Water

• Water is required for

  • Effective interaction of the naturally formed molecules of life
  • Growth and copying of these molecules
  • Formation of compartments allowed the development of internal chemistry different from the surrounding environment
  • Metabolism can only occur when the starting materials are in a watery environment
  • Essential to the development of the first cells and is the medium where life processes take place due to its solvent properties
• Chemical structure of water

  • Polar molecule
  • One O covalently bonded to 2 H
  • Electronegativity: O is partially negative, H is partially positive
• Bonding between water molecules

  1. Partial negative is attracted to the partial positive

  2. Intermolecular force (hydrogen bond)

  3. The charges are partial, bonds are weak

  4. Polar covalent bonds within water molecules and hydrogen bonds between them
• Cohesion


  • Water with water
  • Pulls water molecules together
  • May counteract gravity
  • Surface tension is due to this
• Adhesion


  • Water and other stuff
  • Attracted to polar/charged material
  • Capillary action: adhesion > cohesion
  • Meniscus
  • Xylem -> stops plants drying out
• Water as a medium for metabolism

  • Hydrophilic molecules are attracted to water
  • Aquaporins have a hydrophillic interior
  • Provides a medium for transporting materials
  • Blood uses water as a solvent
  • Dissolved minerals go from the soil to roots
• Physical properties of water

  • Buoyancy - counteracts gravity, increased density means increased buoyancy
  • Water is less dense as a solid due to hydrogen bonding patterns
  • Viscosity - resistance to flow, other liquids > water > air
  • Thermal conductivity - ability to transfer heat, high
  • SHC - how much energy is needed to change the temp, increased due to hydrogen bonds
• Ringed seal (Pupa hispida)


  • Blubber increases buoyancy
  • Streamlined shape decreases drag
  • Thermal conductivity - blubber decreases heat loss
  • Seal pups survive in lairs insulated by trapped air
• Black throated loon


  • Large wings, lift in less buoyant air
  • Hydrodynamic and aerodynamic
  • Oiled exterior feathers exude water
  • Insulated by air trapped in down feathers
• Origin of water on earth

  1. Was too hot for surface water at first

  2. Brought by comets and asteroids
• Reasons for retention of water on earth

  • Gravity -> attraction between two bodies of mass
  • Temperature of earth's atmosphere is the right range for liquid water
  • As a liquid, water supports life
• Solvation with water as a solvent

  • A solute dissolves in a solvent to form a solution
  • Solvation is the interaction of a solvent with the molecules and the ions that dissolve in it
• Hypertonic


  High solute conc, low solute potential
• Hypotonic


  Low solute conc, high solute potential
• Isotonic


  Equal movement in and out
• Crenation


  Shriveled up animal cell
• Normal


  Animal cell in isotonic
• Lysed/cytolysis


  Animal in hypotonic
• Plasmolyzed


  Plant in hypertonic - detaches from cell wall
• Flaccid


  Plant in isotonic
• Turgid


  Plant in hypotonic, swollen vacuole, turgor pressure
• Dynamic equilibrium


  No net change in water of a cell
• Fresh water is hypotonic compared to the cytoplasm
• Contractile vacuoles in paramecium

  • Expels water, prevents cytolysis
• Osmoregulation


  • Maintaining water and salt concentrations
  • Osmotic pressure
  • A form of homeostasis
• Medical applications of isotonic solutions

  • Organ transplants: Crenation/cytolysis leads to tissue or organ death
  • IV fluids: Directly administered to a vein, Support hydration, nutrition, replace lost fluids, medication, Same concentration as blood plasma and tissue fluid
• Water potential


  • Measure of potential energy of water per volume of water
  • kPa
  • Pure water is 0, which is the highest possible value
  • Water potential = solute potential + pressure potential
  • Solute potential: Attraction of water molecules to solute particles, Decreasing the number of free water molecules limits water movement
  • Pressure potential: Physical pressure exerted on a system outwards from a cell, Positive in root hair cells, Negative during transpiration
• Increasing number of solute -> decreasing solute potential
• Modes of transport in blood

  • Dissolved amino acids, glucose and salt
  • Fats are carries in complexes
  • Oxygen is attached to hemoglobin