Life Science
Cell structure, genetics, and body systems are the core of what the ASVAB General Science section tests, nail the vocabulary and the concepts follow.
Formula Reference
- Cell types: prokaryotic (no nucleus, bacteria) vs. eukaryotic (nucleus present, plants/animals)
- Cell organelles: nucleus (DNA), mitochondria (energy/ATP), ribosomes (protein synthesis), cell membrane (selective barrier)
- DNA → RNA → Protein (central dogma of molecular biology)
- Genetics: dominant allele masks recessive; use Punnett squares for cross predictions
- Photosynthesis: CO2 + H2O + light → glucose + O2 (chloroplasts)
- Respiration: glucose + O2 → CO2 + H2O + energy (mitochondria)
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
Nucleus = control center (holds DNA). Mitochondria = energy (ATP). Membrane controls what enters and exits.
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.
Common Pitfalls
- ⚠Confusing mitochondria (energy production) with chloroplasts (photosynthesis), only plant cells have chloroplasts
- ⚠Mixing up DNA and RNA, DNA stays in the nucleus; RNA carries the message out
- ⚠Thinking dominant means 'more common', a dominant allele just masks the recessive one, it can actually be rare in a population
- ⚠Forgetting that arteries carry blood away from the heart (not always oxygenated, the pulmonary artery carries deoxygenated blood)
- ⚠Confusing meiosis (produces 4 sex cells, half the chromosomes) with mitosis (produces 2 identical body cells)
Worked Examples
Q1: A cell has a cell wall, chloroplasts, and a large central vacuole. It is most likely: (A) an animal cell (B) a bacterial cell (C) a plant cell (D) a fungal cell
Answer: Cell walls exist in plants and bacteria, but chloroplasts are exclusive to plants. Large central vacuoles are a plant-cell hallmark. Answer: C
Q2: Two parents are both carriers of a recessive trait (Aa x Aa). What fraction of their offspring will show the recessive phenotype?
Answer: Punnett square gives AA, Aa, Aa, aa. Only aa shows the recessive phenotype: 1 out of 4 = 25%
Q3: Which organ system is primarily responsible for filtering waste from the blood?
Answer: The excretory (urinary) system, specifically the kidneys, filters blood and produces urine. Answer: kidneys/excretory system