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.
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.
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.
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).
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.
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.