water

• Water


  The medium for life
• Water as the medium for life

  • Life probably originated in water
  • Water is required for life as it is the medium for metabolic reactions, a transport medium, and involved in many chemical reactions
• Polar covalent bonds


  Unequal sharing of electrons within water molecules
• Hydrogen bonds


  Bonds formed between water molecules due to the polarity of water
• Polarity of water molecules


  Leads to formation of hydrogen bonds between water molecules
• Cohesion


  • Attraction between the same kind of molecules (water molecules)
• Adhesion


  • Attraction between different kinds of molecules
• Cohesion of water molecules


  Leads to surface tension, allowing animals like water striders to walk on water
• Cohesion and transport in the xylem

  1. Cohesive nature of water molecules allows continuous column of water to move up the xylem

  2. Capillary action in soil and cell walls allows water to move against gravity
• Solvent properties of water


  Water allows a wide variety of hydrophilic substances to dissolve in it, enabling metabolic reactions and transport in plants and animals
• Hydrophobic substances


  Substances that do not readily mix with water, such as lipids, which can be used for energy storage without affecting water potential of cells
• Water is the medium for metabolism, with enzymes and reactants dissolved in aqueous solutions
• Modes of transport in blood


  • Dissolved in plasma (glucose, amino acids, ions)
  • Attached to hemoglobin (oxygen)
  • Lipoprotein complexes (cholesterol, lipids)
• Oxygen


  Non-polar and does not readily dissolve in water
• Metabolism


  The complex network of interdependent and interacting chemical reactions occurring in living organisms
• Enzymes


  Biological catalysts which speed up the rate of chemical reactions. Enzymes are involved in controlling metabolism
• Metabolic reactions occur in aqueous solutions, with the reactants and enzymes dissolved in water
• Hydrophobic substances


  Not charged and do not readily mix with water
• Hydrophobic substances


  • Lipids are hydrophobic, allowing them to be used as an energy store without significantly changing the water potential of cells
  • Lipid hormones are hydrophobic and can pass through the phospholipid bilayer of cell membranes
• Buoyancy


  The ability of a fluid (water or air) to exert an upward force on an object
• Viscosity


  A fluid's resistance to objects passing through it
• Thermal conductivity


  A material's ability to conduct heat
• Specific heat capacity


  The energy needed to raise one kilogram of a material by 1°C
• Water has a much higher thermal conductivity than air. Aquatic animals are more likely to lose heat to the environment and must be adapted to reduce heat loss
• Ringed seals have a layer of insulating blubber to prevent heat loss. Seals will huddle together out of the water (on land), decreasing overall exposed surface area and reducing heat loss
• Black-throated loons are insulated by feathers which are coated with a hydrophobic oil to keep the feathers dry, which reduces heat loss
• Water has a very high specific heat capacity (4.186 J/g°C), as energy is required to break the hydrogen bonds between water molecules. The specific heat capacity of air is much lower than water
• The temperature of large bodies of water is much more stable than air temperature, as the water can absorb or release much more heat energy without experiencing significant temperature change
• Animals' cells (which are primarily composed of water) are also resistant to temperature change, which helps maintain constant body temperature in endotherms such as birds and mammals
• Water has a higher viscosity than air, and many aquatic animals, such as the black-throated loon, have a streamlined body shape which allows them to smoothly move through water
• Liquid water is a denser fluid than air, providing greater buoyancy for aquatic animals and allowing them to float or swim more easily
• The ringed seal has a layer of blubber that provides buoyancy and helps it float on the surface of the water
• The ringed seal (Pusa hispida) lives in the arctic seas
• The streamlined body shape of the seals allow them to efficiently move through water. The flippers use drag to facilitate movement
• Ringed seals are endotherms and are adapted to maintain a constant body temperature. The high specific heat capacity of the water in their bodies helps maintain a stable body temperature
• The black-throated loon is able to adjust its density by changing the volume of air in its air sacs. This allows the bird to control its depth when swimming in water
• The black-throated loon is able to increase its buoyancy in air by increasing its surface area by spreading its wings. The bones of birds are hollow, further reducing their density and increasing the buoyancy of the black-throated loon, allowing it to fly
• The streamlined shape of black-throated loons allow them to efficiently move through air and water. The webbed feet help the birds to move through water
• The black-throated loon is an endotherm that maintains a constant body temperature. The bird's feathers trap air and provide insulation. The feathers are covered in a hydrophobic oil which keeps the feathers dry
• The high specific heat capacity helps the black-throated loon to regulate its body temperature, which is especially important when it is diving into cold water