2.3 Water Is Essential to Life

2.3 Water Is Essential to Life

• Water is a vital molecule with extraordinary properties essential for all life forms.

• Utilization in preserving foods:

  • Dehydrated foods like crackers, instant coffee, and beef jerky have longer shelf lives due to low moisture, preventing microbial decay.

  • Ancient Egyptians used dehydration to preserve human remains (mummies).

• Table 2.3 summarizes key properties of water:

  • Cohesion and Adhesion: Water moves from a plant's roots to its leaves.

  • Dissolves Substances: Examples include salt dissolving in water.

  • Regulates Temperature: Coastal climates are milder due to temperature regulation of water.

  • Expands as it Freezes: Ice floats on water's surface.

  • Chemical Reactant/Product: Water is involved in photosynthesis.

A. Water Is Cohesive and Adhesive

• Cohesion: Water molecules stick together due to hydrogen bonds.

  • Prevents rapid evaporation of water from Earth's surface.

  • High surface tension allows water to form a meniscus in a glass (can fill above the rim).

• Surface Tension: Created by cohesive bonds holding water molecules together, supporting small animals on its surface.

• Adhesion: Water bonds with other substances.

  • Example: Water soaking into paper towels.

  • Essential for plants: water rises through roots and conducting tubes due to cohesion and adhesion, aiding transpiration.

B. Many Substances Dissolve in Water

• Water's ability to dissolve various chemicals is critical for life.

• Example: Dissolving table salt:

  • As salt dissolves, sodium and chloride ions are surrounded by polar water molecules.

• Solvent and Solute: Water is a solvent, while chemicals dissolving in it are solutes.

• Aqueous Solutions: Solutions with water as a solvent.

• Hydrophilic vs. Hydrophobic Substances:

  • Hydrophilic: Polar or charged substances that dissolve in water (e.g., sugar, ions).

  • Hydrophobic: Nonpolar molecules that do not dissolve in water (e.g., oils, fats).

  • Detergents can suspend both fats and water for cleaning due to their dual nature.

C. Water Regulates Temperature

• Water resists temperature changes due to hydrogen bonds, requiring more heat to change temperature than most liquids.

• This property stabilizes body temperature and explains mild coastal climates compared to inland climates.

• Evaporation: Heat is absorbed when water vaporizes, cooling the surface it evaporates from (e.g., sweating helps regulate body temperature).

D. Water Expands As It Freezes

• Water expands when it freezes, causing ice to float on liquid water.

• Ice forms a stable lattice structure with hydrogen bonds, making it less dense than liquid water.

• Impact on Aquatic Life: Ice insulates water below, preventing it from freezing solid and protecting aquatic organisms.

• Organisms have adaptations to survive freezing, such as thick fur or antifreeze proteins in certain fishes.

E. Water Participates in Life's Chemical Reactions

• Water takes part in countless chemical reactions essential to life.

• Chemical Reactions: Molecules rearrange to form new substances; depicted with reactants on the left and products on the right.

  • Example reaction: methane reacting with oxygen to produce carbon dioxide and water.

• Many biological processes occur in aqueous environments with water serving as either a reactant or product.

• Photosynthesis is a primary example where water is necessary for producing glucose and oxygen.