Overview
This lecture discusses the unique properties of water that make it essential for biological systems, focusing on molecular structure, bonding, and roles in organisms.
Molecular Structure & Polarity
- Water (Hâ‚‚O) is a polar molecule shaped like a bent "V" due to oxygen's electronegativity.
- The oxygen atom has a partial negative charge; hydrogen atoms have partial positive charges.
- Polarity enables water molecules to form hydrogen bonds with each other.
Hydrogen Bonding & Properties
- Hydrogen bonds connect water molecules, influencing water's unique behavior in nature.
- Cohesion is the attraction between water molecules, important for surface tension.
- Adhesion is water's attraction to other surfaces, helping water climb plant xylem against gravity.
Biological Importance of Cohesion & Adhesion
- Cohesion pulls water upward in plants and allows insects like water striders to walk on water.
- Surface tension created by cohesion benefits many water-walking animals.
Water as a Solvent
- Water's polarity makes it a powerful solvent, dissolving polar molecules and ionic compounds.
- Many bodily processes rely on water's ability to act as a solvent, such as kidney function and transport in fluids.
Density and Ice Formation
- Water expands and becomes less dense when frozen, so ice floats on liquid water.
- Floating ice insulates aquatic environments, protecting life beneath during freezing conditions.
- This expansion is caused by the stable hydrogen-bonded lattice in ice.
Temperature Regulation
- Water has a high specific heat, meaning it resists rapid temperature changes.
- High specific heat stabilizes environmental and body temperatures for aquatic and terrestrial life.
Evaporative Cooling
- Evaporation removes heat from organisms, cooling animals and plants through loss of energetic water molecules.
- Evaporative cooling protects vital biological processes from heat damage.
Key Terms & Definitions
- Polar molecule — a molecule with uneven distribution of charges resulting in positive and negative regions.
- Hydrogen bond — a weak bond between a hydrogen atom of one molecule and an electronegative atom of another.
- Cohesion — attraction between molecules of the same substance.
- Adhesion — attraction between molecules of different substances.
- Specific heat — the amount of heat needed to raise the temperature of 1g of a substance by 1°C.
Action Items / Next Steps
- Review plant xylem and water transport mechanisms.
- Study the effects of water’s properties on living organisms for exam preparation.