AP Biology Unit 1 Cheat Sheet: Chemistry of Life

TLDR

• Water’s polarity drives cohesion, adhesion, solvent properties, and temperature regulation.

• Four macromolecules — carbohydrates, lipids, proteins, and nucleic acids — each have unique bonds that determine their function.

• Key processes: dehydration synthesis builds polymers, hydrolysis breaks them.

• Know the difference between covalent, ionic, hydrogen, and peptide bonds.

• ✅ Download your free printable AP Biology Unit 1 Cheat Sheet above.

Why Unit 1 Matters

Unit 1, Chemistry of Life, is the bedrock of AP Biology. Every process you’ll study later — from cell energetics to genetics — relies on these fundamental chemical principles. The exam frequently tests whether you can explain how structure determines function, so memorization alone won’t be enough. Being able to apply these basics sets you up for success across the course.

Water: Properties That Make Life Possible

Water’s unique chemistry explains why life exists as it does. Be ready to explain these properties with examples:

• Polarity & Hydrogen Bonds: Partial charges allow H2O molecules to stick together.

• Cohesion: Water to water → surface tension (insects walking on water).

• Adhesion: Water to other surfaces → capillary action in plants.

• High Specific Heat & Vaporization: Resists temperature changes and cools through evaporation.

• Ice Density: Solid water floats, insulating aquatic ecosystems.

• Universal Solvent: Dissolves ions and polar molecules; hydrophobic substances do not mix.

• Buffer Systems: Weak acids and bases regulate pH in cells and blood.

The Four Macromolecules

Key Notes

• Carbohydrates: Alpha linkages (digestible), beta linkages (indigestible to humans).

• Lipids: Not true polymers. Saturated fats are solid; unsaturated are liquid. Phospholipids are amphipathic and form bilayers.

• Proteins: Folding driven by R-group interactions. Four levels of structure. Denaturation alters function.

• Nucleic Acids: DNA is double-stranded and antiparallel. RNA is single-stranded. Base pairing: A–T, G–C (DNA).

Bonds and Reactions You Must Know

• Covalent bonds: Strong, electron sharing.

• Ionic bonds: Attraction of charged ions.

• Hydrogen bonds: Weak but essential in water, DNA, and protein folding.

• Van der Waals/hydrophobic interactions: Weak, but important collectively.

• Dehydration synthesis: Builds polymers, removes water.

• Hydrolysis: Breaks polymers, adds water.

Mini Formula Box

• pH = −log[H⁺]

• pOH = −log[OH⁻]

• pH + pOH = 14 (at 25°C)

• One pH unit = 10× change in [H⁺]

Visual Mnemonics

• Water Molecule: O is δ⁻, H is δ⁺ → dotted lines show hydrogen bonds. Mnemonic: “Opposites attract.”

• Phospholipid Bilayer: Circle heads (polar) with two tails (nonpolar). Mnemonic: “Heads like water, tails hide.”

• Glucose Linkages: Alpha = same orientation (digestible), Beta = alternating (not digestible). Mnemonic: “Alpha same, Beta alternate.”

• DNA Pairing: A–T (2 bonds), G–C (3 bonds). Mnemonic: “Apples in the Tree, Cars in the Garage.”

Common Exam Pitfalls

• Mixing up hydrogen vs covalent bonds in water.

• Calling lipids polymers (they’re not).

• Confusing peptide bonds (between amino acids) with hydrogen bonds (protein folding).

• Forgetting phosphodiester bonds link nucleotides in the backbone, while hydrogen bonds hold base pairs.

• Mislabeling saturated vs unsaturated fats with regard to double bonds and room temperature state.

Tutor Tip

Our Yale tutor says, on the exam, bond names are giveaways. Immediately connect them to the correct macromolecule:

• Glycosidic → Carbohydrate

• Ester → Lipid

• Peptide → Protein

• Phosphodiester → Nucleic Acid

This trick quickly narrows down answer choices.

Start with our free Unit 1 Cheat Sheet and get personalized support from Ivy-League tutors. Book your free AP Biology strategy session today.