IB BIOLOGY TOPIC 9 PLANT BIOLOGY (HL) INTERNATIONAL BACCALAURENTE COMPLETE STUDY GUIDE 2023

Water properties: • Cohesion: like molecules attract to each other • Water is a polar molecule that forms a hydrogen bond with other water molecules. • The negatively charged oxygen atom of one water molecule forms a hydrogen bond with a positively • charged hydrogen atom of another water molecule. This attractive force between these molecules is called cohesion which helps plants draw water from the root through the xylem to the leaf • Adhesion: unlike molecules attract to each other • Capillary action may occur: water will move up the capillary due to the interaction between water molecules and capillariTranspiration: lOMoARcPSD| • Evaporation occurs when some of the light energy absorbed by the leaf is converted to heat , thereby raising the temperature inside the leaf changing the water into water vapour. • Transpiration is the evaporation of water from the leaves, stems and flowers. It is the movement of water vapour out of the leaf through stomata . • The majority of water lost during transpiration is through openings on the bottom of the leaves called stomata. • Transpirational pull results when water evaporates from the leaves and stems. More water is drawn up through the plant to replace the water that is lost. • The loss of water generates a negative pressure and a transpirational pull on water molecules in the xylem. • Transpirational pull results from the combined forces of cohesion and adhesion • Water moves into the roots by osmosis through the cell walls and through the cytoplasm because the concentration of solutes inside the cells is greater than outside the root cells due to active transport of mineral an