Absorption of Water and Minerals

  • Absorption of water refers to the process by which plant roots take in water from the soil. 
  • Roots, particularly the root hairs, are crucial for water absorption. 
  • Absorption occurs through diffusion, where water moves from regions of higher concentration in the soil to lower concentration in the root cells. 
  • Thin-walled extensions of root epidermal cells that significantly increase the surface area for absorption. 
  • Root hairs absorb water along with mineral solutes purely through diffusion. 
  • The experiment with a twig in coloured water highlights the movement of water through vascular bundles, specifically the xylem. 
  • Understanding the mechanism of long-distance transport in plants is crucial for comprehending nutrient and water distribution. 
  • Diffusion is insufficient for long-distance transport due to its slow pace. 
  • Over short distances, diffusion is effective, but for extensive movements, additional mechanisms are required. 
  • The movement of a molecule across a typical plant cell takes about 2.5 seconds for a distance of 50 µm. Calculate the time required for a 1 m distance by diffusion alone. 
  •  Water, minerals, and food are transported by mass or bulk flow systems. 
  • Mass flow involves substances moving en masse due to pressure differences, unlike diffusion where substances move independently. 
  • Bulk movement of substances through plant vascular tissues is termed translocation. 
  • Xylem and phloem are highly specialized vascular tissues associated with translocation. 
  • Xylem primarily translocates water, mineral salts, some organic nitrogen, and hormones from roots to aerial plant parts. 
  • Xylem ensures efficient upward movement of substances against gravity. 
  • Ascent of sap refers to the upward movement of water through the plant, particularly from the roots to the aerial parts. 
  • Phloem translocates a variety of organic and inorganic solutes, predominantly from leaves to other plant parts. 
  • Two-Way Transport: Phloem facilitates bidirectional movement, supporting the overall nutrient distribution. 
  • Vascular Tissue Specialization:

- Roots, Stems, and Leaves: Cross-sections reveal the specialized vascular system in higher plants. 

- Xylem and Phloem: These tissues play distinct roles in nutrient and water transport.