Discussion on the Process of Photosynthesis

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Discussionon the Process of Photosynthesis


Discussionon the Process of Photosynthesis

Photosynthesis is a chemical reaction that uses light to produce ATPenergy. The conditions necessary are water, light energy, and carbon(IV) oxide gas. The paper will discuss the process of photosynthesis.


In the light-dependent stage, a chlorophyll molecule absorbs a photonthen emits an electron. The electron moves to pheophytin. Theelectron passes to quinone molecule that starts a flow of electronsthrough a transport chain. Electron transfer reduces NADP to NADPH.In addition, electron transfer forms a proton gradient that is usedby the enzyme ATP synthase for the synthesis of ATP. Chlorophyll willregain the emitted electron during the breakdown of water moleculeinto hydrogen ion and oxygen ion. Two oxygen ions combine to form amolecule. Oxygen molecule is removed as a by- product (Blankenship,2013).


Photophosphorylation is the conversion of energy from an exitedelectron into pyrophosphate bond. The process occurs when watermolecules are charged by the light and in the presence of P680. Lightenergy makes an electron to move from P680 molecule which is part ofPhotosystem 11. Electron from water molecule split it into hydroxylions and oxygen ions. Two oxygen ions bond to form a molecule (O2)that is removed as waste. The excited electron combines with electronacceptor which starts redox reactions. The electron passes throughelectrons carriers, and it is attached to photosystem 1. The electronis further taken to a higher level after light acting on P700molecule in Photosystem 1. The electron is eventually attached toNADP+ and H+ forming NADPH. An electron fromPhotosystem 11 will replace electron in P700 (Blankenship,2013).


In darkstage, it involves a process called Calvin-Benson cycle where RuBisCOenzyme traps CO2 from the surrounding air. Carbon dioxidebonds with ribulose 1,5-bisphosphate, producing two molecules ofglycerate 3-phosphate. Glycerate 3-phosphate is converted to3-phosphoglyceraldehyde (PGAL). 3-phosphoglyceraldehyde regenerateribulose 1,5-bisphosphate. The 3-phosphate is condensed forminghexose phosphate and finally forms sucrose, cellulose, and starch. Acarbon skeleton is formed from the carbon metabolism. The carbonskeletons are further used for the production of lipids and aminoacids (Zelitch,2012).

CarbonConcentrating Mechanisms

Duringdry seasons, plants minimize opening of the stomata to reduceexcessive water loss. Hence, carbon dioxide will decrease whileoxygen gas increases. Hence, there will be an increase ofphotorespiration through the activity of enzyme oxygenase. Plantsdevelops mechanisms of adaptation to increase carbon dioxideconcentration in the leaves.

C4Carbon Fixation

Plantsusing C4 carbon fixation fixes CO2 in themesophyll cells adding it to phosphoenolpyruvate (PEP). The enzymephosphoenolpyruvate carboxylase speeds up the reaction leading to theformation of oxaloacetic acid. Oxaloacetic acid is transferred tobundle sheath which contains RuBisCO enzyme. Decarboxylation ofoxaloacetic acid is fixed by RuBisCO to a three-carbon3-phosphoglyceric acids. Spliting of RuBisCO from the photolysisprocess minimizes photorespiration while aggravating carbon dioxidefixation (Zelitch,2012). As a result, photosynthetic activity of the leafincreases.

Inconclusion, the process of photosynthesis produces oxygen as aby-product. The oxygen is emitted to the atmosphere and used byanimals for respiration. The process of photosynthesis makes glucosethat is the source of energy for animals. In addition, photosynthesisuses carbon dioxide in the atmosphere, this help in regulation ofcarbon dioxide concentration.


Blankenship,R. E. (2013).&nbspMolecularmechanisms of photosynthesis.John Wiley &amp Sons.

Zelitch,I. (Ed.). (2012).&nbspPhotosynthesis,photorespiration, and plant productivity.Elsevier.