Biology ABSORPTION AND TRANSLOCATION OF SOLUTES

### KEY TOPICS

star Mechanism of Absorption of Elements
star Translocation of Solutes
star Soil as a reservoir of Elements

### MECHANISM OF ABSORPTION OF ELEMENTS

● Much of the studies on color{violet}"mechanism of absorption" of elements by plants has been carried out in color{violet}"isolated cells, tissues or organs".

● These studies revealed that the color{violet}"process of absorption" can be demarcated into color{Brown}"two main phases."

● In the color{violet}"first phase", an initial color{violet}"rapid uptake of ions" into the ‘free space’ or ‘outer space’ of cells – the color{Brown}"apoplast", is color{violet}"passive".

● In the color{violet}"second phase" of uptake, the ions are color{violet}"taken in slowly" into the ‘inner space’ – the color{Brown}"symplast" of the cells.

● The color{violet}"passive movement" of ions into the color{violet}"apoplast" usually occurs through color{Brown}"ion-channels", the trans-membrane proteins that function as color{violet}"selective pores".

● On the other hand, the color{violet}"entry or exit of ions" to and from the color{violet}"symplast" requires the expenditure of color{Brown}"metabolic energy", which is an process.

● The color{violet}"movement of ions" is usually called the inward movement into the cells is color{Brown}"influx" and the outward movement, color{Brown}"efflux".

### TRANSLOCATION OF SOLUTES

● Mineral salts are color{violet}"translocated through xylem" along with the color{violet}"ascending stream" of water, which is pulled up through the plant by color{violet}"transpirational pull".

● Analysis of color{violet}"xylem sap" shows the presence of color{violet}"mineral salts" in it.

● Use of color{violet}"radioisotopes of mineral elements" also substantiate the view that they are color{violet}"transported" through the color{violet}"xylem".

### SOIL AS RESERVOIR OF ESSENTIAL ELEMENTS

● color{violet}"Majority of the nutrients" that are essential for the color{violet}"growth and development" of plants become available to the roots due to color{violet}"weathering and breakdown" of rocks.

● These processes enrich the soil with color{violet}"dissolved ions" and color{violet}"inorganic salts".

● Since they are color{violet}"derived from the rock minerals", their role in plant nutrition is referred to as color{Brown}"mineral nutrition".

● Soil consists of a color{violet}"wide variety" of substances.

● Soil not only supplies color{violet}"minerals" but also harbours color{violet}"nitrogen-fixing bacteria", other microbes, holds water,
supplies air to the roots and acts as a matrix that stabilises the plant.

● Since deficiency of color{violet}"essential minerals" affect the crop-yield, there is often a need for supplying them through color{violet}"fertilisers".

● Both color{violet}"macro-nutrients" (N, P, K, S, etc.) and color{violet}"micro-nutrients" (Cu, Zn, Fe, Mn, etc.) form components of color{violet}"fertilisers" and are applied as per need.