What you'll learn
Unit 1, Chemistry of Life, is the foundation of AP Biology (about 8–11% of the exam). It covers the properties of water, the four major macromolecules, functional groups, and the chemical bonds that hold biological molecules together.
Water and its properties
Water is polar and forms hydrogen bonds, which explains its life-supporting properties:
- Cohesion & adhesion → surface tension and capillary action.
- High specific heat → resists temperature change (energy breaks H-bonds rather than raising temperature).
- High heat of vaporization → evaporative cooling.
- Universal solvent → dissolves polar/ionic substances; nonpolar substances (oils) don't mix.
The four macromolecules
| Macromolecule | Monomer | Key role |
|---|---|---|
| Carbohydrates | Monosaccharides | Energy, structure (cellulose) |
| Lipids | Glycerol + fatty acids | Energy storage, membranes |
| Proteins | Amino acids | Enzymes, structure, transport |
| Nucleic acids | Nucleotides | Store/transmit information |
Monomers join by dehydration synthesis (removing water) and break by hydrolysis (adding water).
Functional groups
The chemical behaviour of a molecule comes from its functional groups: hydroxyl (−OH, polar), carboxyl (−COOH, acidic), amino (−NH₂, basic), phosphate (−PO₄, energy/charge). Carbon's four bonds make diverse skeletons possible.
Protein structure
- Primary: amino acid sequence.
- Secondary: α-helices and β-sheets (H-bonds).
- Tertiary: overall 3-D fold.
- Quaternary: multiple subunits. Shape determines function; denaturation (heat/pH) disrupts it.
Exam tips
- Link structure to function (e.g. why phospholipids form bilayers — amphipathic).
- Be ready to explain water's properties using polarity and hydrogen bonding.
- Practise identifying macromolecules and reactions (dehydration vs hydrolysis).
Common mistakes
- Confusing dehydration synthesis with hydrolysis.
- Forgetting that hydrogen bonds (not covalent bonds) drive water's properties.
- Mixing up the monomers of each macromolecule.