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Mechanism of Absorption of Elements

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Mechanism of Absorption of Elements - Lesson Summary

Mechanism of absorption of elements in plants have revealed two main phases of absorption. The first phase is a passive process, and the second phase is an active process. The first phase involves a rapid uptake of ions from the soil or atmosphere to the outer or free space of cells, called the apoplast. The second phase is the slow movement of the ions from the outer space to the inner space of cells, the symplast.
The first phase involves the movement of elements into the cell wall and intercellular spaces. The absorption of ions happens through the ion exchange process. The passive movement of ions into the outer space of the plasma membrane usually occurs through ion channels. Cations and anions have the tendency to get adsorbed into the root cell wall. These ions get exchanged with the ions in the soil solution. The transmembrane proteins in the ion channel function as selective pores.
The second phase involves the entry or exit of ions to and from the symplast. This requires energy, it is an active process. The movement of ions from the outer space of the cell to the inner space is generally against the concentration gradient, and hence, requires energy. This happens through the carrier mechanism. The carrier gets activated by the expenditure of energy from the ATP molecule. The activated carrier molecule binds with the ions and transfers it into the cell. The inward movement into the cells is called influx, and the outward movement is called efflux. The movement of ions from the root cells to other parts of the plant happens through the xylem tissue. The xylem carries the ions along with water. This is called translocation. Translocation is aided by transpiration. An analysis of water in the xylem shows the presence of mineral salts. Soil provides stability to a plant, along with air and water. It is a reservoir of all the major nutrients needed for the plant. Soil is formed by the weathering of rocks, which provides the soil with minerals. This is termed as mineral nutrition. Soil also contains microbes, such as nitrogen-fixing bacteria, which help plants by fixing nitrogen from the atmosphere into the soil. The deficiency of minerals in the soil affects the plant, and hence, fertilisers are added to the soil. This ensures the supply of the deficient element to the plant. 


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