Water Properties in Plant Biology

Water Properties

• Adhesion: Attraction between different substances (e.g., water and cell walls). Hydrogen bonding occurs between water molecules and cell wall components (like cellulose).

• Cohesion: Attraction between water molecules. Hydrogen bonding between water molecules is the primary cause. This creates a continuous pull through plant vascular tissue.

• Cohesion-tension theory: Water transport in plants. Evaporation from leaves creates a pull (tension) that draws water up the xylem vessels. Cohesion of water molecules helps transmit this pull.

• Transpirational pull: In plants, water movement driven by transpiration (evaporation from leaves). This pull extends through the entire xylem.

• Water's High Specific Heat Capacity: Water absorbs or releases significant heat with little temperature change. This allows organisms to maintain stable internal temperatures and moderate surrounding environments.

• Hydrogen Bonding: Water molecules are attracted to each other by hydrogen bonds, affecting many properties like its high boiling point and high surface tension. These bonds are constantly being broken and reformed in liquid water (which distinguishes liquids from solids).

• Water as a Solvent: Water's polarity allows it to dissolve many substances (solvents). Positive and negative regions within the water molecule allows interactions with other polar or ionic molecules.

• Hydrophilic substances: Substances that are attracted to water. These are polar molecules/ions that readily dissolve and interact with water which allows for the transport of molecules through and across cells.

• Hydrophobic substances: Substances that are not attracted to water. These are non-polar molecules.

• Water Density: Ice is less dense than liquid water. The unique structure of ice, where water molecules form a crystalline lattice, accounts for this unusual property. This allows aquatic life to survive during winter.

• Water's unique properties: Affecting biological processes and the environment as well as enabling life to exist on earth.

Water and Temperature

• Heat absorption/release: Large water bodies moderate temperature extremes. Water absorbs and releases large quantities of heat while undergoing only a small change in temperature.

• Specific Heat: Amount of heat needed to raise the temperature of 1g of substance by 1°C (high in water)

• Evaporation: Transition of liquid to gaseous state. Heat is absorbed to break hydrogen bonds, cooling the remaining liquid.

• Freezing: Water molecules form a lattice structure, making ice less dense than liquid water.