Key Takeaways
- Cells are the basic unit of life—know the difference between prokaryotic (no nucleus) and eukaryotic (nucleus) cells.
- The human body has 11 organ systems; focus on circulatory, respiratory, digestive, and nervous systems for the ASVAB.
- Ecology covers how organisms interact with their environment—understand food chains, ecosystems, and energy flow.
- Genetics basics include DNA, genes, chromosomes, and inheritance patterns (dominant vs. recessive traits).
- Life science questions make up roughly 50% of the General Science subtest.
Life Science
Quick Answer: Life science questions on the ASVAB cover biology basics including cell structure (prokaryotic vs. eukaryotic), human body systems (11 total), ecology (food chains, ecosystems), and genetics (DNA, inheritance). Expect roughly 8 of the 16 General Science questions to cover life sciences.
Cell Biology
All living things are made of cells—the basic unit of life. The ASVAB tests your understanding of cell structure and function.
Types of Cells
| Cell Type | Characteristics | Examples |
|---|---|---|
| Prokaryotic | No nucleus, no membrane-bound organelles, simpler structure | Bacteria, archaea |
| Eukaryotic | Has nucleus, membrane-bound organelles, more complex | Plants, animals, fungi |
Key Cell Organelles
| Organelle | Function | Memory Tip |
|---|---|---|
| Nucleus | Contains DNA, controls cell | "Brain" of the cell |
| Mitochondria | Produces energy (ATP) | "Powerhouse" of the cell |
| Ribosomes | Makes proteins | "Protein factories" |
| Cell Membrane | Controls what enters/exits | "Gatekeeper" |
| Chloroplasts | Photosynthesis (plants only) | "Solar panels" |
| Cytoplasm | Gel-like fluid holding organelles | "Cell jelly" |
| Vacuole | Storage (large in plants) | "Storage tank" |
Cell Processes
| Process | What Happens | Formula/Result |
|---|---|---|
| Mitosis | Cell division (creates identical cells) | 1 cell → 2 identical cells |
| Meiosis | Sex cell division (reduces chromosomes by half) | 1 cell → 4 gametes |
| Photosynthesis | Plants convert sunlight to food | CO₂ + H₂O + Light → Glucose + O₂ |
| Cellular Respiration | Cells convert glucose to energy | Glucose + O₂ → CO₂ + H₂O + ATP |
Human Body Systems
The human body has 11 major organ systems. Focus on these key systems for the ASVAB:
| System | Main Organs | Primary Function |
|---|---|---|
| Circulatory | Heart, blood vessels, blood | Transports oxygen, nutrients, hormones |
| Respiratory | Lungs, trachea, bronchi | Gas exchange (O₂ in, CO₂ out) |
| Digestive | Stomach, intestines, liver | Breaks down food, absorbs nutrients |
| Nervous | Brain, spinal cord, nerves | Controls body, processes information |
| Muscular | Skeletal, smooth, cardiac muscles | Movement and support |
| Skeletal | Bones, joints, cartilage | Support, protection, movement |
| Immune | White blood cells, lymph nodes | Fights infection and disease |
| Endocrine | Glands (thyroid, pituitary) | Produces hormones |
| Excretory | Kidneys, bladder, skin | Removes waste products |
| Reproductive | Sex organs | Produces offspring |
| Integumentary | Skin, hair, nails | Protection, temperature regulation |
Circulatory System Details
| Component | Function | Key Fact |
|---|---|---|
| Heart | Pumps blood | 4 chambers (2 atria, 2 ventricles) |
| Arteries | Carry blood away from heart | Usually carry oxygenated blood |
| Veins | Carry blood to heart | Usually carry deoxygenated blood |
| Capillaries | Exchange site | Smallest blood vessels |
| Red Blood Cells | Carry oxygen | Contain hemoglobin |
| White Blood Cells | Fight infection | Part of immune system |
| Platelets | Blood clotting | Prevent bleeding |
Respiratory System Details
The path of air: Nose/Mouth → Trachea → Bronchi → Bronchioles → Alveoli
- Alveoli: Tiny air sacs where gas exchange occurs
- Diaphragm: Muscle that controls breathing
- Inhalation: Diaphragm contracts, lungs expand
- Exhalation: Diaphragm relaxes, lungs compress
Ecology
Ecology studies how organisms interact with each other and their environment.
Levels of Organization
From smallest to largest: Individual → Population → Community → Ecosystem → Biome → Biosphere
| Level | Definition | Example |
|---|---|---|
| Population | Same species in an area | All deer in a forest |
| Community | All species in an area | Deer, wolves, trees in a forest |
| Ecosystem | Community + physical environment | Forest with soil, water, climate |
| Biome | Large region with similar climate | Temperate forest, desert, tundra |
| Biosphere | All life on Earth | Every ecosystem combined |
Food Chains and Webs
| Level | Role | Example |
|---|---|---|
| Producers | Make their own food (photosynthesis) | Plants, algae |
| Primary Consumers | Eat producers (herbivores) | Rabbits, deer |
| Secondary Consumers | Eat primary consumers (carnivores) | Foxes, snakes |
| Tertiary Consumers | Top predators | Eagles, wolves |
| Decomposers | Break down dead matter | Bacteria, fungi |
Energy Rule: Only about 10% of energy transfers between each level. This is why food chains rarely have more than 4-5 levels.
Ecological Relationships
| Relationship | Description | Example |
|---|---|---|
| Mutualism | Both species benefit | Bees and flowers |
| Commensalism | One benefits, other unaffected | Barnacles on whales |
| Parasitism | One benefits, one harmed | Ticks on dogs |
| Predation | One kills and eats another | Lion eating zebra |
| Competition | Both compete for same resources | Two species of finches |
Genetics
Genetics is the study of heredity—how traits are passed from parents to offspring.
Key Terms
| Term | Definition |
|---|---|
| DNA | Molecule that carries genetic information |
| Gene | Section of DNA that codes for a trait |
| Chromosome | Structure made of DNA and proteins |
| Allele | Different versions of a gene |
| Genotype | Genetic makeup (letters: AA, Aa, aa) |
| Phenotype | Physical expression of genes (what you see) |
Inheritance Patterns
| Term | Meaning | Result |
|---|---|---|
| Dominant | Expressed when one copy present | Written as capital letter (A) |
| Recessive | Only expressed when two copies present | Written as lowercase (a) |
| Homozygous | Two identical alleles | AA or aa |
| Heterozygous | Two different alleles | Aa |
Punnett Square Example
For a cross between Aa × Aa (both parents heterozygous):
| A | a | |
|---|---|---|
| A | AA | Aa |
| a | Aa | aa |
Results: 25% AA, 50% Aa, 25% aa (3:1 phenotype ratio for dominant trait)
Which organelle is known as the "powerhouse" of the cell because it produces ATP (energy)?
In a food chain, which level contains organisms that make their own food through photosynthesis?
If a parent has the genotype Aa for a trait, what percentage of their gametes (sex cells) will carry the dominant allele?
Which type of blood vessel carries oxygenated blood away from the heart to the body?