Cycles of Matter - In-Depth Notes

Chapter 2: Cycles of Matter

2.1 The Role of Water in Cycles of Matter
  • Water is continuously recycled in the biosphere, playing a vital role in sustaining ecosystem dynamics.
  • A biogeochemical cycle refers to the cyclical movement of water and other chemical nutrients through biotic (living) and abiotic (non-living) components of the biosphere.
2.2 The Hydrologic Cycle (Water Cycle)
  • The hydrologic cycle encompasses all phases of water: solid, liquid, and gas.
  • Water acts as a vehicle for transporting various materials across different environments.
  • Multiple processes facilitate the movement of water, including precipitation, evaporation, and transpiration.
Water's Properties
  • Water is recognized as an excellent carrier of dissolved minerals and substances, making it an effective medium for energy transfer due to the following properties:
    1. Universal Solvent: Water can dissolve many types of substances due to its polarity, allowing it to interact with various molecules.
    2. High Boiling and Melting Points: Water remains in liquid form across a wide temperature range due to the presence of hydrogen bonds, which require substantial energy to break.
    3. Cohesive and Adhesive Properties: Water molecules are attracted to each other (cohesion) and to other surfaces (adhesion), affecting how it interacts with environments.
    4. High Heat Capacity: Water can absorb significant amounts of heat without undergoing temperature changes, which helps organisms regulate their internal temperatures.
Hydrogen Bonding and Density
  • Hydrogen bonds between water molecules result in unique properties:
    • Frozen water (ice) is less dense than liquid water, explaining why ice floats.
Water and Life
  • Organisms maintain hydration through various means, including:
    • Metabolic Water: Water produced during cellular respiration (e.g., human: 190 mL; kangaroo rat: 54 mL).
    • Drinking: Direct intake of water (e.g., human: 1045 mL; kangaroo rat: 0 mL).
    • Absorption through Food: Water absorbed by consuming foods with high water content (e.g., human: 665 mL).
    • Evaporation: Water loss through breathing and other physiological processes (e.g., human: 800 mL; kangaroo rat: 43.9 mL).
Water Budget Comparison

  • Human Water Budget:

    • Total Water Gains: 1900 mL
    • Total Water Losses: 1900 mL

  • Ord's Kangaroo Rat Water Budget:

    • Total Water Gains: 60.0 mL
    • Total Water Losses: 60.0 mL
Impacts of Environmental Conditions
  • Factors such as drought and flooding significantly affect water availability and ecosystem health.