Introduction
The Calvin-Benson cycle takes place in all plants, but different species of plants are adapted to use it in differnt ways, largely due to temperature conditions in different enviroments. This Web Quest will help you understand these mechanisms. Enjoy.
Evaluation
C3 Photosynthesis. This type of photosynthesis employs solely the C3 Cycle by which carbon dioxide go through chemical reactions to form carbohydrates. The C3 cyclic reactions also include the regeneration of the CO2-acceptor chemical substrate. Plants exhibiting this mechanism of photosynthesis are called C3 plants.
The C3 cycle can be divided into three stages: CO2 Fixation, Reduction, and Regeneration.
First stage: In CO2 Fixation, the CO2 that diffuses into the stroma of the chloroplast in mesophyll cells is added to the five-carbon acceptor ribulose-1,5-bisphosphate also called diphosphate phosphoglycerate or phosphoglyceric acid as the first stable product. The reaction is catalyzed by the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase.
Second Stage: Carbon Reduction stage follows. Each of the two molecules of 3-PGA undergoes further reactions to produce the three-carbon triose phosphate sugar glyceraldehyde-3-phosphate, also called phosphoglyceraldehyde. A molecule of G3P is first phosphorylated by ATP, producing 1,3-bisphosphoglycerate which is in turn reduced to G3P with NADPH as the reducing agent.
Third stage: The Regeneration stage completes the cycle. Some molecules of G3P go through further reactions which result to the reformation of RuBP, the CO2 acceptor in the C3 cycle.
To complete the process of photosynthesis, the other molecules of G3P leave the cycle and proceed to a series of reactions to form glucose and other sugars, starch, and other organic compounds. It takes six turns of the cycle, or a total of six molecules of CO2, to produce one molecule of glucose.
Examples of plants that undergo C3 photosynthesis: Rice, Wheat, Barley, Rye, Oat, Soybean, peanut, Cotton, Sugar beats, and Tobacco.
Enviromental conditions: Temperate.
C4 Photosynthesis. This mechanism of photosynthesis occurs in two adjoining types of cells, the mesophyll and bundle sheath cells in plant species called C4 plants. Both C3 and C4 cycles operate in the non-light-requiring or Dark Reactions of photosynthesis but spatially, that is, in different cells: C4 in the mesophyll cells immediately followed by C3 cycle in the bundle sheath cells.
CO2 first enters the leaf and into the mesophyll cell. It is then hydrated to produce bicarbonate ion (HCO3-) in the cytoplasm with carbonic anhydrase (CA) as catalyst. This is the first step in C4 photosynthesis, followed by carboxylation reaction utilizing HCO3- instead of CO2 as the inorganic carbon substrate, Hatch and Burnell (1990) emphasized.
Examples of plants that undergo C4 photosynthesis: Acanthaceae, Aizoaceae, Amaranthaceae, Chenopodiaceae, Asteraceae, Boraginaceaa, Capparidaceae, Caryophyllaceae, Euphorbiaceae, Molluginaceae, and Nyctaginaceae.
Enviromental conditions: Tropical or semi-tropical, high light intensity, high temperature, drought conditions.
Credits
Credits:
"Crop Farming or Crop Agriculture: Basics and Practical Methods." CropsReview.Com. Crops Review, 21 Aug. 2014. Web. 29 Sept. 2014.
Image Credits: