What the ASVAB is actually testing
The General Science subtest covers a wide sweep of topics, but life science questions cluster around three areas: cell biology, genetics, and human body systems. You won't be asked to memorize obscure trivia. You will be asked to recognize what organelles do, interpret a basic inheritance pattern, and know how major systems (circulatory, respiratory, digestive, nervous) work.
The test expects breadth over depth. If you know the role of each major cell organelle and the vocabulary of genetics, you're covering most of what appears.
Cell biology: the core concepts
Every cell has a membrane — it controls what enters and leaves. Eukaryotic cells also have a nucleus, which stores DNA. The key organelles to know:
- Mitochondria — generate ATP (energy) through cellular respiration
- Ribosomes — build proteins from amino acids following RNA instructions
- Chloroplasts — found only in plant cells; run photosynthesis
- Cell wall — rigid outer layer in plants, fungi, and bacteria; absent in animal cells
- Vacuoles — storage; plant cells have one large central vacuole
Genetics: the Punnett square shortcut
Know two terms cold: dominant (capital letter, always expressed when present) and recessive (lowercase, only expressed when both copies match).
For any cross, write out the four-box Punnett square. A carrier couple (Aa × Aa) produces: AA, Aa, Aa, aa — so 3 out of 4 offspring show the dominant trait, 1 out of 4 shows recessive.
Body systems: what the test actually asks
You don't need anatomy-course depth. Know the main job of each system:
| System | Primary function |
|---|---|
| Circulatory | Pump blood; deliver O2, remove CO2 |
| Respiratory | Exchange gases (lungs) |
| Digestive | Break down food, absorb nutrients |
| Nervous | Transmit signals; brain/spinal cord |
| Excretory | Filter blood; remove waste via kidneys |
| Endocrine | Hormone regulation |
Common trap: photosynthesis vs. respiration
These two processes are mirror images — the products of one are the inputs of the other. Photosynthesis produces glucose and oxygen; respiration consumes them. Both happen in plants, but only respiration happens in animals.
Study approach
Build vocabulary first — if you know what "mitochondria," "dominant," and "diffusion" mean precisely, most GS life science questions become straightforward. Flashcards by organelle function are the fastest prep.