3.2 Respiration in Plants: The Energy of Life

Introduction: Why Do Plants Respire?

  • Plants need energy (ATP) for life processes (growth, mineral absorption, transport).
  • Respiration: Biochemical process of breaking down organic food (glucose) to release ATP.
  • Occurs in every living cell, 24 hours a day.

Photosynthesis vs. Respiration

Feature Photosynthesis Respiration
Process Anabolic (builds glucose) Catabolic (breaks down glucose)
Energy Stores energy from sunlight Releases chemical energy
Location Chloroplasts Cytoplasm and Mitochondria
Time Only in light Continuously (day and night)
Gases Uses CO₂, releases O₂ Uses O₂, releases CO₂

Gaseous Exchange in Plants

  • Plants lack specialized respiratory systems.
  • Leaves: Through stomata.
  • Stems: Through lenticels (in woody stems).
  • Roots: Through the moist surface of root hairs (from air spaces in soil).

Outline of the Respiration Process

1. Glycolysis (The First Step)

  • Location: Cytoplasm.
  • Process: Glucose (6C) → 2 Pyruvic Acid (3C).
  • Oxygen Requirement: Does not require oxygen (common to aerobic and anaerobic).
  • Net Gain: 2 ATP and 2 NADH.

Outline of the Respiration Process (Continued)

2. Krebs Cycle (The Citric Acid Cycle)

  • Location: Mitochondria.
  • Process: Pyruvic acid completely broken down in cyclic reactions.
  • Oxygen Requirement: Requires oxygen.
  • Significance: Main energy-releasing phase of aerobic respiration; produces CO₂, NADH, FADH₂.

Types of Respiration

1. Aerobic Respiration

  • Definition: Complete breakdown of glucose in the presence of oxygen.
  • Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP.
  • Energy Yield: Large amount of energy (approx. 38 ATP).

Types of Respiration (Continued)

2. Anaerobic Respiration (Fermentation)

  • Definition: Incomplete breakdown of glucose in the absence of oxygen.
  • In Plants/Yeast: Alcoholic Fermentation.
  • Equation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + 2 ATP.
  • Energy Yield: Much smaller amount of energy (only 2 ATP).

Experiments on Respiration

1. CO₂ Production During Respiration

  • Procedure: Compare germinating seeds (respiring) with boiled seeds (non-respiring) in sealed flasks.
  • Observation: Gas from germinating seeds turns limewater milky.
  • Conclusion: CO₂ is produced during respiration.

Experiments on Respiration (Continued)

2. Heat Production During Respiration

  • Procedure: Compare temperature in thermos flasks with germinating seeds vs. boiled seeds.
  • Observation: Flask with germinating seeds shows a significant temperature rise.
  • Conclusion: Heat is produced during respiration.