Survey of the Natural Sciences
What the section tests
Survey of the Natural Sciences (SNS) is a single 90-minute section of 100 multiple-choice items covering biology (about 40), general chemistry (about 30), and organic chemistry (about 30). The questions reward recall plus fast application: you may need to interpret a metabolic pathway, balance a redox reaction, or assign R/S configuration within the same sitting. No scientific calculator is available, so setup and estimation matter as much as the final number.
Core rules and concepts
- Biology: cell structure, molecular genetics (transcription, translation, mutations), Mendelian and population genetics, physiology of major organ systems, development, evolution, and ecology. High-yield: membrane transport, enzyme kinetics, DNA replication, Hardy-Weinberg, and hormone feedback.
- General chemistry: stoichiometry, limiting reagents, gas laws, thermochemistry, equilibrium, acid-base chemistry, solubility, electrochemistry, and atomic/periodic trends.
- Organic chemistry: bonding and hybridization, functional groups, stereochemistry, substitution/elimination, addition, aromaticity, carbonyl chemistry, and IR/NMR/mass spec interpretation.
- Use unit cancellation and estimate before computing. Eliminate answers that violate charge, mass, or periodic trends.
Worked example
How many grams of water form when 4.0 g H2 reacts with 32 g O2? Reaction: 2H2 + O2 -> 2H2O. Moles H2 = 4.0/2.0 = 2.0; moles O2 = 32/32 = 1.0. The equation needs 2 mol H2 per 1 mol O2, so both are exactly consumed; neither is limiting. Moles H2O = moles H2 = 2.0. Mass = 2.0 x 18 = 36 g. A tempting error is to add 4 + 32 = 36 g and call it conservation, which happens to match here but fails when reactants are not stoichiometric.
Traps that cost marks
- Using Celsius in gas-law calculations; convert to kelvin.
- Confusing delta G with standard delta G or reaction rate with equilibrium position.
- Forgetting that stereochemistry questions may require assigning priorities before naming.
- Treating increased transcription as proof of increased protein without considering translation or degradation.
- Overreading biology questions: answer the mechanism asked, not every true statement about the system.