Water and mineral salts are transported into the leaves of a flowering plant through a process called transpiration. Transpiration is the loss of water vapor from the plant’s aerial parts, primarily through the stomata on the leaves. This process relies on a combination of physical and physiological mechanisms to transport water and mineral salts from the roots to the leaves.
The first step in the transport of water and mineral salts is the absorption of water by the roots. The roots of a plant have specialized structures called root hairs that increase their surface area, allowing for more efficient absorption of water and mineral salts from the soil. This process is facilitated by active transport, where energy is expended to move ions against their concentration gradient.
Once water and mineral salts are absorbed by the roots, they move through the root cortex via apoplastic or symplastic pathways. In the apoplastic pathway, water moves through the cell walls and intercellular spaces between cells. In the symplastic pathway, water moves through the cytoplasm of cells via plasmodesmata, which are microscopic channels connecting adjacent cells.
As water moves upward through the root cortex, it reaches the endodermis, a specialized layer of cells that surrounds the vascular tissue. The endodermis acts as a selective barrier due to its presence of Casparian strips, which are bands of suberin (a waxy substance) that block apoplastic movement of water and solutes. Water and mineral salts must cross this barrier to enter the vascular tissue.
Once inside the vascular tissue, water and mineral salts move upward through a network of xylem vessels. Xylem vessels are long, hollow tubes composed of dead cells that provide structural support and serve as conduits for water transport. Water moves up these vessels due to capillary action, cohesion, and adhesion forces.
The final step in transporting water and mineral salts to the leaves is their release into the leaf tissues. Water exits the xylem vessels and enters the mesophyll cells of the leaf, which are specialized for photosynthesis. This movement occurs through the apoplastic and symplastic pathways within the leaf cells.
Overall, the transport of water and mineral salts into the leaves of a flowering plant is a complex process that involves absorption by the roots, movement through the root cortex, crossing the endodermis, ascending through xylem vessels, and entering leaf tissues.
