AQA A2 Unit 4 Photosynthesis

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Energy and ATP

-ATP is the energy currency of the cell. It i made by combining ADP with inorganic phosphate, a reaction that uses energy. Its breakdown releases energy that the cells can use.

-All cell make ATP as a result of respiratation, a series of reactions in which glucose or othe energy-containing substances are oxidised.

-Plants photosynthesise, a series of reactions in which carbon dioxide is reduced to for carbohydrates. These carbohydrates contain energy that has been transferred from energy in the sunlight.

-Photosynthesis takes place in side chloroplasts. It has two main stages: the light-dependent reaction, in which ATP, Reduced NADP and oxygen are formed; and th elight dependent reaction, in which carbon dioxide is converted to carbohydrate using some of the products of the light -dependent reaction

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The Light Dependent Reaction

-The Light-dependent stage of photosyntheis takes place in the thylakoids, were photosynthetic pigments are embedded

-Light energy excites electrons in the Chlorophyll

-Some of this energy is used in photolysis of  water, producing protons, electron and oxygen.

-The protons and electrons are picked up by NADP, producing reduced NADP.

-Energy from the excited eclectrons is used to generate ATP through photophosphorylation. This involves the transfer of electrons along a chain of electron carries arranged in the thylakoid membrane

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The Light-Independent Reaction

-The light-independent stage of photosyntheis takes place in the stroma of the chloroplast

-Carbon dioxideis accepted by the five-carbon compound RuBP to form two molecules of the three-carbon compound glycerate 3-phosphate (GP). This reaction is catatlysed by RUBISCO

-GP is reduced to triose phosphate (TP), with the help of the reduced NADP and ATP generated in the light-dependent reaction.

-One-sixth of the triose phosphate is converted to glucose and other useful organic compounds. Five-sixths is used to regenerate RuBP in the calvin cycle.  

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Limiting Factors

-A foctor that prevents Photosynthesis taking place at a faster rate is known as a limiting factors. Light intensity, temperature and carbon dioxide concentration may all act as limiting factors

-A knowledge of limiting factors can enable growers to increase the yield of grops grown in glasshouses. The cost of maintaining optimum temperature, light intensity and carbon dioxide concentration need to be outwieghed by the greater inome of the crop.

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