Photorespiration And Dark Respiration


  • PHOTORESPIRATION first demonstrated by Decker in 1955 and 1959.

‘The Photorespiration defined as “the Respiration that occurs in green cells in the presence of light resulting into excess evolution of CO2”


“The release of CO2 in Respiration in presence of light.”

  • Always required light to perform.
  • The photorespiration rate of reaction takes place at 25℃-35℃.
  • Depending on oxygen concentration to takes place of this process.
  • Photorespiration is diffrent from Dark Respiration.
  • Photorespiration is also known as the C2 cycle.
  • Photorespiration takes place in different green cells of plants
    as: Pisum
  • It also is known as the oxidative photosynthetic carbon cycle, or C2 photosynthesis.


The three cell-organelles: Chloroplasts, Peroxisomes, and the Mitochondria together actively participate in Photorespiration to form the Site of Photorespiration.


  • It helps to fast the photosynthesis process by increasing the concentration of CO2 in intercellular spaces of leaf tissue.
  • Photorespiration process is important so we can classify the plants in two groups as:

1. Plants without Photorespiration.

2. Plants with Photorespiration.

Pisum Oryza Glycine Capsicum Nicotiana Pisum Petunia Antirrhinum Chlorella Nitella Helianthus Gossiping Phaseolus

CharacteristicsWith PhotorespirationWithout Photorespiration
Enhancement of CO2 assimilation in light and low oxygen.YesNo
CO2 compensation point in light.15 to 150ppm0 ppm
CO2 assimilation rate in intense light.15 to 35 mg CO2/dm2/h50 to 70 mg CO2/dm2/h
CO2 evolution in light.High rateApparently nil
Internal structure of leaf.Diffuse mesophyllMesophyll compact about vascular bundles.
Carbon pathwayCalvin cycleCalvin cycle and HATCH and SLACK pathway both
Carbonic anhydrase activity.HighLow
Translocation rate from leaf.LowHigh
Temperature optimum for photosynthesis and growth.Low to highHigh
  • The photorespiration process can take place in a very low concentration of oxygen too.
  • The rate of Photorespiration decreased with the increase of CO2 in the atmosphere.

Difference Between Photorespiration and Dark Respiration

It takes place only in presence of light.It occurs in light and Dark both conditions.
It occurs only in green cells.It occurs in all living cells.
The respiratory substrate in Photorespiration is 2-carbon glycolic acid.The respiratory substrate in dark Respiration may be carbohydrates, fats or protiens.
Respiratory substrate is immediately formed.Respiratory substrate may be previously stored or immediately formed.
It occurs among chloroplasts, cytoplasm, peroxisomes and mitochondria.It occurs in cytoplasm and mitochondria.
During Photorespiration, hydrogen peroxide (H2O2) is formed.H2O2 is not formed.
ATP molecules are not synthesized.ATP molecules are synthesized.
NADH is oxidised to NAD+.NAD+is reduced to NADH+ H+.
The process of transamination occurs during Photorespiration.This process does not occurs during dark Respiration.
It depends upon O2 concentration and is directly proportional to it.O2 concentration has no affect on this process.
It's maximum rate is in between 25℃-35℃.It's maximum rate is in between 35℃-40℃.