AP Biology: Chemistry of life

• What is responsible for the cohesive property of water?

  Hydrogen bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule.
• CHONPS


  Most common elements in carbon based (organic) molecules

  • carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur
• Types of Bonds:

  Ionic bond - metal atom loses electrons to non metal

  • (Strongest) Covalent bond - two nonmetals share electrons
  • (Weakest) Hydrogen bond - hydrogen attracts an electronegative atom electrostatically
• Four properties of water contribute to Earth’s suitability for life:

  Cohesion and adhesion

  • Ability to moderate temperature
  • Expansion upon freezing
  • Versatility as a solvent - “the universal solvent”
• Water

  Water molecules are polar molecules

  • The oxygen region having a partial negative charge and the hydrogen region a slight positive charge.

  Two water molecules are held together by a hydrogen bond
• What are organisms mostly made of?

  All organisms are made mostly of water and live in an environment dominated by water.
• Specific heat: 


  specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C.
• Water specific heat:

  Water resists changing its temperature because of its high specific heat

  • Heat is absorbed when hydrogen bonds break
  • Heat is released when hydrogen bonds form

  high specific heat of water keeps temperature fluctuations within limits that permit life
• Capillary action: 


  Capillary action is important for moving water around (and all of the things that are dissolved in it)

  • due to the forces of adhesion, cohesion, and surface tension — this is how transcription works.