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Bio Photosynthesis and Photorespiration Flashcards | Quizlet

The and avoid photorespiration and therefore operate at much higher efficiencies in hot and dry climates.

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How are photosynthesis and photorespiration different…

Fructose-1,6-bisphosphate is cleaved by fructose bisphosphate aldolase to form glyceraldehyde-3-phosphate and dihydroxyacetone phosphate, and these triose phosphates can be interconverted in a reaction catalysed by triose phosphate isomerase. Glyceraldehyde-3-phosphate is oxidised to 1,3-bisphosphoglycerate by a nicotinamide adenine dinucleotide (NAD+)-dependent glyceraldehyde 3-P dehydrogenase. Glyceraldehyde 3-P dehydrogenase is sensitive to inhibition by the reduced pyridine nucleotide cofactor (NADH), which must be reoxidised to maintain the flux through the glycolytic pathway. A phosphate group is then transferred from 1,3-bisphosphoglycerate to ADP forming ATP and 3-phosphogylcerate by phosphoglycerate kinase. In the cytosol a bypass is present that can convert glyceraldehyde-3-phosphate directly to 3-phosphoglycerate without phosphorylation by a non-phosphorylating NADP dependent glyceraldehyde 3-phosphate dehydrogenase. The resulting 3-phosphoglycerate is then converted to phosphenolpyruvate (PEP) by the action of phosphoglycerate mutase and then enolase.

It is a cycle because the some of the starting material is regenerated as the process occurs

One hundred million years ago (Mid-Cretaceous), atmospheric CO2 was between 1500 and 3000 µL L–1, or four to ten times post-industrial levels. Atmospheric CO2 declined during the Oligocene (20-30 million years ago) from the high Tertiary levels (>1000 µL L-1), and oscillated between 180 and 300 µL L-1 for the last 1-3 million years. The Oligocene was also a time when the Earth was dry and the tropics were relatively hot. The earliest origins of C4 photosynthesis date back to this period. Curiously, C4 plants remained in low abundance for a long period of time. According to stable carbon isotopic data, a worldwide expansion of C4 grasslands and savannas occurred during the Late Miocene and Pliocene (3 to 8 million years ago), most probably through the displacement of C3 vegetation (Edwards et al. 2010).

Photosynthesis and Photorespiration Flashcards | Quizlet

Thus, the carbon dioxide that was fixed through ATP-dependent processes is released out again through another set of ATP-dependent reactions.

Heber U, Bligny R, Streb P et al. (1996) Photorespiration is essential for the protection of the photosynthetic apparatus of C3 plants against photoinactivation under sunlight. Botanica Acta 109: 307–315.

Kebeish R, Niessen M, Thiruveedhi K et al. (2007) Chloroplastic photorespiratory bypass increases photosynthesis and biomass production in Arabidopsis thaliana. Nature Biotechnology 25: 593–599.

Photosynthesis vs Photorespiration - What's the …

However, when there is an excess buildup of oxygen, as well as under stressful environmental conditions, photorespiration is enhanced.

Rubisco first evolved when the earth’s atmosphere was rich in CO2, but virtually devoid of O2. With the advent of oxygen-producing photosynthesis by land plants, and the resulting increases in atmospheric O2, one key deficiency of this enzyme became apparent. Rubisco would not only catalyse fixation of CO2 but would also permit incorporation of O2 into RuBP to produce, instead of two molecules of 3-PGA, just one molecule of 3-PGA with one molecule of a two-carbon compound, 2-phosphoglycolate (Section 2.3). Indeed, CO2 and O2 compete directly for access to the active sites of Rubisco. So feeble is Rubisco’s ability to distinguish between these two substrates that in air (20% O2) approximately one molecule of O2 is fixed for every three molecules of CO2.

Fixation of O2 and subsequent photorespiration (Section 2.3) is an energy-consuming process, due to competition between O2 and CO2 for RuBP, plus the energy cost of converting the phosphoglycolate product to a form which can be recycled in the PCR cycle. This energy cost is increased at higher temperatures because O2 competes more effectively with CO2 at the active site of Rubisco. Such sensitivity to temperature × O2 explains why CO2 enrichment, which reduces photorespiration, has a proportionally larger effect upon net carbon gain at higher temperatures than at lower temperatures (Section 13.3).

Blackwell RD, Murray AJS, Lea PJ et al. (1988) The value of mutants unable to carry out photorespiration. Photosynthesis Research 16: 155–176.
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  • How does photorespiration affect the calvin cycle

    Photosynthesis Foldable - Practice quizzing yourself on the process of photosynthesis and all the characters involved.

  • Photosynthesis Photorespiration And Plant Productivity …

    Sharkey TD (1988) Estimating the rate of photorespiration in leaves. Physiologia Plantarum 73: 147–152.

  • What is photorespiration? | Yahoo Answers

    Hatch MD (1992) C4 photosynthesis: an unlikely process full of surprises Plant Cell Physiol 33: 333–342

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Does photorespiration affect the rate of photosynthesis

The advantage that comes from this two-stage process is that the active pumping of carbon into the bundle sheath cell and the blocking of oxygen produce an environment with 10-120x as much CO2 available to the Calvin cycle and the tends to be optimally utilized. The high CO2 concentration and the absence of oxygen implies that the system never experiences the detractive effects of .

Where does photorespiration occur

Oxygenic photosynthesis is only possible on the condition of adequate photorespiratory metabolism and life on earth would look very different without it.


Oxygenic photosynthesis is coupled to photorespiratory carbon dioxide losses and this reduces competitiveness of C3 plants in warm environments. Gene technology‐assisted breeding hopes to reduce these losses in crops.


The connection to hot and dry conditions comes from the fact that all the plants will close their stomata in hot and dry weather to conserve moisture, and the continuing fixation of carbon from the air drops the CO2 dramatically from the atmospheric concentration of nominally 380 ppm (2004 value). If the CO2 compensation point is lower on the above scale, the plant can operate in hotter and dryer conditions. The limits are placed by the fact that begins to fix oxygen rather than CO2, undoing the work of photosynthesis. C4 plants shield their rubisco from the oxygen, so can operate all the way down to essentially zero CO2 without the onset of photorespiration.

How can the answer be improved?

The plant photorespiratory C2 cycle spans three organelles: the chloroplast, the peroxisome and the mitochondrion. The enzymes of the core cycle are Rubisco, phosphoglycolate phosphatase (PGP), glycolate oxidase (GOX), serine‐glyoxylate aminotransferase (SGT), glutamate‐glyoxylate aminotransferase (GGT), glycine decarboxylase (GDC), serine hydroxymethyltransferase (SHMT), peroxisomal hydroxypyruvate reductase (HPR1) and glycerate kinase (GLYK). Catalase (CAT) detoxifies hydrogen peroxide. A cytosolic hydroxypyruvate reductase (HPR2) supports HPR1 when the peroxisomal malate dehydrogenase (pMDH) does not provide NADH rapidly enough for hydroxypyruvate reduction. Photorespiratory ammonia is captured by glutamine synthetase (GS2). The produced glutamine is then used by ferredoxin‐dependent glutamate synthase (GOGAT) to recycle 2‐oxoglutarate into fresh glutamate for peroxisomal transamination.

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