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Water and Life - General Biology

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  • Why is a water molecule polar?
    The electrons in water's polar covalent bonds spend more time near oxygen than hydrogen, creating partial negative and positive charges, making the molecule polar.
  • What allows water molecules to form hydrogen bonds?
    Water's polarity causes uneven charge distribution, enabling weak attractions called hydrogen bonds between molecules.
  • Name four properties of water that facilitate life.
    Cohesive behavior, ability to moderate temperature, expansion upon freezing, and versatility as a solvent.
  • What is cohesion in water?
    Hydrogen bonds hold water molecules together, creating cohesion, which results in high surface tension.
  • How does adhesion help plants transport water?
    Adhesion is attraction between water and plant cell walls, helping water move upward against gravity.
  • Define thermal energy and temperature in the context of water.
    Thermal energy is kinetic energy from random molecular motion; temperature is the average kinetic energy of molecules.
  • What is a calorie in terms of water heating?
    A calorie is the heat needed to raise 1 g of water by 1°C or released when 1 g cools by 1°C.
  • What is specific heat and water's specific heat value?
    Specific heat is heat needed to change 1 g of substance by 1°C; water's is 4.184 J/g°C, meaning it resists temperature change.
  • How do hydrogen bonds affect water's specific heat?
    Heat is absorbed when hydrogen bonds break and released when they form, giving water a high specific heat.
  • What is evaporative cooling?
    When water evaporates, molecules with highest kinetic energy leave, cooling the surface left behind.
  • Why does ice float on liquid water?
    Ice is less dense because hydrogen bonds form a crystalline lattice that spaces molecules farther apart.
  • What is a solution, solvent, and solute?
    A solution is a homogeneous liquid mixture; solvent dissolves the solute, which is the dissolved substance.
  • Why is water a versatile solvent?
    Water's polarity allows it to surround ions and polar molecules, forming hydration shells and dissolving many substances.
  • Define hydrophilic and hydrophobic substances.
    Hydrophilic substances have affinity for water; hydrophobic substances repel water, often nonpolar like oils.
  • What is molarity (M)?
    Molarity is the number of moles of solute per liter of solution.
  • What happens during water molecule dissociation?
    Water molecules split into hydronium ions (H3O+) and hydroxide ions (OH-), maintaining dynamic equilibrium.
  • How do acids and bases affect proton concentration?
    Acids increase proton (H+) concentration; bases reduce proton concentration in solution.
  • What is the pH scale range for acidic, neutral, and basic solutions?
    Acidic solutions have pH < 7, neutral is pH 7, and basic solutions have pH > 7.
  • Why are buffers important in biological systems?
    Buffers minimize pH changes by reversibly combining with hydrogen ions, maintaining stable conditions.
  • What is the role of hydrogen bonds in water's unique properties?
    Hydrogen bonds cause cohesion, high specific heat, expansion on freezing, and solvent versatility.