1.1 Water + Elements of life

• Water is made of two hydrogen molecules covalently bonded to an oxygen molecule.

• The oxygen atom pulls most of the electrons in the water molecule toward it, resulting in:
  
    - A slightly negative charge on the oxygen atom
  
    - A slightly positive charge on the hydrogen atoms

• Molecules like water that have distinct regions of charge based on bond structure are called polar compounds.

• The charge structure of water creates a unique shape:
  
    - Hydrogen molecules are concentrated on one side of the oxygen atom.

• The polar nature and shape of water molecules enable them to form hydrogen bonds:
    - Hydrogen bonds are weak bonds that form between a proton in one molecule and an electronegative atom of another.
    - In water, this bond forms between the electronegative oxygen and the slightly positive hydrogen of another water molecule.

• The polar nature of water is crucial for life:
  
    - Water acts as a solvent for many chemicals important to life, facilitating distribution throughout organisms.

Water exhibits properties of cohesion and adhesion:

  - Cohesion:

    - Occurs when molecules of the same kind tend to stick together due to hydrogen bond cohesion

    - Results in surface tension, which minimizes surface area (due to water-air interface and stronger hydrogen bonds among water molecules below)

    - Causes water droplets to form and allows solid matter to float on the surface of water.

  - Adhesion:

    - Tendency of dissimilar molecules to attract each other (e.g., between water and charged molecules)

    - Responsible for capillary action, the movement of liquid through spaces, sometimes against gravity, due to adhesive forces.

    - Cohesive forces pull more water molecules along with the liquid.

  - In plants, capillary action helps move water from roots upward.

• Living matter is predominantly composed of carbon, hydrogen, nitrogen, and oxygen (99% of all living matter).

• Organic molecules, primarily made of carbon, form the basis of life on Earth:
    - Carbon can form four bonds with other elements, making it vital for biological molecules.
    - Carbon-based molecules can have various configurations:
      - Single, double, or triple bonds
      - Shapes including rings, branches, or long chains.

• Carbon is fundamental for major biological macromolecules:
    - Carbohydrates
    - Proteins
    - Lipids
    - Nucleic acids

• Nucleic acids and proteins also depend on nitrogen and phosphorus for their structural components.