Chapter 2: The Chemical Basis of Life – Study Notes

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This section introduces the fundamental building blocks of matter and their relevance to living organisms.

Element: A pure substance consisting of only one type of atom (e.g., Oxygen, Carbon).
Atom: The smallest unit of an element, composed of protons, neutrons, and electrons.
Compound: A substance formed when two or more elements are chemically bonded (e.g., H2O).
Subatomic Particles:
- Protons: Positively charged, determine the element's identity (atomic number).
- Neutrons: Neutral charge, contribute to atomic mass and isotope formation.
- Electrons: Negatively charged, involved in chemical bonding and ion formation.
Isotopes: Atoms of the same element with different numbers of neutrons.
Ions: Atoms or molecules with a net electric charge due to loss or gain of electrons.

Chemical bonds are forces that hold atoms together in compounds. The three major types are covalent, ionic, and hydrogen bonds.

Covalent Bonds: Atoms share electron pairs. Strongest in biological systems.
- Example: The bonds between hydrogen and oxygen in water (H2O).
Ionic Bonds: Formed when electrons are transferred from one atom to another, creating oppositely charged ions that attract each other.
- Example: Sodium chloride (NaCl).
Hydrogen Bonds: Weak attractions between a hydrogen atom in one molecule and an electronegative atom (like oxygen or nitrogen) in another.
- Example: Bonds between water molecules.

Bond Strengths and Lengths:

Bond strength is measured by the amount of energy required to break the bond (kcal/mol or kJ/mol).

Chemical reactions involve the making and breaking of chemical bonds, transforming reactants into products.

Example: Cellular Respiration
- Glucose + Oxygen → Carbon dioxide + Water + ATP + Heat
- Equation:
Oxidation-Reduction (Redox) Reactions:
- Oxidation: Loss of electrons/hydrogen.
- Reduction: Gain of electrons/hydrogen.
- Mnemonic: "OIL RIG" (Oxidation Is Loss, Reduction Is Gain).

Water's unique properties make it essential for life.

Cohesiveness: Water molecules stick together due to hydrogen bonding, creating surface tension.
Thermal Stability: Water resists temperature changes, buffering temperature variation and allowing evaporative cooling.
Ice Floats: Solid water (ice) is less dense than liquid water, allowing it to float and insulate aquatic environments.
Excellent Solvent: Water dissolves many substances (salts, electrolytes, proteins, sugars) due to its polarity.
Lipids: Hydrophobic molecules (like lipids) do not dissolve in water and form barriers (e.g., cell membranes).

The pH scale measures the concentration of hydrogen ions in a solution, indicating its acidity or basicity.

Metabolic acidosis is a physiological condition where acids accumulate in the body, lowering blood pH.

Increased atmospheric CO2 leads to ocean acidification, reducing carbonate ion (CO32-) availability in seawater.

Chemical Reaction:
Impact: Corals use calcium and carbonate to build calcium carbonate reefs; acidification threatens reef formation.

Example: Rising CO2 levels correlate with decreased carbonate ion concentration, impacting marine ecosystems.