question_answer 60)

Various types of transport mechanisms are needed to fulfill the mineral requirements of a plant. Why are they not fulfilled by diffusion alone?

Answer:

                Various types of ions; minerals and organic compound are transported in plants in variousmodes, e.g., (i) Food substances synthesised in leaves are translocated downward towards root and stem. (ii) Similarly food is translocated upwards to the developing leaves, buds and fruits. (iii) Radial transport of food occurs across the stem from the cells of pith, from cortex etc, towards epidermis.                                 (iv) Ions and minerals are transported upwards through xylem. Since, diffusion is a slow process and allows movement of molecules for short distancesonly, it cannot filled and alone carry out the above mentioned^ movements of organic andinorganic substances. Therefore, a need arises for special long distance transport systemsthat permits and move substances at a much faster rate, i.e., mass or bulk flow systemthrough conducting tissues (translocation)