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Active absorption of minerals is the transportation of mineral against its concentration gradient by the use of energy in the form of ATP molecules. The entry or exit of ions to and from the symplast requires requires energy. The inward movement of the ions are called influx and the outward movement is called efflux. 

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The deficiency of silicon produces necrosis and stunted growth.

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Deficiency symptoms : These are the abnormalities produced due to the deficiency of minerals. There are following general deficiency symptoms :

1. Chlorosis
 2. Necrosis
3. Abscission 
4. Fall of leaves
5. Leaf curl 
6. Wilting

 

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When the plant meterial is burnt in air, the organic matter is destroyed and a residue of inorganic salt remains which is called plant ash.

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Hydroponics is technique of growing plants in a nutrient solution. It is the soilless production of plants. It was demonstrated by Julius von Sachs in 1860.