Introduction

Respiration in plants is the process of breaking down glucose to release energy in the form of ATP. Unlike photosynthesis, which stores energy, respiration releases energy for cellular activities.

NEET frequently tests types of respiration, stages, ATP yield, and stoichiometric formulas. Understanding these helps students answer questions on plant metabolism and energy cycles.

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1. Definition and Importance

Definition:

• Plant respiration is a metabolic process by which organic molecules (mainly glucose) are oxidized to release energy.

Importance:

1. Provides energy (ATP) for growth, development, and reproduction

2. Supplies reducing power (NADH, FADH₂) for biosynthetic reactions

3. Maintains metabolic homeostasis

NEET Tip:

• Energy released per glucose: ~36–38 ATP (aerobic)

2. Types of Respiration

a. Aerobic Respiration

• Requires oxygen (O₂)

• Complete breakdown of glucose to CO₂ and H₂O

• Occurs in mitochondria

General Formula:

C6H12O6+6O2→6CO2+6H2O+36–38ATPC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + 36–38 ATPC6​H12​O6​+6O2​→6CO2​+6H2​O+36–38ATP

b. Anaerobic Respiration (Fermentation)

• Occurs without oxygen

• Glucose partially broken down → less ATP

• Types in plants:

  1. Alcoholic fermentation: Glucose → 2 Ethanol + 2 CO₂ + 2 ATP

  2. Lactic acid fermentation: Glucose → 2 Lactic acid + 2 ATP

NEET Tip:

• Anaerobic → 2 ATP/glucose, aerobic → 36–38 ATP/glucose

3. Stages of Aerobic Respiration

H4 bold headings format for NEET-friendly content:

a. Glycolysis (Cytoplasm)

• Glucose (6C) → 2 Pyruvate (3C)

• Net ATP: 2 ATP

• Produces 2 NADH

• Anaerobic stage too → forms pyruvate for fermentation if O₂ absent

NEET Shortcut Formula:
Glucose + 2 NAD⁺ + 2 ADP + 2 Pi → 2 Pyruvate + 2 NADH + 2 ATP

b. Link Reaction (Pyruvate → Acetyl-CoA, Mitochondrial Matrix)

• 2 Pyruvate → 2 Acetyl-CoA + 2 CO₂ + 2 NADH

c. Krebs Cycle (Citric Acid Cycle, Mitochondrial Matrix)

• Each Acetyl-CoA → 3 NADH + 1 FADH₂ + 1 ATP + 2 CO₂

• Total per glucose (2 Acetyl-CoA):

  • NADH → 6

  • FADH₂ → 2

  • ATP → 2

  • CO₂ → 4

NEET Formula:
C₂H₃O-CoA → 3 NADH + 1 FADH₂ + 1 ATP + 2 CO₂

d. Electron Transport Chain (Inner Mitochondrial Membrane)

• NADH and FADH₂ oxidized → H⁺ gradient → ATP via oxidative phosphorylation

• ATP yield:

  • 1 NADH → 3 ATP

  • 1 FADH₂ → 2 ATP

• Total ATP per glucose: ~36–38

e. Summary Table of Aerobic Respiration:

4. Anaerobic Respiration in Plants

• Occurs in oxygen-deficient conditions

• Fermentation pathways:

  • Alcoholic fermentation: Glucose → 2 Ethanol + 2 CO₂ + 2 ATP

  • Lactic acid fermentation: Glucose → 2 Lactic acid + 2 ATP

NEET Tip:

• Alcoholic fermentation → Yeast and some plant tissues

• Lactic acid → Rare in plants but occurs under stress

5. Respiration in Special Plant Tissues

• Roots: Often low O₂ → rely on anaerobic respiration

• Storage organs (tubers): High respiration during sprouting

• Fruits: Increased respiration during ripening (climacteric rise)

NEET Tip:

• Rapid respiration in seeds and fruits → “Respiratory climacteric”

6. Factors Affecting Plant Respiration

1. Oxygen concentration: Limiting factor for aerobic respiration

2. Temperature: Optimum 25–35°C for enzyme activity

3. Water availability: Dehydration slows respiration

4. Substrate availability: Glucose or other sugars

NEET Tip:

• High temperature → increased respiration → faster consumption of stored food.

7. NEET Exam Tips

• Draw respiration diagrams with ATP yield per stage

• Remember glucose → pyruvate → acetyl-CoA → Krebs → ETC → ATP

• Use formulas for numerical questions

• Focus on difference between aerobic and anaerobic respiration

Conclusion

Respiration in plants is a high-yield topic in NEET Biology. Mastery of glycolysis, Krebs cycle, electron transport chain, and aerobic/anaerobic pathways is essential for scoring in MCQs and diagram-based questions.

With this StudentBro.in guide, students can efficiently revise plant respiration formulas, ATP yield, and stages, enhancing speed and accuracy during NEET exams.

Remember: Linking substrate → pathway → product → ATP yield is the key to mastering Respiration in Plants for NEET.