Factors Affecting Respiration

The rate of respiration in plants depends on how efficiently respiratory enzymes work and how easily substrates (food) and oxygen are available. Since respiration is a controlled, enzyme-driven process, any factor that affects enzyme activity, oxygen supply, or substrate availability will affect respiration.

Exam Line: Respiration is influenced by external (environmental) + internal (physiological) factors, and they often act together.

External Factors (Environmental)

1. Temperature

Respiration is enzyme-controlled, so temperature strongly affects it.

  • As temperature increases, enzyme activity increases → respiration increases.
  • The rate rises up to an optimum (usually 30–35°C for many plants).
  • Beyond optimum, enzymes start losing shape (denaturation) → respiration falls.

Key Points to Memorize:

  • Optimum: 30–35°C
  • Very high temperature → enzyme denaturation → respiration decreases
  • Q10 rule: For every 10°C rise, respiration rate becomes about 2 times (within normal range).

2.Oxygen Availability

Oxygen decides whether respiration is aerobic or anaerobic.

  • Adequate O₂ → aerobic respiration (high ATP)
  • Low O₂ → anaerobic respiration / fermentation (very low ATP)
  • No O₂ → aerobic respiration stops because ETS cannot function.

Key Points:

  • Oxygen is the final electron acceptor in ETS.
  • Low oxygen forces cells to use fermentation.

3. Carbon Dioxide (CO₂) Concentration

High CO₂ generally slows respiration.

  • CO₂ can act like an inhibitor for respiratory reactions.
  • In stored fruits/grains, increased CO₂ can reduce respiration rate, slowing spoilage.

Key Point:* High CO₂ → respiration decreases.

4. Water Availability

Water maintains enzyme activity and cellular metabolism.

  • Well-hydrated tissues have active enzymes → respiration is higher.
  • Dehydration reduces enzyme efficiency and slows transport of substrates → respiration falls.

Key Point: Dehydration → enzyme activity drops → respiration decreases.

Internal Factors (Physiological)

1.Protoplasmic Condition (Living Activity Level)

Respiration depends on how metabolically active the tissue is.

  • Young/meristematic tissues (actively dividing) need more ATP → high respiration.
  • Mature or old tissues have lower metabolic demand → lower respiration.

Key Point: Young tissues respire fastest.

2.Nature and Amount of Respiratory Substrate

Respiration rate depends on both availability and type of substrate.

  • More substrate (glucose etc.) → higher respiration.
  • Carbohydrates are commonly used first because they are easy to break down.
  • Fats/proteins may be used in specific conditions (e.g., germinating oil seeds).

Key Point: Substrate availability controls respiration; carbohydrates are preferred.

3.Type of Plant Tissue

Different tissues have different respiration needs.

  • Growing tissues (root tips, shoot tips) → highest respiration
  • Storage tissues → moderate
  • Dormant tissues (seeds, tubers during dormancy) → very low

Key Order: Growing > Storage > Dormant

Important Notes

  • Respiration is highest in young tissues.
  • Q10 ≈ 2 for respiration (within the normal temperature range).
  • Factors usually act simultaneously (not one-by-one).

⚡ One-Line Revision (Super Memory)

✅ Respiration rate depends on: Temperature + O₂ + CO₂ + Water + Tissue activity + Substrate

Memory Capsules – Factors Affecting Respiration

FAST Checklist: T O C W + P S T

  • T = Temperature (optimum 30–35°C, Q10≈2)
  • O = Oxygen (needed for ETS)
  • C = CO₂ (high CO₂ slows respiration)
  • W = Water (hydration increases respiration)
  • P = Protoplasm activity (young tissues high)
  • S = Substrate (more food = more respiration)
  • T = Tissue type (Growing > Storage > Dormant)

Golden Line: Respiration is enzyme-controlled → anything affecting enzymes affects respiration.

Respiration rate depends on: Temperature + O₂ + CO₂ + Water + Tissue activity + Substrate

💡 Questions and Answers

Q1. Why does respiration rate decrease at very high temperatures?

A1:
At very high temperature, respiratory enzymes lose their shape (denature), so reactions slow down and respiration decreases.

Key Points: High temperature → enzyme denaturation → respiration ↓

Q2: Why do young tissues respire more actively than older tissues?

A2:
Young tissues are growing and dividing continuously, so they need more ATP. That’s why their respiration rate is higher.

Key Points: Growth/division → high ATP need → respiration ↑

Q3. Why does lack of water reduce respiration?

A3:
Water is needed for proper enzyme functioning and transport of substances. When tissues are dehydrated, enzymes work slowly and respiration decreases.

Key Points: Dehydration → enzyme activity ↓ + transport ↓ → respiration ↓