Plants - SS2 Biology Lesson Note

Plants have evolved various mechanisms of transportation to move water, nutrients, sugars, hormones, and other substances within their bodies. The main mechanisms of transportation in plants are:

1.       Transpiration and Cohesion-Tension Theory:

·         Transpiration is the process by which water evaporates from the leaves through tiny openings called stomata. This evaporation creates a pulling force that draws water upward from the roots.

·         The cohesion-tension theory explains how water is transported through the xylem tissue in plants. As water evaporates from the leaves, it creates a negative pressure (tension) that pulls water up through the xylem vessels, maintaining a continuous column of water from the roots to the leaves. The cohesion between water molecules helps to maintain the column of water without breaking.

2.       Capillary Action:

·         Capillary action is the ability of water to move upwards in narrow tubes due to adhesive and cohesive forces. This mechanism assists in the movement of water within the xylem vessels against gravity.

3.       Root Pressure:

·         Root pressure is a mechanism that helps to push water from the roots to the upper parts of the plant. Active transport of minerals into the root cells creates a higher solute concentration, which leads to the movement of water into the roots via osmosis. This influx of water creates pressure that forces water up the xylem vessels.

4.       Translocation in Phloem:

·         Translocation is the process by which sugars, amino acids, hormones, and other organic compounds are transported through the phloem tissue in plants.

·         The movement of these substances occurs through a pressure flow mechanism. Sugars are actively loaded into the phloem sieve tubes at source regions (such as leaves) and create a high osmotic pressure. This high pressure pushes the sap containing sugars from source to sink regions (such as roots, fruits, or developing tissues), where the sugars are unloaded and used or stored.

5.       Diffusion and Active Transport:

·         Diffusion and active transport play roles in the movement of ions, minerals, and other solutes within plant tissues. Cells in roots and leaves use active transport to move ions and minerals against concentration gradients, ensuring their uptake and distribution to different parts of the plant.

These mechanisms of transportation work together to ensure the movement of water, nutrients, sugars, hormones, and other substances throughout the plant, supporting growth, metabolism, and overall physiological functions.

Transportation in plants (toppr.com)