A mechanism of water absorption:
Water is absorbed through two mechanisms: active absorption and passive absorption.
Active absorption:
1. Osmotic Active Absorption: This process involves water absorption through osmosis, where water moves into the root xylem against the concentration gradient of the root cell. The high concentration of solutes in the cell sap and the lower concentration in the surrounding soil drive osmotic movement.
2. Concentration Gradient: Osmotic active absorption is facilitated by the concentration gradient between the root cell and the soil. The disparity in solute concentrations prompts the movement of water into the root xylem, aiding in the overall absorption process.
3. Non-Osmotic Active Absorption: In this mechanism, water is absorbed against the cell’s concentration gradient, requiring metabolic energy from the respiration process. The energy expended in respiration becomes essential for water entry into the cell from the soil, and consequently, the rate of water absorption is closely linked to the rate of respiration.
4. Metabolic Energy Utilization: The non-osmotic active absorption of water necessitates the utilization of metabolic energy. This energy is derived from the respiration process, where the plant expends energy to facilitate the movement of water into the cell against its natural concentration gradient.
5. Role of Auxin: Auxin, a plant growth hormone, plays a crucial role in this process by increasing the rate of respiration in plants. As auxin levels rise, so does the rate of respiration, consequently enhancing the metabolic energy available for non-osmotic water absorption. This interplay between auxin, respiration, and water absorption highlights the intricate regulatory mechanisms in plant physiology.
Passive absorption:
1. Water absorption in this process doesn’t rely on metabolic energy; instead, it occurs through passive absorption driven by transpiration.
2. Transpiration pull, a metabolic activity, creates tension or force, facilitating the upward movement of water into the xylem sap.
3. The rate of water absorption increases with a higher transpiration rate, emphasizing the direct relationship between the two processes.