Closed stoma prevents H O loss and CO uptake NADP + malk enzyme Malate Malic acid Vacuole Chloroplast Starch Pyruvate CO Calvin cycle Night: Open stomata Day: Closed stomata and increase of O (Table . ). This condition changes the carboxylase role of RUBISCO into oxygenase. C Cycle takes place in chloroplast, peroxisome and mitochondria.
RUBP is converted into PGA and a 2C-compound phosphoglycolate by Rubisco enzyme in chloroplast. Since the first product is a 2C-compound, this cycle is known as C Cycle . Phosphoglycolate by loss of phosphate becomes glycolate. Glycolate formed in chloroplast enters into peroxisome to form glyoxylate and hydrogen peroxide.
Glyoxylate is converted into glycine and transferred into mitochondria. In mitochondria, two molecules of glycine combine to form serine. Serine enters into peroxisome to form hydroxy pyruvate. Hydroxy pyruvate with help of NADH H becomes glyceric acid.
Glyceric acid is cycled back to chloroplast util ising ATP and becomes Phosphoglyceric acid (PGA) and enters into the Calvin cycle (PCR cycle). Photorespiration does not yield any free energy in the form of ATP. Under certain conditions % of the photosynthetic potential is lost because of Photorespiration (Figure . ).
. . Significance of photorespiration . Glycine and Serine synthesised during this process are precursors of many biomolecules like chlorophyll, proteins, nucleotides.
. It consumes excess NADH H generated. . Glycolate protects cells from Photo oxidation.
. . Carbon Dioxide Compensation Point When the rate of photosynthesis equals the rate of respiration, there is no exchange of oxygen and carbon dioxide and this is called as carbon dioxide compensation point . This will happen at particular light intensity when exchange of gases becomes zero.
When light is not a limiting factor and atmospheric CO concentration is between to ppm the net exchange is zero. . Factors affecting Photosynthesis In , Sachs gave three cardinal points theory explaining minimum, optimum and maximum factors that control photosynthesis. Table .
: Differences between Photorespiration and Dark Respiration Photorespiration Dark respiration . It takes place in photosynthetic green