What the exam asks
- Multiple Choice (Section I): Stimulus sets often describe isotope-labeling experiments (like tracking , , or in cultured cells) or display structural diagrams of unfamiliar biological molecules, asking you to classify them by their elemental composition or identify where a bond is formed or broken.
- Free Response (Section II): In Q1 (experimental results), Q4 (conceptual analysis), or Q5 (analyze a model), you may be asked to explain how nutrient limitation (such as low soil nitrogen or phosphorus) restricts specific cellular processes, or to predict and justify the products of an enzymatic reaction that digests or synthesizes a polymer.
Core ideas
Matter exchange and the elements of life
Living organisms are open systems that must take in matter from the environment to grow, reproduce, and maintain organization. Because atoms are conserved, every atom in a newly synthesized DNA strand, enzyme, or membrane lipid must come from food, water, or inorganic nutrients absorbed from the surroundings.
- Carbon (), Hydrogen (), and Oxygen () form the structural framework of all four macromolecule classes.
- Carbon’s versatility: With four valence electrons, carbon forms up to four stable covalent bonds (single, double, or triple). This allows it to build long chains, branched structures, and rings that serve as the skeletons of organic molecules.
- Nitrogen (), Phosphorus (), and Sulfur () provide specific chemical properties that distinguish the macromolecule classes.
| Macromolecule Class | Core Elements | Additional Key Elements | Where the Key Elements Are Found |
|---|---|---|---|
| Carbohydrates | None (typically in a ratio in monosaccharides) | Carbonyl and multiple hydroxyl () groups | |
| Lipids | (high and , low ) |