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.

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