🌧 R.Q.

Efficiency of respiration

• When glucose is a respiratory substrate, 686 K Cal is released where some energy is conserved as 38 ATP molecules.
• When one ATP molecule is hydrolyzed, the energy released is about 7.6 K Cal per mole of the terminal phosphate group in ATP.
• Efficiency = 38 x 7.6/ 686 = 42 %
• Thus the efficiency of respiration is 40-50%.
• It means respiration is partially efficient and rest energy is lost as heat energy.
• The temp of the test tube containing germinating seed is increased only due to fast respiration.
• In the dormant seed, respiration is slow.

🙋🏼‍♀️ Q. During aerobic respiration of glucose, a plant cell released 42 molecules of CO2. How many ATP will be produced ❓

Soln:

• 6 molecules of CO₂ produced when 38 ATP are released.
• 42 molecules of CO₂ produced are 38 /6 x 42 = 266 ATP.

Respiratory Substrates

• Glucose is the favored substrate for respiration. All carbohydrates are usually first converted into glucose before they are used for respiration. Other substrates can also be respired, as has been mentioned earlier, but then they do not enter the respiratory pathway at the first step.
• Fats would need to be broken down into glycerol and fatty acids first. If fatty acids were to be respired they would first be degraded to acetyl CoA and enter the pathway. Glycerol would enter the pathway after being converted to PGAL.
• The proteins would be degraded by proteases and the individual amino acids (after deamination) depending on their structure would enter the pathway at some stage within the Krebs’ cycle or even as pyruvate or acetyl CoA.

• Glycolysis is also known as oxidative anabolism or catabolic resynthesis, because it links with anabolism of fats and amino acids. An intermediate PGAL is used for the synthesis of glycerol later form fats or lipid. PGA is used for synthesis of Serine, Glycine, Cysteine, Alanine forms from pyruvate.
• Acetyl Co-A is common intermediate (connecting link) between fat, carbohydrate and protein metabolism.
• The sequential process of fatty acid catabolism to acetyl CoA (Oxidation of fats) is called Beta Oxidation.

Respiratory Quotient/Respiratory Ratio

• R.Q. is the ratio of the volume of CO₂ released to the volume of O₂ absorbed in the respiration. It is also called Respiratory Ratio (RR).
• R.Q. = Volume of released CO₂ / Volume of absorbed O₂
• The R.Q. of a plant material is measured by Ganong's Respirometer.
• R.Q. = 1, when substrate is carbohydrate (hexose).

  C₆H₁₂O₆ + 6O₂ + 6H₂O → 6CO₂ + 12H₂O + 686 K.cal

• R.Q. < 1 i.e. RQ is less than unity. When respiratory substrate is highly reduced food.
  • Respiration of fats & protein:

    2C₅₁H₅₈O₆ + 145 O₂ → 102CO₂ + 98H₂O (fat)

    • When substrate is Fat, R.Q. = 0.7
    • When substrate is Protein, R.Q. = 0.8 - 0.9
  • Respiration of Protein
  • With amide formation, RQ = 0.8
  • With ammonia formation, RQ = 0.99
• Respiration in CAM Plants (Succulent plants and red leaves)
  • **R.Q.** = 0
  • i.e. Xerophytes e.g. Opuntia
  • Here oxidation is incomplete

  2C₆H₁₂O₆ + 3O₂ →(Partial Oxidation)→ Malic Acid + 3H₂O + 386 K.Cal

  • R.Q. = CO₂/O₂ = 0/3 = 0
• R.Q. > 1 i.e. R.Q. is more than unity when respiratory substrate is highly oxidized food.
  • Organic acids:

  C₄O₆O₅ (Maic Acid) + 3O₂ → 4CO₂ + 3H₂O

  • R.Q. = CO₂/O₂ = 4/3 = 1.3

  2(COOH)₂ (Oxalic Acid) + O₂ → 4CO₂ + 2H₂O + 60.2 K Cal

  • R.Q. = CO₂/O₂ = 4/1 = 4
• Anaerobic respiration:

  C₆H₁₂O₆ →(Zymase)→ 2C₂H₅OH + 21 K.Cal

  • R.Q. = CO₂/O₂ = 2/0 = ∞

👉🏻 Difference between Aerobic Respiration and Anaerobic Respiration

👉🏻 Difference between Respiration and Photosynthesis

👉🏻 Difference between Respiration and Photorespiration

Factors affecting respiration (Aerobic)

External Factors

Temperature

• The increase in temperature increases the rate of respiration following the Vant Hoff's law.
• Vant Hoff’s Law: The respiration rate increases two or three times for every rise of 10°C i.e. Q₁₀ = 2 or Q₁₀ = 3. This marked increase in respiration rate is only in between the range of 0°- 45°C. The optimum temp. of respiration is 30°C.
• At high temperature, there is a decrease in respiration rate and the responsible factor is called Time Factor.
• At very low temp., the respiration rate is very low i.e. insignificant.
• Therefore vegetables and fruits are generally stored at very low temperature just to minimize the catabolic effects of respiration.

Light

• The effect of light is indirect on respiration rate.
• Light increases the respirable material by increasing photosynthesis.
• Light also increases the temperature.
• Light affects the opening and closing of stomata also.

Concentration of O₂ in the atmosphere

• Oxygen is essential for aerobic respiration but its concentration in the atmosphere is almost constant thereby not affecting the rate.

CO₂ concentration

• Since its concentration in the atmosphere is also constant, therefore it has no effect on respiration rate. But its concentration is variable in the soil air, therefore its high concentration in the soil air, inhibits all those activities of plant which require energy.

Water

• The slight change in the water content does not affect the respiration rate.
• The shortage of water may increase the respiration rate but the very low content of water (e.g. dry seeds and stored tubers) minimizes the respiration rate.

Injury

• The sugar content of the injured or wounded portion of the plant is suddenly increased because the conversion of starch to sugar is increased due to the increase in the rate of respiration.

Certain chemical compounds

• Certain enzymatic inhibitors like cyanides, azides, carbon monoxide, iodoacetate chloroform, ether etc. reduces the rate of respiration.

Mechanical effects

• The gentle rubbing or bending of the leaf blade increases the respiration rate but high wind or storm closes the stomata to cutoff the O₂ supply.

Internal Factor

Protoplasmic factors

• Younger cells which have more of active protoplasm respire more rapidly than older cells. The older cells have less protoplasm due to larger vacuoles. The rate is also affected by the quantities of respiratory enzymes present in the protoplasm. In the old age (i.e. senescence), the respiration rate declines.

Concentration of respiratory material

• If other factors are not limiting, the respiration rate increases with the increase in the respiratory substrate.

Pasteur Effect

• Generally the increase in respiratory substrate or oxygen, increases the rate of respiration.
• But there are many cases where oxygen reduces the rate of sugar breakdown and even conserve it, is called Pasteur Effect.

Climacteric Rise

• The rate of respiration varies with the age of respirable cell in meristmatic cells respiration is high and becomes steady in the growing stages.
• In the maturing fruit or in the ripening of fruits, there is the production of ethylene which increases the respiration rate.
• This rise in the rate of respiration is called the climacteric rise.

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