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MODULE - 2 Absorption, Transport and Water Loss in Plants Forms and Function of Plants and Animals 8 Notes ABSORPTION, TRANSPORT AND WATER LOSS IN PLANTS Water is the most important component of living cells. It enters the plants through roots and then moves to other parts and is also lost by transpiration through the leaves. There are several phenomena involved in the movement of water about which you will study in this lesson. OBJECTIVES After completing this lesson, you will be able to : define the terms permeability, diffusion, osmosis and plasmolysis; define and differentiate between the active and passive absorption; explain imbibition, water potential, turgor pressure and wall pressure, wilting; describe the pathways of water from root hair up to leaf; describe the mechanism of translocation of solutes in plants; explain the process and significance of transpiration; list the factors affecting the rate of transpiration; explain the opening and closing mechanism of stomata (potassium ions theory) and list the factors affecting stomatal movement; explain the process of guttation and list the factors affecting rate of guttation. 8.1 FOUR BASIC PHENOMENA-PERMEABILITY, DIFFUSION, OSMOSIS AND PLASMOLYSIS 8.1.1 Permeability Permeability is the property of a membrane to allow the passage of the substances through it. The plant cell wall is permeable because it allows both solvent and solute molecules to pass through it. Cuticle layer is impermeable. All biological membranes (cell membrane, mitochondrial membrane, nuclear membrane etc.) are selectively permeable as they allow penetration of only solvent molecules but not the solute molecules. 192 BIOLOGY
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