Anaerobic Breathing

occurs in the absence of O₂ (in yeast, some bacteria, and oxygen-deficient plant situations).
generates lactic acid or ethanol + CO₂.
A lot less energy (only two ATP).

Substrates for Respiration

The primary source of carbohydrates is glucose.
Fats (used during famine; produces more energy).
In an energy crisis, proteins are the last resort.

Respiratory Steps Glycolysis takes place in the cytoplasm.

2 Pyruvate + 2 ATP + 2 NADH = Glucose

The TCA cycle, often known as the Krebs cycle, occurs in the mitochondrial matrix.
The pyruvate was fully oxidized.
generates ATP, CO₂, FADH₂, and NADH.

System of Electron Transport (ETS)

mitochondrial inner membrane.
As electrons move through carriers, oxidative phosphorylation produces ATP.
As the last electron acceptor, O₂ creates water.

The Amphibolic Path

Although respiration breaks down glucose, it also uses intermediates for anabolism, which produces lipids, amino acids, and other substances.
Respiration is hence amphibolic.

Formula for Respiratory Quotient (RQ):

RQ is equal to the volume of CO2 developed divided by the volume of O2 eaten. Carbohydrates produce RQ = 1, fats produce RQ < 1, while organic acids produce RQ > 1.

NEET MCQs with Concept Explanations

Q1. Respiration is mainly carried out in plants through:
A) Stomata only
B) Lenticels only
C) Root hairs only
D) All of the above

Answer : D) All of the above

Concept Explanation : Plants respire through all structures – stomata (leaves), lenticels (stems), root hairs (roots).

Q2. How many ATP molecules are produced from one molecule of glucose in aerobic respiration?
A) 2
B) 8
C) 36–38
D) 4

Answer : C) 36–38
Concept Explanation : Complete oxidation of glucose via glycolysis, TCA, and ETS yields ~36–38 ATP.

Q3. Where does glycolysis occur?
A) Cytoplasm
B) Mitochondrial matrix
C) Inner mitochondrial membrane
D) Chloroplast

Answer : A) Cytoplasm
Concept Explanation : Glycolysis = universal process in cytoplasm.

Q4. In anaerobic respiration in yeast, the end products are:
A) Lactic acid + CO₂
B) Ethanol + CO₂
C) H₂O + CO₂
D) Pyruvic acid

Answer : B) Ethanol + CO₂
Concept Explanation : Yeast converts pyruvate → ethanol + CO₂ (fermentation).

Q5. Respiratory quotient (RQ) for carbohydrates is:
A) 0.7
B) 1
C) >1
D) <1

Answer : B) 1

Concept Explanation : For glucose: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O → RQ = 6/6 = 1.

Q6. Which is the final electron acceptor in ETS?
A) NAD⁺
B) FAD
C) O₂
D) ATP

Answer : C) O₂
Concept Explanation : Oxygen is the terminal electron acceptor → forms water.

Q7. Respiration is called an amphibolic pathway because:
A) It involves both catabolism and anabolism
B) It occurs in plants and animals
C) It occurs with or without oxygen
D) It occurs in cytoplasm

Answer : A) It involves both catabolism and anabolism
Concept Explanation : Respiratory intermediates also build biomolecules → dual role.

Q8. In which step of respiration is maximum ATP formed?
A) Glycolysis
B) Link reaction
C) Krebs cycle
D) ETS

Answer : D) ETS
Concept Explanation : ETS produces ~34 ATP → highest yield.

Q9. The common pathway for aerobic and anaerobic respiration is:
A) Krebs cycle
B) Glycolysis
C) ETS
D) Fermentation

Answer : B) Glycolysis
Concept Explanation : Glycolysis occurs in both aerobic and anaerobic respiration, converting glucose to pyruvate.

Q10. Which enzyme catalyzes the conversion of pyruvate to acetyl-CoA?
A) Hexokinase
B) Pyruvate dehydrogenase
C) Lactate dehydrogenase
D) ATP synthase

Answer : B) Pyruvate dehydrogenase
Concept Explanation : Link reaction: Pyruvate → Acetyl-CoA in mitochondrial matrix via pyruvate dehydrogenase.

Q11. Number of NADH produced in one turn of Krebs cycle is:
A) 2
B) 3
C) 4
D) 1

Answer : B) 3

Concept Explanation : Each turn produces 3 NADH, 1 FADH₂, 1 ATP (substrate level).

Q12. Which of the following processes does NOT occur in mitochondria?
A) Krebs cycle
B) ETS
C) Glycolysis
D) Oxidative phosphorylation

Answer : C) Glycolysis
Concept Explanation : Glycolysis = cytoplasm; mitochondria handle Krebs + ETS.

Q13. Pasteur effect is:
A) Inhibition of glycolysis by oxygen
B) Increase in respiration due to lack of oxygen
C) Formation of lactic acid under anaerobic condition
D) Production of ethanol in yeast

Answer : A) Inhibition of glycolysis by oxygen

Concept Explanation : When O₂ is present, anaerobic glycolysis slows down = Pasteur effect.

Q14. Which of the following produces maximum ATP per gram?
A) Carbohydrates
B) Proteins
C) Fats
D) Organic acids

Answer : C) Fats
Concept Explanation : Fats are highly reduced → more hydrogen atoms → more ATP on oxidation.

Q15. Which intermediate of Krebs cycle is used for amino acid synthesis?
A) Citrate
B) α-Ketoglutarate
C) Succinyl-CoA
D) Malate

Answer : B) α-Ketoglutarate
Concept Explanation : α-Ketoglutarate is precursor for glutamate and other amino acids.

Q16. In anaerobic respiration of glucose, the net gain of ATP is:
A) 0
B) 1
C) 2
D) 4

Answer : B) 1
Concept Explanation : Only glycolysis operates → 2 ATP per glucose molecule.

Q17. Where is cytochrome system located?
A) Cytoplasm
B) Plasma membrane
C) Inner mitochondrial membrane
D) Outer mitochondrial membrane

Answer : C) Inner mitochondrial membrane
Concept Explanation : ETS (cytochrome chain) is embedded in cristae of mitochondria.

Q18. Which of the following is an amphibolic pathway?
A) Photosynthesis
B) Respiration
C) Fermentation
D) Glycolysis

Answer : B) Respiration
Explanation : Respiration is both catabolic (energy release) and anabolic (biosynthesis intermediates).

Q19. Net ATP produced from complete oxidation of 1 molecule of glucose in prokaryotes is:
A) 36
B) 38
C) 34
D) 40

Answer : B) 38
Concept Explanation : Prokaryotes don’t lose ATP in transport of NADH into mitochondria, hence 38 ATP.

Q20. The site of oxidative phosphorylation is:
A) Cytoplasm
B) Mitochondrial matrix
C) Inner mitochondrial membrane
D) Outer mitochondrial membrane

Answer : C) Inner mitochondrial membrane
Concept Explanation : ETS + ATP synthase are located on inner mitochondrial membrane (cristae).

Important for NEET

Glycolysis = ubiquitous cytoplasm.
Pyruvate enters mitochondria by the link reaction.
Complete oxidation results in the Krebs cycle, which releases CO2.
ETS = oxygen essential, ATP powerhouse.
Less ATP results from anaerobic respiration.
The RQ value aids in substrate identification.
The amphibolic route is respiratory.

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