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MECHANISM of MINERAL SALTS ABSORPTION In addition to carbon, hydrogen and oxygen, plant needs essential elements absorbed by roots, deficiency in these elements leads to: Disturbance or stop in plant growth, No flowers No fruits They are two groups : 1) MACRO - NUTRIENT : 7 , needed in considerable amounts , (Mg - I - S - Ph - N - Ca - and K) 2) MICRO - NUTRIENT : 8, needed in very small amounts, mg/liter, they activate enzymes, copper, iodine, zinc, molybdenum, aluminum, boron, chlorine and manganese. Mechanism : 1)Ionic diffusion : solutes in the soil are either positive ions , cations ( K and Ca ) or negative ions , anions ( SO4 , NO3 , and Cl ) , they behave independently of each other and of water . They move by diffusion from soil solution through the wet cellulose walls . Under certain conditions CATIONS EXCHANGE may take place, Na ions get out and replaced by K ions. 2) Selectively permeability when ions reach semipermeable cell membrane, some are selected ( required by the plant ) and pass inwards , while others are not , regardless their sizes , concentrations and charges . 3) Active Transport is the passage of substances through cell membrane by the help of chemical energy supplied during respiration of root tissues , that move these ions against concentration gradient . EXPERIMENT was done on NITELLA ALGA that lives in Swamps : A) concentration of ions in its cell sap is higher than in swamp indicating that the cell use some energy to absorb these ions . B) concentration of ions is variable , some are higher than others , indicating that ions are selectively absorbed according to cell requirement . NOTE : Aerobic Respiration needs the presence of sugar and oxygen which are essential to absorb salts by active transport . EXPERIMENT on BARLEY plant to show the effect of the presence or absence of Oxygen on absorption of sulphate ions : Barley plant was supplied with sulphate ions SO4 , containing radio active sulphur . Absorbed sulphates was estimated by using " Geiger Counter " in aerobic and in anaerobic conditions . Observations : absorption of sulphate ions was less in anaerobic than in aerobic conditions . Conclusion : active transport helps ions absorbed by plant cells using energy produced during aerobic respiration .