2.56B: Understand that Transpiration is the Evaporation of Water from the Surface of a Plant

TRANSPIRATION: Loss of Water vapour from stems and leaves of plants - inevitable consequence of gas exchange

TRANSPIRATION IN XYLEM

x Diagram Showing the Process of Transpiration in Plants

PROCESS: Cohesion: Force of attraction between Water molecules which allow Water to stick together Adhesion: Force of attraction between Water molecules and other polar molecules - e.g Cellulose in plant cell wall Water is transported throughout the plant via Xylem Water is heated into Water vapour by sunlight in Spongy Mesophyll, transpiring out of Stomata which are pores on the underside of leaves Loss of Water via transpiration creates negative pressure, causing transpiration pull of Water molecules up the Xylem to form a continuous transpiration stream As a result, more Water is absorbed by the roots of the plant via osmosis

FUNCTIONS: Constant uptake and transport of Mineral ions in plant (e.g Nitrates as a source of Amino acid to build Protein) Maintaining turgidity of cells for plant growth Provide Water to Photosynthesising cells in for Photosynthesis Evaporative cooling of plant leaves to maintain optimum temperature for optimum enzyme activity