Lecture: Water and Its Importance

Guiding Questions

• What physical and chemical properties of water make it essential for life?
• What are the challenges and opportunities of water as a habitat?

Lecture Objectives

• Understand how water serves as the medium of life.
• Discuss the properties of water resulting from polarity and hydrogen bonding.
• Explore the benefits and challenges of water as a habitat.
• Learn about the origin of water on Earth and its role in the evolution of life.

Water as the Medium of Life

• Early life likely appeared in warm oceans, not ponds as Darwin suggested.
• Phospholipids form micelles in water, concentrating substances inside and facilitating reactions.
• Biological molecules and reactions occur in water today.
• Hydrogen bonding is key to water's properties:
  • Water (H₂O): oxygen is more electronegative, creating polar covalent bonds.
  • Oxygen side: partially negative; hydrogen side: partially positive.
  • Hydrogen bonding: weak attractions between water molecules due to polarity.

Properties Due to Polarity and Hydrogen Bonding

Cohesion and Adhesion

• Cohesion: Water molecules attract each other (e.g., water moving up xylem in plants).
• Adhesion: Water molecules attract non-water substances (e.g., soil particles).
• Surface Tension: Allows insects like raft spiders to walk on water.
• Capillary Action: Water moves up tiny tubes, crucial in plants and mosses.

Solvent Properties

• Water is a universal solvent for polar and some non-polar substances.
• Solvation: Process of dissolving substances (e.g., salt in water).
• Metabolism: Depends on water to dissolve metabolites for reactions.

Transport in Biological Systems

• Plants: Use xylem for water/minerals and phloem for nutrients.
• Humans: Blood (plasma) transports dissolved substances, aided by lipoprotein complexes for non-polar molecules.

Water as a Habitat

Buoyancy and Viscosity

• Buoyancy supports organisms like fish (swim bladders) and cyanobacteria (gas vesicles).
• Viscosity affects energy needed for movement; seawater is more viscous than freshwater.

Thermal Properties

• Water is a decent thermal conductor and coolant with high heat capacity.
• High specific heat buffers temperature changes, providing stability for life.

Challenges and Opportunities

• Comparison: Bird (Arctic Loon) vs. Seal (Ranged Seal) in energy usage and insulation needs.
• Need more energy to maintain temperature in water due to its properties.

Origin of Water on Earth

• Water likely came from asteroid impacts after Earth's formation.
• Retained due to Earth’s gravity and hydrogen bonding.
• Goldilocks Zone: Ideal for liquid water, supporting potential life on exoplanets.

Conclusion

• Water's polarity and hydrogen bonding make it essential for life.
• It offers unique challenges and opportunities as a habitat due to its physical and thermal properties.
• The origin and retention of water on Earth were crucial for the evolution of life.